Although hypoxia (lack of oxygen in body tissues) is perhaps the most physiological inducer of th... more Although hypoxia (lack of oxygen in body tissues) is perhaps the most physiological inducer of the wild-type p53 gene, the mechanism of this induction is unknown. Cells may detect low oxygen levels through a haem-containing sensor protein. The hypoxic state can be mimicked by using cobalt chloride and the iron chelator desferrioxamine: like hypoxia, cobalt chloride and desferrioxamine activate hypoxia-inducible factor 1alpha (HIF-1alpha), which stimulates the transcription of several genes that are associated with hypoxia. Here we show that these treatments induce accumulation of wild-type p53 through HIF-1alpha-dependent stabilization of p53 protein. Induction of p53 does not occur in either a mutant hepatoma cell line that is unable to induce HIF-1alpha or embryonic stem cells derived from mice lacking HIF-1beta. HIF-1alpha is found in p53 immunoprecipitates from MCF7 cells that express wild-type p53 and are either hypoxic or have been exposed to desferrioxamine. Similarly, anti-h...
Drugs that target novel surfaces on the androgen receptor and/or novel AR regulatory mechanisms a... more Drugs that target novel surfaces on the androgen receptor and/or novel AR regulatory mechanisms are promising alternatives for the treatment of hormone refractory prostate cancer. The 52 kDa FK506 Binding Protein (FKBP52) has been shown to be an important positive regulator of AR in cellular and whole animal models and represents an attractive target for the treatment of prostate cancer. We have identified a surface region on the androgen receptor (AR) hormone binding domain that, when mutated, displays a greater dependence on FKBP52 for normal function. In addition, we have developed a series of small molecules that inhibit the FKBP52 regulation of AR function by binding to a novel regulatory surface on the AR hormone binding domain. This surface, termed BF3, is also hypothesized to be the FKBP52 binding domain on AR. SPR studies have confirmed that these inhibitors disrupt FKBP52 function through interaction with the AR hormone binding domain. These novel compounds do not compete ...
The ability of Heat Shock Protein 90 (Hsp90) to hydrolyze ATP is essential for its chaperone func... more The ability of Heat Shock Protein 90 (Hsp90) to hydrolyze ATP is essential for its chaperone function. The co-chaperone Aha1 stimulates Hsp90 ATPase activity, tailoring the chaperone function to specific "client" proteins. The intracellular signaling mechanisms directly regulating Aha1 association with Hsp90 remain unknown. Here, we show that c-Abl kinase phosphorylates Y223 in human Aha1 (hAha1), promoting its interaction with Hsp90. This, consequently, results in an increased Hsp90 ATPase activity, enhances Hsp90 interaction with kinase clients, and compromises the chaperoning of non-kinase clients such as glucocorticoid receptor and CFTR. Suggesting a regulatory paradigm, we also find that Y223 phosphorylation leads to ubiquitination and degradation of hAha1 in the proteasome. Finally, pharmacologic inhibition of c-Abl prevents hAha1 interaction with Hsp90, thereby hypersensitizing cancer cells to Hsp90 inhibitors both in vitro and ex vivo.
The benzoquinone ansamycin geldanamycin (GA) stimulates proteasome-mediated degradation of plasma... more The benzoquinone ansamycin geldanamycin (GA) stimulates proteasome-mediated degradation of plasma membrane-associated ErbB2, a receptor tyrosine kinase. Drug sensitivity is mediated by ErbB2's kinase domain and occurs subsequent to the disruption of Hsp90 interaction with this domain. Full-length ErbB2 is efficiently processed via the endoplasmic reticulum (ER) and Golgi network, so that at steady state most of the detectable protein is plasma membrane associated. However, previous studies have also demonstrated the GA sensitivity of newly synthesized ErbB2, normally a minor component of the total cellular pool of the kinase. Drug sensitivity of nascent ErbB2 is distinguished by 2 characteristics--protein instability and inability to traverse the ER. As nascent ErbB2 can associate with both cytoplasmic Hsp90 and its ER luminal homolog Grp 94, also a GA-binding protein, the purpose of this study was to examine the relative contributions of the cytoplasmic and ER luminal domains o...
The cell fate determinant Numb is aberrantly expressed in cancer. Numb is alternatively spliced w... more The cell fate determinant Numb is aberrantly expressed in cancer. Numb is alternatively spliced with one isoform containing an extended proline rich region (PRR(L) ) compared to the other (PRR(S) ). PRR(L) was recently reported to enhance proliferation of breast and lung cancer cells. However, the importance of Numb alternative splicing in hepatocellular carcinoma (HCC) remain unexplored. We report here that Numb PRR(L) expression is increased in HCC and is associated with early recurrence and reduced overall survival after surgery. In a panel of HCC cell lines, PRR(L) generally promotes and PRR(S) suppresses proliferation, migration, invasion and colony formation. PRR(S) knockdown leads to increased Akt phosphorylation and c-Myc expression, and Akt inhibition or c-Myc silencing dampens the proliferative impact of Numb PRR(S) knockdown. In the cell models explored in this study, alternative splicing of Numb PRR isoforms is coordinately regulated by the splicing factor Rbfox2 and the...
Beta-catenin undergoes both serine and tyrosine phosphorylation. Serine phosphorylation in the am... more Beta-catenin undergoes both serine and tyrosine phosphorylation. Serine phosphorylation in the amino terminus targets beta-catenin for proteasome degradation, whereas tyrosine phosphorylation in the COOH terminus influences interaction with E-cadherin. We examined the tyrosine phosphorylation status of beta-catenin in melanoma cells expressing proteasome-resistant beta-catenin, as well as the effects that perturbation of beta-catenin tyrosine phosphorylation had on its association with E-cadherin and on its transcriptional activity. Beta-catenin is tyrosine phosphorylated in three melanoma cell lines and associates with both the ErbB2 receptor tyrosine kinase and the LAR receptor tyrosine phosphatase. Geldanamycin, a drug which destabilizes ErbB2, caused rapid cellular depletion of the kinase and loss of its association with beta-catenin without perturbing either LAR or beta-catenin levels or LAR/beta-catenin association. Geldanamycin also stimulated tyrosine dephosphorylation of be...
Chronic myelogenous leukemia (CML) is a clonal disorder of a pluripotent hematopoietic stem cells... more Chronic myelogenous leukemia (CML) is a clonal disorder of a pluripotent hematopoietic stem cells characterized by a chimeric bcr-abl gene giving rise to a p210(Bcr-Abl) protein with dysregulated tyrosine kinase activity. Radicicol, a macrocyclic antifungal antibiotic, binds to the N-terminal of heat shock protein 90 (Hsp90) and destabilizes Hsp90-associated proteins such as Raf-1. This study investigated the effect of radicicol, novel oxime derivatives of radicicol (KF25706 and KF58333), and herbimycin A (HA), a benzoquinoid ansamycin antibiotic, on the growth and differentiation of human K562 CML cells. Although KF25706 and KF58333 induced the expression of glycophorin A in K562 cells, radicicol and HA caused erythroid differentiation transiently. Cell cycle analysis showed that G(1) phase accumulation was observed in K562 cells treated with KF58333. KF58333 treatment depleted p210(Bcr-Abl), Raf-1, and cellular tyrosine phosphorylated proteins in K562 cells, whereas radicicol and ...
In previous studies, patients with mild or inactive Crohn's disease were found to have increa... more In previous studies, patients with mild or inactive Crohn's disease were found to have increased suppressor T-cell activity. To further characterize suppressor T cells in Crohn's disease, studies were carried out with the use of monoclonal antibodies. Excessive suppressor activity was eliminated by removal of OKT 8+ lymphocytes by complement-mediated lysis. However, the percentage of OKT 8+ (or Leu 2a+) cells and the ratio of OKT 4+ to OKT 8+ (or Leu 3a+ to Leu 2a+) cells were not significantly different from normal. Although the subgroup of patients with increased suppression of immunoglobulin synthesis had a significantly lower mean Leu 3a to Leu 2a ratio than that of normal subjects, in the whole group of Crohn's patients studied, neither the percentage of Leu 2a+ cells nor the ratio of Leu 3a+ to Leu 2a+ cells correlated with excessive suppression of immunoglobulin synthesis. A subpopulation of Leu 2a+ lymphocytes reactive with the monoclonal antibody HNK-1 (Leu 2a+ ...
Many tumors undergo a dramatic metabolic shift known as the Warburg effect in which glucose utili... more Many tumors undergo a dramatic metabolic shift known as the Warburg effect in which glucose utilization is favored and oxidative phosphorylation is downregulated, even when oxygen availability is plentiful. However, the mechanistic basis for this switch has remained unclear. Recently several independent groups identified tumor necrosis factor receptor-associated protein 1 (TRAP1), a mitochondrial molecular chaperone of the heat shock protein 90 (Hsp90) family, as a key modulator of mitochondrial respiration. Although all reports agree that this activity of TRAP1 has important implications for neoplastic progression, data from the different groups only partially overlap, suggesting that TRAP1 may have complex and possibly contextual effects on tumorigenesis. In this review we analyze these recent findings and attempt to reconcile these observations.
Current topics in microbiology and immunology, 1988
... reduction in c-myc protein expression correlates with inhibition of cell growth and DNA synth... more ... reduction in c-myc protein expression correlates with inhibition of cell growth and DNA synthesis. Loke SL, Stein C, Zhang X, Avigan M, Cohen J, Neckers LM. PMID: 3063445 [PubMed - indexed for MEDLINE]. MeSH Terms: ...
The N-myc gene is transiently expressed during normal embryonic development and abnormally expres... more The N-myc gene is transiently expressed during normal embryonic development and abnormally expressed in several tumors of neuroendocrine origin. Little is known of the function of the N-myc gene product in either normal or neoplastic tissue. We utilized synthetic antisense oligodeoxynucleotides to specifically inhibit N-myc gene expression in the neuroepithelioma cell line CHP100. These cells contain single copy N-myc alleles but overexpress c-myc. N-myc antisense oligomer treatment was found to be growth inhibitory without affecting levels of c-myc protein. N-myc antisense oligomer-treated cells also lost the characteristic cellular heterogeneity displayed by CHP100 in vitro.
The Journal of pharmacology and experimental therapeutics, 1977
Although hydroxylation of tryptophan (TP) is considered to be the rate-limiting step in serotonin... more Although hydroxylation of tryptophan (TP) is considered to be the rate-limiting step in serotonin synthesis, the mechanism whereby tryptophan hydroxylase (TPH) participates in the regulation of serotonin synthesis is still in question. Since the brain TP concentration is probably near the Km for tryptophan hydroxylase, changes in brain TP content could affect the rate of its hydroxylation. However, it has not been established whether in vivo the activity of TPH and TP in several brain nuclei and other regions of rat brain after treatments known to lower brain TP levels. Chlorimipramine, loading with neutral amino acids and a TP-deficient diet decreased the TP content of some, but not all, brain regions studied. Whenever TP decrease withe TP injections. Several brain nuclei accumulate TP at different rates after a TP load. These data suggest possible mechanisms for regulation of serotonin synthesis in the face of fluctuating plasma levels of TP.
Background: Mitochondria contain their own DNA genome (mtDNA), as well as specific DNA replicatio... more Background: Mitochondria contain their own DNA genome (mtDNA), as well as specific DNA replication and protein synthesis machineries. Relaxation of the circular, double-stranded mtDNA relies on the presence of topoisomerase activity. Three different topoisomerases have been identified in mitochondria: Top1mt, Top3a and a truncated form of Top2b.
Hereditary leiomyomatosis and renal cell cancer (HLRCC) is an inherited cancer syndrome linked to... more Hereditary leiomyomatosis and renal cell cancer (HLRCC) is an inherited cancer syndrome linked to biallelic inactivation of the gene encoding the tricarboxylic acid cycle enzyme fumarate hydratase (FH). Individuals with HLRCC are at risk to develop cutaneous and uterine leiomyomas and an aggressive form of kidney cancer. Pseudohypoxic drive-the aberrant activation of cellular hypoxia response pathways despite normal oxygen tension-is considered to be a likely mechanism underlying the etiology of this tumor. Pseudohypoxia requires the oxygen-independent stabilization of the alpha subunit of the hypoxia-inducible transcription factor (HIF-1alpha). Under normoxic conditions, proline hydroxylation of HIF-1alpha permits VHL recognition and subsequent targeting for proteasomal degradation. Here, we demonstrate that inactivating mutations of FH in an HLRCC-derived cell line result in glucose-mediated generation of cellular reactive oxygen species (ROS) and ROS-dependent HIF-1alpha stabiliz...
Patients with germline fumarate hydratase (FH) mutation are predisposed to develop aggressive kid... more Patients with germline fumarate hydratase (FH) mutation are predisposed to develop aggressive kidney cancer with few treatment options and poor therapeutic outcomes. Activity of the proto-oncogene ABL1 is upregulated in FH-deficient kidney tumors and drives a metabolic and survival signaling network necessary to cope with impaired mitochondrial function and abnormal accumulation of intracellular fumarate. Excess fumarate indirectly stimulates ABL1 activity, while restoration of wild-type FH abrogates both ABL1 activation and the cytotoxicity caused by ABL1 inhibition or knockdown. ABL1 upregulates aerobic glycolysis via the mTOR/HIF1α pathway and neutralizes fumarate-induced proteotoxic stress by promoting nuclear localization of the antioxidant response transcription factor NRF2. Our findings identify ABL1 as a pharmacologically tractable therapeutic target in glycolytically dependent, oxidatively stressed tumors.
Growing evidence indicates that inflammation is a contributing factor leading to cancer developme... more Growing evidence indicates that inflammation is a contributing factor leading to cancer development. However, pathways involved in this progression are not well understood. To examine whether HIF-1α is a factor linking inflammation and tumorigenesis, we investigated whether the HIF-1 signaling pathway was stimulated by the pro-inflammatory cytokine interleukin-1β (IL-1β) in A549 cells. We find that IL-1β up-regulated HIF-1α protein under
Although hypoxia (lack of oxygen in body tissues) is perhaps the most physiological inducer of th... more Although hypoxia (lack of oxygen in body tissues) is perhaps the most physiological inducer of the wild-type p53 gene, the mechanism of this induction is unknown. Cells may detect low oxygen levels through a haem-containing sensor protein. The hypoxic state can be mimicked by using cobalt chloride and the iron chelator desferrioxamine: like hypoxia, cobalt chloride and desferrioxamine activate hypoxia-inducible factor 1alpha (HIF-1alpha), which stimulates the transcription of several genes that are associated with hypoxia. Here we show that these treatments induce accumulation of wild-type p53 through HIF-1alpha-dependent stabilization of p53 protein. Induction of p53 does not occur in either a mutant hepatoma cell line that is unable to induce HIF-1alpha or embryonic stem cells derived from mice lacking HIF-1beta. HIF-1alpha is found in p53 immunoprecipitates from MCF7 cells that express wild-type p53 and are either hypoxic or have been exposed to desferrioxamine. Similarly, anti-h...
Drugs that target novel surfaces on the androgen receptor and/or novel AR regulatory mechanisms a... more Drugs that target novel surfaces on the androgen receptor and/or novel AR regulatory mechanisms are promising alternatives for the treatment of hormone refractory prostate cancer. The 52 kDa FK506 Binding Protein (FKBP52) has been shown to be an important positive regulator of AR in cellular and whole animal models and represents an attractive target for the treatment of prostate cancer. We have identified a surface region on the androgen receptor (AR) hormone binding domain that, when mutated, displays a greater dependence on FKBP52 for normal function. In addition, we have developed a series of small molecules that inhibit the FKBP52 regulation of AR function by binding to a novel regulatory surface on the AR hormone binding domain. This surface, termed BF3, is also hypothesized to be the FKBP52 binding domain on AR. SPR studies have confirmed that these inhibitors disrupt FKBP52 function through interaction with the AR hormone binding domain. These novel compounds do not compete ...
The ability of Heat Shock Protein 90 (Hsp90) to hydrolyze ATP is essential for its chaperone func... more The ability of Heat Shock Protein 90 (Hsp90) to hydrolyze ATP is essential for its chaperone function. The co-chaperone Aha1 stimulates Hsp90 ATPase activity, tailoring the chaperone function to specific "client" proteins. The intracellular signaling mechanisms directly regulating Aha1 association with Hsp90 remain unknown. Here, we show that c-Abl kinase phosphorylates Y223 in human Aha1 (hAha1), promoting its interaction with Hsp90. This, consequently, results in an increased Hsp90 ATPase activity, enhances Hsp90 interaction with kinase clients, and compromises the chaperoning of non-kinase clients such as glucocorticoid receptor and CFTR. Suggesting a regulatory paradigm, we also find that Y223 phosphorylation leads to ubiquitination and degradation of hAha1 in the proteasome. Finally, pharmacologic inhibition of c-Abl prevents hAha1 interaction with Hsp90, thereby hypersensitizing cancer cells to Hsp90 inhibitors both in vitro and ex vivo.
The benzoquinone ansamycin geldanamycin (GA) stimulates proteasome-mediated degradation of plasma... more The benzoquinone ansamycin geldanamycin (GA) stimulates proteasome-mediated degradation of plasma membrane-associated ErbB2, a receptor tyrosine kinase. Drug sensitivity is mediated by ErbB2's kinase domain and occurs subsequent to the disruption of Hsp90 interaction with this domain. Full-length ErbB2 is efficiently processed via the endoplasmic reticulum (ER) and Golgi network, so that at steady state most of the detectable protein is plasma membrane associated. However, previous studies have also demonstrated the GA sensitivity of newly synthesized ErbB2, normally a minor component of the total cellular pool of the kinase. Drug sensitivity of nascent ErbB2 is distinguished by 2 characteristics--protein instability and inability to traverse the ER. As nascent ErbB2 can associate with both cytoplasmic Hsp90 and its ER luminal homolog Grp 94, also a GA-binding protein, the purpose of this study was to examine the relative contributions of the cytoplasmic and ER luminal domains o...
The cell fate determinant Numb is aberrantly expressed in cancer. Numb is alternatively spliced w... more The cell fate determinant Numb is aberrantly expressed in cancer. Numb is alternatively spliced with one isoform containing an extended proline rich region (PRR(L) ) compared to the other (PRR(S) ). PRR(L) was recently reported to enhance proliferation of breast and lung cancer cells. However, the importance of Numb alternative splicing in hepatocellular carcinoma (HCC) remain unexplored. We report here that Numb PRR(L) expression is increased in HCC and is associated with early recurrence and reduced overall survival after surgery. In a panel of HCC cell lines, PRR(L) generally promotes and PRR(S) suppresses proliferation, migration, invasion and colony formation. PRR(S) knockdown leads to increased Akt phosphorylation and c-Myc expression, and Akt inhibition or c-Myc silencing dampens the proliferative impact of Numb PRR(S) knockdown. In the cell models explored in this study, alternative splicing of Numb PRR isoforms is coordinately regulated by the splicing factor Rbfox2 and the...
Beta-catenin undergoes both serine and tyrosine phosphorylation. Serine phosphorylation in the am... more Beta-catenin undergoes both serine and tyrosine phosphorylation. Serine phosphorylation in the amino terminus targets beta-catenin for proteasome degradation, whereas tyrosine phosphorylation in the COOH terminus influences interaction with E-cadherin. We examined the tyrosine phosphorylation status of beta-catenin in melanoma cells expressing proteasome-resistant beta-catenin, as well as the effects that perturbation of beta-catenin tyrosine phosphorylation had on its association with E-cadherin and on its transcriptional activity. Beta-catenin is tyrosine phosphorylated in three melanoma cell lines and associates with both the ErbB2 receptor tyrosine kinase and the LAR receptor tyrosine phosphatase. Geldanamycin, a drug which destabilizes ErbB2, caused rapid cellular depletion of the kinase and loss of its association with beta-catenin without perturbing either LAR or beta-catenin levels or LAR/beta-catenin association. Geldanamycin also stimulated tyrosine dephosphorylation of be...
Chronic myelogenous leukemia (CML) is a clonal disorder of a pluripotent hematopoietic stem cells... more Chronic myelogenous leukemia (CML) is a clonal disorder of a pluripotent hematopoietic stem cells characterized by a chimeric bcr-abl gene giving rise to a p210(Bcr-Abl) protein with dysregulated tyrosine kinase activity. Radicicol, a macrocyclic antifungal antibiotic, binds to the N-terminal of heat shock protein 90 (Hsp90) and destabilizes Hsp90-associated proteins such as Raf-1. This study investigated the effect of radicicol, novel oxime derivatives of radicicol (KF25706 and KF58333), and herbimycin A (HA), a benzoquinoid ansamycin antibiotic, on the growth and differentiation of human K562 CML cells. Although KF25706 and KF58333 induced the expression of glycophorin A in K562 cells, radicicol and HA caused erythroid differentiation transiently. Cell cycle analysis showed that G(1) phase accumulation was observed in K562 cells treated with KF58333. KF58333 treatment depleted p210(Bcr-Abl), Raf-1, and cellular tyrosine phosphorylated proteins in K562 cells, whereas radicicol and ...
In previous studies, patients with mild or inactive Crohn's disease were found to have increa... more In previous studies, patients with mild or inactive Crohn's disease were found to have increased suppressor T-cell activity. To further characterize suppressor T cells in Crohn's disease, studies were carried out with the use of monoclonal antibodies. Excessive suppressor activity was eliminated by removal of OKT 8+ lymphocytes by complement-mediated lysis. However, the percentage of OKT 8+ (or Leu 2a+) cells and the ratio of OKT 4+ to OKT 8+ (or Leu 3a+ to Leu 2a+) cells were not significantly different from normal. Although the subgroup of patients with increased suppression of immunoglobulin synthesis had a significantly lower mean Leu 3a to Leu 2a ratio than that of normal subjects, in the whole group of Crohn's patients studied, neither the percentage of Leu 2a+ cells nor the ratio of Leu 3a+ to Leu 2a+ cells correlated with excessive suppression of immunoglobulin synthesis. A subpopulation of Leu 2a+ lymphocytes reactive with the monoclonal antibody HNK-1 (Leu 2a+ ...
Many tumors undergo a dramatic metabolic shift known as the Warburg effect in which glucose utili... more Many tumors undergo a dramatic metabolic shift known as the Warburg effect in which glucose utilization is favored and oxidative phosphorylation is downregulated, even when oxygen availability is plentiful. However, the mechanistic basis for this switch has remained unclear. Recently several independent groups identified tumor necrosis factor receptor-associated protein 1 (TRAP1), a mitochondrial molecular chaperone of the heat shock protein 90 (Hsp90) family, as a key modulator of mitochondrial respiration. Although all reports agree that this activity of TRAP1 has important implications for neoplastic progression, data from the different groups only partially overlap, suggesting that TRAP1 may have complex and possibly contextual effects on tumorigenesis. In this review we analyze these recent findings and attempt to reconcile these observations.
Current topics in microbiology and immunology, 1988
... reduction in c-myc protein expression correlates with inhibition of cell growth and DNA synth... more ... reduction in c-myc protein expression correlates with inhibition of cell growth and DNA synthesis. Loke SL, Stein C, Zhang X, Avigan M, Cohen J, Neckers LM. PMID: 3063445 [PubMed - indexed for MEDLINE]. MeSH Terms: ...
The N-myc gene is transiently expressed during normal embryonic development and abnormally expres... more The N-myc gene is transiently expressed during normal embryonic development and abnormally expressed in several tumors of neuroendocrine origin. Little is known of the function of the N-myc gene product in either normal or neoplastic tissue. We utilized synthetic antisense oligodeoxynucleotides to specifically inhibit N-myc gene expression in the neuroepithelioma cell line CHP100. These cells contain single copy N-myc alleles but overexpress c-myc. N-myc antisense oligomer treatment was found to be growth inhibitory without affecting levels of c-myc protein. N-myc antisense oligomer-treated cells also lost the characteristic cellular heterogeneity displayed by CHP100 in vitro.
The Journal of pharmacology and experimental therapeutics, 1977
Although hydroxylation of tryptophan (TP) is considered to be the rate-limiting step in serotonin... more Although hydroxylation of tryptophan (TP) is considered to be the rate-limiting step in serotonin synthesis, the mechanism whereby tryptophan hydroxylase (TPH) participates in the regulation of serotonin synthesis is still in question. Since the brain TP concentration is probably near the Km for tryptophan hydroxylase, changes in brain TP content could affect the rate of its hydroxylation. However, it has not been established whether in vivo the activity of TPH and TP in several brain nuclei and other regions of rat brain after treatments known to lower brain TP levels. Chlorimipramine, loading with neutral amino acids and a TP-deficient diet decreased the TP content of some, but not all, brain regions studied. Whenever TP decrease withe TP injections. Several brain nuclei accumulate TP at different rates after a TP load. These data suggest possible mechanisms for regulation of serotonin synthesis in the face of fluctuating plasma levels of TP.
Background: Mitochondria contain their own DNA genome (mtDNA), as well as specific DNA replicatio... more Background: Mitochondria contain their own DNA genome (mtDNA), as well as specific DNA replication and protein synthesis machineries. Relaxation of the circular, double-stranded mtDNA relies on the presence of topoisomerase activity. Three different topoisomerases have been identified in mitochondria: Top1mt, Top3a and a truncated form of Top2b.
Hereditary leiomyomatosis and renal cell cancer (HLRCC) is an inherited cancer syndrome linked to... more Hereditary leiomyomatosis and renal cell cancer (HLRCC) is an inherited cancer syndrome linked to biallelic inactivation of the gene encoding the tricarboxylic acid cycle enzyme fumarate hydratase (FH). Individuals with HLRCC are at risk to develop cutaneous and uterine leiomyomas and an aggressive form of kidney cancer. Pseudohypoxic drive-the aberrant activation of cellular hypoxia response pathways despite normal oxygen tension-is considered to be a likely mechanism underlying the etiology of this tumor. Pseudohypoxia requires the oxygen-independent stabilization of the alpha subunit of the hypoxia-inducible transcription factor (HIF-1alpha). Under normoxic conditions, proline hydroxylation of HIF-1alpha permits VHL recognition and subsequent targeting for proteasomal degradation. Here, we demonstrate that inactivating mutations of FH in an HLRCC-derived cell line result in glucose-mediated generation of cellular reactive oxygen species (ROS) and ROS-dependent HIF-1alpha stabiliz...
Patients with germline fumarate hydratase (FH) mutation are predisposed to develop aggressive kid... more Patients with germline fumarate hydratase (FH) mutation are predisposed to develop aggressive kidney cancer with few treatment options and poor therapeutic outcomes. Activity of the proto-oncogene ABL1 is upregulated in FH-deficient kidney tumors and drives a metabolic and survival signaling network necessary to cope with impaired mitochondrial function and abnormal accumulation of intracellular fumarate. Excess fumarate indirectly stimulates ABL1 activity, while restoration of wild-type FH abrogates both ABL1 activation and the cytotoxicity caused by ABL1 inhibition or knockdown. ABL1 upregulates aerobic glycolysis via the mTOR/HIF1α pathway and neutralizes fumarate-induced proteotoxic stress by promoting nuclear localization of the antioxidant response transcription factor NRF2. Our findings identify ABL1 as a pharmacologically tractable therapeutic target in glycolytically dependent, oxidatively stressed tumors.
Growing evidence indicates that inflammation is a contributing factor leading to cancer developme... more Growing evidence indicates that inflammation is a contributing factor leading to cancer development. However, pathways involved in this progression are not well understood. To examine whether HIF-1α is a factor linking inflammation and tumorigenesis, we investigated whether the HIF-1 signaling pathway was stimulated by the pro-inflammatory cytokine interleukin-1β (IL-1β) in A549 cells. We find that IL-1β up-regulated HIF-1α protein under
Uploads
Papers by Len Neckers