Deubiquitinating Enzyme Usp12 is a Novel Co-Activator of the Androgen Receptor

“The androgen receptor (AR), a member of the nuclear receptor family, is a transcription factor involved in prostate cell growth, homeostasis and transformation. AR is a key protein in growth and development of both normal and malignant prostate making it a common therapeutic target in prostate cancer (PCa). AR is regulated by an interplay of multiple post-translational modifications including ubiquitination. We and others have shown that the AR is ubiquitinated by a number of E3 ubiquitin ligases, including MDM2, CHIP and NEDD4 which can result in its proteosomal degradation or enhanced transcriptional activity. As ubiquitination of AR causes a change in AR activity or stability and impacts both survival and growth of PCa cells, deubiquitination of these sites has an equally important role. Hence deubiquitinating enzymes (DUBs) could offer novel therapeutic targets. We performed an siRNA screen to identify DUBs that regulate AR, in that screen ubiquitin specific protease 12 (Usp12) was identified as a novel positive regulator of AR. Usp12 is a poorly characterised protein with few known functions and requires the interaction with two cofactors, Uaf-1 and WDR20, for its enzymatic activity. In this report we demonstrate that Usp12, in complex with Uaf-1 and WDR20, deubiquitinates the AR to enhance receptor stability and transcriptional activity. Our data shows that Usp12 acts in a pro-proliferative manner by stabilising AR and enhancing its cellular function.”


Cisplatin Causes Cell Death via TAB1 Regulation of p53/MDM2/MDMX Circuitry

“The interdependence of p53 and MDM2 is critical for proper cell survival and cell death and, when altered, can lead to tumorigenesis. Mitogen-activated protein kinase (MAPK) signaling pathways function in a wide variety of cellular processes, including cell growth, migration, differentiation, and death. Here we discovered that transforming growth factor β-activated kinase 1 (TAK1)-binding protein 1 (TAB1), an activator of TAK1 and of p38α, associates with and inhibits the E3 ligase activity of MDM2 toward p53 and its homolog, MDMX. Depletion of TAB1 inhibits MDM2 siRNA-mediated p53 accumulation and p21 induction, partially rescuing cell cycle arrest induced by MDM2 ablation. Interestingly, of several agents commonly used as DNA-damaging therapeutics, only cell death caused by cisplatin is mitigated by knockdown of TAB1. Two mechanisms are required for TAB1 to regulate apoptosis in cisplatin-treated cells. First, p38α is activated by TAB1 to phosphorylate p53 N-terminal sites, leading to selective induction of p53 targets such as NOXA. Second, MDMX is stabilized in a TAB1-dependent manner and is required for cell death after cisplatin treatment. Interestingly TAB1 levels are relatively low in cisplatin-resistant clones of ovarian cells and in ovarian patient’s tumors compared with normal ovarian tissue. Together, our results indicate that TAB1 is a potential tumor suppressor that serves as a functional link between p53-MDM2 circuitry and a key MAPK signaling pathway.”


Cisplatin Causes Cell Death via TAB1 Regulation of p53/MDM2/MDMX Circuitry

“The interdependence of p53 and MDM2 is critical for proper cell survival and cell death and, when altered, can lead to tumorigenesis. Mitogen-activated protein kinase (MAPK) signaling pathways function in a wide variety of cellular processes, including cell growth, migration, differentiation, and death. Here we discovered that transforming growth factor β-activated kinase 1 (TAK1)-binding protein 1 (TAB1), an activator of TAK1 and of p38α, associates with and inhibits the E3 ligase activity of MDM2 toward p53 and its homolog, MDMX. Depletion of TAB1 inhibits MDM2 siRNA-mediated p53 accumulation and p21 induction, partially rescuing cell cycle arrest induced by MDM2 ablation. Interestingly, of several agents commonly used as DNA-damaging therapeutics, only cell death caused by cisplatin is mitigated by knockdown of TAB1. Two mechanisms are required for TAB1 to regulate apoptosis in cisplatin-treated cells. First, p38α is activated by TAB1 to phosphorylate p53 N-terminal sites, leading to selective induction of p53 targets such as NOXA. Second, MDMX is stabilized in a TAB1-dependent manner and is required for cell death after cisplatin treatment. Interestingly TAB1 levels are relatively low in cisplatin-resistant clones of ovarian cells and in ovarian patient’s tumors compared with normal ovarian tissue. Together, our results indicate that TAB1 is a potential tumor suppressor that serves as a functional link between p53-MDM2 circuitry and a key MAPK signaling pathway.”


Cisplatin Causes Cell Death via TAB1 Regulation of p53/MDM2/MDMX Circuitry

“The interdependence of p53 and MDM2 is critical for proper cell survival and cell death and, when altered, can lead to tumorigenesis. Mitogen-activated protein kinase (MAPK) signaling pathways function in a wide variety of cellular processes, including cell growth, migration, differentiation, and death. Here we discovered that transforming growth factor β-activated kinase 1 (TAK1)-binding protein 1 (TAB1), an activator of TAK1 and of p38α, associates with and inhibits the E3 ligase activity of MDM2 toward p53 and its homolog, MDMX. Depletion of TAB1 inhibits MDM2 siRNA-mediated p53 accumulation and p21 induction, partially rescuing cell cycle arrest induced by MDM2 ablation. Interestingly, of several agents commonly used as DNA-damaging therapeutics, only cell death caused by cisplatin is mitigated by knockdown of TAB1. Two mechanisms are required for TAB1 to regulate apoptosis in cisplatin-treated cells. First, p38α is activated by TAB1 to phosphorylate p53 N-terminal sites, leading to selective induction of p53 targets such as NOXA. Second, MDMX is stabilized in a TAB1-dependent manner and is required for cell death after cisplatin treatment. Interestingly TAB1 levels are relatively low in cisplatin-resistant clones of ovarian cells and in ovarian patient’s tumors compared with normal ovarian tissue. Together, our results indicate that TAB1 is a potential tumor suppressor that serves as a functional link between p53-MDM2 circuitry and a key MAPK signaling pathway.”


Stapled α−Helical Peptide Drug Development: A Potent Dual Inhibitor of MDM2 and MDMX for p53-Dependent Cancer Therapy

“Stapled α−helical peptides have emerged as a promising new modality for a wide range of therapeutic targets. Here, we describe the development of a stapled α−helical peptide lead molecule for the treatment of cancers that possess the intact p53 tumor suppressor protein but are resistant to drug therapy because of the overexpression of inhibitory proteins MDM2 and MDMX. The molecule ATSP-7041 is a highly potent dual inhibitor of both MDM2 and MDMX that is shown to effectively reactivate the p53 tumor suppressor pathway in a mechanism-dependent manner in p53-positive cancers in vitro and in vivo.”


NRAS Mutation in Melanoma: A Challenging Target


Among melanomas, BRAF-mutated disease gets the vast majority of attention. Fifty percent of melanomas harbor BRAF mutations, which can be targeted with BRAF inhibitors. However, despite its notoriety, BRAF is not the only important melanoma mutation.

Another melanoma-linked mutation can be found in the NRAS gene. Like BRAF mutations, NRAS mutations are ‘driver mutations’—a tumor with an NRAS mutation is dependent on the mutation for its growth and survival. Continue reading…


Restoring p53 Function in Human Melanoma Cells by Inhibiting MDM2 and Cyclin B1/CDK1-Phosphorylated Nuclear iASPP

“Nearly 90% of human melanomas contain inactivated wild-type p53, the underlying mechanisms for which are not fully understood. Here, we identify that cyclin B1/CDK1-phosphorylates iASPP, which leads to the inhibition of iASPP dimerization, promotion of iASPP monomer nuclear entry, and exposure of its p53 binding sites, leading to increased p53 inhibition. Nuclear iASPP is enriched in melanoma metastasis and associates with poor patient survival. Most wild-type p53-expressing melanoma cell lines coexpress high levels of phosphorylated nuclear iASPP, MDM2, and cyclin B1. Inhibition of MDM2 and iASPP phosphorylation with small molecules induced p53-dependent apoptosis and growth suppression. Concurrent p53 reactivation and BRAFV600E inhibition achieved additive suppression in vivo, presenting an alternative for melanoma therapy…”