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TAF6 orchestrates transcription programs and apoptosis in the absence of p53

ABSTRACT: The decision of metazoan cells to live or undergo programmed cell death hinges on the balance between the levels of pro- versus anti-apoptotic gene products. The general RNA polymerase II (Pol II) transcription factor, TFIID, plays a central role in the regulation of gene expression through its core promoter recognition and co-activator functions. The core TFIID subunit TAF6 is a co-activator for the pro-apoptotic p53 tumour suppressor protein. Our previous studies identified a specialized isoform of TAF6, termed TAF6 that can specifically be induced in apoptosis. To elucidate the impact of TAF6 on gene expression and cell death, we employed modified antisense oligonucleotides to enforce expression of endogenous TAF6. The induction of endogenous TAF6 triggered apoptosis in several cancer cell lines. Importantly, TAF6 also induces apoptosis in tumor cell lines devoid of p53, placing TAF6 function downstream of p53. Microarray experiments uncovered a TAF6-induced transcriptome landscape displaying enhanced expression of genes of the Notch, oxidative stress, integrin, p53 and apoptosis pathways. Our data show that the TAF6 pathway is a pivotal signalling nexus that controls pro-apoptotic gene expression programs. Keywords: Treatment with splice site switching antisense oligonucleotides, induction of apoptosis

ORGANISM(S): Homo sapiens

PROVIDER: GSE8752 | GEO | 2010/11/27

SECONDARY ACCESSION(S): PRJNA102021

REPOSITORIES: GEO

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Project description:Metastatic malignant melanoma is the deadliest skin cancer type, and it is characterized by its high resistance to apoptosis. The main driving mutations in melanoma cause hyperactivation of genes within the ERK pathway, with BRAF mutations being the most frequent ones, followed by NRAS, NF1 and MEK mutations. Increasing evidence shows that the MST2/Hippo pathway is also deregulated in this cancer type. While mutations are rare, MST2/Hippo pathway core proteins expression levels are often dysregulated in melanoma. The expression of the tumour suppressor RASSF1A, a bona fide activator of the pro-apoptotic MST2 pathway, is silenced by promoter methylation in over half of melanomas and correlates with poor prognosis. Here, using mass spectrometry-based interaction proteomics we identified Second Mitochondria-derived Activator of Caspases (SMAC) as a novel LATS1 interactor. We show that RASSF1A-dependent activation of the pro-apoptotic MST2 pathway promotes LATS1-SMAC interaction and negatively regulates the anti-apoptotic signal mediated by the members of the IAP family. Moreover, proteomic experiments identified a common cluster of the apoptotic regulator that bind to SMAC and LATS1. Mechanistic analysis show that the LATS1-SMAC complex promotes XIAP ubiquitination and its subsequent degradation which ultimately results apoptosis. Importantly, we show that the oncogenic BRAFV600E mutant prevents the pro-apoptotic signal mediated by the LAST1-SMAC complex while treatment of melanoma cell lines with BRAF inhibitors promotes this complex, indicating that inhibition of the LATS1-SMAC might be necessary for BRAFV600E-driven melanoma. Finally, we show that LATS1-SMAC interaction is regulated by the SMAC mimetic Birinapant which requires the inhibition of C-IAP1 and the degradation of XIAP, indicating that the MST2/Hippo pathway is part of the mechanism of action of Birinapant. Overall, the current work shows SMAC-dependent apoptosis is regulated by the LATS1 tumour suppressor and supports the idea that LATS1 is a signalling hub that regulates the crosstalk between the MST2 pathway, the apoptotic network and the RAF/ERK pathway.

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TAF6 orchestrates transcription programs and apoptosis in the absence of p53

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