hSirT1-Dependent Regulation of the PCAF-E2F1-p73 Apoptotic Pathway in Response to DNA Damage

Abstract

The NAD؉ -dependent histone deacetylase hSirT1 regulates cell survival and stress responses by inhibiting p53-, NF-B-, and E2F1-dependent transcription. Here we show that the hSirT1/PCAF interaction controls the E2F1/p73 apoptotic pathway. hSirT1 represses E2F1-dependent P1p73 promoter activity in untreated cells and inhibits its activation in response to DNA damage. hSirT1, PCAF, and E2F1 are corecruited in vivo on theP1p73 promoter. hSirT1 deacetylates PCAF in vitro and modulates PCAF acetylation in vivo. In cells exposed to apoptotic DNA damage, nuclear NAD ؉ levels decrease and inactivate hSirT1 without altering the hSirT1 interaction with PCAF and hSirT1 binding to the P1p73 promoter. hSirT1, the mammalian homologue of Sir2 (silent information regulator 2), is a NAD-dependent class III deacetylase (15, 33) that regulates cell survival, stress responses, and metabolism by inhibiting p53 (3, 18, 19, 28)-, E2F1 (1, 30)-, NF-B (31)-, and Forkhead (2)-dependent transcription. The role of hSirT1 in the regulation of mammalian cell survival in response to DNA damage is supported by several observations. hSirT1-deficient mice display increased levels of radiation-induced apoptosis and p53 hyperacetylation (4). hSirT1-dependent deacetylation attenuates the ability of p53 to trans-activate the cell cycle (p21) and apoptotic (bax) target genes (19,28). The constitutive expression of the tumor suppressor hypermethylated in cancer 1 (Hic1) represses hSirT1 transcription, thereby allowing the accumulation of acetylated p53 species and the enhancement of p53-mediated growth arrest and apoptosis in response to DNA damage (3). hSirT1 deacetylase function also modulates p53-independent pathways involved in the DNA damage response. The targeted disruption of the SirT1 gene in p53-deficient cells strongly sensitizes cells to radiation-, cisplatin-, and etoposide-induced cell death (20). hSirT1 deacetylates the DNA damage repair protein Ku70, and deacetylated Ku70 prevents Bax translocation to mitochondria to initiate apoptosis (5). hSirT1 maintains the Nijmegen breakage syndrome protein (NBS1) hypoacetylated and susceptible to be phosphorylated by ATM in response to DNA damage (32). Finally, etoposide treatment results in the E2F1-dependent induction of hSirT1 expression, and the abrogation of hSirT1 expression sensitizes cells to E2F1-dependent apoptosis (30).The E2F family of transcription factors has critical roles in the control of cell proliferation and apoptosis (7). E2F transcriptional activity is tightly regulated during the cell cycle through the association with pRb or the related pocket proteins p107 and p130, leading, in quiescent cells, to the recruitment of transcriptional corepressors, including histone deacetylases (HDACs), methyltransferases, and polycomb group proteins, onto the promoters of proliferation-associated E2F target genes (7). As cells progress into the cell cycle, cyclin-dependent kinases phosphorylate pRb, releasing free E2F and allowing it to interact with transcriptional coactivators, and direc...

Enhanced Expression of PCAF Endows Apoptosis Resistance in Cisplatin-Resistant Cells

“…6A and B). It has been reported that SirT1 represses E2F1-dependent p73 promoter activity and apoptosis (21,22). SirT1 expression was upregulated in PCAF-overexpressing cells (Fig.…”

“…6A and B). The deacetylase SirT1, binds to E2F1 and inhibits the PCAF-E2F1-p73 apoptotic pathway (21,22), and was upregulated in PCAF-overexpressing cells (Fig. 6B).…”

Phospho-ΔNp63α is a key regulator of the cisplatin-induced microRNAome in cancer cells

“…p300, PCAF, HDAC, and DNMT) might provide the necessary support (Supplementary Figures S1-S6). [27][28][29][30][31][32] Recent report showed that HDAC1/2 are present at the promoter regions of DNp63-repressed targets in keratinocytes, indicating a direct requirement for HDAC1/2 in DNp63-mediated repression. 39 Materials and Methods Cells and reagents.…”

“…[27][28][29][30][31][32] Moreover, because miRNAs are processed from capped, polyadenylated transcripts, a complex RNA-processing machinery 26,33 may also be involved in the regulation of miRNA expression and may be potentially affected by CIS exposure. However, this study was exclusively focused on the CIS/p-DNp63a functional relationship regarding the miRNA expression in HNSCC cells.…”

Dynamical Aspects of Apoptosis

“…After that, p300/CBP acetylates p53 on lysine 373, allowing the selective recognization of the promoter sites of pro-apoptotic genes like PUMA, BAX and BAK by p53 (Pietsch et al, 2008). It is noteworthy that the formation of the p53-p300 complex is reversible, and p300 is separated from the complex by the removal of the acetyl group of p53 (Pediconi et al, 2009). The enzyme responsible for this step is the SIRT1 deacetylase (Tanno et al, 2006;Pediconi et al, 2009).…”