Transcriptional activators interact with multisubunit coactivators that modify chromatin structure or recruit the general transcriptional machinery to their target genes. Budding yeast cells respond to amino acid starvation by inducing an activator of amino acid biosynthetic genes, Gcn4p. We conducted a comprehensive analysis of viable mutants affecting known coactivator subunits from the Saccharomyces Genome Deletion Project for defects in activation by Gcn4p in vivo. The results confirm previous findings that Gcn4p requires SAGA, SWI/SNF, and SRB mediator (SRB/MED) and identify key nonessential subunits of these complexes required for activation. Among the numerous histone acetyltransferases examined, only that present in SAGA, Gcn5p, was required by Gcn4p. We also uncovered a dependence on CCR4-NOT, RSC, and the Paf1 complex. In vitro binding experiments suggest that the Gcn4p activation domain interacts specifically with CCR4-NOT and RSC in addition to SAGA, SWI/SNF, and SRB/MED. Chromatin immunoprecipitation experiments show that Mbf1p, SAGA, SWI/SNF, SRB/MED, RSC, CCR4-NOT, and the Paf1 complex all are recruited by Gcn4p to one of its target genes (ARG1) in vivo. We observed considerable differences in coactivator requirements among several Gcn4p-dependent promoters; thus, only a subset of the array of coactivators that can be recruited by Gcn4p is required at a given target gene in vivo.Eukaryotic activator proteins stimulate transcription by binding to their target genes and carrying out two general functions: (i) altering the locations or structures of nucleosomes and (ii) recruiting TATA-binding protein (TBP), other general transcription factors (GTFs), and RNA polymerase II (RNA PolII) to the promoter. Most activators carry out these functions indirectly by recruiting multisubunit complexes, collectively called coactivators (39,70,90). One class of coactivators uses ATP hydrolysis to displace nucleosomes and thereby expose or obscure protein binding sites in the promoter (91,124). Each of the nucleosome remodeling complexes of Saccharomyces cerevisiae, known as SWI/SNF, RSC, ISW1, and ISW2, contains a different subunit harboring the ATPase activity of the complex (reviewed in references 70 and 91). Although each has been implicated in transcriptional activation in vivo (5,38,51,85,123), only the nonessential SWI/SNF complex has been shown to interact physically with activators (93, 139) and be recruited to a promoter for nucleosome remodeling and transcriptional activation in vitro (45,96,139). Recruitment of the SWI/SNF complex by yeast activators has also been demonstrated in living yeast cells by chromatin immunoprecipitation (ChIP) assays (24, 126).Another class of coactivators alters chromatin structure by acetylation of lysines in the amino-terminal tails of histones. This modification destabilizes higher-order chromatin structure (116) and also may stimulate binding of other coactivator proteins containing a bromodomain (9,91,120,135). The SAGA complex is the best-characterized yeast coactivato...

BACKGROUND AND PURPOSE Salinomycin (Sal) has recently been shown to inhibit various cancer stem cells. Here, we investigated whether Sal could sensitize cancer cells to the effects of doxorubicin (DOX) or etoposide (ETO). EXPERIMENTAL APPROACH Using the Comet assay, immunocytochemistry and Western blot analysis, we assessed the ability of Sal to increase DNA breakage. We performed a cell proliferation assay to determine cell viability, cellular detachment, increased pre‐G1 region, Annexin V staining and TUNEL assay to measure the ability of Sal to increase apoptosis. KEY RESULTS Sal increased DNA breakage and phosphorylated levels of p53 and H2AX. Sal also induced the formation of DNA foci with pH2AX and 53BP1. Furthermore, Sal increased the sensitivity of cancer cells to the apoptotic effects of DOX or ETO. We found that pH2AX, pBRCA1, p53BP1 and pChk1 levels were greatly increased after co‐treatment of Sal with DOX or ETO. The level of anti‐apoptotic p21 protein was increased by DOX or ETO but decreased by Sal, which increased proteasome activity. CONCLUSIONS AND IMPLICATIONS This is the first study to report that Sal increases DNA damage, and this effect plays an important role in the increased apoptosis caused by Sal. Overall, we demonstrated that the ability of Sal to sensitize cancer cells to the effects of DOX or ETO is associated with an increase in DNA damage and a decrease in anti‐apoptotic protein p21 levels. These results may contribute to the development of Sal‐based chemotherapy for cancer patients receiving DOX or ETO treatment.

Wild-type transcriptional activation by Gcn4p is dependent on multiple coactivators, including SAGA, SWI/SNF, Srb mediator, CCR4-NOT, and RSC, which are all recruited by Gcn4p to its target promoters in vivo. It was not known whether these coactivators are required for assembly of the preinitiation complex (PIC) or for subsequent steps in the initiation or elongation phase of transcription. We find that mutations in subunits of these coactivators reduce the recruitment of TATA binding protein (TBP) and RNA polymerase II (Pol II) by Gcn4p at ARG1, ARG4, and SNZ1, implicating all five coactivators in PIC assembly at Gcn4p target genes. Recruitment of Pol II at SNZ1 and ARG1 was eliminated by mutations in TBP or by deletion of the TATA box, indicating that TBP binding is a prerequisite for Pol II recruitment by Gcn4p. However, several mutations in SAGA subunits and deletion of SRB10 had a greater impact on promoter occupancy of Pol II versus TBP, suggesting that SAGA and Srb mediator can promote Pol II binding independently of their stimulatory effects on TBP recruitment. Our results reveal an unexpected complexity in the cofactor requirements for the enhancement of PIC assembly by a single activator protein.

Transcriptional activation by Gcn4p is dependent on the coactivators SWI/SNF, SAGA, and Srb Mediator, which are recruited by Gcn4p and stimulate assembly of the preinitiation complex (PIC) at the ARG1 promoter in vivo. We show that recruitment of all three coactivators is nearly simultaneous with binding of Gcn4p at ARG1 and is followed quickly by PIC formation and elongation by RNA polymerase II (

Sirtuins (SIRTs), NAD+-dependent class III histone deacetylases (HDACs), play an important role in the regulation of cell division, survival and senescence. Although a number of effective SIRT inhibitors have been developed, little is known about the specific mechanisms of their anticancer activity. In this study, we investigated the anticancer effects of sirtinol, a SIRT inhibitor, on MCF-7 human breast cancer cells. Apoptotic and autophagic cell death were measured. Sirtinol significantly inhibited the proliferation of MCF-7 cells in a concentration-dependent manner. The IC50 values of sirtinol were 48.6 µM (24 h) and 43.5 µM (48 h) in MCF-7 cells. As expected, sirtinol significantly increased the acetylation of p53, which has been reported to be a target of SIRT1/2. Flow cyto-metry analysis revealed that sirtinol significantly increased the G1 phase of the cell cycle. The upregulation of Bax, downregulation of Bcl-2 and cytochrome c release into the cytoplasm, which are considered as mechanisms of apoptotic cell death, were observed in the MCF-7 cells treated with sirtinol. The annexin V-FITC assay was used to confirm sirtinol-induced apoptotic cell death. Furthermore, the expression of LC3-II, an autophagy-related molecule, was significantly increased in MCF-7 cells after sirtinol treatment. Autophagic cell death was confirmed by acridine orange and monodansylcadaverine (MDC) staining. Of note, pre-treatment with 3-methyladenine (3-MA) increased the sirtinol-induced MCF-7 cell cytotoxicity, which is associated with blocking autophagic cell death and increasing apoptotic cell death. Based on our results, the downregulation of SIRT1/2 expression may play an important role in the regulation of breast cancer cell death; thus, SIRT1/2 may be a novel molecular target for cancer therapy and these findings may provide a molecular basis for targeting SIRT1/2 in future cancer therapy.