Inhibition of Polyomavirus ori- Dependent DNA Replication by mSin3B

Abstract

When tethered in cis to DNA, the transcriptional corepressor mSin3B inhibits polyomavirus (Py) oridependent DNA replication in vivo. Histone deacetylases (HDACs) appear not to be involved, since tethering class I and class II HDACs in cis does not inhibit replication and treating the cells with trichostatin A does not specifically relieve inhibition by mSin3B. However, the mSin3B L59P mutation that impairs mSin3B interaction with N-CoR/SMRT abrogates inhibition of replication, suggesting the involvement of N-CoR/SMRT. Py large T antigen interacts with mSin3B, suggesting an HDAC-independent mechanism by which mSin3B inhibits DNA replication.The mammalian Sin3 (mSin3) transcriptional corepressor is associated with many distinct protein complexes, among which, the mSin3/histone deacetylases (HDAC)/RbAp48 complex is predominant (reviewed in references 4 and 59). This complex is recruited by unliganded nuclear hormone receptors through N-CoR/SMRT (nuclear receptor corepressor/silencing mediator for retinoid and thyroid receptors) (2,32,34,45,57,102), the methylated CpG-binding protein MeCP2 (40, 58), Mad/ Max and Mxi/Max heterodimers (71), p53 (56), and other proteins (reviewed in reference 15) to repress the transcription of specific targets.At least two forms of mSin3B are found in mammalian cells due to alternative mRNA splicing: the full-length mSin3B (mSin3B LF ) containing four paired amphipathic ␣-helix (PAH) and a short form mSin3B (mSin3B SF ) containing only the first two PAH domains and lacking the HDAC1/2-interacting domain (2). HDAC1 and -2 interact with mSin3A (or -B) protein through domains within the C terminus, starting at PAH3 (2, 92), and HDAC7 interacts with PAH1 of mSin3 (42), whereas HDAC5, as well as HDAC7, indirectly interacts with mSin3 through N-CoR/SMRT (37,42). N-CoR/SMRT also acts as a corepressor in an mSin3-HDAC complex (2,32,34,45,57,102). The L59P substitution in PAH1 impairs interaction with N-CoR/SMRT and partially reduces corepressor activity (2). Not all active Sin3 complexes require either HDAC activity or even the presence of HDACs (2,41,45,92,100).HDAC-dependent p53-mediated transcriptional repression requires mSin3 (56, 103). The p53 protein also represses in vitro replication of simian virus 40 (SV40) DNA and polyomavirus (Py) DNA (19,55,82,86) and nuclear DNA replication in the Xenopus egg extracts (14). Whether or not mSin3 is required for p53 mediated repression of DNA replication is not known.HDAC complexes recruited by pRB to deacetylate histones and nonhistone proteins important for transcription also contain mSin3 (8, 46, 50, 51). pRB's control of cell cycle progression and DNA replication depends, at least in part, upon repressing transcription of E2F-regulated genes through both HDAC-dependent and -independent mechanisms (31, 46). That control of DNA replication by pRB might involve mechanisms besides transcriptional repression is suggested by observations including: (i) interaction of pRB with the replication-licensing factor MCM7 inhibits DNA replication in vitro (...

Inhibition of Transcription and DNA Replication by the Papillomavirus E8⁁E2C Protein Is Mediated by Interaction with Corepressor Molecules

“…Furthermore, we found that the inhibition of the replication of HPV31 origin by a Gal4-Krab protein was also independent from HDAC activity. Comparable to these observations, a Gal4-mSin3B fusion protein repressed T-Ag-dependent replication of the polyomavirus origin also independently from HDAC activity (44).…”

“…The inhibition of T-antigen (T-Ag)-dependent replication by mSin3B is independent of HDAC activity and the presence of HDACs at the origin but requires the interaction with nuclear corepressor (N-CoR)/silencing mediator of retinoid and thyroid receptor proteins (44). This suggests that corepressor complexes have the ability to restrict DNA virus replication but that this activity is independent from histone modifications.…”

“…The constructs expressing Gal4-TRIM28 (pG4M polyII-mTIF1␤; TRIM28 is (tripartite motif-containing 28 [GeneID 10155]), Gal4-HP1␤ (pG4M polyII-mHP1␤), and Gal4-HP1␥ (pG4M polyII-mHP1␥) were a kind gift of R. Losson, Strasbourg, France (24). Plasmids pGALO Gal4-mSin3B, pGal4-HDAC1, and pGal4-HDAC2 were kind gifts from W. Folk (44). Plasmid pMhsHP1a was constructed by inserting the PCR-amplified HP1␣ coding sequence using IMAGE clone 3448801 (RZPD, Germany) into pM (Clontech, Heidelberg, Germany).…”

“…In addition to a role in transcriptional repression, the mSin3B protein, which is a central component of SIN3 complexes, has been demonstrated to interfere with viral DNA replication when targeted to the polyomavirus origin of replication (44). The inhibition of T-antigen (T-Ag)-dependent replication by mSin3B is independent of HDAC activity and the presence of HDACs at the origin but requires the interaction with nuclear corepressor (N-CoR)/silencing mediator of retinoid and thyroid receptor proteins (44).…”

“…6). We also tested in the transient replication assay a Gal4-mSin3B fusion protein that has been shown to inhibit the T-Agdependent replication of the polyomavirus origin (44). SIN3 proteins are central parts of multiprotein complexes involved in transcription repression and associate both with class I HDACs and SETDB1 but have so far not been linked to TRIM28 (18,33).…”