Collagen type I is the primary component of the extracellular matrix (ECM). Repression of
collagen type I gene (
COL1A2) transcription by the pro-inflammatory
cytokine interferon gamma (IFN-γ) in vascular smooth muscle cells (VSMCs) is a key step during
atherogenesis that leads to the destabilization of the
atherosclerotic plaque. The epigenetic mechanism underlying IFN-γ induced
COL1A2 repression is not clearly appreciated. We show here that Sin3B, a component of the eukaryotic
histone deacetylase (HDAC) complex, was recruited to
COL1A2 transcription start site in response to IFN-γ treatment in VSMCs paralleling
COL1A2 repression.
Short hairpin RNA (
shRNA) mediated silencing of Sin3B abrogated
collagen repression by IFN-γ and blocked the erasure of active histone marks and the accumulation of repressive histone marks on
COL1A2 transcription start site as evidenced by
chromatin immunoprecipitation (ChIP) assays. Sin3B cooperated with G9a, a
histone H3K9
methyltransferase, to induce a repressive
chromatin structure surrounding the
collagen gene transcription start site in response to IFN-γ stimulation. Sin3B was recruited by regulatory factor for X-box 5 (RFX5) to the
collagen site through a mechanism that involved HDAC2 mediated deacetylation of RFX5. Together, our data indicate that a repressor complex that contains RFX5, HDAC2, Sin3B, and G9a is responsible for IFN-γ induced
COL1A2 repression in VSMCs. Targeting individual component of this complex will likely yield potential therapeutic solutions against
atherosclerosis.