HIC1 epigenetically represses CIITA transcription in B lymphocytes

Publication date: Available online 6 October 2016
Source:Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanisms
Author(s): Sheng Zeng, Yuyu Yang, Xian Cheng, Bisheng Zhou, Ping Li, Yuhao Zhao, Xiaocen Kong, Yong Xu
Differentiation of B lymphocytes into isotope-specific plasma cells represents a hallmark event in adaptive immunity. During B cell maturation, expression of class II transactivator (CIITA) gene is down-regulated although the underlying epigenetic mechanism is not completely defined. Here we report that hypermethylated in cancer 1 (HIC1) was up-regulated in differentiating B lymphocytes paralleling CIITA repression. Over-expression of HIC1 directly repressed endogenous CIITA transcription in B cells. Reporter assay and chromatin immunoprecipitation (ChIP) assay confirmed that HIC1 bound to the proximal CIITA type III promoter (−545/−113); mutation of a conserved HIC1 site within this region abrogated CIITA trans-repression. More important, depletion of HIC1 with small interfering RNA (siRNA) restored CIITA expression in differentiating B cells. Mechanistically, HIC1 preferentially interacted with and recruited DNMT1 and DNMT3b to the CIITA promoter to synergistically repress CIITA transcription. On the contrary, silencing of DNMT1/DNMT3b or inhibition of DNMT activity with 5-aza-dC attenuated CIITA trans-repression. Therefore, our data identify HIC1 as a novel factor involved in B cell differentiation acting as an epigenetic repressor of CIITA transcription.



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