Epigenetic Regualtion Of The CIITA In Heat-shocked Cells

MHC-Ⅱ (Major Histocompatibility Complex Class-Ⅱ) molecules, constitutively expressed on the surface of mammalian cells, are critical immune regulators which responsible for presenting extracellular antigen to CD4+T lymphocytes and activating the adaptive immune system to clear pathogen. CIITA(class II transactivator) is a master tansriptional activator for the transcription of MHC-Ⅱ and play a central role in the process of antigen presentation. CIITA gene transcription is controled by an intricate promotor region which consists of four different, cell specific promotors and have four different transcription products. MHC-I and MHC-Ⅱ are not expressed or low expressed on the surface of many sorts of tumor cells. For the defects in antigen presentation pathway, tumor cells can protect itself from the immunological surveillance and clearance with its low immunogenicity.Epigenetics refers to the study of mechanisms which alter gene expression without altering the primary DNA sequence. Epigenetic mechanisms are heritable and reversible.. Epigenetic mechanisms include DNA methylation, chromatin remodeling, histone modifications and non-coding RNA, etc. Recently, there is growing evidence that the regulation of immune cells differentiation, maturation and acitvation are under the control of epigenetic mechanisms. And in the process of tumorigenesis, disorders in epigenetic mechanisms are an important reason. Notably, tumorigenesis is associated with its low immunogenicity and the disfunction of immune cells. So, we speculated that the epigenetic mechanisms occupy the key point link the immune disfunction to tumorigenesis.Gene expression of CIITA are inhibited by DNA methylation and histone H3K27trimethylation on its promotor regions in tumor cells. If CIITA gene was induced to express in tumor cells, MHC-Ⅱ expression would be up-regulated too and then tumor associated antigens would be presented into CD4+T lymphocytes and lead to specific anti-tumor immuno responses filnally.In our research, we demonstrated that heat shock could induce CIITA and HLA-DRa expression. Recently, many researchers reported that heat shock proteins90,60,70were co-activators of innate immunity system and hsp90played an important role in MHC Ⅱ antigen presentation patyway. Our research showed that hsp90didn't participate in the process of heat shock indued CIITA expression. By the further research, we demonstrated that heat shock could activate JAK-STAT pathway, lead to EZH2ubiquitination and degradation by26S preatosome pathway. Heat shock-induced EZH2degradation could be blocked by JAK2inhibitor, AG490, and JAK2knock-down. EZH2degradation would decrease the modification level of global histone H3K27trimethylation, histone H3K27trimethylation modification at the promotor region of CIITA-IV and inhibit the following transcription activation of CⅡTA-Ⅳ in MCF-7cells.In sum, our research demonstrated that heat shock-induced EZH2degradation activated gene transcription of CⅡTA. And this result is a solid example in which circumstance factors induced MHC Ⅱ expression and immunogenicity recovery in tumor cells by epigenetic mechanisms. Hsp90is an evolutionarily conserved molecular chaperone that participates in stabilizing and activating more than200proteins, referred to as Hsp90'clients'. Many of which are essential for constitutive cell signalling and adaptive responses to stress. Cancer cells can use the Hsp90chaperone machinery to protect an array of mutated and over expressed oncoproteins from misfolding and degradation. Therefore, Hsp90is recognized as a crucial facilitator of oncogene addiction and cancer cell survival. Hsp90protein is typically induced by heat shock or other environmental stress via the interaction of an activated heat shock factors (HSF) with heat shock elements (HSE) within the promotor of the heat shock genes.In the Hsp90protein family, there are two cytoplasm isoforms of Hsp90in mammalian cells. Despite their amino acid sequences are highly identical, the two Hsp90isoforms are encoded by two genes positioned on distinct chromosomes and are designated as hsp90a and hsp90β genes. Hsp90a and hsp90β, although highly homologous, have functional differences in normal surroundings or under cell stress. Hsp90a and hsp90β mainly functions as homodimers. However, functions and regulation for Hsp90heterodimers are not fully understand.In this study, we show that heat shock and H2O2can promote subcellular co-localization and interaction between Hsp90a and hsp90β in Jurkat cells. TSA, a HDAC inhibitor, can lead to hsp90a and Hsp90β hyperacetylation, inhibit the subcellular co-localization and interaction between Hsp90a and hsp90β under cell stress. These data indicate that cell stress induced hsp90heterodimers may have specific functions which dependent on its acetylation status. Furthermore, We need more works to prove the mechanisms and functions of Hsp90heterodimers both physiologically and under heat shock.