Function and regulation of class II transactivator in the immune system.

The class II transactivator (CIITA) is a potent and critical transcriptional regulator. It activates genes necessary for antigen presentation function. It also regulates cytokine gene expression in CD4 T cells. We recently found that CIITA prevents cell death by inhibiting Fas ligand (FasL) gene expression. Thus, CIITA regulates multiple immune responses. The activation and the repression function of CIITA are mediated by its interaction with other transcription factors. To activate the target gene, CIITA interacts with DNA binding proteins and recruits the coactivator CBP/p300 to the promoter forming an enhanceosome necessary for transcription. In addition, CIITA interacts with self. Inter- and intramolecular interactions of CIITA are essential for transactivation function. Each domain of CIITA has a distinct role and all domains are required for CIITA activity. However, the regulatory mechanisms of CIITA interaction with self and other proteins are poorly understood and remain to be investigated.