Class II transactivator (CIITA) mediates transcriptional repression of pdk4 gene by interacting with hypermethylated in cancer 1 (HIC1)

Increased accumulation and/or impaired utilization of fatty acid in extra-adipose tissues are implicated in the pathogenesis of insulin resistance and type 2 diabetes. Pyruvate dehydrogenase kinase 4 (Pdk4) is a key enzyme involved in fatty oxidation and energy expenditure, and its expression can be repressed by pro-inflammatory stimuli. Previously, we have shown that class II transactivator (CIITA) mediates the adverse effect of interferon gamma (IFN-c) in skeletal muscle cells by cooperating with hypermethylated in cancer 1 (HIC1) to repress silent informa- tion regulator 1 (SIRT1) transcription. Building upon this finding, we report here that CIITA interacted with HIC1 via the GTP-binding domain (GBD) while HIC1 interacted with CIITA via the BTB/POZ domain. The GBD domain was required for CIITA to repress SIRT1 transcription probably acting as a bridge for CIITA to bind to HIC1 and consequently to bind to the SIRT1 promoter. IFN-c stimulation, CIITA over-expression, or HIC1 over- expression repressed Pdk4 promoter activity while silencing either CIITA or HIC1 normalized Pdk4 expression in the presence of IFN-c. An increase in SIRT1 expression or activity partially rescued Pdk4 expression in the pre- sence of CIITA, but SIRT1 inhibition abrogated Pdk4 normalization even in the absence of CIITA. Taken together, our data have identified a HIC1-CIITA-SIRT1 axis that regulates Pdk4 transcription in response to IFN-c stimula- tion.