Roles for 19S ATPases in transcriptional elongation

Components of the 26S proteasome include a 19S regulatory particle which recognizes ubiquitinated proteins and a 20S proteolytic core in which proteins are degraded. We and others have shown 19S ATPases act as mediators of transcriptional activation and play important roles in gene expression. Major histocompatibility class II (MHC II) molecules present extracellular antigens to CD4 + T cells to activate the immune response. Expression of MHC II is regulated at the level of transcription by the Class II Transactivator (CIITA) whose association with the MHC II promoter is necessary for dynamic phosphorylation of RNA Pol II and elongation of MHC II transcripts. We have previously shown that the 19S ATPase S6a is inducibly recruited to promoter and coding regions of actively transcribing CIITA genes. As elongation by RNA Pol II has emerged as a regulated step in gene expression, we next investigated roles for 19S ATPases in transcriptional elongation at CIITA genes. We first demonstrate dynamic ATPase association with components of the basal elongation machinery. We next show 19S ATPases are recruited to CIITA coding regions coordinate with Pol II recruitment. Notably, RNAi mediated knockdown of 19S ATPase S6a significantly diminishes recruitment of Pol II to CIITA coding regions. These studies indicate transcriptional regulation by 19S ATPases as a novel mechanism of regulating mammalian gene expression. Research supported by grants from the American Cancer Society, the Georgia Cancer Coalition, (to S.F. Greer) and a Ph.D. Fellowship from the Molecular Basis of Disease Program (to A.D. Truax).