Functional Analysis of CCR4-NOT Complex in Pancreatic β Cell

Functional analysis of CCR4-NOT complex in pancreatic β cellPancreatic β cells are responsible for production and secretion of insulin in response to increasing blood glucose levels. Therefore, defects in pancreatic β cell function lead to hyperglycemia and diabetes mellitus. While extensive research has focused on signaling, transcriptional, and epigenetic regulation in β cells, how post-transcriptional mechanisms influence the β cell gene expression program is largely unknown. The carbon catabolite repression 4 (CCR4)–negative on TATA-less (NOT) complex (CCR4-NOT complex), a major deadenylase conserved in eukaryotes, catalyzes mRNA deadenylation which is the rate limiting step in mRNA decay pathway. The CCR4-NOT complex has been implicated in the development of metabolic diseases. However, whether the CCR4-NOT complex affects β cell function is not addressed. In this thesis, I aim to understand the importance of post-transcriptional regulation in β cells by generating mice lacking the Cnot3 gene, which encodes an essential CCR4-NOT complex subunit, in β cells. Suppression of CNOT3 in β cells caused β cell dysfunction and diabetes. This was associated with the decreased expression of β cell-specific genes and increased expression of genes specifically repressed in β cells, called “β cell disallowed genes”. By combining whole transcriptome and proteome analyses and subsequent validations using quantitative PCR (qPCR) and immunoblot analyses, I found that mRNA and protein expression patterns were largely different from normal β cells upon CNOT3 suppression, which was clearly relevant to the observed phenotypes. I also found that some β cell disallowed genes were stabilized in the absence of CNOT3, suggesting that their expression was maintained at low levels under the control of the CCR4-NOT complex. Together, this study uncovered mRNA deadenylation by CCR4-NOT complex as a novel molecular mechanism by which β cell identity and function are regulated.Okinawa Institute of Science and Technology Graduate Universit