CK2 regulates somatostatin expression in pancreatic delta cells

Pancreatic and duodenal homeobox protein (PDX)1 is a major transcription factor for the regulation of insulin, glucagon and somatostatin (SST) expression. PDX1 is phosphorylated by CK2 and inhibition of this kinase results in an increased insulin and decreased glucagon secretion. Therefore, we speculated in this study that CK2 also affects SST expression. To test this, we analyzed the effects of the two CK2 inhibitors CX-4945 and SGC as well as of PDX1 overexpression on SST expression and secretion in RIN14B cells by qRT-PCR, luciferase assays, Western blot and ELISA. SST expression and secretion were additionally assessed in isolated murine and human islets exposed to the CK2 inhibitors. Moreover, we determined the expression and secretion of the pancreatic endocrine hormones in CX-4945-treated mice. We found a suppressed SST expression in RIN14B cells due to a methylated SST promoter, which could be abolished by DNA demethylation. Under these conditions, we showed that CK2 inhibition increases SST gene expression and secretion. Additional experiments with overexpression of a CK2-phosphorylation mutant of PDX1 verified that SST expression is regulated by CK2. The exposure of isolated murine and human islets to CX-4945 or SGC as well as the treatment of mice with CX-4945 revealed that CK2 also regulates SST expression under physiological conditions. Taken together, these findings not only demonstrate that CK2 controls SST expression in pancreatic δ-cells but also emphasize the crucial role of this kinase in regulating the main hormones of the endocrine pancreas.