In accordance with the present invention, it has been discovered that glucose and
incretin hormones promote
pancreatic islet cell survival via the
calcium and cAMP dependent induction, respectively, of the
transcription factor CREB. Specifically, a signaling module has been identified which mediates cooperative effects of
calcium and cAMP on
islet cell gene expression by stimulating the
dephosphorylation and nuclear entry of TORC2, a cytoplasmic
CREB coactivator. The module comprises a cAMP regulated snf1-like
kinase called SIK2 and the
calcium regulated
phosphatase calcineurin, both of which associate with TORC2 in the
cytoplasm. TORC2 is repressed under basal conditions through a
phosphorylation dependent interaction with 14-3-3 proteins. cAMP and calcium signals stimulate
CREB target gene expression via complementary effects on TORC2
dephosphorylation; cAMP disrupts TORC2-associated activity of SIK2 or related family members, whereas calcium induces TORC2
dephosphorylation via calcineurin. These findings provide a novel mechanism by which CREB activates cellular
gene expression, depending on
nutrient and energy status, and facilitate development of assays to identify compounds which modulate the role of TORCs. In accordance with the present invention, it has been discovered that fasting and energy-sensing pathways regulate the gluconeogenic program in liver by modulating the nuclear entry of a transcriptional coactivator called
Transducer of Regulated CREB Activity 2 (TORC2). Hepatic TORC2 over-expression induces fasting hyperglycemia, whereas knockdown of TORC2 leads to fasting
hypoglycemia and silencing of the gluconeogenic program. Since a majority of individuals with
Type II diabetes exhibit fasting hyperglycemia due to elevated hepatic
gluconeogenesis, compounds that enhance TORC2
phosphorylation will find use as therapeutic agents in this setting.