Cyclin-dependent kinase 5 promotes pancreatic β-cell survival via Fak-Akt signaling pathways

Abstract

OBJECTIVE - Cyclin-dependent kinase 5 (CDK5) regulatory subunit-associated protein 1-like 1 has recently been linked to type 2 diabetes by genome-wide association studies. While CDK5 and its regulatory protein p35 are both expressed and display enzymatic activity in pancreatic β-cells, their precise role in the β-cell remains unknown. Because type 2 diabetes is characterized by a deficit in β-cell mass and increased β-cell apoptosis, we investigated the role of CDK5 in β-cell survival. RESEARCH DESIGN AND METHODS - We used INS 832/13 cells, rat islets isolated from wild-type or human islet amyloid polypeptide (h-IAPP) transgenic rats, and pancreatic tissue from rats and humans with and without type 2 diabetes and investigated the effect of CDK5/p35 inhibition (by small interfering RNA or by chemical inhibition) as well as CDK5/p35 over-expression on β-cell vulnerability to apoptosis. RESULTS - CDK5 inhibition led to increased β-cell apoptosis. To identify the mechanisms involved, we examined the phosphorylation state of focal adhesion kinase (Fak)Ser732, a known target of CDK5. Following CDK5 inhibition, the phosphorylation of Fak Ser732 decreased with resulting attenuation of phosphatidylinositol 3-kinase (PI3K)/Akt survival pathway. Conversely, CDK5 overexpression increased FakSer732 phosphorylation and protected β-cells against apoptosis induced by the inhibition of the β-1 integrin signaling pathway. Also, FakSer732 phosphorylation was less abundant in b-cells in both h-IAPP transgenic rats and humans with type 2 diabetes. CONCLUSIONS - This study shows that by regulating Fak phosphorylation and subsequently PI3K/Akt survival pathway, CDK5 plays a previously unrecognized role in promoting β-cell survival. © 2011 by the American Diabetes Association.