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 overexpression 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 FakSer732 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 β-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.
This article contains Supplementary Data online at http://diabetes.diabetesjournals.org/lookup/suppl/doi:10.2337/db10-1048/-/DC1.
- Received July 26, 2010.
- Accepted December 21, 2010.
- © 2011 by the American Diabetes Association.
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