AKAP79 INHIBITS CALCINEURIN THROUGH A SITE DISTINCT FROM THE IMMUNOPHILIN-BINDING REGION

Targeting of protein kinases and phosphatases provides additional spec ificity to substrate selectivity in cellular signaling. In the case of the Ca2+/calmodulin-dependent protein phosphatase calcineurin, AKAP79 has been shown to bind calcineurin and inhibit its activity in vitro (Coghlan, V., Perrino, B. A., Howard, M., Langeberg, L. K., Hicks, J. B., Gallatin, W. M., and Scott, J. D. (1995) Science 267, 108-111). In the present study, we characterized the binding regions on calcineuri n A (CnA) and AKAP79 that are important for this interaction. Residues 30-98 and 311-336 on CnA and residues 108-280 on AKAP79 were found to be important for binding. The binding of CnA by AKAP79 does not requi re the calcineurin B subunit, and occurs in a region distinct from whe re the immunosuppressant-immunophilin complex bind. AKAP79 also bound to CnA in cells transfected with AKAP79 and CnA. To determine the func tion of AKAP79-calcineurin interaction in intact cells, we measured th e dephosphorylation and subsequent activation of NFAT, a transcription factor that is a substrate for calcineurin, Overexpression of AKAP79 inhibited NFAT dephosphorylation, resulting in a decrease in NFAT acti vation. These results demonstrated that AKAP79 can bind to and inhibit calcineurin activity in vivo, suggesting a physiological role for AKA P79-calcineurin interaction in NFAT-mediated signaling.