Cyclic‐AMP‐dependent protein kinase A regulates apoptosis by stabilizing the BH3‐only protein Bim

Abstract

The proapoptotic Bcl2 homology domain 3(BH3)-only protein Bim is controlled by stringent post-translational regulation, predominantly through alterations in phosphorylation status. To identify new kinases involved in its regulation, we carried out a yeast two-hybrid screen using a non-spliceable variant of the predominant isoform-Bim EL -as the bait and identified the regulatory subunit of cyclic-AMP-dependent protein kinase A-PRKAR1A-as an interacting partner. We also show that protein kinase A (PKA) is a Bim EL isoform-specific kinase that promotes its stabilization. Inhibition of PKA or mutation of the PKA phosphorylation site within Bim EL resulted in its accelerated proteasome-dependent degradation. These results might have implications for human diseases that are characterized by abnormally increased PKA activity, such as the Carney complex and dilated cardiomyopathy.

Mechanisms of cyclic AMP/protein kinase A- and glucocorticoid-mediated apoptosis using S49 lymphoma cells as a model system

“…3E). When overexpressed, Bim (extralong) and PKA-RIα interact, an interaction that is required for the subsequent phosphorylation and stabilization of Bim by PKA-Cα (35). Consistent with those results in overexpressing cells, immunoprecipitation of endogenous PKA-RIα in WT and kin -S49 cells revealed that PKA-RIα interacts with Bim in WT cells incubated with CPT-cAMP (15) (Fig.…”

“…Bim not only mediates cAMP/PKA-promoted apoptosis of S49 cells but also is involved in glucocorticoid-promoted apoptosis of S49, other lymphoma, and immature lymphoid cells (15,35). The data here imply that another mechanism, the mitochondrial protein AIF, is involved in glucocorticoid-promoted apoptosis in kin -cells.…”

Loss of Prkar1a leads to Bcl-2 family protein induction and cachexia in mice

“…There was also a marked increase Figure S1c). However, the contribution of Bim protein stabilization 11 to apoptosis in these MEFs is yet to be determined. Collectively, these data show that inducible deletion of Prkar1a triggers apoptosis and consequently reduced colony formation in MEFs by causing an upregulation of Bim expression.…”

“…33 In contrast, another report identified Prkar1a as a weak tumour promoter, 9 and our previous work revealed that increased PKA activity can elicit apoptosis, consistent with the notion that PRKAR1a may promote tumorigenesis. 11,12,34 We therefore hypothesized that Prkar1a loss or haploinsufficiency on its own would not be sufficient to promote tumour development. Tumorigenesis does not result from a single oncogenic mutation but is driven by a series of oncogenic lesions, each conferring some growth advantage.…”

“…Findings from our laboratory and others revealed that increased PKA activity caused transcriptional induction as well as posttranslational stabilization of the proapoptotic BH3-only protein BIM. [11][12][13] Moreover, PKA activation has been shown to promote differentiation and block proliferation in certain cell lines. [14][15][16][17] Increased PKA activity has also been reported to cause cardiomyocyte apoptosis, thereby leading to cardiomyopathy.…”