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[摘要]：Phosphorylation of the BH3 (Bcl-2 homology domain 3)-only protein BAD (Bcl-2/Bcl-X-L-antagonist, causing cell death) can either directly disrupt its association with the pro-survival proteins Bcl-X-L and/or Bcl-2, or cause association of BAD with 14-3-3 proteins. In the present study, we further characterize phosphorylation of BAD at Ser(170), a unique site with unclear function. We provide further evidence that mutation of Ser(170) to a phospho-mimetic aspartic acid residue (S170D) can have a profound inhibitory effect on the pro-apoptosis function of BAD. Furthermore, mutated BAD with an alanine substitution inhibited cell proliferation, slowing progression specifically through S-phase. We identify the kinase responsible for phosphorylation at this site as CaMKII-gamma (gamma isoform of Ca2+/calmodulin-dependent kinase II), but not the other three isoforms of CaMKII, revealing an extraordinary specificity among these closely related kinases. Furthermore, cytokine treatment increased BAD-Ser(170)-directed CaMKII-gamma activity and phosphorylation of CaMICII-gamma at an activating site, and CaMKII activity directed to the BAD-Ser(170) site was elevated during S-phase. Treating cells with a selective inhibitor of CaMKII caused apoptosis in cells expressing BAD, but not in cells expressing the BAD-S170D mutant. The present study provides support for BAD-Ser(170) phosphorylation playing a key role not only in regulating BAD's pro-apoptotic activity, but also in cell proliferation. |
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