p90Rsk, MEK2(MAP2K2), IGF-1 receptor, 18.104.22.168, IRS-1, PP2A catalytic, PI3K reg class IA, MEK1(MAP2K1), p70 S6 kinase1, Adenylate cyclase type I, BAD, 14-3-3, p70 S6 kinase2, Shc, PtdIns(4,5)P2, Cytochrome c, Bcl-XL, Erk (MAPK1/3), Calcineurin A (catalytic), PP2C, PI3K cat class IA, PP1-cat alpha, GRB2, AKT(PKB), PDK (PDPK1), G-protein beta/gamma, PtdIns(3,4,5)P3, SOS, ATP cytosol, PKA-cat (cAMP-dependent), Bax, EGFR, PKA-reg (cAMP-dependent), BAD, c-Raf-1, Bcl-2, CDK1 (p34), 22.214.171.124, H-Ras, cAMP, JNK1(MAPK8), G-protein alpha-s
BAD is a member of the BCL-2 family. BCL-2 family members are regulators of the programmed cell death pathways.
BAD induces apoptosis by inhibiting antiapoptotic BCL-2-family members - BCL-x, Bcl-2, thereby allowing two other pro-apoptotic proteins, BAK and BAX, to aggregate and induce release of cytochrome c, followed by caspase activation and apoptosis .
Proapoptotic activity of BAD is regulated through its phosphorylation. Only the nonphosphorylated BAD heterodimerized with BCL-xl or Bcl-2. Phosphorylated BAD is sequestered in the cytosol by binding to 14-3-3 .
It is generally believed that survival factors induce activation of specific antiapoptotic kinases, which modulate the activity of BAD .
In response to the activation of a insulin-like growth factor receptor ( IGF-1R ) and epidermal growth factor receptor ( EGFR ) occur activation phosphatidylinositol 3-kinase ( PI3K ) signaling cascade, which result to activation protein kinase B (PKB, also called Akt ) and 70-kDa ribosomal protein S6 kinases ( P70 S6 kinase 1 and P70 S6 kinase 1 2). AKT and P70 S6 kinases phosphorylate Ser-136 and inhibition of BAD . Growth factors also activate RAS-ERK signaling cascade. The 90-kDa ribosomal S6 kinase ( p90RSK ), a downstream effector in the MAPK signaling cascade, inactivates the pro-apoptotic protein BAD by phosphorylation it at serine 112 , .
Cyclin-dependent kinase 1( CDK1) catalyzes phosphorylation of BAD at a distinct site, serine 128. The phosphorylation of BAD serine 128 inhibits the interaction of growth factor-induced serine 136-phosphorylated BAD with 14-3-3 proteins and, thereby, induces BAD-mediated apoptosis .
It is not known what kinases phosphorylate BAD at Ser170 .
In response to interleukin-3 stimulus, mitogen-activated protein kinase 8 ( JNK1 ) can phosphorilate BAD. JNK1 phosphorylates BAD at threonine 201, thereby inhibiting BAD association with the antiapoptotic molecule BCL-XL and BCL-2 .
Under certain stress conditions, BAD is activated by dephosphorylation. Protein phosphotase 1 alpha ( PP1A ), protein phosphatases 2A ( PP2A ), 2B ( PP2B, calcineurin) and 2C ( PP2C )can participapate in thisprocess , , , . These phosphotases act on Ser112 and Ser136 and, except PP2B, also can dephosphorylated Ser155. Only PP2C gives priority to P-Ser(155) compared to P-Ser(112) and P-Ser(136) on BAD .
Dephosphorylated BAD is released from 14-3-3 and becomes free to interact with anti-apoptotic Bcl-2 family members, thereby activating the apoptotic effector machinery .