Regulation of BAD phosphorylation at serine 112 by the Ras-mitogen-activated protein kinase pathway.
The function of the pro-apoptotic molecule BAD is regulated by phosphorylation of two sites, serine-112 (Ser-112) and serine-136 (Ser-136). Phosphorylation at either site results in loss of the ability of BAD to heterodimerize with the survival proteins BCL-XL or BCL-2. Phosphorylated BAD binds to 14-3-3 and is sequestered in the cytoplasm. It has been shown that phosphorylation of BAD at Ser-136 is mediated by the serine/threonine protein kinase Akt-1/PKB which is downstream of phosphatidylinositol 3-kinase (PI3K). The signaling process leading to phophorylation of BAD at Ser-112 has not been identified. In this study, we show that phosphorylation of the two serine residues of BAD is differentially regulated. While Ser-136 phosphorylation is concordant with activation of Akt, Ser-112 phosphorylation does not correlate with Akt activation. Instead, we demonstrate that activated Ras and Raf, which are upstream of mitogen-activated protein kinases (MAPK), stimulate selective phosphorylation of BAD at Ser-112. Furthermore, phosphorylation of Ser-112, but not Ser-136 requires activation of the MAPK pathway as the MEK inhibitor, PD 98059, blocks EGF-, as well as activated Ras- or Raf-mediated phosphorylation of BAD at Ser-112. Therefore, the PI3K-Akt and Ras-MAPK pathways converge at BAD by mediating phosphorylation of distinct serine residues.
Fang
X
X
Department of Molecular Oncology, University of Texas MD Anderson Cancer Center, Houston 77030, USA.
Yu
S
S
Eder
A
A
Mao
M
M
Bast
R C
RC
Boyd
D
D
Mills
G B
GB
D016475:3T3 Cells; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D006801:Humans; D020935:MAP Kinase Signaling System; D051379:Mice; D010766:Phosphorylation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism*; D051025:bcl-Associated Death Protein; D018631:ras Proteins / Q000378:metabolism*
C494819:BAD protein, human; C494820:Bad protein, mouse; D002352:Carrier Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051025:bcl-Associated Death Protein; D012694:Serine; D018631:ras Proteins