Bcl-2 protects endothelial cells against gamma-radiation via a Raf-MEK-ERK-survivin signaling pathway that is independent of cytochrome c release.
The Bcl-2 oncoprotein is a potent inhibitor of apoptosis and is overexpressed in a wide variety of malignancies. Until recently, it was generally accepted that Bcl-2 primarily mediates its antiapoptotic function by regulating cytochrome c release from mitochondria. However, more recent studies have shown that Bcl-2 is present on several intracellular membranes and mitochondria may not be the only site where Bcl-2 exercises its survival function. In this study, we investigated if Bcl-2 can protect endothelial cells against gamma-radiation by a cytochrome c-independent signaling pathway. Human dermal microvascular endothelial cells (HDMEC), when exposed to gamma-radiation, exhibited a time-dependent activation of caspase-3 that was associated with increased cytochrome c release from mitochondria. Bcl-2 expression in endothelial cells (HDMEC-Bcl-2) significantly inhibited irradiation-induced caspase-3 activation. However, Bcl-2-mediated inhibition of caspase-3 was significantly reversed by inhibition of the Raf-mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK)-ERK pathway. Interestingly, caspase-3 activation in HDMEC-Bcl-2 cells was not associated with cytochrome c release. We also observed that endothelial cell Bcl-2 expression significantly increased the expression of survivin and murine double minute-2 (Mdm2) via the Raf-MEK-ERK pathway. Endothelial cells expressing Bcl-2 also inhibited gamma-radiation-induced activation of p38 MAPK and p53 accumulation. Inhibition of p53 accumulation in HDMEC-Bcl-2 could be due to the enhanced expression of Mdm2 in these cells. Taken together, these results show three mechanisms by which Bcl-2 may mediate endothelial cell cytoprotection independently of cytochrome c release: (a) increased survivin expression, (b) inhibition of p53 accumulation, and (c) inhibition of p38 MAPK.
Kumar
Pawan
P
Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, 1011 North University Avenue, Ann Arbor, MI 48109, USA. pksuri@umich.edu
Coltas
Ila K
IK
Kumar
Bhavna
B
Chepeha
Douglas B
DB
Bradford
Carol R
CR
Polverini
Peter J
PJ
D017209:Apoptosis / Q000502:physiology / Q000528:radiation effects; D053148:Caspase 3 / Q000378:metabolism; D061945:Caspase Inhibitors; D045304:Cytochromes c / Q000378:metabolism*; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects*; D004789:Enzyme Activation / Q000528:radiation effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism*; D005720:Gamma Rays; D006258:Head and Neck Neoplasms / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D020935:MAP Kinase Signaling System / Q000502:physiology* / Q000528:radiation effects; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000502:physiology*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000096:biosynthesis; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D011836:Radiation Tolerance / Q000502:physiology / Q000528:radiation effects; D000077022:Survivin; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D015854:Up-Regulation; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism
C107489:BIRC5 protein, human; D061945:Caspase Inhibitors; D051034:Inhibitor of Apoptosis Proteins; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D000077022:Survivin; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D045304:Cytochromes c; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D019908:Proto-Oncogene Proteins c-raf; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D053148:Caspase 3