Abstract
The small GTPase Rac1 has emerged as an important regulator of cell survival and apoptosis, but the mechanisms involved are not completely understood. In this report, constitutively active Rac1 is shown to stimulate the phosphorylation of the Bcl-2 family member Bad, thereby suppressing drug-induced caspase activation and apoptosis in human lymphoma cells. Rac1 activation leads to human Bad phosphorylation specifically at serine-75 (corresponding to murine serine-112) both in vivo and in vitro. Inhibition of constitutive and activated Rac1-induced Bad phosphorylation by a cell-permeable competitive peptide inhibitor representing this Bad phosphorylation site sensitizes lymphoma cells to drug-induced apoptosis. The data show further that endogenous protein kinase A is a primary catalyst of cellular Bad phosphorylation in response to Rac activation, while Akt is not involved. These findings define a mechanism by which active Rac1 promotes lymphoma cell survival and inhibits apoptosis in response to cancer chemotherapy drugs.
MeSH terms
-
Animals
-
Apoptosis / physiology*
-
Carrier Proteins / genetics
-
Carrier Proteins / metabolism*
-
Caspases / metabolism
-
Cell Line, Tumor
-
Cell Survival / physiology*
-
Cyclic AMP-Dependent Protein Kinases / antagonists & inhibitors
-
Cyclic AMP-Dependent Protein Kinases / metabolism
-
Drug Resistance, Neoplasm
-
Enzyme Activation
-
Etoposide / metabolism
-
Humans
-
Lymphoma / metabolism*
-
Mice
-
Nucleic Acid Synthesis Inhibitors / metabolism
-
Phosphorylation
-
Protein Serine-Threonine Kinases / metabolism
-
Proto-Oncogene Proteins / metabolism
-
Proto-Oncogene Proteins c-akt
-
Recombinant Fusion Proteins / genetics
-
Recombinant Fusion Proteins / metabolism
-
Serine / metabolism*
-
Signal Transduction / physiology
-
bcl-Associated Death Protein
-
rac1 GTP-Binding Protein / genetics
-
rac1 GTP-Binding Protein / metabolism*
Substances
-
BAD protein, human
-
Bad protein, mouse
-
Carrier Proteins
-
Nucleic Acid Synthesis Inhibitors
-
Proto-Oncogene Proteins
-
Recombinant Fusion Proteins
-
bcl-Associated Death Protein
-
Serine
-
Etoposide
-
AKT1 protein, human
-
Protein Serine-Threonine Kinases
-
Proto-Oncogene Proteins c-akt
-
Cyclic AMP-Dependent Protein Kinases
-
Caspases
-
rac1 GTP-Binding Protein