Phosphatidylinositol 3-kinase (PI3K) is essential for both G protein-coupled receptor (GPCR)- and receptor tyrosine kinase (RTK)-mediated cancer cell migration. Here, we have shown that maximum migration is achieved by full activation of phosphatidylinositol 3,4,5-trisphosphate-dependent Rac exchanger 1 (P-Rex1) in the presence of Gbetagamma and PI3K signaling pathways. Lysophosphatidic acid (LPA)-induced migration was higher than that of epidermal growth factor (EGF)-induced migration; however, LPA-induced activation of Akt was lower than that stimulated by EGF. LPA-induced migration was partially blocked by either Gbetagamma or RTK inhibitor and completely blocked by both inhibitors. LPA-induced migration was synergistically increased in the presence of EGF and vice versa. In correlation with these results, sphingosine-1-phosphate (S1P)-induced migration was also synergistically induced in the presence of insulin-like growth factor-1 (IGF-1). Finally, silencing of P-Rex1 abolished the synergism in migration as well as in Rac activation. Moreover, synergistic activation of MMP-2 and cancer cell invasion was attenuated by silencing of P-Rex1. Given these results, we suggest that P-Rex1 requires both Gbetagamma and PI3K signaling pathways for synergistic activation of Rac, thereby inducing maximum cancer cell migration and invasion.
Cell Line, Tumor ; *Cell Movement/drug effects ; Enzyme Activation/drug effects ; GTP-Binding Protein beta Subunits/*metabolism ; GTP-Binding Protein gamma Subunits/*metabolism ; Guanine Nucleotide Exchange Factors/metabolism ; Humans ; Lysophospholipids/pharmacology ; Neoplasms/enzymology/*metabolism ; Phosphatidylinositol 3-Kinases/*metabolism ; Proto-Oncogene Proteins c-akt/metabolism ; Receptors, G-Protein-Coupled/metabolism ; Signal Transduction

Stimulatory heterotrimeric GTP-binding proteins (Gs protein) stimulate cAMP generation in response to various signals, and modulate various cellular phenomena such as proliferation and apoptosis. This study aimed to investigate the effect of Gs proteins on gamma ray-induced apoptosis of lung cancer cells and its molecular mechanism, as an attempt to develop a new strategy to improve the therapeutic efficacy of gamma radiation. Expression of constitutively active mutant of the alpha subunit of Gs (GalphasQL) augmented gamma ray-induced apoptosis via mitochondrial dependent pathway when assessed by clonogenic assay, FACS analysis of PI stained cells, and western blot analysis of the cytoplasmic translocation of cytochrome C and the cleavage of caspase-3 and ploy(ADP-ribose) polymerase (PARP) in H1299 human lung cancer cells. GalphasQL up-regulated the Bak expression at the levels of protein and mRNA. Treatment with inhibitors of PKA (H89), SP600125 (JNK inhibitor), and a CRE-decoy blocked GalphasQL-stimulated Bak reporter luciferase activity. Expression of GalphasQL increased basal and gamma ray-induced luciferase activity of cAMP response element binding protein (CREB) and AP-1, and the binding of CREB and AP-1 to Bak promoter. Furthermore, prostaglandin E2, a Galphas activating signal, was found to augment gamma ray-induced apoptosis, which was abolished by treatment with a prostanoid receptor antagonist. These results indicate that Galphas augments gamma ray-induced apoptosis by up-regulation of Bak expression via CREB and AP-1 in H1299 lung cancer cells, suggesting that the efficacy of radiotherapy of lung cancer may be improved by modulating Gs signaling pathway.
Apoptosis/*radiation effects ; Cell Line, Tumor ; Cyclic AMP Response Element-Binding Protein/metabolism ; GTP-Binding Protein alpha Subunits, Gs/*metabolism ; *Gamma Rays ; Heterotrimeric GTP-Binding Proteins/metabolism ; Humans ; Lung/*cytology/physiology/radiation effects ; Lung Neoplasms ; Transcription Factor AP-1/metabolism ; *Up-Regulation ; bcl-2 Homologous Antagonist-Killer Protein/*metabolism

Bile Duct Neoplasms ; genetics ; pathology ; Bile Ducts, Extrahepatic ; Cholangiocarcinoma ; genetics ; pathology ; Female ; GTP-Binding Protein gamma Subunits ; genetics ; Gene Expression Regulation, Neoplastic ; Humans ; Male ; Middle Aged ; Neoplasm Staging ; RNA, Messenger ; genetics ; metabolism ; Reverse Transcriptase Polymerase Chain Reaction

Heterotrimeric GTP-binding proteins (G proteins) transduce extracellular signals into intracellular signals by activating effector molecules including adenylate cyclases that catalyze cAMP formation, and thus regulate various cellular responses such as metabolism, proliferation, and apoptosis. cAMP signaling pathways have been reported to protect cells from ionizing radiation-induced apoptosis, but however, the protective mechanism is not clear. Therefore, this study aimed to investigate the signaling molecules and the mechanism mediating the anti-apoptotic action of cAMP signaling system in radiation-induced apoptosis. Stable expression of a constitutively active mutant of G alpha s (G alpha sQL) protected gamma ray-induced apoptosis which was assessed by analysis of the cleavages of PARP, caspase-9, and caspase-3 and cytochrome C release in SH-SY5Y human neuroblastoma cells. G alpha sQL repressed the gamma ray-induced down-regulation of Bcl-xL protein, but transfection of Bcl-xL siRNA increased the gamma ray-induced apoptosis and abolished the anti-apoptotic effect of G alpha sQL. G alpha sQL decreased the degradation rate of Bcl-xL protein, and it also restrained the decrease in Bcl-xL mRNA by increasing the stability following ionizing irradiation. Furthermore, prostaglandin E2 that activates G alpha s was found to protect gamma ray-induced apoptosis, and the protective effect was abolished by treatment with prostanoid receptor antagonist specific to EP2/4R subtype. Moreover, specific agonists for adenosine A1 receptor that inhibits cAMP signaling pathway augmented gamma ray-induced apoptosis. From this study, it is concluded that Galphas-cAMP signaling system can protect SH-SY5Y cells from gamma ray-induced apoptosis partly by restraining down-regulation of Bcl-xL expression, suggesting that radiation-induced apoptosis can be modulated by GPCR ligands to improve the efficiency of radiation therapy.
Apoptosis/*physiology/*radiation effects ; Base Sequence ; Cell Line, Tumor ; Cyclic AMP/metabolism ; DNA Primers/genetics ; Down-Regulation/radiation effects ; GTP-Binding Protein alpha Subunits, Gs/*metabolism ; Gamma Rays ; Humans ; Neuroblastoma/genetics/metabolism/pathology ; RNA, Small Interfering/genetics ; Signal Transduction ; bcl-X Protein/genetics/*metabolism