G alpha 13-mediated transformation and apoptosis are permissively dependent on basal ERK activity.
We previously reported that the alpha-subunit of heterotrimeric G13 protein induces either mitogenesis and neoplastic transformation or apoptosis in a cell-dependent manner. Here, we analyzed which signaling pathways are required for G alpha 13-induced mitogenesis or apoptosis using a novel mutant of G alpha 13. We have identified that in human cell line LoVo, the mutation encoding substitution of Arg260 to stop codon in mRNA of G alpha 13 subunit produced a mutant protein (G alpha 13-T) that lacks a COOH terminus and is endogenously expressed in LoVo cells as a polypeptide of 30 kDa. We found that G alpha 13-T lost its ability to promote proliferation and transformation but retained its ability to induce apoptosis. We found that full-length G alpha 13 could stimulate Elk1 transcription factor, whereas truncated G alpha 13 lost this ability. G alpha 13-dependent stimulation of Elk1 was inhibited by dominant-negative extracellular signal-regulated kinase (MEK) but not by dominant-negative MEKK1. Similarly, MEK inhibitor PD-98059 blocked G alpha 13-induced Elk1 stimulation, whereas JNK inhibitor SB-203580 was ineffective. In Rat-1 fibroblasts, G alpha 13-induced cell proliferation and foci formation were also inhibited by dominant-negative MEK and PD-98059 but not by dominant-negative MEKK1 and SB-203580. Whereas G alpha 13-T alone did not induce transformation, coexpression with constitutively active MEK partially restored its ability to transform Rat-1 cells. Importantly, full-length but not G alpha 13-T could stimulate Src kinase activity. Moreover, G alpha 13-dependent stimulation of Elk1, cell proliferation, and foci formation were inhibited by tyrosine kinase inhibitor, genistein, or by dominant-negative Src kinase, suggesting the involvement of a Src-dependent pathway in the G alpha 13-mediated cell proliferation and transformation. Importantly, truncated G alpha 13 retained its ability to stimulate apoptosis signal-regulated kinase ASK1 and c-Jun terminal kinase, JNK. Interestingly, the apoptosis induced by G alpha 13-T was inhibited by dominant-negative ASK1 or by SB-203580.
Department of Pharmacology, University of Illinois, Chicago, IL 60612, USA.
Vyacheslav A
VA
Adarichev
Rita
R
Vaiskunaite
Jiaxin
J
Niu
Irina V
IV
Balyasnikova
Tatyana A
TA
Voyno-Yasenetskaya
D000230:Adenocarcinoma / Q000235:genetics / Q000473:pathology; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002471:Cell Transformation, Neoplastic; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D005347:Fibroblasts / Q000502:physiology; D044365:GTP-Binding Protein alpha Subunits, G12-G13; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008934:Mitogens / Q000494:pharmacology; D008968:Molecular Conformation; D009154:Mutation; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D008934:Mitogens; D020928:Mitogen-Activated Protein Kinases; D044365:GTP-Binding Protein alpha Subunits, G12-G13