Gprc5a deletion enhances the transformed phenotype in normal and malignant lung epithelial cells by eliciting persistent Stat3 signaling induced by autocrine leukemia inhibitory factor.
Signal transducers and activators of transcription 3 (Stat3) is activated by cytokines and growth factors in lung cancers and regulates expression of genes implicated in cell growth, survival, and transformation. Previously, we found that mice with a deletion of the G protein-coupled receptor, family C, group 5, member a (Gprc5a) gene develop lung tumors, indicating that Gprc5a is a tumor suppressor. Herein, we show that epithelial cells from Gprc5a knockout mouse lung (Gprc5a(-/-) cells) survive better in vitro in medium deprived of exogenous growth factors and form more colonies in semisolid medium than their counterparts from wild-type mice (Gprc5a(+/+) cells). Stat3 tyrosine 705 phosphorylation and expression of several Stat3-regulated antiapoptotic genes were higher in Gprc5a(-/-) than in Gprc5a(+/+) cells. Both cell types secreted leukemia inhibitory factor (Lif); however, whereas Stat3 activation was persistent in Gprc5a(-/-) cells, it was transient in Gprc5a(+/+) cells. Lung adenocarcinoma cells isolated from Gprc5a(-/-) mice also exhibited autocrine Lif-mediated Stat3 activation. The level of Socs3, the endogenous Stat3 inhibitory protein, was higher in Gprc5a(+/+) than in Gprc5a(-/-) cells, and expression of the tumor suppressor stabilized Socs3. Inhibition of Stat3 signaling in Gprc5a(-/-) normal and cancer cells by the Janus-activated kinase 2 inhibitor AG490 or by a dominant negative Stat3(Y705F) increased starvation-induced apoptosis and inhibited colony formation. These results show that persistent Stat3 activation is important for the survival and transformation of Gprc5a(-/-) lung cells and suggest that the tumor suppressive effects of Gprc5a are mediated, at least in part, by inhibition of Stat3 signaling through Socs3 stabilization.
Department of Thoracic/Head and Neck Medical Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
Yulong
Y
Chen
Jiong
J
Deng
Junya
J
Fujimoto
Humam
H
Kadara
Taoyan
T
Men
Dafna
D
Lotan
Reuben
R
Lotan
D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002448:Cell Adhesion; D002465:Cell Movement; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000378:metabolism / Q000473:pathology*; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D053605:Leukemia Inhibitory Factor / Q000494:pharmacology*; D008168:Lung / Q000378:metabolism / Q000473:pathology*; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010641:Phenotype; D012333:RNA, Messenger / Q000235:genetics; D043562:Receptors, G-Protein-Coupled / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D017384:Sequence Deletion; D015398:Signal Transduction
C116760:GPRC5A protein, human; C554251:GPRC5A protein, mouse; D053605:Leukemia Inhibitory Factor; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; D050796:STAT3 Transcription Factor