Fibronectin stimulates non-small cell lung carcinoma cell growth through activation of Akt/mammalian target of rapamycin/S6 kinase and inactivation of LKB1/AMP-activated protein kinase signal pathways.
The Akt/mammalian target of rapamycin (mTOR)/ribosomal protein S6 kinase (p70S6K) pathway is considered a central regulator of protein synthesis and of cell proliferation, differentiation, and survival. However, the role of the Akt/mTOR/p70S6K pathway in lung carcinoma remains unknown. We previously showed that fibronectin, a matrix glycoprotein highly expressed in tobacco-related lung disease, stimulates non-small cell lung carcinoma (NSCLC) cell growth and survival. Herein, we explore the role of the Akt/mTOR/p70S6K pathway in fibronectin-induced NSCLC cell growth. We found that fibronectin stimulated the phosphorylation of Akt, an upstream inducer of mTOR, and induced the phosphorylation of p70S6K1 and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), two downstream targets of mTOR in NSCLC cells (H1792 and H1838), whereas it inhibited the phosphatase and tensin homologue deleted on chromosome 10, a tumor suppressor protein that antagonizes the phosphatidylinositol 3-kinase/Akt signal. In addition, treatment with fibronectin inhibited the mRNA and protein expression of LKB1 as well as the phosphorylation of AMP-activated protein kinase (AMPKalpha), both known to down-regulate mTOR. Rapamycin, an inhibitor of mTOR, blocked the fibronectin-induced phosphorylation of p70S6K and 4E-BP1. Akt small interfering RNA (siRNA) and an antibody against the fibronectin-binding integrin alpha5beta1 also blocked the p70S6K phosphorylation in response to fibronectin. In contrast, an inhibitor of extracellular signal-regulated kinase 1/2 (PD98095) had no effect on fibronectin-induced phosphorylation of p70S6K. Moreover, the combination of rapamycin and siRNA for Akt blocked fibronectin-induced cell proliferation. Taken together, these observations suggest that fibronectin-induced stimulation of NSCLC cell proliferation requires activation of the Akt/mTOR/p70S6K pathway and is associated with inhibition of LKB1/AMPK signaling.
Han
ShouWei
S
Department of Medicine, Division of Pulmonary, Allergy and Critical Care Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA. shan2@emory.edu
Khuri
Fadlo R
FR
Roman
Jesse
J
D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases; D002289:Carcinoma, Non-Small-Cell Lung / Q000201:enzymology* / Q000473:pathology; D048708:Cell Growth Processes / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D005353:Fibronectins / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D006801:Humans; D039081:Integrin alpha5beta1 / Q000502:physiology; D008175:Lung Neoplasms / Q000201:enzymology* / Q000473:pathology; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D051059:PTEN Phosphohydrolase / Q000235:genetics; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases
D005353:Fibronectins; D039081:Integrin alpha5beta1; D009097:Multienzyme Complexes; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011494:Protein Kinases; C546842:MTOR protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; C109790:STK11 protein, human; D058570:TOR Serine-Threonine Kinases; D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human; D020123:Sirolimus