p70 Ribosomal S6 kinase is required for airway smooth muscle cell size enlargement but not increased contractile protein expression.
We examined the contribution of p70 ribosomal S6 kinase (p70S6K) to airway smooth muscle hypertrophy, a structural change found in asthma. In human airway smooth muscle cells, transforming growth factor (TGF)-beta, endothelin-1, and cardiotrophin-1 each induced phosphorylation of p70S6K and ribosomal protein S6 while increasing cell size, total protein synthesis, and relative protein abundance of alpha-smooth muscle actin and SM22. Transfection of myocytes with siRNA against either p70S6K or S6, or infection with retrovirus encoding a kinase-dead p70S6K, reduced cell size and protein synthesis but had no effect on contractile protein expression per mg total protein. Infection with a retrovirus encoding a constitutively active, rapamycin-resistant (RR) p70S6K increased cell size but not contractile protein expression. siRNA against S6 decreased cell size in myocytes expressing RR p70S6K. Finally, TGF-beta treatment, but not RR p70S6K expression, increased KCl-induced fractional shortening. Together, these data suggest that p70S6K activation is both required and sufficient for airway smooth muscle cell size enlargement but not contractile protein expression. Further, ribosomal protein S6 is required for p70S6K-mediated cell enlargement. Finally, we have shown for the first time in a functional cell system that p70S6K-mediated myocyte enlargement alone, without preferential contractile protein expression, is insufficient for increased cell shortening.
Deng
Huan
H
University of Michigan, 1150 W. Medical Center Dr., Ann Arbor, MI 48109-5688, USA.
Hershenson
Marc B
MB
Lei
Jing
J
Bitar
Khalil N
KN
Fingar
Diane C
DC
Solway
Julian
J
Bentley
J Kelley
JK
D056151:Airway Remodeling; D000818:Animals; D001249:Asthma / Q000139:chemically induced / Q000201:enzymology / Q000473:pathology / Q000503:physiopathology; D049108:Cell Enlargement; D002478:Cells, Cultured; D003285:Contractile Proteins / Q000096:biosynthesis*; D016207:Cytokines / Q000378:metabolism; D004195:Disease Models, Animal; D019332:Endothelin-1 / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D006984:Hypertrophy; D008168:Lung / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology / Q000503:physiopathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008840:Microfilament Proteins / Q000096:biosynthesis; D009119:Muscle Contraction; D009124:Muscle Proteins / Q000096:biosynthesis; D009130:Muscle, Smooth / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology / Q000503:physiopathology; D009154:Mutation; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D010047:Ovalbumin; D010641:Phenotype; D010766:Phosphorylation; D011189:Potassium Chloride / Q000494:pharmacology; D034622:RNA Interference; D038601:Ribosomal Protein S6 / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000235:genetics / Q000378:metabolism*; D014161:Transduction, Genetic; D016212:Transforming Growth Factor beta / Q000378:metabolism
D003285:Contractile Proteins; D016207:Cytokines; D019332:Endothelin-1; D008840:Microfilament Proteins; D009124:Muscle Proteins; D038601:Ribosomal Protein S6; D016212:Transforming Growth Factor beta; C051615:transgelin; D011189:Potassium Chloride; D010047:Ovalbumin; C092073:cardiotrophin 1; D038762:Ribosomal Protein S6 Kinases, 70-kDa