TGF-beta 1 modulates EGF-stimulated phosphatidylinositol 3-kinase activity in human airway smooth muscle cells.
Regulation of phosphatidylinositol (PI) 3-kinase plays an important role in modulating cellular function. We have previously shown that transforming growth factor (TGF)-beta 1 inhibited epidermal growth factor (EGF)-induced human airway smooth muscle (hASM) cell proliferation and that PI 3-kinase activation is a necessary signaling event in mitogen-induced hASM cell growth. In this study, we postulated that TGF-beta 1 may modulate EGF-induced PI 3-kinase activation. To date, no study has examined the effects of TGF-beta 1 on PI 3-kinase activity. In cultured hASM cells, EGF induced a 5.7 +/- 1.2-fold activation of PI 3-kinase compared with diluent-treated cells. Although TGF-beta 1 alone did not alter PI 3-kinase activation, TGF-beta 1 markedly enhanced EGF-induced PI 3-kinase activity, with a 16.6 +/- 1.9-fold increase over control cells treated with diluent alone. EGF significantly increased the association of PI 3-kinase with tyrosine phosphorylated proteins, and TGF-beta 1 pretreatment before EGF stimulation apparently did not alter this association. Interestingly, TGF-beta 1 did not modulate EGF-induced p70 S6 kinase activity, which is important for the progression of cells from the G0 to the G1 phase of the cell cycle. Immunoprecipitation of type I and type II TGF-beta receptors showed that PI 3-kinase was associated with both type I and type II TGF-beta receptors. TGF-beta 1, however, enhanced PI 3-kinase activity associated with the type I TGF-beta receptor. Although in some cell types inhibition of PI 3-kinase and treatment of cells with TGF-beta 1 mediate apoptosis, cell cycle analysis and DNA ladder studies show that PI 3-kinase inhibition or stimulation of hASM cells with TGF-beta 1 did not induce myocyte apoptosis. Although the inhibitory effects of TGF-beta 1 on hASM cell growth are not mediated at the level of PI 3-kinase and p70 S6 kinase, we now show that activation of the TGF-beta 1 receptor modulates PI 3-kinase activity stimulated by growth factors in hASM cells.
Krymskaya
V P
VP
Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
Hoffman
R
R
Eszterhas
A
A
Ciocca
V
V
Panettieri
R A
RA
D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D019000:Phosphotyrosine / Q000378:metabolism; D012137:Respiratory System; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D010750:Phosphoproteins; D016212:Transforming Growth Factor beta; D019000:Phosphotyrosine; D004815:Epidermal Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D019893:Ribosomal Protein S6 Kinases