Cooperative regulation of GSK-3 by muscarinic and PDGF receptors is associated with airway myocyte proliferation.
Muscarinic receptors and platelet-derived growth factor (PDGF) receptors synergistically induce proliferation of airway smooth muscle (ASM), but the pathways that regulate these effects are not yet completely identified. We hypothesized that glycogen synthase kinase-3 (GSK-3), a kinase that represses several promitogenic signaling pathways in its unphosphorylated form, is cooperatively inhibited by PDGF and muscarinic receptors in immortalized human ASM cell lines. PDGF or methacholine alone induced rapid GSK-3 phosphorylation. This phosphorylation was sustained only for PDGF; however, methacholine potentiated PDGF-induced sustained GSK-3 phosphorylation. Synergistic effects of methacholine also were observed on PDGF-induced retinoblastoma protein (Rb) phosphorylation and cell proliferation. Suppression of GSK-3 inhibitory function using SB 216763 also augmented PDGF-induced Rb phosphorylation and cell cycle progression; this synergy was similar in magnitude to that seen for methacholine with PDGF. GSK-3 phosphorylation induced by methacholine required PKC, since it was abolished by GF 109203X and Gö 6976; however, inhibition of PKC had no effect on cell responses to PDGF. PKC inhibition also specifically abolished the synergistic effect of methacholine on PDGF-induced GSK-3 phosphorylation and cell proliferation. Collectively, these results show that GSK-3 plays a key repressive role in ASM cell proliferation. Moreover, muscarinic receptors mediate PKC-dependent GSK-3 inhibition, and this appears to be a primary mechanism underpinning augmentation of PDGF-induced cell growth.
Gosens
Reinoud
R
Departments of Physiology, University of Manitoba, Winnipeg. r.gosens@rug.nl
Dueck
Gordon
G
Rector
Edward
E
Nunes
Raquel O
RO
Gerthoffer
William T
WT
Unruh
Helmut
H
Zaagsma
Johan
J
Meurs
Herman
H
Halayko
Andrew J
AJ
D015153:Blotting, Western; D049109:Cell Proliferation; D002478:Cells, Cultured; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D047468:Immunoprecipitation; D016210:Methacholine Chloride / Q000494:pharmacology; D018721:Muscarinic Agonists / Q000494:pharmacology; D032389:Myocytes, Smooth Muscle / Q000502:physiology*; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism*; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism*; D012137:Respiratory System / Q000166:cytology / Q000378:metabolism*; D016160:Retinoblastoma Protein; D015398:Signal Transduction
D018721:Muscarinic Agonists; D010982:Platelet-Derived Growth Factor; D011976:Receptors, Muscarinic; D016160:Retinoblastoma Protein; D016210:Methacholine Chloride; D017479:Receptors, Platelet-Derived Growth Factor; D000071679:Glycogen Synthase Kinase 3 beta; D011493:Protein Kinase C; D038362:Glycogen Synthase Kinase 3