p42/p44 MAP kinase activation is localized to caveolae-free membrane domains in airway smooth muscle.
Caveolae are abundant plasma membrane invaginations in airway smooth muscle that may function as preorganized signalosomes by sequestering and regulating proteins that control cell proliferation, including receptor tyrosine kinases (RTKs) and their signaling effectors. We previously demonstrated, however, that p42/p44 MAP kinase, a critical effector for cell proliferation, does not colocalize with RTKs in caveolae of quiescent airway myocytes. Therefore, we investigated the subcellular sites of growth factor-induced MAP kinase activation. In quiescent myocytes, though epidermal growth factor receptor (EGFR) was almost exclusively found in caveolae, p42/p44 MAP kinase, Grb2, and Raf-1 were absent from these membrane domains. EGF induced concomitant phosphorylation of caveolin-1 and p42/p44 MAP kinase; however, EGF did not promote the localization of p42/p44 MAP kinase, Grb2, or Raf-1 to caveolae. Interestingly, stimulation of muscarinic M(2) and M(3) receptors that were enriched in caveolae-deficient membranes also induced p42/p44 MAP kinase phosphorylation, but this occurred in the absence of caveolin-1 phosphorylation. This suggests that the localization of receptors to caveolae and interaction with caveolin-1 is not directly required for p42/p44 MAP kinase phosphorylation. Furthermore, we found that EGF exposure induced rapid translocation of EGFR from caveolae to caveolae-free membranes. EGFR trafficking coincided temporally with EGFR and p42/p44 MAP kinase phosphorylation. Collectively, this indicates that although caveolae sequester some receptors associated with p42/p44 MAP kinase activation, the site of its activation is associated with caveolae-free membrane domains. This reveals that directed trafficking of plasma membrane EGFR is an essential element of signal transduction leading to p42/p44 MAP kinase activation.
Gosens
Reinoud
R
Department of Physiology, University of Manitoba, Manitoba Institute of Child Health, Winnipeg, Manitoba, Canada. r.gosens@rug.nl
Dueck
Gordon
G
Gerthoffer
William T
WT
Unruh
Helmut
H
Zaagsma
Johan
J
Meurs
Herman
H
Halayko
Andrew J
AJ
D021941:Caveolae / Q000502:physiology; D051242:Caveolin 1 / Q000032:analysis; D002455:Cell Division; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology* / Q000648:ultrastructure; D002966:Clathrin / Q000032:analysis; D066246:ErbB Receptors / Q000378:metabolism*; D006801:Humans; D008168:Lung / Q000201:enzymology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009130:Muscle, Smooth / Q000201:enzymology*; D011976:Receptors, Muscarinic / Q000032:analysis
D051242:Caveolin 1; D002966:Clathrin; D011976:Receptors, Muscarinic; D066246:ErbB Receptors; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3