Activation of Gab1 in pancreatic acinar cells: effects of gastrointestinal growth factors/hormones on stimulation, phosphospecific phosphorylation, translocation and interaction with downstream signaling molecules.
The scaffolding/adapter protein, Gab1, is a key signaling molecule for numerous stimuli including growth factors and G protein-coupled-receptors (GPCRs). A number of questions about Gab1 signaling remain and little is known about the ability of gastrointestinal (GI) hormones/neurotransmitters/growth factors to activate Gab1. Therefore, we examined their ability to activate Gab1 and explored the mechanisms involved using rat pancreatic acini. HGF and EGF stimulated total Gab1 tyrosine phosphorylation (TyrP) and TyrP of Gab1 phospho-specific sites (Y307, Y627), but not other pancreatic growth factors, GI GPCRs (CCK, bombesin, carbachol, VIP, secretin), or agents directly activating PKC or increasing Ca2+. HGF-stimulated Y307 Gab1 TyrP differed in kinetics from total and Y627. Neither GF109203X, nor inhibition of Ca2+ increases altered HGF's effect. In unstimulated cells>95% of Gab1 was cytosolic and HGF stimulated a 3-fold increase in membrane Gab1. HGF stimulated equal increases in pY307 and pY627 Gab1 in cytosol/membrane. HGF stimulated Gab1 association with c-Met, Grb2, SHP2, PI3K, Shc, Crk isoforms and CrkL, but not with PLCgamma1. These results demonstrate that only a subset of pancreatic growth factors (HGF/EGF) stimulates Gab1 signaling and no pancreatic hormones/neurotransmitters. Our results with Gab1 activation with different growth factors, the role of PKC, and its interaction with distant signaling molecules suggest the cellular mechanisms of Gab1 signaling show important differences in different cells. These results show that Gab1 activation plays a central role in HGF's ability to stimulate intracellular transduction cascades in pancreatic acinar cells and this action likely plays a key role in HGF's ability to alter pancreatic cell function (i.e., growth/regeneration).
Hoffmann
K Martin
KM
Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bldg. 10, Room 9C-103, 10 CENTER DR MSC 1804, Bethesda, MD, 20892-1804, United States.
Tapia
Jose A
JA
Jensen
Robert T
RT
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000502:physiology; D005768:Gastrointestinal Hormones / Q000502:physiology*; D006133:Growth Substances / Q000502:physiology*; D017228:Hepatocyte Growth Factor / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D010179:Pancreas / Q000166:cytology / Q000378:metabolism*; D010750:Phosphoproteins / Q000096:biosynthesis / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism*
C490896:Gab1 protein, rat; D005768:Gastrointestinal Hormones; D006133:Growth Substances; D010750:Phosphoproteins; D014443:Tyrosine; D004815:Epidermal Growth Factor; D017228:Hepatocyte Growth Factor; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D002118:Calcium