Insulin-dependent phosphorylation of DPP IV in liver. Evidence for a role of compartmentalized c-Src.
Dipeptidyl peptidase IV (DPP IV, CD26, EC 3.4.14.5) serves as a model aimed at elucidating protein sorting signals. We identify here, by MS, several tyrosine-phosphorylated proteins in a rat liver Golgi/endosome (G/E) fraction including DPP IV. We show that a pool of DPP IV is tyrosine-phosphorylated. Maximal phosphorylation was observed after 2 min following intravenous insulin injection. DPP IV coimmunoprecipitated with the cellular tyrosine kinase Src (c-Src) with maximal association also observed after 2 min following insulin injection. DPP IV was found phosphorylated after incubation of nonsolubilized G/E membranes with [gamma-32P]ATP. The c-Src inhibitor PP2 inhibited DPP IV phosphorylation. Oriented proteolysis experiments indicate that a large pool of c-Src is protected in G/E fractions. Following injection of the protein-tyrosine phosphatase inhibitor bpV(phen), DPP IV levels markedly decreased by 40% both in plasma membrane and G/E fractions. In the fraction designated Lh, DPP IV levels decreased by 50% 15 min following insulin injection. Therefore, a pool of DPP IV is tyrosine-phosphorylated in an insulin-dependent manner. The results suggest the presence of a yet to be characterized signalling mechanism whereby DPP IV has access to c-Src-containing signalling platforms.
Pediatric Research Unit, CRCHUL/CHUQ, Faculty of Medicine, Laval University, Québec, Canada.
Nicolas
N
Bilodeau
Annie
A
Fiset
Guy G
GG
Poirier
Suzanne
S
Fortier
Marie-Claude
MC
Gingras
Josée N
JN
Lavoie
Robert L
RL
Faure
D000595:Amino Acid Sequence; D000818:Animals; D000081247:CSK Tyrosine-Protein Kinase; D002451:Cell Compartmentation; D018819:Dipeptidyl Peptidase 4 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011992:Endosomes / Q000201:enzymology / Q000648:ultrastructure; D005260:Female; D006056:Golgi Apparatus / Q000201:enzymology / Q000648:ultrastructure; D007328:Insulin / Q000378:metabolism*; D008099:Liver / Q000201:enzymology* / Q000276:immunology / Q000378:metabolism / Q000648:ultrastructure; D013058:Mass Spectrometry; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D019061:src-Family Kinases
D007328:Insulin; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; D018819:Dipeptidyl Peptidase 4