Characterization of a membrane tyrosine phosphatase in AR42J cells: regulation by somatostatin.
A phosphotyrosyl protein phosphatase (PTPase) activity has been characterized in the plasma membranes of confluent AR42J pancreatic tumor cells using 32P-labeled poly(Glu, Tyr) as substrate. Membrane PTPase activity exhibited an apparent Michaelis constant of 3 microM and an apparent maximal velocity of 0.9 nmol.min-1.mg-1. It was inhibited by orthovanadate, zinc, poly(Glu,Tyr) and was stimulated by EDTA and dithiothreitol. Gel filtration of solubilized plasma membranes gave a peak of enzyme activity at a relative molecular weight of 70,000. Plasma membrane PTPase activity was changed during AR42J cell growth. At the beginning of culture, the control PTPase activity was minimal. Over the 5 days of culture, PTPase activity increased to reach a maximum (3.5-fold over control activity) preceding confluency by 2 days. Then the high level of PTPase activity was sustained until confluency. Incubation of the cells with the stable somatostatin analogue SMS 201-995 (SMS) resulted in a rapid and transient activation of crude membrane PTPase activity. Activation reached a maximum level within 5 min of addition and return to control levels within 20 min. The effect of SMS was dose dependent with half-maximal and maximal activation occurring at 6 pM and 0.1 nM SMS respectively.
Tahiri-Jouti
N
N
Institut National de la Santé de la Recherche Médicale U 151, CHU Rangueil L3, Toulouse, France.
Cambillau
C
C
Viguerie
N
N
Vidal
C
C
Buscail
L
L
Saint Laurent
N
N
Vaysse
N
N
Susini
C
C
D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology*; D002712:Chlorides / Q000494:pharmacology; D002850:Chromatography, Gel; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D036341:Intercellular Signaling Peptides and Proteins; D007700:Kinetics; D015282:Octreotide / Q000494:pharmacology*; D010190:Pancreatic Neoplasms; D010455:Peptides / Q000494:pharmacology; D017027:Protein Tyrosine Phosphatases / Q000302:isolation & purification / Q000378:metabolism*; D013004:Somatostatin / Q000502:physiology*; D014638:Vanadates / Q000494:pharmacology; D015032:Zinc / Q000494:pharmacology; D017967:Zinc Compounds
D002712:Chlorides; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D017967:Zinc Compounds; C027606:L-glutamic acid-L-tyrosine copolymer; D014638:Vanadates; D013004:Somatostatin; C016837:zinc chloride; D017027:Protein Tyrosine Phosphatases; D015032:Zinc; D015282:Octreotide