Regulation of membrane-associated tyrosine phosphatases in UMR 106.06 osteoblast-like cells.
Protein tyrosine phosphatases play an important role in cell metabolism. Three distinct protein tyrosine phosphatase activities have been identified in an osteoblast-like cell line, UMR 106.06. These activities comprised two membrane-associated phosphatases and one cytosolic phosphatase of apparent molecular mass > 153 kDa, 80 kDa and 40 kDa respectively, estimated by gel filtration. On the basis of differences in apparent molecular mass, proteolytic-digestion profiles, substrate specificities and responses to a range of extracellular influences and inhibitor molecules, the two membrane-associated tyrosine phosphatases are distinct proteins. Tyrosine phosphatase activity in UMR 106.06 cells was sensitive to cell density. Cells at confluence contained membrane protein tyrosine phosphatase with specific activity 9-fold higher than cells at medium or low cell density. This elevation in membrane tyrosine phosphatase activity was due specifically to an increase in the high-molecular-mass enzyme. This phosphatase was also responsive to extracellular matrix components. This activity was elevated in cells grown on a collagen type-I matrix independently of cell density. Membrane and cytosolic protein tyrosine phosphatases were differentially regulated by a variety of agents including phorbol 12-myristate 13-acetate, parathyroid hormone, epidermal growth factor, okadaic acid and transforming growth factor beta. These observations suggest that regulatory influences control tyrosine phosphorylation in UMR 106.06 cells including cell-cell contact, cell-matrix contact and signal transduction involving tyrosine and serine/threonine phosphorylation events.
Southey
M C
MC
St. Vincents Institute of Medical Research, Fitzroy, Victoria, Australia.
Findlay
D M
DM
Kemp
B E
BE
D000818:Animals; D002451:Cell Compartmentation; D002452:Cell Count; D002460:Cell Line; D003094:Collagen / Q000494:pharmacology; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D008566:Membranes / Q000201:enzymology; D010006:Osteoblasts / Q000201:enzymology*; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000187:drug effects / Q000302:isolation & purification; D051381:Rats; D013379:Substrate Specificity; D014357:Trypsin / Q000494:pharmacology
D003094:Collagen; D017027:Protein Tyrosine Phosphatases; D014357:Trypsin