Different in vitro and in vivo activity of low Mr phosphotyrosine protein phosphatase on epidermal growth factor receptor.
Low Mr phosphotyrosine protein phosphatase is a cytosolic enzyme which dephosphorylates platelet-derived growth factor and insulin receptor in vivo, thus reducing cellular mitogenic response to such growth factors. Following cell stimulation with platelet-derived growth factor the phosphatase undergoes a redistribution from the citosol to the Triton X-100-insoluble fraction where its activity upon the growth factor receptor is intense. Previous research uncovered evidence that low Mr phosphotyrosine protein phosphatase dephosphorylates the epidermal growth factor receptor in vitro. Here we demonstrate that in vivo the enzyme is not active on the phosphorylated epidermal growth factor receptor and it does not influence the mitogenic response of cells. Since the enzyme distribution is not affected by epidermal growth factor stimulation, involvement of a recruitment mechanism in the definition of low Mr phosphotyrosine protein phosphatase substrate specificity is hypothesized.
Department of Biochemical Sciences, University of Firenze, Viale Morgagni 50, Firenze, 50134, Italy.
S
S
Rigacci
R
R
Marzocchini
M
M
Bucciantini
A
A
Berti
D016475:3T3 Cells; D000818:Animals; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism* / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection
D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D017027:Protein Tyrosine Phosphatases