title: Growth arrest induced by transforming growth factor beta 1 is accompanied by protein phosphatase activation in human keratinocytes.
abstract: Protein phosphorylation and dephosphorylation are involved in regulation of cell growth. We tested the hypothesis that the growth inhibitory effect of transforming growth factor beta 1 (TGF-beta 1) involves activation of protein phosphatases. Exposure of human keratinocytes in culture to 400 pM TGF-beta 1 for 48 h led to 80% inhibition of DNA synthesis as measured by nuclear labeling. Incubation of cultured keratinocytes with 400 pM TGF-beta 1 rapidly activated (within 30 min) protein serine/threonine phosphatase, measured using phosphorylase as a substrate. Based on several criteria, including neutralization of activity with specific antibodies and inhibitor-2, TGF-beta 1-activated phosphorylase phosphatase was identified as protein phosphatase 1. TGF-beta 1 did not have rapid effects on protein serine/threonine phosphatase activity (type 2A) measured with histone phosphorylated by protein kinase C or on protein tyrosine phosphatase activity. However, protein tyrosine phosphatase was activated at 48 h, coincident with growth arrest. Differentiation, induced by the combination of TGF-beta 1 plus calcium or by serum, was not accompanied by further serine/threonine or tyrosine phosphatase activation. We conclude that induction of growth arrest in keratinocytes by TGF-beta 1 involves acute activation of protein phosphatase 1, while activation of protein tyrosine phosphatase may represent an additional mechanism for maintaining cells in a growth-arrested state.
authors.affiliation: Department of Pediatrics, Brown University, Providence, Rhode Island 02912.
authors.forename: P A
authors.initials: PA
authors.lastname: Gruppuso
authors.forename: R
authors.initials: R
authors.lastname: Mikumo
authors.forename: D L
authors.initials: DL
authors.lastname: Brautigan
authors.forename: L
authors.initials: L
authors.lastname: Braun
mesh_terms: D002454:Cell Differentiation; D002478:Cells, Cultured; D004789:Enzyme Activation; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D009500:Neutralization Tests; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D054645:Protein Phosphatase 1; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D016212:Transforming Growth Factor beta; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1