Specific dephosphorylation by phosphatases 1 and 2A of a nuclear protein structurally and immunologically related to nucleolin. Possible influence on the regulation of rRNA synthesis.
A new nuclear substrate (N-60) for phosphatase 1 and 2Ac has been described. In contrast to nucleolin (C23), to which it is structurally and immunologically related, N-60 becomes dephosphorylated to 51% and 41% by phosphatases 1 and 2Ac, respectively, within 10 min. Incubation up to 20 min led to a complete dephosphorylation of N-60. The two other phosphatases tested (2B and 2C) did not dephosphorylate protein N-60 to the same extent as phosphatases 1 and 2Ac. In the case of nucleolin only 18% phosphate was released by all four phosphatases tested. The activity of both phosphatases, 1 and 2A, could be blocked by tumour promoter okadaic acid (100 nM) when N-60 was used as a substrate. These results support the notion that the observed okadaic-acid-induced hyperphosphorylation of N-60 in intact human fibroblasts may be caused by specific inhibition of phosphatases involved in the process of rDNA transcription.
Schneider
H R
HR
Institut für Humangenetik, Universität des Saarlandes, Homburg, Federal Republic of Germany.
Mieskes
G
G
Issinger
O G
OG
D000818:Animals; D001921:Brain / Q000201:enzymology; D002417:Cattle; D006706:Homeostasis; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D009132:Muscles / Q000201:enzymology; D009687:Nuclear Proteins / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D054645:Protein Phosphatase 1; D012335:RNA, Ribosomal / Q000096:biosynthesis*; D016601:RNA-Binding Proteins; D011817:Rabbits; D051381:Rats; D013379:Substrate Specificity; D000097796:Nucleolin
D009687:Nuclear Proteins; D010749:Phosphoprotein Phosphatases; D010750:Phosphoproteins; D054645:Protein Phosphatase 1; D012335:RNA, Ribosomal; D016601:RNA-Binding Proteins; D000097796:Nucleolin