Specific dephosphorylation by phosphatases 1 and 2A of a nuclear protein structurally and immunologically related to nucleolin

• Published in: European journal of biochemistry Vol. 180; no. 2; pp. 449 - 455
• Main Authors: SCHNEIDER, Helge R., MIESKES, Gottfried, ISSINGER, Olaf‐Georg
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.03.1989
• ISSN: 0014-2956; 1432-1033
• DOI: 10.1111/j.1432-1033.1989.tb14667.x

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.