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Lymphocyte Phosphatase-Associated Phosphoprotein Is a Substrate of Protein Kinase CK2

T. D. Tsoy1,2,a, N. A. Kruglova1,2, and A. V. Filatov1,2,b*

1Institute of Immunology National Research Center, Federal Medical-Biological Agency, 115522 Moscow, Russia

2Lomonosov Moscow State University, Faculty of Biology, 119234 Moscow, Russia

* To whom correspondence should be addressed.

Received June 26, 2018; Revision received August 14, 2018
Lymphocyte phosphatase-associated phosphoprotein (LPAP) is a molecular partner of CD45 phosphatase that plays a key role in the regulation of antigen-specific activation of lymphocytes. The functions of LPAP still remain unknown. We believe that studying LPAP phosphorylation pathways could shed light on its functions. In this work, we studied the phosphorylation of LPAP ectopically expressed in non-lymphoid cells in order to determine the effect of LPAP interaction partners on its phosphorylation. We found that phosphorylation at Ser153 and Ser163 in non-hematopoietic HEK293 cells was conserved, while phosphorylation at Ser99 and Ser172 was almost absent. The pattern of LPAP phosphorylation in K562 erythroid and U937 myeloid cells expressing endogenous CD45 protein was similar to that observed in T and B lymphocytes. We demonstrated for the first time that LPAP is a substrate for protein kinase CK2 that phosphorylates it at Ser153, presumably ensuring LPAP resistance to degradation.
KEY WORDS: LPAP, phosphorylation, ectopic expression, casein kinase 2, human lymphocytes

DOI: 10.1134/S0006297918110081