Tyrosine kinase participates in phosphorylation of the Ro60 ribonucleoprotein

Studies of Ro ribonucleoprotein are important in rheumatology, since anti-Ro antibodies are probably involved in the pathogenesis of congenital heart block and subacute cutaneous lupus erythematosus. In addition, the phosphorylation-dephosphorylation cycle modulates binding of ribonucleoproteins to RNA, a process that might affect the antigenicity and function of the Ro protein. The present study was designed to determine whether Ro can be phosphorylated by tyrosine kinase. To answer this question, synchronized HEp-2 cells were phosphorylated in vivo with exogenous 32P, and Ro ribonucleoprotein previously subjected to metabolic radiolabeling was immunoprecipitated by monoclonal anti-Ro antibodies and examined by SDS-PAGE and autoradiography. The main results were as follows: first, Ro ribonucleoprotein was phosphorylated in vivo; second, Ro was found to have phosphorylable tyrosine residues; third, tyrosine kinase participated in the phosphorylation of Ro; and fourth, phosphorylation did not change the recognition pattern of Ro by anti-Ro antibodies. In conclusion, Ro60 is phosphorylated by tyrosine kinase.