EFFECT OF 1-BETA-D-ARABINO-FURANOSYL-CYTOSINE (ARA-C) INDUCTION OF K562 CELLS ON EXPRESSION OF RH AND OTHER BLOOD-GROUP ACTIVE PROTEINS

K562 cells undergoing differentiation induced by 1-beta-D-arabino-fura nosyl-cytosine (ara-C) were examined as a model for studying the biosy nthesis and regulation of Rh and other blood group active membrane pro teins. Untreated and ara-C-induced K562 cells were analysed for the ex pression of these proteins using monoclonal antibodies in combination with now cytometry. The major membrane proteins glycophorins A and C r emained unaltered upon induction by ara-C, The display of LFA-3 (CD58) and DAF (CD55) by uninduced K562 was one order of magnitude lower tha n that of the glycophorins; following ara-C treatment there was a 50% rise in LFA-3 but a modest decrease in the level of DAF expression. Th e expression by untreated K562 cells of Rh, Lutheran and Kell proteins as well as the Rh D antigen was low, whereas that of CD44 and band 3 protein was negligible. Following induction by ara-C the levels of Rh and Kell proteins rose up to 7- and 3.5-fold respectively, and there w as an increase in RhD-antigen expression. In contrast, ara-C induction of K562 cells failed to augment their display of Lutheran, CD44 and b and 3 proteins. Analysis of Rh transcripts following the purification and RT-PCR analysis of K562 mRNA showed that uninduced K562 cells cont ain two distinct mRNAs corresponding to Rh Ce (1.8 kb) and Rh D (3.5 k b). The apparent concentration of each mRNA increased following induct ion with ara-C, K562 plasma membranes also contained Rh polypeptides a s determined by immunoblot analysis using anti-Rh polypeptide rabbit p olyclonal sera raised to Rh synthetic peptide, A novel hybrid Rh trans cript corresponding to exons 1-4 of RHD and exons 5-10 of RHCE has bee n cloned and sequenced from ara-C induced K562 cells, and may have ari sen by general recombination between the RHD and RHCE genes.