PROCESSING AND SECRETION OF RAT ALPHA(1)-MICROGLOBULIN-BIKUNIN EXPRESSED IN EUKARYOTIC CELL-LINES

The precursor protein alpha(1)-microglobulin-bikunin was cleaved to th e same degree whether expressed in CHO cells or in mutated CHO cells, RPE.40 cells, suggested to lack a functional form of the intracellular protease furin. Thus, alpha(1)-microglobulin-bikunin probably is not cleaved in vivo by furin. However, simultaneous overexpression of the precursor and furin in COS, CHO and RPE.40 cells increased the cleavag e, suggesting that compartmentalisation and concentrations of protease and precursor are important for the cleavage, besides the in vitro sp ecificity. Expression of alpha(1)-microglobulin and bikunin alone gave different protein patterns on SDS-PAGE as compared to expression of t he precursor and subsequent cleavage, suggesting that the precursor pr otein is important for the post-translational handling of alpha(1)-mic roglobulin and bikunin.