Processing and secretion of rat α1‐microglobulin‐bikunin expressed in eukaryotic cell lines

Abstract
The precursor protein α1-microglobulin-bikunin was cleaved to the 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, α1-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 cleavage, suggesting that compartmentalisation and concentrations of protease and precursor are important for the cleavage, besides the in vitro specificity. Expression of α1-microglobulin and bikunin alone gave different protein patterns on SDS-PAGE as compared to expression of the precursor and subsequent cleavage, suggesting that the precursor protein is important for the post-translational handling of α1-microglobulin and bikunin.