CLEAVAGE SITE MUTANTS OF THE SUBTYPE-B INSULIN-RECEPTOR ARE UNCLEAVEDAND FULLY FUNCTIONAL

The insulin receptor (IR) is a membrane-bound glycoprotein composed of alpha and beta subunits derived from a common precursor. This process ing is observed for both subtypes A and B of the IR and its physiologi cal importance is poorly understood. In order to investigate the funct ional consequences of the absence of IR precursor cleavage, using site -directed mutagenesis of the hIRB cDNA, we have produced two mutants r eplacing the sequence Arg-Lys-Arg-Arg by either His-Lys-His-Arg or Arg -Lys-Arg-Ser. These two mutants, stably expressed in CHO, were structu rally and functionally characterized in comparison to the wild-type hu man IR. These mutations result in the production of uncleaved receptor s which are expressed normally at the cell surface. These receptors bi nd insulin with a normal affinity and activate the tyrosine-kinase res ulting in normal phosphorylation of the receptors. These uncleaved rec eptors can mediate both the metabolic and mitogenic effects of insulin . These results provide evidence for a fully functional uncleaved insu lin receptor of the B subtype (exon 11+) in contrast to the uncleaved A subtype (exon 11-) described in the literature, which shows a reduce d affinity for insulin and cannot therefore correctly transduce the in sulin signal. (C) 1997 Elsevier Science Ireland Ltd.