Primary Structure of a Putative Serine Protease Specific for IGF-binding Proteins

From a subtracted cDNA library we have isolated a cDNA clone coding for a novel transformation-sensitive protein which is expressed by human fibroblasts, but not by their matched SV40 transformed counterparts. This protein has a molecular mass of 51 kDa and is highly related to the HtrA family of serine proteases from bacteria. At the N-terminal end, it contains an IGF-binding domain which may modulate the activity of the associated serine protease. Our data are consistent with the assumption that the novel protein represents one of the proteases that regulate the availability of IGFs by cleaving IGF-binding proteins.