MDCK cells secrete neutral proteases cleaving insulin-like growth factor-binding protein-2 to -6

Shalamanova, Liliana, Bernd Kfibler, Jens-Gerd Scharf, and Thomas Braulke. MDCK cells secrete neutral proteases cleaving insulin-like growth factor-binding protein-2 to -6. Am J Physiol Endocrinol Metab 281: E 1221-E 1229, 2001.--Proteolysis of insulin-like growth factor-binding proteins (IGFBPs) may be an important mechanism to regulate IGF availability and IGF-independent functions of IGFBPs. We analyzed the secretion of IGFBP proteases in Madin-Darby canine kidney (MDCK) cells. The results showed that several specific proteases were secreted, cleaving IGFBP-2 to -6 at neutral pH. The proteolytic activity against IGFBP-6 differed at least from IGFBP-5 protease activity in its sensitivity both to IGF-II and to the hydroxamic acid-based disintegrin metalloprotease inhibitor, as well as serine protease inhibitors. During partial purification steps, the serine protease inhibitor-sensitive fraction with IGFBP-6 protease activity was separated from fractions characterized by the presence of a 30-kDa disintegrin immunoreactive band. Whereas the IGFBP-4 and -6 proteases are predominantly secreted across the basolateral membrane, the majority of IGFBPs are sorted to the apical mediun~ from filter-grown cells. These studies indicate that the side-specific secretion of several distinct IGFBP proteases with partially overlapping IGFBP specificities may be another level in the regulation of IGF-dependent epithelial functions. insulin-like growth factor-binding proteins and proteases; polarized sorting; disintegrin metalloprotease Received 15 November 2000; accepted in final form 16 July 2001