HaCaT human keratinocytes express IGF-II, IGFBP-6, and an acid-activated protease with activity against IGFBP-6

• Published in: American journal of physiology: endocrinology and metabolism 1999-03, Vol.276 (3), p.E536
• Main Authors: Marinaro, Joe A, Hendrich, Elke C, Leeding, Kerri S, Bach, Leon A
• Format: Article
• Language: English
• ISSN: 1522-1555
• DOI: 10.1152/ajpendo.1999.276.3.E536

The insulin-like growth factor (IGF) system plays an important role in skin. HaCaT human keratinocytes proliferate in response to IGFs and synthesize IGF-binding protein-3 (IGFBP-3). Recently, IGFBP-6 was also identified by NH -terminal sequencing, but it has not been identified by Western ligand blotting. In the present study, IGFBP-6 was detected in HaCaT-conditioned medium by use of immunoblotting and Western ligand blotting with I-labeled IGF-II. Proteolytic activity against IGFBPs, an important mechanism for regulation of their activity, was then studied. An acid-activated, cathepsin D-like protease that cleaved both IGFBP-6 and IGFBP-3 was detected. Although proteolysis did not substantially reduce the size of immunoreactive IGFBP-6, it greatly reduced the ability of IGFBP-6 to bind I-IGF-II as determined by Western ligand blotting and solution assay. HaCaT keratinocytes do not express IGF-I mRNA, but IGF-II mRNA and protein expression was detected. These observations suggest the possibility of an autocrine IGF-II loop that is regulated by the relative expression of IGF-II, IGFBP-3, and IGFBP-6, and IGFBP proteases in these keratinocytes, although demonstration of this loop requires further study.