MDCK cells secrete neutral proteases cleaving insulin-like growth factor-binding protein-2 to -6.
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 medium 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.
Shalamanova
L
L
University of Hamburg, Children's Hospital, Department of Biochemistry, D-20246 Hamburg, Germany.
Kübler
B
B
Scharf
J G
JG
Braulke
T
T
D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002460:Cell Line; D017077:Culture Media, Conditioned; D004285:Dogs; D010450:Endopeptidases / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000378:metabolism*; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000378:metabolism*; D007457:Iodine Radioisotopes
D017077:Culture Media, Conditioned; D018970:Insulin-Like Growth Factor Binding Protein 1; D018976:Insulin-Like Growth Factor Binding Protein 6; D007457:Iodine Radioisotopes; D010450:Endopeptidases