Regulation of IGFBP secretion and modulation of cell growth in MDBK cells.
The ability of IGF binding proteins (IGFBP) to modulate cell growth and IGF-I responsiveness of epithelial cells was examined using the Madin-Darby bovine kidney (MDBK) cell line. The predominant IGFBP present in conditioned media (CM) of untreated cells was found to be IGFBP-2. Following exposure to forskolin, the abundance of IGFBP-2 in CM was decreased, while IGFBP-3 and -4 were induced. These changes corresponded with alterations in mRNA abundance. Growth of MDBK cells in serum-free media was stimulated by addition of 2.5 to 50 ng/ml of IGF-I in a dose responsive manner. Coincubation with equimolar amounts of IGF-I and exogenous bovine IGFBP-3 potentiated the growth response observed with IGF-I alone. In order to alter endogenous IGFBP-3 secretion, cells were exposed to transfection with an expression vector containing sense IGFBP-3 cDNA. Following selection and amplification with methotrexate, cells underwent a permanent alteration in cell morphology, exhibiting characteristics of transporting epithelia. This was associated with secretion of IGFBP-3 under basal conditions. Secretion of IGFBP-3 was due to expression of endogenous IGFBP-3 and not to expression of the transgene. Cells expressing IGFBP-3 under basal conditions grew slower in serum, but were more responsive to 100 ng/ml of IGF-1 in serum-free media compared to wild-type MDBK cells. The role of IGFBP-3 in mediating these responses requires further study.
Cohick
W S
WS
University of North Carolina School of Medicine, Division of Endocrinology, Chapel Hill 27599-7170.
Clemmons
D R
DR
D000818:Animals; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D004247:DNA; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D018971:Insulin-Like Growth Factor Binding Protein 2; D018974:Insulin-Like Growth Factor Binding Protein 4; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007668:Kidney / Q000378:metabolism; D013002:Somatomedins; D014162:Transfection
D002352:Carrier Proteins; D018971:Insulin-Like Growth Factor Binding Protein 2; D018974:Insulin-Like Growth Factor Binding Protein 4; D018969:Insulin-Like Growth Factor Binding Proteins; D013002:Somatomedins; D005576:Colforsin; D007334:Insulin-Like Growth Factor I; D004247:DNA