Insulin-like growth factor binding proteins in human breast cancer cells: relationship to hIGFBP-2 and hIGFBP-3.
Human breast cancer cells (HBCC) secrete at least four different forms of IGFBPs. We have previously demonstrated that hIGFBP-1 is a minor component of IGFBPs secreted by Hs578T cells and is absent in CM from MCF-7 cells. In our present report, we describe the immunological and structural relationship of HBCC IGFBPs to hIGFBP-2 and hIGFBP-3. Analysis of conditioned media (CM) from Hs578T by Western ligand blotting revealed three IGFBPs of apparent Mr = 38K, 28K, and 24K; CM from MCF-7 revealed only two IGFBPs, of apparent Mr = 31K and 24K. Immunoprecipitation studies with polyclonal antibodies raised against hIGFBP-2 and hIGFBP-3 demonstrated that the 38K IGFBP in Hs578T CM is immunologically related to hIGFBP-3, while the 31K IGFBP in MCF-7 cells is related to the hIGFBP-2. Analysis by Northern blot demonstrated that MCF-7 cells contained mRNA for hIGFBP-2, while Hs578T cells contained the mRNA characteristic of the hIGFBP-3. The identity of the 24K IGFBP remains unknown, and may represent a distinct IGFBP. Of note, assay of CM following removal of BPs by acid chromatography demonstrated no detectable IGF-I or -II. The role of these IGFBPs in HBCC is of interest in view of the potential modulation of IGF actions by these proteins.
Department of Pediatrics, Stanford University Medical School, California 94305.
D D
DD
De Leon
B
B
Bakker
D M
DM
Wilson
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Lamson
R G
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Rosenfeld
D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism*; D002352:Carrier Proteins / Q000032:analysis / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002460:Cell Line; D005260:Female; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D012334:RNA, Neoplasm / Q000302:isolation & purification; D011994:Recombinant Proteins / Q000378:metabolism; D013002:Somatomedins / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000378:metabolism*
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D012334:RNA, Neoplasm; D011994:Recombinant Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II