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.
De Leon
D D
DD
Department of Pediatrics, Stanford University Medical School, California 94305.
Bakker
B
B
Wilson
D M
DM
Lamson
G
G
Rosenfeld
R G
RG
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