Characterization of insulin-like growth factor binding proteins from human breast cancer cells.
The insulin-like growth factor binding proteins (IGF-BPs) are structurally and immunologically distinct from the IGF type 1 or type 2 receptors and are characterized by two major forms: a large, GH-dependent BP found in human plasma (Mr = 150 k) and a small GH-independent BP (Mr = 28-42 k) present in human plasma, amniotic fluid, and HEP G2 cells. Using affinity cross-linking techniques, we have identified several binding proteins secreted by human breast cancer cell lines (Hs578T, MDA-231, T-47D, and MCF-7). Under nonreducing conditions these proteins migrated at an apparent Mr = 35, 28, 27, and 24 k, while reducing conditions revealed bands of apparent Mr = 35, 32, 27, and 24 k. Competitive binding studies in T-47D-conditioned media demonstrated that these BPs bound more IGF-II than IGF-I, and that IGF-II potently inhibited binding of either IGF-I or -II. Immunological studies using a polyclonal antibody against the HEP G2 small BP revealed no immunoreactive BP in conditioned media from MCF-7 and T-47D and only slight immunoreactivity in conditioned media from Hs578T and MDA 231. Analysis by Northern blot, using a probe from the cDNA sequence of the HEP G2 BP, demonstrated that Hs578T and MDA-231 cell lines contained small amounts of the 1.65 kilobase mRNA characteristic of the HEP G2 BP, while MCF-7 and T-47D tested negative.(ABSTRACT TRUNCATED AT 250 WORDS)
De Leon
D D
DD
Department of Pediatrics, Stanford University Medical Center, California 94305.
Wilson
D M
DM
Bakker
B
B
Lamsom
G
G
Hintz
R L
RL
Rosenfeld
R G
RG
D015152:Blotting, Northern; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism*; D002352:Carrier Proteins / Q000302:isolation & purification*; D004591:Electrophoresis, Polyacrylamide Gel; 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
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II