Motility response to insulin-like growth factor-I (IGF-I) in MCF-7 cells is associated with IRS-2 activation and integrin expression.
In MCF-7L cells, insulin-like growth factor-I (IGF-I) stimulates activation of insulin receptor substrate-1 (IRS-1) and enhances cell proliferation. While others have shown that IGF-I enhances cell motility in MCF-7 cells, we have not been able to demonstrate this. To determine if the source of MCF-7 cells account for these reported differences, we examined the MCF-7 cells available from the American Type Culture Collection (MCF-7/ATCC) and compared them to the MCF-7L cells maintained in our laboratory. Both MCF-7L and MCF-7/ATCC grew in response to 5 nM IGF-I and 1 nM estradiol. However, only MCF-7/ATCC demonstrated IGF-I stimulated motility. Immunoprecipitation of IRS substrates followed by anti-phosphotyrosine blotting demonstrated that both IRS-1 and IRS-2 were activated by IGF-I in these cells. However, MCF-7/ATCC cells had greater phosphorylation of IRS-2 compared to MCF-7L. Immunoblots showed that levels of IRS-1 and IRS-2 were comparable between cell lines. We have previously shown that fibronectin-binding integrins are necessary for IGF-stimulated motility. Similar levels of beta1 integrin were detected in both strains of MCF-7. However, low levels of alpha5 and alpha3 were detected in MCF-7L cells whereas high levels of alpha3 and alpha5 integrin were expressed in MCF-7/ATCC cells. Inhibition of integrin function by a blocking antibody or inhibitory peptide diminished IGF-mediated motility in MCF-7/ATCC. In MCF-7/ATCC cells, IGF-I stimulation was associated with a movement of IRS-2 to the leading edge of filopodia. Thus, patterns of integrin expression among breast cancer cell lines may partially explain the different motility behavior of cells in response to IGF-I. IRS-2 activation and integrin occupancy are both required for IGF-stimulated motility.
Department of Medicine, University of Minnesota Cancer Center, Minneapolis, MN 55455, USA.
Xihong
X
Zhang
Sailaja
S
Kamaraju
Fumihiko
F
Hakuno
Tomohiro
T
Kabuta
Shin-Ichiro
S
Takahashi
Deepali
D
Sachdev
Douglas
D
Yee
D001943:Breast Neoplasms / Q000473:pathology*; D045744:Cell Line, Tumor / Q000187:drug effects; D002465:Cell Movement / Q000187:drug effects*; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D016023:Integrins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins / Q000378:metabolism
C526297:IRS2 protein, human; D055504:Insulin Receptor Substrate Proteins; D016023:Integrins; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D007334:Insulin-Like Growth Factor I