Involvement of Insulin-Like Growth Factor-I Secretion and All-Trans-Retinoic Acid-Induced Decrement in Viability in MCF-7 Cells.

Background/Aim: Insulin-like growth factor-I (IGF-I) is associated with survival, apoptosis and proliferation in MCF-7 cells. All-trans-retinoic acid (RA) is used as a cancer therapeutic, but the use of RA in cancer therapy is limited by the unpredictable resistance of cancer cells to drug action. Furthermore, the relationship of IGF-I with RA-induced decrement in cell viability has yet to be elucidated. Materials and Methods: MCF-7 cells were grown as confluent monolayers. To demonstrate the signaling pathways and roles of IGF-I, we suppressed endogenous target IGF-I with specific small interfering RNA treatment. Protein kinase C-δ and insulin receptor substrate 1 (IRS-1) protein levels were analyzed by Western blot. Radioimmunoassays were used to assess the concentration of endogenous IGF-I, and RT-PCR was used to assess IGF-I mRNA expression. Cell viability was analyzed with the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay. Results: We showed that RA treatment resulted in a dose- and time-dependent decrease in the secretion and synthesis of IGF-I. Subsequently, we found that suppression of IGF-I and IRS-1 protein decreased cell viability. In contrast, suppression of protein kinase C-δ and stimulation of IGF-I protected cells from RA-induced decrement in cell viability. The combination of RA treatment with IGF-I or IRS-1 small interfering RNA resulted in an additive decrease in cell viability. Conclusion: These results indicate that IGF-I plays an important role in the effect of RA and that suppression of IGF-I is implicated in the RA-induced inhibition of cell viability in MCF-7 cells. Copyright © 2011 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]