Insulin Receptor Substrate-1 Regulates the Transformed Phenotype of BT-20 Human Mammary Cancer Cells

Abstract

Although originating from a human breast cancer, BT-20 cells do not form colonies in soft agar. BT-20 cells do not express insulin receptor substrate-1 (IRS-1), which is known to promote both normal and abnormal growth and to inhibit differentiation. Stable expression of IRS-1 confers to BT-20 cells the ability to form colonies in soft agar. BT-20 cells form tumors in xenografts in mice, but the size of tumors is twice as large when the cells express IRS-1. The increased transformed phenotype is characterized by occupancy of the rDNA and cyclin D1 promoters by IRS-1 and the activation of the cyclin D1, c-myc, and rDNA promoters. In addition, the retinoblastoma protein, which is detectable in the rDNA promoter of quiescent BT-20/IRS-1 cells, is replaced by IRS-1 after insulinlike growth factor-I stimulation. Our results indicate that in BT-20 human mammary cancer cells, expression of IRS-1 activates promoters involved in cell growth and cell proliferation, resulting in a more transformed phenotype. Targeting of IRS-1 could be effective in inhibiting the proliferation of mammary cancer cells. [Cancer Res 2007;67(5):2124-30]

Growth inhibition by microRNAs that target the insulin receptor substrate-1

“…9,15,16 IRS-1 expression is often increased in human cancers 22 and increased or ectopic expression of IRS-1 causes cell transformation, i.e., ability to form colonies in soft agar and tumors in mice. 15,[23][24][25][26][27][28][29][30] Conversely, downregulation of IRS-1 (by antisense or siRNA) reverses the transformed phenotype. [30][31][32][33] One intriguing aspect of IRS-1 downregulation is that cells that do not express IRS-1 survive, although they have a tendency to differentiate (see above).…”

“…15,[23][24][25][26][27][28][29][30] Conversely, downregulation of IRS-1 (by antisense or siRNA) reverses the transformed phenotype. [30][31][32][33] One intriguing aspect of IRS-1 downregulation is that cells that do not express IRS-1 survive, although they have a tendency to differentiate (see above). A similar situation occurs with the IGF-IR.…”

Depletion of insulin receptor substrate 2 reverses oncogenic transformation induced by v-src

“…BT-20 breast cancer cells and 32D-derived cells have been previously described [7] . Mutant IRS-2 plasmids have been previously described [6] .…”

“…Nuclear translocation is considered to be one of the most important steps in the process of cellular transformation [7] . Following subcellular fractionation, IRS-2 was present in the nuclear fraction of R-/v-src and BT-20 cells ( Figure 5A).…”

“…MEFs that contain disrupted IGF-1R genes, referred to as R-cells, are resistant to transformation induced by numerous viral and cellular oncogenes, including the SV40 T antigen, the activated Ha-ras oncogene, the bovine papillomavirus E5 protein, the human papillomavirus E7 protein, the Ewing's sarcoma fusion protein, and activated src. To www.nature.com/aps Sun HZ et al Acta Pharmacologica Sinica npg date, the only oncogenes known to transform R-cells are v-src and a mutant of Gα13 [7] . The observation that v-src is one of only two oncogenes to transform R-cells is quite remarkable because MEFs have a strong tendency to become transformed.…”