IRS-1 expression and activation are not sufficient to activate downstream pathways and enable IGF-I growth response

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Updated: Oct 18, 2026

Profiling of Estrogen-regulated MicroRNAs in Breast Cancer Cells
16:24

Profiling of Estrogen-regulated MicroRNAs in Breast Cancer Cells

Published on: February 21, 2014

J G Jackson1, D Yee

  • 1Department of Medicine, Division of Medical Oncology, University of Texas Health Science Center at San Antonio, San Antonio, TX, 78284-7884, USA.

Growth Hormone & IGF Research : Official Journal of the Growth Hormone Research Society and the International IGF Research Society
|November 2, 1999
PubMed

IGF-responsive breast cancer cells activate insulin receptor substrate (IRS)-1 after IGF-I treatment. To determine if IRS-1 expression was sufficient to enable IGF-responsiveness, two IGF-I unresponsive breast cancer cell lines (MDA-MB-435A and MDA-MB-468) were transfected with IRS-1. While IGF-I caused tyrosine phosphorylation of IRS-1 in both transfected cell lines, increased MAP kinase activity was not seen. IGF-I treatment of 435A IRS-1 transfected cells resulted in minimal increased PI3 kinase activity associated with IRS-1, while IRS-2/PI3 kinase was greatly reduced. In MDA-MB-468 IRS-1 transfected cells, IGF-I caused increased IRS-1 associated PI3 kinase activity compared to parental cells, but at levels far below those observed in IGF-responsive MCF-7 cells. The transfected cells were also not responsive to IGF-I in monolayer growth. Thus, IRS-1 expression and activation alone are insufficient to mediate a proliferative response to IGF-I in breast cancer cells, and it is likely that maximal activation of downstream signaling pathways must also occur.

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