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Oncogene. 2015 Jul 23;34(30):3968-76. doi: 10.1038/onc.2014.328. Epub 2014 Oct 6.

P-REX1 creates a positive feedback loop to activate growth factor receptor, PI3K/AKT and MEK/ERK signaling in breast cancer.

Author information

1
Department of Pharmacology and Toxicology, Norris Cotton Cancer Center, Geisel School of Medicine at Dartmouth, Dartmouth-Hitchcock Medical Center, Lebanon, NH, USA.
2
1] Department of Medicine, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN, USA [2] Breast Cancer Research Program, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN, USA.
3
Proteomics Laboratory, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN, USA.
4
1] Department of Breast Medical Oncology, MD Anderson Cancer Center, University of Texas, Houston, TX, USA [2] Department of Systems Biology, MD Anderson Cancer Center, University of Texas, Houston, TX, USA.
5
Department of Systems Biology, MD Anderson Cancer Center, University of Texas, Houston, TX, USA.
6
1] Department of Medicine, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN, USA [2] Breast Cancer Research Program, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN, USA [3] Department of Cancer Biology, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN, USA.
7
1] Department of Pharmacology and Toxicology, Norris Cotton Cancer Center, Geisel School of Medicine at Dartmouth, Dartmouth-Hitchcock Medical Center, Lebanon, NH, USA [2] Comprehensive Breast Cancer Program, Norris Cotton Cancer Center, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA.

Abstract

Phosphatidylinositol 3-kinase (PI3K) promotes cancer cell survival, migration, growth and proliferation by generating phosphatidylinositol 3,4,5-trisphosphate (PIP3) in the inner leaflet of the plasma membrane. PIP3 recruits pleckstrin homology domain-containing proteins to the membrane to activate oncogenic signaling cascades. Anticancer therapeutics targeting the PI3K/AKT/mTOR (mammalian target of rapamycin) pathway are in clinical development. In a mass spectrometric screen to identify PIP3-regulated proteins in breast cancer cells, levels of the Rac activator PIP3-dependent Rac exchange factor-1 (P-REX1) increased in response to PI3K inhibition, and decreased upon loss of the PI3K antagonist phosphatase and tensin homolog (PTEN). P-REX1 mRNA and protein levels were positively correlated with ER expression, and inversely correlated with PI3K pathway activation in breast tumors as assessed by gene expression and phosphoproteomic analyses. P-REX1 increased activation of Rac1, PI3K/AKT and MEK/ERK signaling in a PTEN-independent manner, and promoted cell and tumor viability. Loss of P-REX1 or inhibition of Rac suppressed PI3K/AKT and MEK/ERK, and decreased viability. P-REX1 also promoted insulin-like growth factor-1 receptor activation, suggesting that P-REX1 provides positive feedback to activators upstream of PI3K. In support of a model where PIP3-driven P-REX1 promotes both PI3K/AKT and MEK/ERK signaling, high levels of P-REX1 mRNA (but not phospho-AKT or a transcriptomic signature of PI3K activation) were predictive of sensitivity to PI3K inhibitors among breast cancer cell lines. P-REX1 expression was highest in estrogen receptor-positive breast tumors compared with many other cancer subtypes, suggesting that neutralizing the P-REX1/Rac axis may provide a novel therapeutic approach to selectively abrogate oncogenic signaling in breast cancer cells.

PMID:
25284585
PMCID:
PMC4387124
DOI:
10.1038/onc.2014.328
[Indexed for MEDLINE]
Free PMC Article

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