IRS4 induces mammary tumorigenesis and confers resistance to HER2-targeted therapy through constitutive PI3K/AKT-pathway hyperactivation

Abstract

In search of oncogenic drivers and mechanisms affecting therapy resistance in breast cancer, we identified Irs4, a poorly studied member of the insulin receptor substrate (IRS) family, as a mammary oncogene by insertional mutagenesis. Whereas normally silent in the postnatal mammary gland, IRS4 is found to be highly expressed in a subset of breast cancers. We show that Irs4 expression in mammary epithelial cells induces constitutive PI3K/AKT pathway hyperactivation, insulin/IGF1-independent cell proliferation, anchorage-independent growth and in vivo tumorigenesis. The constitutive PI3K/AKT pathway hyperactivation by IRS4 is unique to the IRS family and we identify the lack of a SHP2-binding domain in IRS4 as the molecular basis of this feature. Finally, we show that IRS4 and ERBB2/HER2 synergistically induce tumorigenesis and that IRS4-expression confers resistance to HER2-targeted therapy. Taken together, our findings present the cellular and molecular mechanisms of IRS4-induced tumorigenesis and establish IRS4 as an oncogenic driver and biomarker for therapy resistance in breast cancer.

Insulin receptor substrate 4 (IRS4) is a constitutive active oncogenic driver collaborating with HER2 and causing therapeutic resistance

“…1B for a schematic overview). IRS4 -expression could also rapidly be attained in naive HER2+ breast cancer cell lines by culturing the cells for several passages in medium with increasing concentrations of trastuzumab or lapatinib, indicating selection for IRS4 -expressing cells under the pressure of the drugs 5 . Hence, our data suggest that IRS4 can cause both primary resistance to trastuzumab or lapatinib, as well as acquired resistance during treatment, thus likely plays a role in relapse in breast cancer patients.…”

“…Hence, our data suggest that IRS4 can cause both primary resistance to trastuzumab or lapatinib, as well as acquired resistance during treatment, thus likely plays a role in relapse in breast cancer patients. Importantly, we also showed that treating HER2+ breast cancer cells expressing IRS4 with a HER2-targeting drug in combination with a PI3K-specific inhibitor abrogated IRS4-mediated resistance, even in suboptimal doses 5 . This finding may inspire the field to keep investigating the combination of HER2-targeted drugs with PI3K, AKT and/or mTOR inhibitors, despite the limited success of initial clinical trials.…”

“…However, both primary and secondary resistance are common and are often associated with PI3K-pathway hyperactivation 9 . Indeed, we showed that expression of IRS4 in various cell lines with ERBB2 overexpression greatly reduced the sensitivity to HER2-directed therapeutic agents 5 . Moreover, we observed that IRS4 synergistically accelerates tumorigenesis in vitro and in vivo when co-expressed with HER2 , most likely due to the combined potent activation of the PI3K-pathway by IRS4 and the RAS/RAF/MEK/ERK (mitogen-activated protein kinase, MAPK) pathway by HER2 (see Fig.…”

“…A frequently tagged gene in these screens was Irs4 , but not the closely related family members Irs1 and Irs2 . We recently reported that IRS4 has a growth factor independent activity, in contrast to IRS1 and IRS2 5 . Specifically, we demonstrated that IRS4 has a high basal signal transduction activity and a sustained activity upon upstream stimulation due to a lacking Src homology phosphatase 2 (Shp2)-binding site.…”

“…). We found that IRS4 was mainly expressed in human epidermal growth factor receptor 2 (HER2, encoded by the ERBB2 gene) positive and triple negative, but scarcely in luminal A or B breast cancers 5 . HER2-targeting therapy using monoclonal antibodies trastuzumab or pertuzumab, and the tyrosine kinase inhibitor lapatinib greatly improves the prognosis of HER2+ breast cancer patients.…”