Insertional mutagenesis in a HER2-positive breast cancer model reveals ERAS as a driver of cancer and therapy resistance.

Personalized medicine for cancer patients requires a deep understanding of the underlying genetics that drive cancer and the subsequent identification of predictive biomarkers. To discover new genes and pathways contributing to oncogenesis and therapy resistance in HER2+ breast cancer, we performed Mouse Mammary Tumor Virus (MMTV)-induced insertional mutagenesis screens in ErbB2/cNeu-transgenic mouse models. The screens revealed 34 common integration sites (CIS) in mammary tumors of MMTV-infected mice, highlighting loci with multiple independent MMTV integrations in which potential oncogenes are activated, most of which had never been reported as MMTV CIS. The CIS most strongly associated with the ErbB2-transgenic genotype was the locus containing Eras (ES cell-expressed Ras), a constitutively active RAS-family GTPase. We show that upon expression, Eras acts as a potent oncogenic driver through hyperactivation of the PI3K/AKT pathway, in contrast to other RAS proteins that signal primarily via the MAPK/ERK pathway and require upstream activation or activating mutations to induce signaling. We additionally show that ERAS synergistically enhances HER2-induced tumorigenesis and, in this role, can functionally replace ERBB3/HER3 by acting as a more powerful activator of PI3K/AKT signaling. Although previously reported as pseudogene in humans, we observed ERAS RNA and protein expression in a substantial subset of human primary breast carcinomas. Importantly, we show that ERAS induces primary resistance to the widely used HER2-targeting drugs Trastuzumab (Herceptin) and Lapatinib (Tykerb/Tyverb) in vivo, and is involved in acquired resistance via selective upregulation during treatment in vitro, indicating that ERAS may serve as a novel clinical biomarker for PI3K/AKT pathway hyperactivation and HER2-targeted therapy resistance.

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

Insulin receptor substrate 4 (IRS4) belongs to a family of cytoplasmic docking proteins mediating signals from cell surface receptors to downstream effectors. While IRS1 and IRS2 mediate signals from an active receptor, we found that IRS4 hyperactivates the phosphatidylinositol phosphate kinase (PI3K)-pathway independent of upstream signals and is irresponsive to feedback regulation causing cancer and resistance to human epidermal growth factor receptor 2 (HER2) targeted therapy.

RSPO3 expands intestinal stem cell and niche compartments and drives tumorigenesis.

OBJECTIVE: The gross majority of colorectal cancer cases results from aberrant Wnt/ß-catenin signalling through adenomatous polyposis coli (APC) or CTNNB1 mutations. However, a subset of human colon tumours harbour, mutually exclusive with APC and CTNNB1 mutations, gene fusions in RSPO2 or RSPO3, leading to enhanced expression of these R-spondin genes. This suggested that RSPO activation can substitute for the most common mutations as an alternative driver for intestinal cancer. Involvement of RSPO3 in tumour growth was recently shown in RSPO3-fusion-positive xenograft models. The current study determines the extent into which solely a gain in RSPO3 actually functions as a driver of intestinal cancer in a direct, causal fashion, and addresses the in vivo activities of RSPO3 in parallel. DESIGN: We generated a conditional Rspo3 transgenic mouse model in which the Rspo3 transgene is expressed upon Cre activity. Cre is provided by cross-breeding with Lgr5-GFP-CreERT2 mice. RESULTS: Upon in vivo Rspo3 expression, mice rapidly developed extensive hyperplastic, adenomatous and adenocarcinomatous lesions throughout the intestine. RSPO3 induced the expansion of Lgr5+ stem cells, Paneth cells, non-Paneth cell label-retaining cells and Lgr4+ cells, thus promoting both intestinal stem cell and niche compartments. Wnt/ß-catenin signalling was modestly increased upon Rspo3 expression and mutant Kras synergised with Rspo3 in hyperplastic growth. CONCLUSIONS: We provide in vivo evidence that RSPO3 stimulates the crypt stem cell and niche compartments and drives rapid intestinal tumorigenesis. This establishes RSPO3 as a potent driver of intestinal cancer and proposes RSPO3 as a candidate target for therapy in patients with colorectal cancer harbouring RSPO3 fusions.

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

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.

Calorie restriction in the filamentous fungus Podospora anserina.

Calorie restriction (CR) is a regimen of reduced food intake that, although the underlying mechanism is unknown, in many organisms leads to life span extension. Podospora anserina is one of the few known ageing filamentous fungi and the ageing process and concomitant degeneration of mitochondria have been well-studied. CR in P. anserina increases not only life span but also forestalls the ageing-related decline in fertility. Here we review what is known about CR in P. anserina and about possibly involved mechanisms like enhanced mitochondrial stability, reduced production of reactive oxygen species and changes in the OXPHOS machinery. Additionally, we present new microscopic data on mitochondrial dynamics under rich nutritional and CR conditions at different points in life. Lines that have grown under severe CR for more than 50x the normal life span, show no accumulation of age-related damage, though fecundity is reduced in some of these lines. Finally, we discuss the possible role of CR in P. anserina in nature and the effect of CR at different points in life.