RSPO3 expands intestinal stem cell and niche compartments and drives tumorigenesis

Abstract

ObjectiveThe gross majority of colorectal cancer cases results from aberrant Wnt/β-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.DesignWe 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.ResultsUpon 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/β-catenin signalling was modestly increased upon Rspo3 expression and mutant Kras synergised with Rspo3 in hyperplastic growth.ConclusionsWe 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.

LGRs receptors as peculiar GPCRs involved in cancer

“…A similar conclusion has been reached with the Apc min/+ line used as a model for human familial adenomatous polyposis [81]. In addition, overexpression of the Rspondin 3 ligand in the Lgr4 +ve/ Lgr5 +ve cells also leads to rapid adenoma and adenocarcinoma development, associated with expansion of the Lgr4 +ve/ Lgr5 +ve cells but also of Lgr4 +ve/ Lgr5 -ve cells [82]. In mammary glands, oncogenic mutation in the Lgr6 +ve cells induces expansion of luminal cells generating tumor development [72].…”

Comprehensive characterization of RSPO fusions in colorectal traditional serrated adenomas

“…TSAs with RSPO fusions tended to show pronounced ectopic crypt formation and diminished slit‐like serration. Interestingly, exogenous expression of Rspo3 in mouse intestinal epithelial cells results in the promotion of ectopic crypt formation and expansion of cells constituting the stem cell niche . The pronounced ectopic crypt formation in RSPO fusion‐positive TSAs may reflect the physiological role of R‐spondin in stem cell niche formation.…”

WNT Signaling and Colorectal Cancer

“…Though correlative, this pattern suggests either synthetic lethality, as has been shown for coincident RAS-MAPK alterations [33], or that these events are functionally redundant. Indeed, enforced expression of RSPO1 or RSPO3 can drive proliferation in the intestine in animal models, but in both cases seems to be due to a paracrine effect of the secreted RSPO ligand [34, 35]. Further work will be required to determine whether RSPO rearrangements alone are sufficient to drive tumor development in the intestine.…”