Clinical value of R-spondins in triple-negative and metaplastic breast cancers

Abstract

Background:RSPO ligands, activators of the Wnt/β-catenin pathway, are overexpressed in different cancers. The objective of this study was to investigate the role of RSPOs in breast cancer (BC).Methods:Expression of RSPO and markers of various cancer pathways were measured in breast tumours and cell lines by qRT–PCR. The effect of RSPO on the Wnt/β-catenin pathway activity was determined by luciferase assay, western blotting, and qRT–PCR. The effect of RSPO2 inhibition on proliferation was determined by using RSPO2 siRNAs. The effect of IWR-1, an inhibitor of the Wnt/β-catenin pathway, was examined on the growth of an RSPO2-positive patient-derived xenograft (PDX) model of metaplastic triple-negative BC.Results:We detected RSPO2 and RSPO4 overexpression levels in BC, particularly in triple-negative BC (TNBC), metaplastic BC, and triple-negative cell lines. Various mechanisms could account for this overexpression: presence of fusion transcripts involving RSPO, and amplification or hypomethylation of RSPO genes. Patients with RSPO2-overexpressing tumours have a poorer metastasis-free survival (P=3.6 × 10−4). RSPO2 and RSPO4 stimulate Wnt/β-catenin pathway activity. Inhibition of RSPO expression in a TN cell line inhibits cell growth, and IWR-1 significantly inhibits the growth of an RSPO2-overexpressing PDX.Conclusions:RSPO overexpression could therefore be a new prognostic biomarker and therapeutic target for TNBC.

Wnt signaling in human and mouse breast cancer: Focusing on Wnt ligands, receptors and antagonists

“…In mice mammary gland, Lgr5 + cells are chiefly within the Lin − CD24 + CD49f high subpopulation; they can differentiate into both basal and luminal mammary epithelial cells, and regenerate functional mammary glands . In human breast cancers, both Lgr5 and Rspo are overexpressed with activation of the Wnt/β‐catenin pathway, which contributes to increased tumor growth, metastasis and stemness . Tenascin C (TNC) is an extracellular matrix protein abundantly expressed by mammary stem cells .…”

“…37,38 In human breast cancers, both Lgr5 and Rspo are overexpressed with activation of the Wnt/β-catenin pathway, which contributes to increased tumor growth, metastasis and stemness. 39,40 Tenascin C (TNC) is an extracellular matrix protein abundantly expressed by mammary stem cells. 41 Produced by breast cancer cells in which~90% is CD44 + CD24 − , TNC maintains the expression of Lgr5 and the response of Lgr5 to Wnt ligands, and is associated with aggressive lung metastasis.…”

Downregulation of Lgr6 inhibits proliferation and invasion and increases apoptosis in human colorectal cancer

“…Previous studies have revealed that Lgr6 activates multiple signaling pathways, including the Wnt/β-catenin pathway (34,37); however, no studies have focused on its role in activating the PI3K/AKT pathway in cRc. In the present study, AKT/PI3K was inactivated when Lgr6 was inhibited by siRNA, indicating that the role of Lgr6 in cRc may partly depend on the PI3K/AKT pathway.…”

Aberrant WNT/CTNNB1 Signaling as a Therapeutic Target in Human Breast Cancer: Weighing the Evidence

“…Note that all of these components function at the level of ligand and receptor binding. The top two hits, RSPO2 and FZD6, have both been linked to reduced metastasis free survival, but likely operate via different WNT signaling mechanisms (Corda et al, 2017;Coussy et al, 2017). It should be stressed that in this respect, breast cancer is not unique.…”

“…In contrast, copy number gain of the FZD6 gene, which can be readily detected in human breast cancer cohorts ( Figure 1B) and most predominantly in TNBC, most likely exerts its effects on cell motility and invasion via alternative, non-canonical WNT signaling mechanisms (Corda et al, 2017). For other components, such as RSPO2, RSPO4 and to a lesser extent LGR5 and LGR6, the overexpression of which is enriched in TNBC, the mechanism is more likely to involve amplification of the WNT/CTNNB1 signaling response (Coussy et al, 2017). Importantly, the separation between canonical and non-canonical WNT signaling is not black and white.…”