R‐spondin 2 Drives Liver Tumor Development in a Yes‐Associated Protein‐Dependent Manner

Abstract

Each year, more than 25,000 people succumb to liver cancer in the United States, and this neoplasm represents the second cause of cancer‐related death globally. R‐spondins (RSPOs) are secreted regulators of Wnt signaling that function in development and promote tissue stem cell renewal. In cancer, RSPOs 2 and 3 are oncogenes first identified by insertional mutagenesis screens in tumors induced by mouse mammary tumor virus and by transposon mutagenesis in the colonic epithelium of rodents. RSPO2 has been reported to be activated by chromosomal rearrangements in colorectal cancer and overexpressed in a subset of hepatocellular carcinoma. Using human liver tumor gene expression data, we first discovered that a subset of liver cancers were characterized by high levels of RSPO2 in contrast to low levels in adjacent nontumor tissue. To determine if RSPOs are capable of inducing liver tumors, we used an in vivo model from which we found that overexpression of RSPO2 in the liver promoted Wnt signaling, hepatomegaly, and enhanced liver tumor formation when combined with loss of transformation‐related protein 53 (Trp53). Moreover, the Hippo/yes‐associated protein (Yap) pathway has been implicated in many human cancers, influencing cell survival. Histologic and gene expression studies showed activation of Wnt/β‐catenin and Hippo/Yap pathways following RSPO2 overexpression. We demonstrate that knockdown of Yap1 leads to reduced tumor penetrance following RSPO2 overexpression in the context of loss of Trp53. Conclusion: RSPO2 overexpression leads to tumor formation in the mouse liver in a Hippo/Yap‐dependent manner. Overall, our results suggest a role for Yap in the initiation and progression of liver tumors and uncover a novel pathway activated in RSPO2‐induced malignancies. We show that RSPO2 promotes liver tumor formation in vivo and in vitro and that RSPO2's oncogenic activity requires Hippo/Yap activation in hepatocytes. Both RSPO2 and YAP1 are suggested to represent novel druggable targets in Wnt‐driven tumors of the liver.

The Matrix Revolution: Matricellular Proteins and Restructuring of the Cancer Microenvironment

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The RSPO‐LGR4/5‐ZNRF3/RNF43 module in liver homeostasis, regeneration, and disease

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Targeting ligand-dependent wnt pathway dysregulation in gastrointestinal cancers through porcupine inhibition

“…Elevated Wnt3/4/5a and suppression of SFRPs have also been observed, an expression pattern that did not correlate with CTNNB1 mutations but was associated with loss of differentiation and cirrhosis, and activation of PCP pathways ( Bengochea et al, 2008 ). Functional overexpression of RSPO2 with combined loss of transformation-related protein 53 (TP53) led to development of liver cancer in mice models ( Conboy et al, 2019 ), implicating a role for extracellular Wnt ligands in liver tumorigenesis.…”