Loss of RSPO3 as a potential mechanism of greater invasiveness in prostate cancer.

Abstract

333 Background: While prostate cancer can often manifest as an indolent disease, locally-advanced or metastatic disease can cause significant morbidity or mortality. Better understanding of molecular mechanisms leading to more aggressive presentations can lead to identification of prognostic or predictive biomarkers, as well as to possible therapeutic targets. Methods: We describe the generation of prostate cancer cell lines that have been selected through a course of hypofractionated radiotherapy. We show that R-spondin 3, a protein implicated previously as a marker of aggressive disease in colorectal and non-small cell lung cancer, is downregulated in these cell lines compared to parental cells. Then, we test the functional consequences of R-spondin 3 downregulation by siRNA-mediated interference using in vitro assays of radiation resistance, proliferation, and invasiveness . Experiments investigating any change in metastatic propensity following R-spondin 3 downregulation are forthcoming. We further investigate signaling pathways that may be implicated in the mechanism of R-spondin 3 action. Lastly, we use the Oncomine Platform to look for any changes in R-spondin 3 levels between normal prostate tissue and prostate adenocarcinoma. Results: Although siRNA-mediated loss of R-spondin 3 does not confer radiation resistance in vitro, it does result in increased invasiveness in Matrigel assays. Paradoxically, R-spondin 3 downregulation results in decreased proliferation. Interference with R-spondin 3 also results in decreased β-catenin, ERK, and Akt signaling, but increased JNK signaling. In support of our in vitro results, R-spondin 3 expression is lower in human prostate adenocarcinoma compared to normal prostate in several gene expression datasets. Conclusions: Our preliminary data suggest that R-spondin 3 loss may lead to increased disease aggression via altered cell signaling. R-spondin 3 downregulation may represent a potential biomarker to identify patients at greater risk of developing locally advanced or metastatic disease, or a potential mechanism to target in future therapeutic efforts.