Reduced BMP signaling due to BMPR1A germline mutations in juvenile polyposis

Abstract

Introduction Juvenile polyposis (JP) is characterized by the development of hamartomatous polyps that collectively carry a high risk of malignant transformation. Germline mutations in the gene for bone morphogenetic protein receptor 1A (BMPR1A) and the tumor suppressor SMAD4 predispose to JP. We set out to evaluate the effect of JP BMPR1A mutations on downstream signaling through the bone morphogenetic protein (BMP) pathway. Methods Mutations found in JP patients were individually recreated in a wild-type (WT) BMPR1A expression vector using a PCR-based site directed mutagenesis (SDM) approach. SDM vectors were then cotransfected with a BMP responsive element luciferase vector (BRE-Luc) and a Renilla internal control into HEK-293T cells. Light units reflecting downstream signaling strength were then quantified after 48 hours. Student's t-test was used for statistical analysis. Results Twenty-two SDM JP mutants were created (14 nonsense and 8 missense). After adjusting for transfection efficiency, BMP signaling was found to be altered for 19 mutations, 17 of which were lower than WT. Two missense and 1 nonsense mutation did not lead to a significant change in activity. Compared to WT, the mean decrease in luciferase for nonsense mutations was 73.1% (p Conclusions To date, JP BMPR1A mutations have not been systematically studied in an in vitro model or been shown to affect downstream signaling. This study confirms that the BMPR1A mutations found in JP patients lead to loss of BMP signaling, which is the likely mechanism leading to this phenotype.