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Dzip1 Regulates Mammalian Cardiac Valve Development Through A Cby1-b Catenin Mechanism
LILONG GUO, Tyler Beck, Cortney Gensemer, Jordan Morningstar, Richel Biggs, Natalie Koren.
Medical University of South Carolina, CHARLESTON, SC, USA.

OBJECTIVE:Mitral valve prolapse (MVP) is a common and progressive cardiovascular disease with developmental origins. How developmental errors contribute to disease pathogenesis are not well understood.
METHODS:Yeast-two hybrid and co-immunoprecipitation were performed to identify protein-protein interactions. Immunofluorescent staining was adopted to evaluate protein expression on tissue. In vitro TOP Flash assay was used to quantify b-catenin activity.
RESULTS:A multimeric complex was identified that consists of the MVP gene Dzip1, Cby1, and b-catenin. Co-expression during valve development revealed overlap at the basal body of the primary cilia. Biochemical studies revealed a DZIP1 peptide required for stabilization of the complex and suppression of b-catenin activities. Decoy peptides generated against this interaction motif altered nuclear vs cytosolic levels of b-catenin with effects on transcriptional activity. A mutation within this domain was identified in a family with inherited non-syndromic MVP. This novel mutation and our previously identified DZIP1S24R variant resulted in reduced DZIP1 and CBY1 stability and increased b-catenin activities. The b-catenin target gene, MMP2 was up-regulated in the Dzip1S14R/+ valves and correlated with loss of collagenous ECM matrix and myxomatous phenotype.
CONCLUSIONS:Dzip1 functions to restrain b-catenin signaling through a CBY1 linker during cardiac development. Loss of these interactions results in increased nuclear b-catenin/Lef1 and excess MMP2 production, which correlates with developmental and postnatal changes in ECM and generation of a myxomatous phenotype.


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