INTRODUCTION: We previously detected a 2-fold increase of CacyBP/SIP gene expression encoding calcyclin‑binding protein (CacyBP/SIP) and increased CacyBP/SIP dimerization in the striatum of YAC128 mice, a model of Huntington’s disease (HD). In these mice, mutated huntingtin is overexpressed in neurons. In agreement with the suggested role of CacyBP/ SIP in β‑catenin degradation, we observed a decrease in total protein ubiquitination and a higher level of β‑catenin in the striatum of HD mice as compared to wild‑type animals. AIM(S): To check if there is a relationship between the level of CacyBP/SIP dimerization in the YAC128 model and β‑catenin signaling and neuronal neurodegeneration. METHOD(S): To impair or increase the ability of CacyBP/SIP to dimerize, mutations in its coiled‑coil dimerization domain were computationally designed using the crystal structure as a template and the Rosetta energy function and molecular dynamics methods. Native gel electrophoresis was used to confirm the effects of mutations in dimer stabilization and destabilization. In cultures of medium spiny neurons (MSNs) isolated from the striatum of YAC128 mice, CacyBP/SIP mutants were overexpressed by lentiviruses and used to analyze the level of β‑catenin and its ubiquitination by immunoprecipitation and western blotting. RESULTS: In HD MSNs in which wild‑type CacyBP/SIP was overexpressed, the level of β‑catenin and its ubiquitination was unchanged relative to the control vector. The effects of mutations leading to increased (K21W and a double mutant T30R, S33E) or decreased ability of CacyBP/SIP to dimerize (D11A, E14A, and L18A) on β‑catenin homeostasis are being analyzed. CONCLUSIONS: CacyBP/SIP protein mutants with different abilities to dimerize allow us to establish the role of dimerization on the β‑catenin level, which might be related to HD pathology. FINANCIAL SUPPORT: Supported by National Science Centre in Poland. Grant no. 2014/15/D/NZ3/05181 to MC.
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