Endocrine Abstracts

Introduction: As a tumor-suppressor gene, armadillo repeat-containing 5 (ARMC5) gene regulates steroidogenesis and cell apoptosis in manner of second-hit model. Mutations of ARMC5 gene will disturb its normal function, leading to reduced cortisol synthesis and cell apoptosis, which is acknowledged as a frequent cause of primary bilateral macronodular adrenal hyperplasia (PBMAH). Not until another somatic ARMC5 mutation occur in germline mutation carriers, will they manifest as PBMAH. The underlying pathogenesis has always been of great interest among researchers, however, still remains mystery.

Matherials and methods: This study was conducted in a Chinese family with hereditary PBMAH, including four members from two generations. Gene test was conducted in the blood samples and adrenal tissues. In vitro experiments were introduced to explored gene expression of wild type and mutants at transcription and translation levels. Further investigations were conducted to trace the subcellular location, degradation pathway and stability of wild type and mutant protein.

Results: Gene test discovered one germline (mutant 1: c.337dupG, p.A113Gfs*7) and two somatic (mutant 2: c.1157G>A; p.W386X, mutant 3: c.1900G>T, p.E634X) ARMC5 gene mutation sites. In vitro experiments indicated significantly increased mRNA levels of all the mutants along with significantly increased protein content of mutant 2 and 3 than that of wild type, however, the mutant 1 protein cannot be detected with western blot. Extensive subcellular localization experiment demonstrated that wild type protein was localized in both cytoplasm and nucleus, while, the mutants were accumulated primarily in the nucleus. As regard to protein degradation pathway experiment, it proved that wild type and mutant 1 protein were degraded through ubiquitin-proteasome pathway and lysosomal pathway, respectively. Based on the different degradation rate of wild type, mutant 2, and mutant 3, we inferred that the protein stability of the mutant 2>wild type>mutant3.

Conclusion: This study discovered three novel ARMC5 gene mutation sites which extended the spectrum of the mutation. In vitro experiments demonstrated significant differences at transcription and translation levels between the wild type and mutants. In addition, mutant protein presented different subcellular location, degradation pathway, and stability compared with that of wild type. Taking the lead from these findings, we inferred that these protein property alterations might influence its normal function, leading to PBMAH progression.