Department of Metabolic Medicine and.
Department of Adipose Management, Osaka University Graduate School of Medicine, Osaka, Japan.
JCI Insight. 2022 Aug 22;7(16):e151390. doi: 10.1172/jci.insight.151390.
Inactivating mutations of ARMC5 are responsible for the development of bilateral macronodular adrenal hyperplasia (BMAH). Although ARMC5 inhibits adrenocortical tumor growth and is considered a tumor-suppressor gene, its molecular function is poorly understood. In this study, through biochemical purification using SREBF (SREBP) as bait, we identified the interaction between SREBF and ARMC5 through its Armadillo repeat. We also found that ARMC5 interacted with CUL3 through its BTB domain and underwent self-ubiquitination. ARMC5 colocalized with SREBF1 in the cytosol and induced proteasome-dependent degradation of full-length SREBF through ubiquitination. Introduction of missense mutations in Armadillo repeat of ARMC5 attenuated the interaction between SREBF, and introduction of mutations found in BMAH completely abolished its ability to degrade full-length SREBF. In H295R adrenocortical cells, silencing of ARMC5 increased full-length SREBFs and upregulated SREBF2 target genes. siARMC5-mediated cell growth was abrogated by simultaneous knockdown of SREBF2 in H295R cells. Our results demonstrate that ARMC5 was a substrate adaptor protein between full-length SREBF and CUL3-based E3 ligase, and they suggest the involvement of the SREBF pathway in the development of BMAH.
ARMC5 的失活突变可导致双侧结节性肾上腺增生（Bilateral Macronodular Adrenal Hyperplasia，BMAH）的发生。虽然 ARMC5 抑制肾上腺皮质肿瘤的生长，被认为是一种肿瘤抑制基因，但它的分子功能仍知之甚少。在这项研究中，我们通过使用 SREBF（固醇调节元件结合蛋白）作为诱饵进行生化纯化，发现了 SREBF 和 ARMC5 之间通过其 Armadillo 重复序列的相互作用。我们还发现 ARMC5 通过其 BTB 结构域与 CUL3 相互作用，并发生自身泛素化。ARMC5 与 SREBF1 在细胞质中共定位，并通过泛素化诱导全长 SREBF 的蛋白酶体依赖性降解。在 ARMC5 的 Armadillo 重复序列中引入错义突变会减弱 SREBF 之间的相互作用，而在 BMAH 中发现的突变则完全消除了其降解全长 SREBF 的能力。在 H295R 肾上腺皮质细胞中，沉默 ARMC5 会增加全长 SREBFs 并上调 SREBF2 靶基因。在 H295R 细胞中同时敲低 SREBF2 可阻断 siARMC5 介导的细胞生长。我们的研究结果表明，ARMC5 是全长 SREBF 和基于 CUL3 的 E3 连接酶之间的底物衔接蛋白，并提示 SREBF 通路参与了 BMAH 的发生。
