The tripartite motif (TRIM) proteins constitute a family of ubiquitin E3 ligases involved in a multitude of cellular processes, including protein homeostasis and autophagy. TRIM32 is characterized by six protein-protein interaction domains termed NHL, various point mutations in which are associated with limb-girdle-muscular dystrophy 2H (LGMD2H). Here, we show that TRIM32 is an autophagy substrate. Lysosomal degradation of TRIM32 was dependent on ATG7 and blocked by knockout of the five autophagy receptors p62 (also known as SQSTM1), NBR1, NDP52 (also known as CALCOCO2), TAX1BP1 and OPTN, pointing towards degradation by selective autophagy. p62 directed TRIM32 to lysosomal degradation, while TRIM32 mono-ubiquitylated p62 on lysine residues involved in regulation of p62 activity. Loss of TRIM32 impaired p62 sequestration, while reintroduction of TRIM32 facilitated p62 dot formation and its autophagic degradation. A TRIM32LGMD2H disease mutant was unable to undergo autophagic degradation and to mono-ubiquitylate p62, and its reintroduction into the TRIM32-knockout cells did not affect p62 dot formation. In light of the important roles of autophagy and p62 in muscle cell proteostasis, our results point towards impaired TRIM32-mediated regulation of p62 activity as a pathological mechanisms in LGMD2H.

中文翻译：

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TRIM32，而不是其与肌营养不良症相关的突变体，正调控p62 / SQSTM1并靶向自噬降解。

三方基序（TRIM）蛋白构成泛素E3连接酶家族，涉及许多细胞过程，包括蛋白质稳态和自噬。TRIM32的特征是六个蛋白质-蛋白质相互作用域（称为NHL），其中的各个点突变与肢带-肌肉-肌营养不良症2H（LGMD2H）相关。在这里，我们显示TRIM32是自噬底物。TRIM32的溶酶体降解取决于ATG7，并被敲除5种自噬受体p62（也称为SQSTM1），NBR1，NDP52（也称为CALCOCO2），TAX1BP1和OPTN阻止，这表明选择性自噬可导致降解。p62将TRIM32定向到溶酶体降解，而TRIM32在赖氨酸残基上的单泛素化p62参与了p62活性的调节。TRIM32的缺失损害了p62的螯合，而TRIM32的重新引入促进了p62点的形成及其自噬降解。TRIM32LGMD2H疾病突变体无法进行自噬降解并不能单泛素化p62，并且将其重新引入TRIM32敲除细胞不会影响p62点的形成。鉴于自噬和p62在肌肉细胞蛋白稳定中的重要作用，我们的研究结果表明TRIM32介导的p62活性调节受损，这是LGMD2H的病理机制。