Selective proteolysis of the histone H3 N-terminal tail (H3NT) is frequently observed during eukaryotic development, generating a cleaved histone H3 (H3cl) product within a small, but significant, portion of the genome. Although increasing evidence supports a regulatory role for H3NT proteolysis in gene activation, the nuclear H3NT proteases and the biological significance of H3NT proteolysis remain largely unknown. In this study, established cell models of skeletal myogenesis were leveraged to investigate H3NT proteolysis. These cells displayed a rapid and progressive accumulation of a single H3cl product within chromatin during myoblast differentiation. Using conventional approaches, we discovered that the canonical extracellular matrix (ECM) protease, matrix metalloproteinase 2 (MMP-2), is the principal H3NT protease of myoblast differentiation that cleaves H3 between K18-Q19. Gelatin zymography demonstrated progressive increases in nuclear MMP-2 activity, concomitant with H3cl accumulation, during myoblast differentiation. RNAi-mediated depletion of MMP-2 impaired H3NT proteolysis and resulted in defective myogenic gene activation and myoblast differentiation. Supplementation of MMP-2 ECM activity in MMP-2-depleted cells was insufficient to rescue defective H3NT proteolysis and myogenic gene activation. This study revealed that MMP-2 is a novel H3NT protease and the principal H3NT protease of myoblast differentiation. The results indicate that myogenic signaling induces MMP-2-dependent H3NT proteolysis at early stages of myoblast differentiation. Importantly, the results support the necessity of nuclear MMP-2 H3NT protease activity, independent of MMP-2 activity in the ECM, for myogenic gene activation and proficient myoblast differentiation.

中文翻译：

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MMP-2 是一种新的组蛋白 H3 N 末端蛋白酶，是肌源性基因激活所必需的

在真核生物发育过程中经常观察到组蛋白 H3 N 末端尾 (H3NT) 的选择性蛋白水解，在基因组的一小部分但重要的部分中产生切割的组蛋白 H3 (H3cl) 产物。尽管越来越多的证据支持 H3NT 蛋白水解在基因激活中的调节作用，但核 H3NT 蛋白酶和 H3NT 蛋白水解的生物学意义仍然很大程度上未知。在这项研究中，利用已建立的骨骼肌生成细胞模型来研究 H3NT 蛋白水解。这些细胞在成肌细胞分化过程中显示出染色质内单个 H3cl 产物的快速和渐进性积累。使用常规方法，我们发现典型的细胞外基质 (ECM) 蛋白酶、基质金属蛋白酶 2 (MMP-2)、是成肌细胞分化的主要 H3NT 蛋白酶，它在 K18-Q19 之间切割 H3。明胶酶谱显示在成肌细胞分化过程中，核 MMP-2 活性逐渐增加，同时伴随着 H3cl 的积累。RNAi 介导的 MMP-2 消耗会损害 H3NT 蛋白水解，并导致有缺陷的成肌基因激活和成肌细胞分化。在 MMP-2 耗尽的细胞中补充 MMP-2 ECM 活性不足以挽救有缺陷的 H3NT 蛋白水解和肌原性基因激活。该研究表明，MMP-2 是一种新型 H3NT 蛋白酶，是成肌细胞分化的主要 H3NT 蛋白酶。结果表明，肌源性信号传导在成肌细胞分化的早期阶段诱导 MMP-2 依赖性 H3NT 蛋白水解。重要的，