Control of cell proliferation and differentiation by heme bindiny transcription factor Bachl

转录抑制因子Bach 1是血红素的感受器和效应器，调节血红素加氧酶-1和珠蛋白基因的表达。血红素与巴赫尔结合，抑制其DNA结合活性并诱导其核输出。我们发现，氯化血红素进一步诱导降解内源性巴赫尔在NIH 3 T3细胞，小鼠胚胎成纤维细胞，和小鼠红白血病细胞。与此相反，琥珀酰丙酮，血红素合成的抑制剂，造成积累的巴赫尔在小鼠胚胎成纤维细胞，表明生理水平的血红素调节巴赫尔营业额。氯化血红素处理诱导多泛素化和过表达的巴赫尔的快速降解。HOIL-1是一种识别血红素结合的氧化铁调节蛋白2的泛素蛋白连接酶，当两者在NIH 3 T3细胞中过表达时，发现HOIL-1与巴赫尔结合。HOIL-1依赖于巴赫尔的完整血红素结合基序，在纯化的体外泛素化系统中刺激巴赫尔的多聚泛素化。显性负性HOIL-1在小鼠红白血病细胞中的表达导致内源性巴赫尔的更高稳定性，提高了小鼠红白血病中血红素调节降解涉及HOIL-1的可能性。细胞这些结果表明，血红素在细胞内调节巴赫尔的多聚泛素化和降解。此外，我们在本研究中发现，巴赫尔抑制氧化应激诱导的细胞衰老。与野生型对照小鼠胚胎成纤维细胞相比，Bachl缺陷小鼠胚胎成纤维细胞（MEFs）在体外对氧的反应中表现出深刻的细胞衰老。Bachl缺陷MEFs的表达谱表明，几个基因的过度表达可能是负责氧诱导的细胞衰老。

The transcription repressor Bach1 is a sensor and an effecter of heme that regulates the expression of heme oxygenase-1 and globin genes. Heme binds to Bachl, inhibiting its DNA binding activity and inducing its nuclear export. We found that hemin further induced the degradation of endogenous Bachl in NIH3T3 cells, murine embryonic fibroblasts, and murine erythroleukemia cells. In contrast, succinylacetone, an inhibitor of heme synthesis, caused accumulation of Bachl in murine embryonic fibroblasts, indicating that physiological levels of heme regulated the Bachl turnover. Poly-ubiquitination and rapid degradation of overexpressed Bachl were induced by hemin treatment. HOIL-1, an ubiquitin-protein ligase which recognizes heme-bound, oxidized iron regulatory protein 2, was found to bind with Bachl when both were overexpressed in NIH3T3 cells. HOIL-1 stimulated the poly-ubiquitination of Bachl in a purified in vitro ubiquitination system depending on the intact heme binding motifs of Bachl. Expression of dominant negative HOIL-1 in murine erythroleukemia cells resulted in higher stability of endogenous Bachl, raising the possibility that the heme-regulated degradation involved HOIL-1 in murine erythroleukemia. cells. These results suggest that heme within a cell regulates the poly-ubiquitination and degradation of Bachl.In addition, we found in this study that Bachl inhibits oxidative stress-induced cellular senescence. Bachl-deficient murine embryonic fibroblasts (MEFs) showed profound cellular senescence in response to oxygen in vitro as compared to wild-type control MEFs. Expression profiling of Bachl-deficient MEFs suggested that overexpression of several genes might be responsible for the oxygen-induced cellular senescence.