Induction mechanism of V-J recombination by signaling molecules of the IL-7 receptor

IL-7受体(IL-7R)通过促进T细胞的存活和增殖，以及诱导T细胞受体和免疫球蛋白基因的V(D)J重组，在淋巴细胞发育中发挥重要作用。为了确定IL-7R诱导基因重排的分子机制，我们研究了STAT5在TCRγ基因种系转录中的作用。我们的结果表明，IL-7R激活的STAT5与Jγ片段5‘端的共同基序结合，并诱导生殖系转录。我们还发现，构成活性形式的STAT5诱导生殖系转录，恢复TCRSTAT5基因的V-J重组，并部分挽救T细胞从IL-7R^&T细胞前体细胞的发育，特别是有利于γδT细胞。因此，这些结果揭示了STAT5在T细胞发育中的潜在作用，并暗示STAT5可能通过诱导生殖系转录物来控制TCRγ基因的可及性。接下来，为了确定STAT5诱导的生殖系转录与TcRγ基因的可及性之间的联系的分子机制，我们研究了转录辅助激活因子和组蛋白乙酰化在TcRγ基因中的作用。我们证明了细胞因子刺激迅速将STAT5和转录共激活因子招募到5‘Jγ生殖系启动子，并增加了组蛋白乙酰化、生殖系转录和在BA/F3细胞中的可及性。我们还发现，在IL-7R缺乏的胸腺细胞前体细胞中，TcRγ基因座的组蛋白乙酰化显著减少，活性STAT5的引入恢复了TcRγ基因座的组蛋白乙酰化和可及性。因此，这些结果表明，STAT5通过招募转录共激活因子和诱导组蛋白乙酰化来控制Jγ区的局部可及性。我们的研究还暗示了STAT5在TcRγ增强子(Eγ)对全基因位点可及性控制中的潜在作用。

IL-7 receptor (IL-7R) plays critical roles in lymphocyte development by promoting survival and proliferation and by inducing V(D)J recombination in TCR and Ig loci. To identify the molecular mechanism of the induction of gene rearrangement by IL-7R, we characterized the role of Stat5 in the germline transcription of TCRγ genes. Our results demonstrated that IL-7R-activated Stat5 binds to consensus motifs in 5' regions of Jγ segments and induces germline transcripts. We also found that a constitutively-active form of Stat5 induces germline transcription, restores V-J recombination of TCRγ genes, and partially rescues T cell development from IL-7R^<-/-> T cell precursors, especially in favor of γδ T cells. Therefore, these results revealed a potential role of Stat5 in T cell development, and implied that Stat5 may control the accessibility of the TCRγ locus by the induction of germline transcripts. Next, to identify the molecular mechanism that links the Stat5-induced germline transcription to the accessibility of the TCRγ locus, we characterized the role of transcriptional coactivators and histone acetylation in TCRγ genes. We demonstrated that cytokine stimulation rapidly recruits Stat5 and transcriptional coactivators to the 5'Jγ germline promoter and increases histone acetylation, germline transcription, and accessibility in Ba/F3 cells. We also show that histone acetylation of the TCRγ locus is significantly reduced in IL-7R-deficient thymocyte precursors and that introduction of active Stat5 restores the histone acetylation and accessibility of the TCRγ locus. Therefore, these results suggested that Stat5 controls local accessibility of the Jγ region by recruiting the transcriptional coactivators and inducing histone acetylation. Our study also implied a potential role of Stat5 in the locus-wide accessibility control by the TCRγ enhancer (Eγ).