DNA double-strand breaks are repaired through either non-homologous end joining(NHEJ) or homologous recombination repair(HRR) pathway.The well-characterized regulatory mechanisms of double-strand break repair(DSBR) are mainly found at the level of complicated repair protein interactions and modifications.Regulation of DSBR at the transcriptional level was also reported.In this study,we found that DSBR can be regulated by miR-34a at the post-transcriptional level.Specifically,miR-34a,which can be activated by DNA damages,represses DSBR activities by impairing both NHEJ and HRR pathways in cultured cells.The repression is mainly through targeting the critical DSBR promoting factor SIRT1,as ectopically expressed SIRT1 without 3'-UTR can rescue the inhibitory roles of miR-34a on DSBR.Further studies demonstrate that SIRT1 conversely represses miR-34a expression.Taken together,our data show that miR-34a is a new repressor of DSBR and the mutual inhibition between miR-34a and SIRT1 may contribute to regulation of DNA damage repair.
Spatial expression patterns of homeobox （HOX） genes delineate positional identity of primary fibroblasts from different topo- graphic sites. The molecular mechanism underlying the establishing or maintaining of HOX gene expression pattern remains an attractive developmental issue to be addressed. Our previous work suggested a critical role of CTCF/cobesin-mediated high- er-order chromatin structure in RA-induced HOXA activation in human teratocarcinoma NT2/D1 cells. This study investigated the recruitment of CTCF and cohesin, and the higher-order chromatin structure of the HOXA locus in fetal lung and adult foreskin fibroblasts, which display complementary HOXA gene expression patterns. Chromatin contacts between the CTCF-binding sites were observed with lower frequency in human foreskin fibroblasts. This observation is consistent with the lower level of cohesin recruitment and 5＇ HOXA gene expression in the same cells. We also showed that CTCF-binding site A56 （CBSA56） related chromatin structures exhibit the most notable changes in between the two types of cell, and hence may stand for one of the key CTCF-binding sites for cell-type specific chromatin structure organization. Together, these results im- ply that CTCF/cohesin coordinates HOXA cluster higher-order chromatin structure and expression during development, and provide insight into the relationship between cell-type specific chromatin organization and the spatial collinearity.
WANG XingXU MiaoZHAO GuangNianLIU GuoYouHAO DeLongLV XiangLIU DePei
Studies on the chaperone protein α-hemoglobin stabilizing protein （AHSP） reveal that abundant AHSP in erythroid cells en-hance the cells＇ tolerance to oxidative stress imposed by excess a-hemoglobin in pathological conditions. However, the poten-tial intracellular modulation of AHSP expression itself in response to oxidative stress is still unknown. The present study ex-amined the effect and molecular mechanism of STAT3, an oxidative regulator, on the expression of AHSP. AHSP expression increased in K562 cells upon cytokine IL-6-induced STAT3 activation and decreased in STAT3 knock-down K562 cells. Reg-ulation of AHSP in oxidative circumstance was then examined in α-globin-overloaded K562 cells, and real-time PCR showed strengthened expression of both AHSP and STAT3. ChIP analysis showed binding of STAT3 to AHSP promoter and binding was significantly augmented with IL6 stimulation and upon α-globin overexpression. Dual luciferase reporter assays of the wildtype and mutated SB3 element, an IL-6RE site, in the AHSP promoter in K562 cells highlighted the direct regulatory ef-fect of STAT3 on AHSP gene. Finally, direct binding of STAT3 to SB3 site of AHSP promoter was confirmed with EMSA as-says. Our work reveals an adaptive AHSP regulation mediated by the redox-sensitive STAT3 signaling pathway, and provides clues to the therapeutic strategy for AHSP enhancement.
CAO CongZHAO GuoWeiYU WeiXIE XueMinWANG WenTianYANG RuiFengLV XiangLIU DePei
