Czochor Jennifer R, Sulkowski Parker, Glazer Peter M
Department of Genetics, Yale University, New Haven, Connecticut.
Department of Genetics, Yale University, New Haven, Connecticut. Department of Therapeutic Radiology, Yale University, New Haven, Connecticut.
Mol Cancer Res. 2016 Apr;14(4):363-73. doi: 10.1158/1541-7786.MCR-15-0399. Epub 2016 Feb 5.
miR-155 is an oncogenic miRNA that is often overexpressed in cancer and is associated with poor prognosis. miR-155 can target several DNA repair factors, including RAD51, MLH1, and MSH6, and its overexpression results in an increased mutation frequency in vitro, although the mechanism has yet to be fully understood. Here, we demonstrate that overexpression of miR-155 drives an increased mutation frequency both in vitro and in vivo, promoting genomic instability by affecting multiple DNA repair pathways. miR-155 overexpression causes a decrease in homologous recombination, but yields a concurrent increase in the error-prone nonhomologous end-joining pathway. Despite repressing established targets MLH1 and MSH6, the identified mutation pattern upon miR-155 overexpression does not resemble that of a mismatch repair-deficient background. Further investigation revealed that all four subunits of polymerase delta, a high-fidelity DNA replication, and repair polymerase are downregulated at the mRNA level in the context of miR-155 overexpression. FOXO3a, a transcription factor and known target of miR-155, has one or more putative binding site(s) in the promoter of all four polymerase delta subunits. Finally, suppression of FOXO3a by miR-155 or by siRNA knockdown is sufficient to repress the expression of the catalytic subunit of polymerase delta, POLD1, at the protein level, indicating that FOXO3a contributes to the regulation of polymerase delta levels.
Taken together, miR-155 overexpression drives an increase in mutation frequency via multifaceted impact on DNA damage response and DNA repair pathways.
miR-155是一种致癌性微小RNA，在癌症中常过度表达，且与预后不良相关。miR-155可靶向多种DNA修复因子，包括RAD51、MLH1和MSH6，其过度表达在体外导致突变频率增加，尽管其机制尚未完全明确。在此，我们证明miR-155的过度表达在体外和体内均会导致突变频率增加，通过影响多种DNA修复途径促进基因组不稳定。miR-155的过度表达导致同源重组减少，但同时易错非同源末端连接途径增加。尽管抑制了已确定的靶点MLH1和MSH6，但miR-155过度表达时所确定的突变模式并不类似于错配修复缺陷背景下的模式。进一步研究发现，在miR-155过度表达的情况下，DNA复制和修复的高保真聚合酶δ的所有四个亚基在mRNA水平均下调。FOXO3a是一种转录因子且是miR-155的已知靶点，在所有四个聚合酶δ亚基的启动子中具有一个或多个假定结合位点。最后，通过miR-155或siRNA敲低抑制FOXO3a足以在蛋白质水平抑制聚合酶δ的催化亚基POLD1的表达，表明FOXO3a有助于调节聚合酶δ的水平。
综上所述，miR-155的过度表达通过对DNA损伤反应和DNA修复途径的多方面影响导致突变频率增加。
