牛白血病病毒（BLV）在我国广泛流行，但其致病机制尚未完全阐明。申请人分离了BLV中国流行株，建立的细胞和奶牛感染模型初步揭示：BLV感染显著降低奶牛生产性能、抑制奶牛乳腺上皮细胞（BMECs）增殖、显著上调miR-342并下调KIFC1基因。KIFC1是参与细胞有丝分裂的重要基因，其mRNA 3´UTR存在miR-342靶向结合位点，申请人推断BLV由miR-324/KIFC1介导调控BMECs增殖。本研究利用转染、RNAi等过表达/沉默BMECs中KIFC1基因，探明其对细胞增殖的作用，构建BLV/miR-324/KIFC1调控轴；采用双荧光素酶报告基因试验等，探究BLV非结构蛋白Tax和Rex对miR-342、KIFC1基因表达和BMECs增殖的调控。本研究旨在揭示BLV感染下调KIFC1抑制BMECs增殖的分子机制，为阐明BLV的致病机理和提高奶牛生产性能提供实验支撑和理论依据。

Bovine leukemia virus (BLV) is widespread in China, but its pathogenesis is largely unknown. In previous studies, we have isolated the epidemic strains of BLV to establish the infection models in bovine mammary epithelial cells (BMECs) and dairy cattle. We have preliminarily revealed that BLV infection was significantly associated with the reduction of milk yield and the inhibition of the proliferation of BMECs. The expression levels of miR-342 and KIFC1 gene were up-regulated and down-regulated in peripheral blood leucocytes and BMECs of BLV infected cows. KIFC1 is an important gene involved in cell mitosis, and the 3´UTR of mRNA has a targeting binding site of miR-342. BLV was supposed to inhibit the proliferation of BMECs via the regulation of miR-324 /KIFC1. In this study, transfection and RNA interference (RNAi) will be applied to increase and decrease the expression levels of KIFC1 gene in BMECs, respectively, to explore its regulation on cell proliferation. Double luciferase reporter assay will be applied to study the regulation of the non-structural proteins (Tax and Rex) of BLV and the expressions of miR-342 and KIFC1, and the proliferation of BMECs. This study will reveal the molecular mechanism of the inhibition of the proliferation of BMECs regulated by the expression of KIFC1 after BLV infection. This study will provide experimental support and theoretical basis for elucidating the pathogenic mechanism of BLV and improving the production performance of cows.