Department of Microbiology and Immunology, Meharry Medical College, Nashville, Tennessee 37208, USA. and.
J Biol Chem. 2011 Jan 7;286(1):469-79. doi: 10.1074/jbc.M110.164384. Epub 2010 Nov 2.
UbcH5c, a member of the UbcH5 family of protein ubiquitin conjugase E2 enzymes, is a critical component of biological processes in human cells, being the initial ubiquitinating enzyme of substrates like IκB, TP53, and cyclin D1. We report here that the metastasis regulator protein SLUG inhibits the expression of UbcH5c directly through chromatin remodeling and thus, among other downstream effects, elevates the level of cyclin D1, thus enhancing the growth rates of breast cancer cells. Overexpression of SLUG in the SLUG-deficient breast cancer cells significantly decreased the levels of mRNA and protein of UbcH5c but only elevated the protein levels of cyclin D1. On the contrary, knockdown of SLUG in SLUG-high breast cancer cells elevated the levels of UbcH5c while decreasing the level of cyclin D1 protein. SLUG is recruited at the E2-box sequence at the UbcH5c gene promoter along with the corepressor CtBP1 and the effector HDAC1 to silence the expression of this gene. Knockdown of UbcH5c in the SLUG-deficient human breast cells elevated the level of cyclin D1 as well as the rates of proliferation and invasiveness of these cells. Whereas the growth rates of the cells are enhanced due to overexpression of SLUG or knockdown of UbcH5c in the breast cancer cells tested, ER(+) cells also acquire resistance to the anti-estrogen 4-hydroxytamoxifen due to the rise of cyclin D1 levels in these cells. This study thus implicates high levels of SLUG and low levels of UbcH5c as a determinant in the progression of metastatic breast cancer.
UbcH5c 是泛素连接酶 E2 家族 UbcH5 的成员，是人类细胞中生物过程的关键组成部分，是 IκB、TP53 和 cyclin D1 等底物的初始泛素化酶。我们在这里报告，转移调节蛋白 SLUG 通过染色质重塑直接抑制 UbcH5c 的表达，因此，除了其他下游效应外，还会升高 cyclin D1 的水平，从而增强乳腺癌细胞的生长速度。在 SLUG 缺陷型乳腺癌细胞中过表达 SLUG 会显著降低 UbcH5c 的 mRNA 和蛋白水平，但仅升高 cyclin D1 蛋白水平。相反，在 SLUG 高表达的乳腺癌细胞中敲低 SLUG 会升高 UbcH5c 的水平，同时降低 cyclin D1 蛋白水平。SLUG 与核心抑制因子 CtBP1 和效应因子 HDAC1 一起募集到 UbcH5c 基因启动子的 E2 盒序列，从而沉默该基因的表达。在 SLUG 缺陷型人乳腺癌细胞中敲低 UbcH5c 会升高 cyclin D1 水平以及这些细胞的增殖和侵袭率。虽然在测试的乳腺癌细胞中过表达 SLUG 或敲低 UbcH5c 会增强细胞的生长速度，但由于这些细胞中 cyclin D1 水平的升高，ER(+) 细胞也对抗雌激素 4-羟基他莫昔芬产生了耐药性。因此，本研究表明高水平的 SLUG 和低水平的 UbcH5c 是转移性乳腺癌进展的决定因素。
