Laboratory of Molecular Biology, University Hospital, Charles University, Prague, Czech Republic.
Biochem Biophys Res Commun. 2010 Feb 12;392(3):454-9. doi: 10.1016/j.bbrc.2010.01.048. Epub 2010 Jan 18.
The microphthalmia-associated transcription factor (MITF) is required for melanocyte development, maintenance of the melanocyte-specific transcription, and survival of melanoma cells. MITF positively regulates expression of more than 25 genes in pigment cells. Recently, it has been demonstrated that expression of several MITF downstream targets requires the SWI/SNF chromatin remodeling complex, which contains one of the two catalytic subunits, Brm or Brg1. Here we show that the expression of MITF itself critically requires active SWI/SNF. In several Brm/Brg1-expressing melanoma cell lines, knockdown of Brg1 severely compromised MITF expression with a concomitant downregulation of MITF targets and decreased cell proliferation. Although Brm was able to substitute for Brg1 in maintaining MITF expression and melanoma cell proliferation, sequential knockdown of both Brm and Brg1 in 501mel cells abolished proliferation. In Brg1-null SK-MEL-5 melanoma cells, depletion of Brm alone was sufficient to abrogate MITF expression and cell proliferation. Chromatin immunoprecipitation confirmed the binding of Brg1 or Brm to the promoter of MITF. Together these results demonstrate the essential role of SWI/SNF for expression of MITF and suggest that SWI/SNF may be a promissing target in melanoma therapy.
小眼畸形相关转录因子（MITF）是黑素细胞发育、维持黑素细胞特异性转录和黑素瘤细胞存活所必需的。MITF 正向调节色素细胞中超过 25 个基因的表达。最近，已经证明几个 MITF 下游靶基因的表达需要 SWI/SNF 染色质重塑复合物，该复合物包含两个催化亚基之一，Brm 或 Brg1。在这里，我们表明 MITF 本身的表达严重依赖于活性的 SWI/SNF。在几个表达 Brm/Brg1 的黑色素瘤细胞系中，Brg1 的敲低严重影响了 MITF 的表达，同时下调了 MITF 的靶基因并降低了细胞增殖。虽然 Brm 能够替代 Brg1 维持 MITF 表达和黑色素瘤细胞增殖，但在 501mel 细胞中连续敲低 Brm 和 Brg1 则会导致增殖完全被废除。在 Brg1 缺失的 SK-MEL-5 黑素瘤细胞中，单独耗尽 Brm 就足以使 MITF 表达和细胞增殖。染色质免疫沉淀证实了 Brg1 或 Brm 与 MITF 启动子的结合。这些结果共同证明了 SWI/SNF 对于 MITF 表达的重要作用，并表明 SWI/SNF 可能是黑色素瘤治疗的一个有前途的靶点。
