The present study examined the expression and biological functions of bromodomain-containing protein 4 (BRD4) in skin squamous cell carcinoma (SCC) cells. Our results show that BRD4 mRNA and protein expression was upregulated in human skin SCC cells, as compared to its level in the normal skin keratinocytes and fibroblasts. Treatment with BRD4 inhibitors, JQ1 and CPI203, resulted in proliferation inhibition, apoptosis and cell cycle arrest in both established (A431 cell line) and primary skin SCC cells. Furthermore, BRD4 knockdown (by targeted shRNAs) or knockout (by CRISPR/Cas9) largely inhibited A431 cell proliferation. Reversely, forced-overexpression of BRD4 in A431 cells facilitated cell proliferation. We show that BRD4 is required for the expression of several oncogenes, including cyclin D1, Bcl-2 and MYC. BRD4 inhibition, knockdown or knockout significantly decreased above oncogene expression in SCC cells. In vivo, CRISPR/Cas9-mediated BRD4 knockout significantly suppressed A431 xenograft tumor growth in severe combined immunodeficient (SCID) mice. Together, our results suggest that BRD4 could be a novel and pivotal oncogenic protein of skin SCC.

本研究检查了含溴结构域蛋白4（BRD4）在皮肤鳞状细胞癌（SCC）细胞中的表达和生物学功能。我们的结果表明BRD4 mRNA与正常皮肤角质形成细胞和成纤维细胞中的水平相比，人类皮肤SCC细胞中的蛋白表达上调。使用BRD4抑制剂JQ1和CPI203进行治疗，会导致既定的（A431细胞系）和原代皮肤SCC细胞的增殖抑制，凋亡和细胞周期停滞。此外，BRD4敲低（通过靶向shRNA）或敲除（通过CRISPR / Cas9）在很大程度上抑制了A431细胞的增殖。相反，在A431细胞中BRD4的强制过表达促进了细胞增殖。我们显示，BRD4是表达几种癌基因（包括细胞周期蛋白D1，Bcl-2和MYC）所必需的。在SCC细胞中，BRD4的抑制，敲低或敲除明显高于癌基因表达。体内，CRISPR / Cas9介导的BRD4敲除显着抑制了严重联合免疫缺陷（SCID）小鼠中A431异种移植瘤的生长。在一起，我们的结果表明BRD4可能是皮肤SCC的一种新的和关键的致癌蛋白。