Department of Biochemistry and Molecular Biology, School of Medicine, University of Maryland-Baltimore, Baltimore, MD, United States; Marlene and Stewart Greenebaum Comprehensive Cancer Center, University of Maryland-Baltimore, Baltimore, MD, United States.
Department of Otorhinolaryngology-Head and Neck Surgery, University of Maryland-Baltimore, Baltimore, MD, United States.
Exp Cell Res. 2019 Jan 1;374(1):85-93. doi: 10.1016/j.yexcr.2018.11.010. Epub 2018 Nov 17.
Expression of the metastasis suppressor NME1 in melanoma is associated with reduced cellular motility, invasion, and metastasis, but mechanisms underlying these activities are not completely understood. Herein we report a novel mechanism through which NME1 drives formation of large, stable focal adhesions (FAs) in melanoma cells via induction of integrin β3 (ITGβ3), and in one cell line, concomitant suppression of integrin β1 (ITGβ1) transcripts. Forced expression of NME1 resulted in a strong activation of the promoter region (-301 to +13) of the ITGB3 gene. Chromatin immunoprecipitation (ChIP) analysis revealed the transcriptional induction was associated with direct recruitment of NME1 and an increase in the epigenetic activation mark, acetylation of histone 3 on lysine 27 (H3K27Ac) to a 1 kb stretch of 5'-flanking sequence of the ITGB3 gene. Unexpectedly, NME1 did not affect the amount either ITGβ1 or ITGβ3 proteins were internalized and recycled, processes commonly associated with regulating expression of integrins at the cell surface. The ability of NME1 to suppress motile and invasive phenotypes of melanoma cells was dependent on its induction of ITGβ3. Expression of ITGβ3 mRNA was associated with increased disease-free survival time in melanoma patients of the TCGA collection, consistent with its potential role as an effector of the metastasis suppressor function of NME1. Together, these data indicate metastasis suppressor activity of NME1 in melanoma is mediated by induction of ITGB3 gene transcription, with NME1-driven enrichment of ITGβ3 protein at the cell membrane resulting in attenuated cell motility through the stabilization of large focal adhesions.
黑色素瘤中转移抑制因子 NME1 的表达与细胞迁移、侵袭和转移减少有关，但这些活性的潜在机制尚不完全清楚。在此，我们报道了一种新的机制，通过该机制，NME1 通过诱导整合素 β3（ITGβ3），在黑色素瘤细胞中驱动大而稳定的焦点黏附（FA）的形成，并且在一个细胞系中，同时抑制整合素 β1（ITGβ1）转录本。强制表达 NME1 导致 ITGB3 基因启动子区域（-301 至+13）的强烈激活。染色质免疫沉淀（ChIP）分析显示，转录诱导与 NME1 的直接募集以及组蛋白 3 赖氨酸 27 乙酰化（H3K27Ac）在 ITGB3 基因 5'侧翼序列 1kb 区域的表观遗传激活标记的增加有关。出乎意料的是，NME1 并不影响 ITGβ1 或 ITGβ3 蛋白内化和回收的量，这些过程通常与调节整合素在细胞表面的表达有关。NME1 抑制黑色素瘤细胞迁移和侵袭表型的能力取决于其对 ITGβ3 的诱导。TCGA 黑色素瘤患者中 ITGβ3 mRNA 的表达与无病生存时间的增加有关，这与其作为 NME1 转移抑制功能的效应因子的潜在作用一致。总之，这些数据表明 NME1 在黑色素瘤中的转移抑制活性是通过诱导 ITGB3 基因转录介导的，NME1 驱动的 ITGβ3 蛋白在细胞膜上的富集导致大焦点黏附的稳定，从而减弱细胞迁移。
