Molecular Oncology and Epigenetics Laboratory, The First Affiliated Hospital of Chongqing Medical University, Chongqing, China.
PLoS One. 2012;7(1):e29783. doi: 10.1371/journal.pone.0029783. Epub 2012 Jan 18.
Breast cancer (BrCa) is a complex disease driven by aberrant gene alterations and environmental factors. Recent studies reveal that abnormal epigenetic gene regulation also plays an important role in its pathogenesis. Ubiquitin carboxyl- terminal esterase L1 (UCHL1) is a tumor suppressor silenced by promoter methylation in multiple cancers, but its role and alterations in breast tumorigenesis remain unclear.
METHODOLOGY/PRINCIPAL FINDINGS: We found that UCHL1 was frequently downregulated or silenced in breast cancer cell lines and tumor tissues, but readily expressed in normal breast tissues and mammary epithelial cells. Promoter methylation of UCHL1 was detected in 9 of 10 breast cancer cell lines (90%) and 53 of 66 (80%) primary tumors, but rarely in normal breast tissues, which was statistically correlated with advanced clinical stage and progesterone receptor status. Pharmacologic demethylation reactivated UCHL1 expression along with concomitant promoter demethylation. Ectopic expression of UCHL1 significantly suppressed the colony formation and proliferation of breast tumor cells, through inducing G0/G1 cell cycle arrest and apoptosis. Subcellular localization study showed that UCHL1 increased cytoplasmic abundance of p53. We further found that UCHL1 induced p53 accumulation and reduced MDM2 protein level, and subsequently upregulated the expression of p21, as well as cleavage of caspase3 and PARP, but not in catalytic mutant UCHL1 C90S-expressed cells.
CONCLUSIONS/SIGNIFICANCE: UCHL1 exerts its tumor suppressive functions by inducing G0/G1cell cycle arrest and apoptosis in breast tumorigenesis, requiring its deubiquitinase activity. Its frequent silencing by promoter CpG methylation may serve as a potential tumor marker for breast cancer.
乳腺癌（BrCa）是一种由异常基因改变和环境因素驱动的复杂疾病。最近的研究表明，异常的表观遗传基因调控在其发病机制中也起着重要作用。泛素羧基末端酯酶 L1（UCHL1）是一种在多种癌症中被启动子甲基化沉默的肿瘤抑制因子，但它在乳腺癌发生中的作用和改变仍不清楚。
方法/主要发现：我们发现 UCHL1 在乳腺癌细胞系和肿瘤组织中经常下调或沉默，但在正常乳腺组织和乳腺上皮细胞中易于表达。在 10 个乳腺癌细胞系中的 9 个（90%）和 66 个原发性肿瘤中的 53 个（80%）检测到 UCHL1 的启动子甲基化，但在正常乳腺组织中很少见，这与晚期临床分期和孕激素受体状态呈统计学相关。药物去甲基化可重新激活 UCHL1 的表达，并伴有启动子去甲基化。外源性表达 UCHL1 可通过诱导 G0/G1 细胞周期阻滞和细胞凋亡，显著抑制乳腺癌细胞的集落形成和增殖。亚细胞定位研究表明，UCHL1 增加了 p53 的细胞质丰度。我们进一步发现，UCHL1 诱导 p53 积累并降低 MDM2 蛋白水平，随后上调 p21 的表达，以及切割 caspase3 和 PARP，但在催化突变体 UCHL1 C90S 表达的细胞中没有。
结论/意义：UCHL1 通过诱导 G0/G1 细胞周期阻滞和细胞凋亡在乳腺癌发生中发挥其肿瘤抑制功能，需要其去泛素酶活性。其启动子 CpG 甲基化的频繁沉默可能成为乳腺癌的潜在肿瘤标志物。
