Role of metastasis-associated lung adenocarcinoma transcript-1 (MALAT-1) in pancreatic cancer

Metastasis-associated lung adenocarcinoma transcript-1 (MALAT-1) is a long non-coding RNA (lncRNA) that is a negative prognostic factor for patients with pancreatic cancer and several other tumors. In this study, we show that knockdown of MALAT-1 in Panc1 and other pancreatic cancer cell lines decreases cell proliferation, survival and migration. We previously observed similar results for the lncRNAs HOTTIP and HOTAIR in Panc1 cells; however, RNAseq comparison of genes regulated by MALAT-1 shows minimal overlap with HOTTIP/HOTAIR-regulated genes. Analysis of changes in gene expression after MALAT-1 knockdown shows that this lncRNA represses several tumor suppressor-like genes including N-myc downregulated gene-1 (NDRG-1), a tumor suppressor in pancreatic cancer that is also corepressed by EZH2 (a PRC2 complex member). We also observed that Specificity proteins Sp1, Sp3 and Sp4 are overexpressed in Panc1 cells and Sp knockdown or treatment with small molecules that decrease Sp proteins expression also decrease MALAT-1 expression. We also generated Kras-overexpressing p53L/L;LSL-KrasG12DL/+;p48Cre+/- (p53L/L/KrasG12D) and p53L/+;LSLKrasG12DL/+;p48Cre+/- (p53L/+/KrasG12D) mice which are p53 homo- and heterozygous, respectively. These mice rapidly develop pancreatic ductal adenocarcinoma-like tumors and were crossed with MALAT-1-/- mice. We observed that the loss of one or two MALAT-1 alleles in these Ras overexpressing mice does not significantly affect the time to death; however, the loss of MALAT-1 in the p53-/+ (heterozygote) mice slightly increases their lifespan.

转移相关肺腺癌转录本1（Metastasis-associated lung adenocarcinoma transcript-1, MALAT-1）是一种长链非编码RNA（long non-coding RNA, lncRNA），作为胰腺癌及多种其他肿瘤患者的不良预后因子。本研究证实，在Panc1及其他胰腺癌细胞系中敲低MALAT-1，可抑制细胞增殖、存活与迁移能力。我们此前在Panc1细胞中针对长链非编码RNA HOTTIP与HOTAIR也曾观测到类似实验结果；但通过RNA测序（RNAseq）对MALAT-1调控的基因与HOTTIP/HOTAIR调控的基因进行比对分析后发现，二者的调控靶基因重合度极低。对MALAT-1敲低后基因表达变化的分析显示，该长链非编码RNA可抑制多种抑癌样基因，其中包括N-myc下调基因1（N-myc downregulated gene-1, NDRG-1）——这是一种胰腺癌抑癌基因，同时也可被PRC2复合物成员EZH2共同抑制。我们还观测到，特异性蛋白Sp1、Sp3与Sp4在Panc1细胞中呈高表达状态；敲低Sp蛋白或使用可降低Sp蛋白表达的小分子化合物进行处理，同样会下调MALAT-1的表达水平。此外，我们构建了两种过表达Kras的基因工程小鼠：p53L/L;LSL-KrasG12DL/+;p48Cre+/-（记为p53L/L/KrasG12D）与p53L/+;LSL-KrasG12DL/+;p48Cre+/-（记为p53L/+/KrasG12D），二者分别为p53纯合子与杂合子。这类小鼠可快速形成胰腺导管腺癌样肿瘤，我们将其与MALAT-1基因敲除（MALAT-1-/-）小鼠进行杂交繁育。实验结果表明，在这些过表达Ras的小鼠中，丢失一个或两个MALAT-1等位基因并不会显著影响其存活时长；但在p53+/-（杂合子）小鼠中，缺失MALAT-1可略微延长其生存寿命。