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A lincRNA connected to cell mortality and epigenetically-silenced in most common human cancers

ABSTRACT: - Gene expression changes linked to two step immortalization of human mammary epithelial cells (HMEC). - A lincRNA, MORT, associated with the mortal state, was identified - MORT is silenced by DNA methylation in immortal mammary epithelial cells Abstract: Immortality is an essential characteristic of human carcinoma cells. We recently developed an efficient, reproducible method that immortalizes human mammary epithelial cells (HMEC) in the absence of gross genomic changes by targeting two critical senescence barriers. Consistent transcriptomic changes associated with immortality were identified using microarray analysis of isogenic normal finite pre-stasis, abnormal finite post-stasis, and immortal HMECs from four individuals. 277 genes consistently changed in cells that transitioned from post-stasis to immortal. Gene ontology analysis of affected genes revealed biological processes significantly altered in the immortalization process. These immortalization-associated changes showed striking similarity to the gene expression changes seen in The Cancer Genome Atlas (TCGA) clinical breast cancer data. The most dramatic change in gene expression seen during the immortalization step was the down-regulation of an unnamed, incompletely annotated transcript that we called MORT, for mortality, since its expression was closely associated with the mortal, finite lifespan phenotype. We show here that MORT (ZNF667-AS1) is expressed in all normal finite lifespan human cells examined to date and is lost in immortalized HMEC. MORT gene silencing at the mortal/immortal boundary was due to DNA hypermethylation of its CpG island promoter. This epigenetic silencing is also seen in human breast cancer cell lines and in a majority of human breast tumor tissues. The functional importance of DNA hypermethylation in MORT gene silencing is supported by the ability of 5-aza-2’-deoxycytidine to reactivate MORT expression. Analysis of TCGA data revealed deregulation of MORT expression due to DNA hypermethylation in 15 out of the 17 most common human cancers. The epigenetic silencing of MORT in a large majority of the common human cancers suggests a potential fundamental role in cellular immortalization during human carcinogenesis.

ORGANISM(S): Homo sapiens

PROVIDER: GSE72353 | GEO | 2015/10/05

SECONDARY ACCESSION(S): PRJNA293859

REPOSITORIES: GEO

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Project description:Molecular distinctions between the stasis and telomere attrition senescence barriers in cultured human mammary epithelial cells Normal human epithelial cells in culture have generally shown a limited proliferative potential of ~10-40 population doublings before encountering a stress-associated senescence barrier (stasis) associated with elevated levels of cyclin-dependent kinase inhibitors p16 and/or p21. We now show that simple changes in media composition can expand the proliferative potential of human mammary epithelial cells (HMEC) initiated as primary cultures to 50-60 population doublings, followed by p16(+), senescence-associated b-galactosidase(+) stasis. We compared the properties of growing and senescent pre-stasis HMEC with growing and senescent post-selection HMEC, i.e., cells grown in a serum-free medium that overcame stasis via silencing of p16 expression and that display senescence associated with telomere dysfunction. Cultured pre-stasis populations contained cells expressing markers associated with luminal and myoepithelial HMEC lineages in vivo, in contrast to the basal-like phenotype of the post-selection HMEC. Gene transcript and protein expression, DNA damage-associated markers, mean TRF length, and genomic stability, differed significantly between HMEC populations at the stasis vs. telomere attrition senescence barriers. Senescent isogenic fibroblasts showed greater similarity to HMEC at stasis than at telomere attrition, although their gene transcript profile was distinct from HMEC at both senescence barriers. These studies support our model of the senescence barriers encountered by cultured HMEC in which the first barrier, stasis, is Rb-mediated and independent of telomere length, while a second barrier (agonescence or crisis) results from telomere attrition leading to telomere dysfunction. Additionally, the ability to maintain long-term growth of genomically stable multi-lineage pre-stasis HMEC populations can greatly enhance experimentation with normal HMEC.

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A lincRNA connected to cell mortality and epigenetically-silenced in most common human cancers

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