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Global mapping of polyadenylation site use in proliferating and quiescent (contact-inhibited and serum-starved) cells

ABSTRACT: Purpose: To determine genes that undergo alternative polyadenylation in proliferating versus quiescent fibroblasts. Methods: Three different biological replicates (fibroblast strains, 10-1, 12-1, and 12-2) were used for generating proliferating and quiescent (7-day contact inhibited and 7-day serum-starved) cells. RNA extracted from these cells were used for library preparation. cDNA fragments were enriched for the junction between the poly(A) site and the end of the 3' UTR using a modified high throughput sequencing protocol (GnomeGen). cDNA libraries were created according to Gnome-Gen RNA-seq library preparation kit for RNA profiling except Amgen Ampure XP beads were used instead of the Gnome-gen size selector product to remove ligation reaction products before proceeding to the reverse transcription step. The libraries were sequenced on an Illumina HiSeq 2000 instrument. The sequencing reaction wasa run for 147 cycles. Reads from pol(A) enriched cDNA libraries were aligned to the genome using the STAR alignment algorithm after the computational removal of untemplated adenosines. Results: Polyadenylation site selection was significantly altered in approximately 10% of genes in quiescent compared with proliferating fibroblasts. Contact inhibited and serum starved fibroblasts had similar polyadenylation site selection profiles. Conclusions: Quiescence is associated with changes in polyadenylation site selection.

ORGANISM(S): Homo sapiens

PROVIDER: GSE117337 | GEO | 2018/07/19

REPOSITORIES: GEO

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Project description:Background: Although quiescence—reversible cell-cycle arrest—is a key part in the life history and fate of many mammalian cell types, the mechanisms of gene regulation in quiescent cells are poorly understood. We sought to clarify the role of microRNAs as regulators of the cellular functions of quiescent human fibroblasts. Results: Using microarrays, we discovered that the expression of the majority of profiled microRNAs differed between proliferating and quiescent fibroblasts. Fibroblasts induced into quiescence by contact inhibition or serum starvation had similar microRNA profiles, indicating common changes induced by distinct quiescence signals. By analyzing the gene expression patterns of microRNA target genes with quiescence, we discovered a strong regulatory function for miR-29, which is downregulated with quiescence. Using microarrays and immunoblotting, we confirmed that miR-29 targets genes encoding collagen and other extracellular matrix proteins and that those target genes are induced in quiescence. In addition, overexpression of miR-29 resulted in more rapid cell cycle re-entry from quiescence. We also found that let-7 and miR-125 were upregulated in quiescent cells. Overexpression of either one alone resulted in slower cell cycle re-entry from quiescence, while the combination of both together slowed cell cycle re-entry even further. Conclusions: microRNAs regulate key aspects of fibroblast quiescence including the proliferative state of the cells as well as their gene expression profiles, in particular, the induction of extracellular matrix proteins in quiescent fibroblasts. microRNAs in human neonatal dermal fibroblasts in 3 cell cycle conditions (proliferating, 4 days serum starved, 7 days contact inhibited) were analyzed by one color microarray. 3 separate fibroblast cell lines from different human donors were analyzed for each condition, with two separate labeling and hybridization samples for each cell line. In total, 18 samples were hybridized to the microRNA microarray.

Project description:Many cells in mammals exist in the state of quiescence, which is characterized by reversible exit from the cell cycle. Quiescent cells are widely reported to exhibit reduced size, nucleotide synthesis, and metabolic activity. Much lower glycolytic rates have been reported in quiescent compared with proliferating lymphocytes. In contrast, we show here that primary human fibroblasts continue to exhibit high metabolic rates when induced into quiescence via contact inhibition. By monitoring isotope labeling through metabolic pathways and quantitatively identifying fluxes from the data, we show that contact-inhibited fibroblasts utilize glucose in all branches of central carbon metabolism at rates similar to those of proliferating cells, with greater overflow flux from the pentose phosphate pathway back to glycolysis. Inhibition of the pentose phosphate pathway resulted in apoptosis preferentially in quiescent fibroblasts. By feeding the cells labeled glutamine, we also detected a “backwards” flux in the tricarboxylic acid cycle from α-ketoglutarate to citrate that was enhanced in contact-inhibited fibroblasts; this flux likely contributes to shuttling of NADPH from the mitochondrion to cytosol for redox defense or fatty acid synthesis. The high metabolic activity of the fibroblasts was directed in part toward breakdown and resynthesis of protein and lipid, and in part toward excretion of extracellular matrix proteins. Thus, reduced metabolic activity is not a hallmark of the quiescent state. Quiescent fibroblasts, relieved of the biosynthetic requirements associated with generating progeny, direct their metabolic activity to preservation of self integrity and alternative functions beneficial to the organism as a whole. mRNAs were analyzed by two color microarray from two separate human neonatal dermal fibroblasts cell lines in proliferating, 7 days contact inhibition, or 14 days contact inhibition. Contact inhibited samples were co-hybridized to proliferating samples as a control, while an additional array co-hybridized the two proliferating samples to analyze reproducibility.

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Global mapping of polyadenylation site use in proliferating and quiescent (contact-inhibited and serum-starved) cells

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