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Genome wide mapping of polyadenylation sites in proliferating and contact-inhibited cells and cells with knockdown of cleavage and polyadenylation factors

ABSTRACT: Purpose: Quiescence is a state of reversible cell cycle exit. Levels of polyadenylation factors decreases when proliferating cells become quiescent. The goals of this study are to determine the differential use of polyadenylation sites (changes in alternative polyadenylation) in quiescent vs. proliferating cells and also upon knockdown of polyadenylation factors. Methods: Two biological replicates of human dermal fibroblasts (12-1 and 12-3) were used for polyadeylation-site enriched RNA-seq on an Illumina HiSeq 2500 to compare quiescent vs. proliferating cells and polyadenylation factor knockdown vs. control cells. The reads were aligned to the human genome (hg19) uisng Tophat (2.0.14). The resulting bam files were used as an input to a python script provided by Gruber et al. (PMID: 27382025) to determine the counts for each polyadenylation site. Results: We observed a shift toward greater use of distal polyadenylation sites when the fibroblasts entered quiescence. We observed significant overlap between the genes that shift to greater distal site use with quiescence and CstF-64 or CPSF73 knockdown. Conclusions: The shift to greater distal site use with quiescence may reflect in part the reduced levels of cleavage and polyadenylation factors.

ORGANISM(S): Homo sapiens

PROVIDER: GSE117033 | GEO | 2018/08/28

REPOSITORIES: GEO

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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.

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.

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Genome wide mapping of polyadenylation sites in proliferating and contact-inhibited cells and cells with knockdown of cleavage and polyadenylation factors

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