Project description:p53 is a potent tumor suppressor and commonly mutated in human cancers. Recently, we demonstrated that p53 genes act to restrict retrotransposons in germ line tissues of flies and fish but whether this activity is conserved in somatic human cells is not known. Here we show that p53 constitutively restrains human LINE1s by cooperatively engaging sites in the 5’UTR and stimulating local deposition of repressive histone marks at these transposons. Consistent with this, the elimination of p53 or the removal of corresponding binding sites in LINE1s, prompted these retroelements to become hyperactive. Concurrently, p53 loss instigated chromosomal rearrangements linked to LINE sequences and also provoked inflammatory programs that were dependent on reverse transcriptase produced from LINE1s. Taken together, our observations establish that p53 continuously operates at the LINE1 promoter to restrict autonomous copies of these mobile elements in human cells. Our results further suggest that constitutive restriction of these retroelements may help to explain tumor suppression encoded by p53, since erupting LINE1s produced acute oncogenic threats when p53 was absent.
Project description:Transposable elements (TEs) are mobile sequences that engender widespread mutations and thus are a major hazard that must be silenced. The most abundant active class of TEs in mammalian genomes is long interspersed element class 1 (LINE1). Here, we report that LINE1 transposition is suppressed in the male germline by transcription factors encoded by a rapidly evolving X-linked homeobox gene cluster. LINE1 transposition is repressed by many members of this RHOX transcription factor family, including those with different patterns of expression during spermatogenesis. One family member—RHOX10—suppresses LINE1 transposition during fetal development in vivo when the germline would otherwise be susceptible to LINE1 activation because of epigenetic reprogramming. We provide evidence that RHOX10 suppresses LINE transposition by inducing Piwil2, which encodes a key component in the Piwi-interacting (pi) RNA pathway that protects against TEs. The ability of RHOX transcription factors to suppress LINE1 is conserved in humans, but is lost in RHOXF2 mutants from several infertile human patients, raising the possibility that loss of RHOXF2 causes human infertility by allowing uncontrolled LINE1 expression in the germline. Together, our results support a model in which the Rhox gene cluster is in an evolutionary arms race with TEs, resulting in expansion of the Rhox gene cluster to suppress TEs in different biological contexts.
Project description:Cholesterol is essential for membrane biogenesis, cell proliferation and differentiation. The role of cholesterol in cancer development and the regulation of cholesterol synthesis are still under active investigation. Here we show that under normal-sterol conditions,p53 directly represses the expression of SQLE, a rate-limiting and the first oxygenation enzyme in cholesterol synthesis,in a SREBP2-independent manner. Through transcriptional downregulation of SQLE, p53 represses cholesterol production in vivo and in vitro, leading to tumor growth suppression. Inhibition of SQLE using small interfering RNA (siRNA) or terbinafine (a SQLE inhibitor) reverses the increased cell proliferation caused by p53 deficiency. Conversely, SQLE overexpression or cholesterol addition promotes cell proliferation, particularly in p53 wild-type cells. More importantly, pharmacological inhibition or shRNA-mediated silencing of SQLE restricts nonalcoholic fatty liver disease (NAFLD) -induced liver tumorigenesis in p53 knockout mice. Therefore, our findings reveal a role for p53 in regulating SQLE and cholesterol biosynthesis, and further demonstrate that downregulation of SQLE is critical for p53-mediated tumor suppression.
Project description:Transposable elements make up nearly half of mammalian genomes, yet are generally described as ‘junk DNA’ or genome parasites. The LINE1 retrotransposon is the most abundant class and is thought to be deleterious for cells, but it is paradoxically expressed at high levels during early development. Here, we report that LINE1 plays essential roles in mouse embryonic stem (ES) cells and pre-implantation embryos. In ES cells, LINE1 acts as a nuclear RNA scaffold that recruits Nucleolin and Kap1/Trim28 to repress Dux, the master activator of a gene expression program specific to the 2-cell stage. In parallel, LINE1 RNA mediates binding of Nucleolin and Kap1 to rDNA, thereby promoting rRNA synthesis and ES cell self-renewal. In embryos, LINE1 RNA is required for silencing of Dux, proper synthesis of rRNA and exit from the 2-cell stage. These results reveal an essential partnership between nuclear LINE1 RNA and chromatin factors in the regulation of transcription, developmental potency and ES cell self-renewal.
Project description:Transposable elements make up nearly half of mammalian genomes, yet are generally described as ‘junk DNA’ or genome parasites. The LINE1 retrotransposon is the most abundant class and is thought to be deleterious for cells, but it is paradoxically expressed at high levels during early development. Here, we report that LINE1 plays essential roles in mouse embryonic stem (ES) cells and pre-implantation embryos. In ES cells, LINE1 acts as a nuclear RNA scaffold that recruits Nucleolin and Kap1/Trim28 to repress Dux, the master activator of a gene expression program specific to the 2-cell stage. In parallel, LINE1 RNA mediates binding of Nucleolin and Kap1 to rDNA, thereby promoting rRNA synthesis and ES cell self-renewal. In embryos, LINE1 RNA is required for silencing of Dux, proper synthesis of rRNA and exit from the 2-cell stage. These results reveal an essential partnership between nuclear LINE1 RNA and chromatin factors in the regulation of transcription, developmental potency and ES cell self-renewal.
Project description:Transposable elements make up nearly half of mammalian genomes, yet are generally described as ‘junk DNA’ or genome parasites. The LINE1 retrotransposon is the most abundant class and is thought to be deleterious for cells, but it is paradoxically expressed at high levels during early development. Here, we report that LINE1 plays essential roles in mouse embryonic stem (ES) cells and pre-implantation embryos. In ES cells, LINE1 acts as a nuclear RNA scaffold that recruits Nucleolin and Kap1/Trim28 to repress Dux, the master activator of a gene expression program specific to the 2-cell stage. In parallel, LINE1 RNA mediates binding of Nucleolin and Kap1 to rDNA, thereby promoting rRNA synthesis and ES cell self-renewal. In embryos, LINE1 RNA is required for silencing of Dux, proper synthesis of rRNA and exit from the 2-cell stage. These results reveal an essential partnership between nuclear LINE1 RNA and chromatin factors in the regulation of transcription, developmental potency and ES cell self-renewal.
Project description:This SuperSeries is composed of the following subset Series: GSE32180: MIWI catalysis is required for piRNA amplification-independent LINE1 transposon silencing [microarray] GSE32184: MIWI catalysis is required for piRNA amplification-independent LINE1 transposon silencing [deep sequencing] Refer to individual Series