Meta-Biol

• Pathways

TP53 (p53) undergoes methylation on several lysine and arginine residues, which modulates its transcriptional activity.

PRMT5, recruited to TP53 as part of the ATM-activated complex that includes TTC5, JMY and EP300 (p300), methylates TP53 arginine residues R333, R335 and R337. PRMT5-mediated methylation promotes TP53-stimulated expression of cell cycle arrest genes (Shikama et al. 1999, Demonacos et al. 2001, Demonacos et al. 2004, Adams et al. 2008, Adams et al. 2012). SETD9 (SET9) methylates TP53 at lysine residue K372, resulting in increased stability and activity of TP53 (Chuikov et al. 2004, Couture et al. 2006, Bai et al. 2011).

TP53 transcriptional activity is repressed by SMYD2-mediated methylation of TP53 at lysine residue K370 (Huang et al. 2006). Dimethylation of TP53 at lysine residue K373 by the complex of methyltransferases EHMT1 and EHMT2 also represses TP53-mediated transcription (Huang et al. 2010). The chromatin compaction factor L3MBTL1 binds TP53 monomethylated at lysine K382 by SETD8 (SET8) and, probably through changing local chromatin architecture, represses transcription of TP53 targets (West et al. 2010). The histone lysine-specific demethylase LSD1 interacts with TP53 and represses p53-mediated transcriptional activation (Huang et al. 2007). PRMT1 and CARM1 can also modulate p53 functions in a cooperative manner (An et al. 2004).

RNA polymerase II (Pol II) is the central enzyme that catalyses DNA- directed mRNA synthesis during the transcription of protein-coding genes. Pol II consists of a 10-subunit catalytic core, which alone is capable of elongating the RNA transcript, and a complex of two subunits, Rpb4/7, that is required for transcription initiation.
The transcription cycle is divided in three major phases: initiation, elongation, and termination. Transcription initiation include promoter DNA binding, DNA melting, and initial synthesis of short RNA transcripts. The transition from initiation to elongation, is referred to as promoter escape and leads to a stable elongation complex that is characterized by an open DNA region or transcription bubble. The bubble contains the DNA-RNA hybrid, a heteroduplex of eight to nine base pairs. The growing 3-end of the RNA is engaged with the polymerase complex active site. Ultimately transcription terminates and Pol II dissocitates from the template.

Gene expression encompasses transcription and translation and the regulation of these processes. RNA Polymerase I Transcription produces the large preribosomal RNA transcript (45S pre-rRNA) that is processed to yield 18S rRNA, 28S rRNA, and 5.8S rRNA, accounting for about half the RNA in a cell. RNA Polymerase II transcription produces messenger RNAs (mRNA) as well as a subset of non-coding RNAs including many small nucleolar RNAs (snRNA) and microRNAs (miRNA). RNA Polymerase III Transcription produces transfer RNAs (tRNA), 5S RNA, 7SL RNA, and U6 snRNA. Transcription from mitochondrial promoters is performed by the mitochondrial RNA polymerase, POLRMT, to yield long transcripts from each DNA strand that are processed to yield 12S rRNA, 16S rRNA, tRNAs, and a few RNAs encoding components of the electron transport chain. Regulation of gene expression can be divided into epigenetic regulation, transcriptional regulation, and post-transcription regulation (comprising translational efficiency and RNA stability). Epigenetic regulation of gene expression is the result of heritable chemical modifications to DNA and DNA-binding proteins such as histones. Epigenetic changes result in altered chromatin complexes that influence transcription. Gene Silencing by RNA mostly occurs post-transcriptionally but can also affect transcription. Small RNAs originating from the genome (miRNAs) or from exogenous RNA (siRNAs) are processed and transferred to the RNA-induced silencing complex (RISC), which interacts with complementary RNA to cause cleavage, translational inhibition, or transcriptional inhibition.