| Summary: | 碩士 === 中興大學 === 分子生物學研究所 === 95 === PARP2 (poly(ADP-ribose) polymerase 2) is a member of the PARP family. It synthesizes poly(ADP-ribose) (PAR), using NAD+ as a cofactor, and then transfers the PAR onto acceptor proteins to achieve the unique post-translational modification, poly(ADP-ribosyl)ation. There are 17 members in the PARP family, identified by a catalytic domain, PARP domain. PARPs are involved in many cellular resposes through more than 30 substrates, most of them are nuclear proteins, which are involved in pathways including transcriptional regulation, telomere cohesion, cell division, intracellular trafficking and energy metabolism. Recent studies show that PARP1 affects transcription through (i) modifying histones, causing decondensation of the chromatin structure, or (ii) acting as an activator or a coactivator involved in different protein complexes of transcription factors. However, the function of PARP2 in transcription is still unclear.
Our previous studies show PARP2 interacts with the transcription factor PAX3 (Dr. Yang Lab, unpublished results). That indicates PARP2 may be involved in transcription. Here we show that PARP2 represses transcription with the transcriptional assay. Furthermore, we demonstrate that PARP2-mediated gene repression depends on its enzyme activity. We also determine that the amino acids 281-521 region of PARP2 is the repression domain. Our results later show that PARP2 interacts with histone deacetylases HDAC1, 2, 3, 5, 7, 8, 10, SirT1 and and histone acetyltransferase PCAF and histone methyltransferase SETDB1, M33, hPC2 and histone demethylase LSD1, JMJD2A. In transcriptional assay, HDAC5, HDAC7 and JMJD2A enhance PARP2’s repressional activity, and HDAC1, HDAC3, M33 and hPC2 decreased PARP2’s repressional activity. In addition to histone modifiers, PARP2 also interacts with gene silencing proteins, like HP1 (heterochromatin protein 1) family and KAP1, a corepressor. HP1α decreases PARP2’s repressional activity but increased its nucleolar localization. PARP2 interacts with transcription factor YY1 and enhances its repressional activity on YY1 native promoter, the c-myc promoter. HDAC5 and 7 interact with PARP2 at aminoacids 1-280 and amino acids 281-521. JMJD2A interacts with PARP2 at amino acids 1-280. Finally, we found that PARP1, Ku80 and Ku70 are members of the PARP2 protein complex but none of them affect PARP2’s repressional activity.
In summary, we have shown that the mechanism by which PARP2 represses transcription may involve its binding to promoters through YY1 and the recruitment of HDAC5, HDAC7 and JMJD2A to repress transcription. We found that PARP1, Ku80 and Ku70 are members of the PARP2 protein complex.
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