Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.1.21 (thymidine kinase)
 7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Repression of basal transcription of a 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) responsive 25-hydroxyvitamin D3-24-hydroxylase (CYP24) promoter construct as observed in kidney cells in the absence of ligand and this repression was dependent on a functional vitamin D response element (VDRE). Basal repression was also seen with a construct where a consensus DR-3-type VDRE was fused to the thymidine kinase promoter. Expression of a dominant negative vitamin D receptor (VDR) isoform that strongly bound to the VDRE motif in the CYP24 promoter ablated basal repression. This VDR isoform lacked sequence in the hinge- and ligand-binding domains implicating one or both of these domains in basal repression. It is well known that thyroid hormone and retinoic acid receptors silence basal transcription of target genes in the absence of ligands and this repressor function can be mediated by the nuclear receptor corepressor N-CoR. Two variants of N-CoR have been described, RIP13a and RIP13delta1. N-CoR and the variants contain two receptor interaction domains, ID-I and ID-II, which are identical except region ID-II in RIP13delta1 has an internal deletion. We have used the mammalian two hybrid system to investigate whether VDR, in the absence of ligand 1,25-(OH)2D3, can interact with these domains. The data showed that unliganded VDR does not interact with either ID-I or ID-II from RIP13a and RIP13delta1, but does interact strongly with a composite domain of ID-I and ID-II from RIP13delta1 (but not from RIP13a) and this strong interaction is abrogated in the presence of ligand. This finding implicates RIP13delta1 in VDR-dependent basal repression of the promoter constructs under investigation. However, over-expression of RIP13delta1 in kidney cell lines did not alter basal expression of the CYP24 promoter construct. It is concluded that either the level of endogenous RIP13delta1 in these kidney cells permits maximal repression or that repression occurs by a mechanism that is independent of RIP13delta1. Alternatively, repression may be dependent on RIP13delta1 but requires an additional cofactor that is limiting in these cells.
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PMID:Repression of basal transcription by vitamin D receptor: evidence for interaction of unliganded vitamin D receptor with two receptor interaction domains in RIP13delta1. 968 55

The leukaemia-associated eight-twenty-one (ETO) family members ETO, MTG16 (Myeloid Translocation Gene on chromosome 16) and MTGR1 (Myeloid Transforming Gene-Related protein1) are putative transcriptional repressor proteins, which form complexes with coregulatory nuclear corepressors such as SIN3 (SWI-Independent) and N-CoR (Nuclear receptor Co Repressor). In acute myeloid leukaemia (AML), fusion proteins involving the transcription factor AML1 and corepressors ETO or MTG16 are recurrently found. We investigated transcriptional repression by the ETO family members ETO and MTG16 with attention to the conserved Nervy Homology Regions (NHRs) and the interacting corepressors human SIN3B (hSIN3B) and N-CoR. Transcriptional repression was examined in a cell line by a GAL4-thymidine kinase luciferase reporter to which the corepressors were tethered through a binding domain. ETO- and MTG16-mediated repression was found to be independent of deletion of the oligomerization NHR2, but deletion of NHR4 and in particular combined deletion of NHR2 and NHR4 lowered the capacity for repression. An interaction was observed between the corepressors hSIN3B and N-CoR and these two proteins cooperated for transcriptional repression independent of co-transfected ETO and MTG16. Transcriptional repression mediated by ETO and MTG16 was only slightly strengthened by coexpression of hSIN3B or N-CoR and was dependent on HDAC activity. Our data indicate that ETO family member-mediated oligomerization and repression can be distinct events and that interaction between ETO family members and hSIN3B or N-CoR may not necessarily strengthen transcriptional repression.
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PMID:Transcriptional repression by leukaemia-associated ETO family members can be independent of oligomerization and coexpressed hSIN3B and N-CoR. 1858 23