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Biomedical subjects

Tim J Yen

Publications and source records attributed to Tim J Yen.

22 records · Page 2Linked to original sources
PubMed2002

Assembly of the SMRT-histone deacetylase 3 repression complex requires the TCP-1 ring complex.

The acetylation of histone tails is a primary determinant of gene activity. Histone deacetylase 3 (HDAC3) requires the nuclear receptor corepressor SMRT for HDAC enzyme activity. Here we report that HDAC3 interacts with SMRT only after priming by cellular chaperones including the TCP-1 ring complex (TRiC), which is required for proper folding of HDAC3 in an ATP-dependent process. SMRT displaces TRiC from HDAC3, yielding an active HDAC enzyme. The SMRT-HDAC3 repression complex thus joins the VHL-elongin BC tumor suppression complex and the cyclin E-Cdk2 cell cycle regulation complex as critical cellular machines requiring TRiC for proper assembly and function. The strict control of HDAC3 activity underscores the cellular imperative that histone deacetylation occur only in targeted regions of the genome.

Adenosine Triphosphate↗
PubMed2002

Chfr regulates a mitotic stress pathway through its RING-finger domain with ubiquitin ligase activity.

Resistance to chemotherapy targeting microtubules could be partially because of the delay in chromosome condensation and segregation during mitosis. The Chfr pathway has been defined recently, and its activation causes a delay in chromosome condensation in response to mitotic stress. Because Chfr contains a RING-finger domain, we tested whether Chfr inhibits chromosome condensation through an ubiquitin (ubiquitin)-dependent pathway. In the presence of purified E1, Ubc4, or Ubc5, and ubiquitin, Chfr catalyzes its own ubiquitination in vitro, an activity requiring the RING domain. In vivo, overexpressed Chfr but not a RING domain mutant is spontaneously ubiquitinated. Our studies with DLD1 cells stably expressing wild-type Chfr and Chfr lacking the RING domain indicated that the RING-finger deletion mutant was defective in inhibiting chromosome condensation after Taxol treatment. In addition, Chfr expression increases the survival rate after Taxol treatment, an activity requiring the RING domain. Preliminary studies indicate that Chfr expression is cell cycle regulated and is dependent on its ubiquitin ligase activity. It is very likely that the Chfr-mediated ubiquitin-dependent pathway is a critical component of the response to mitotic stress.

Amino Acid Sequence↗
PubMed2002

Expression and behaviour of CENP-E at kinetochores during mouse spermatogenesis.

Centromere protein E (CENP-E) is a microtubule motor protein localised in the outer kinetochore plate and in the fibrous corona that relocalises to the midzone in early anaphase. While its expression in somatic cells has been widely analysed, an accurate description of its behaviour during the two meiotic divisions has not yet been reported. We have carefully analysed by immunofluorescence the subcellular distribution of CENP-E during mouse spermatogenesis. CENP-E first appears during late diakinesis/early prometaphase I as very bright C-shaped or "crescent" signals at each homologous centromere. These crescent CENP-E signals are also observed in unaligned prometaphase I bivalents that are not attached to spindle microtubules, while in bioriented metaphase I bivalents two kinds of fainter signals are observed. Thus, some bivalents present a plate-like signal while others show a pair of spots representing sister kinetochores at each homologous centromere. Double labelling of CENP-E with CENP-G and an anti-centromere serum indicates that in meiosis CENP-E is also located at the outer kinetochore plate and the fibrous corona. During early anaphase I CENP-E relocalises from kinetochores to the midzone where it is detected as fibrous strands, although some residual labelling persists at kinetochores until telophase I. During this stage CENP-E is detected as two parallel plates at the intercellular bridge. The general pattern of labelling during meiosis II is similar to that found during meiosis I. Our results suggest that CENP-E is implicated in the spindle checkpoint, and in chromosome alignment, during the two meiotic divisions in vertebrate males. We also demonstrate that the centromere changes its structure once alignment of all bivalents at the metaphase I plate has been reached.

Anaphase↗