No abstract

The role of histone deacetylase 1 and 2 (HDAC1 and HDAC2) in regulating cartilage-specific gene expression was explored in primary human chondrocytes. HDAC1 and HDAC2 protein levels were elevated in chondrocytes from osteoarthritic patients, consistent with a down-regulation of some cartilage marker genes. When expressed in these cells, HDAC1 and HDAC2 repressed aggrecan and collagen 2(alpha1) expression but differed in their repression of collagen 9(alpha1), collagen 11(alpha1), dermatopontin, and cartilage oligomeric matrix protein (COMP). To identify the basis of these differences between HDAC1 and HDAC2, their carboxy-terminal domains (CTDs) were deleted, which led to proteins that retained enzymatic activity but were unable to repress cartilage gene expression. Further, exchange of the CTDs between HDAC1 and HDAC2 led to proteins that were enzymatically active but displayed altered target gene specificity, indicating that these CTDs can function independently of HDAC enzymatic activity, to target the HDACs to specific genes. The Snail transcription factor was identified as a mediator of HDAC1 and HDAC2 repression of the collagen 2(alpha1) gene, via its interaction with the HDAC1 and 2 CTDs. The data indicate that the CTD serves a novel function within HDAC1 and HDAC2, to mediate repression of cartilage-specific gene expression in human chondrocytes.

Expression of the human T lymphotropic virus type I (HTLV-I) transactivator͞oncoprotein, Tax, leads to faulty mitosis as reflected by chromosome aneuploidy, cytokinesis failure, and formation of micro-and multinucleated cells. Here we show that HTLV-I-transformed T cells progress through S͞G2͞M phases of the cell cycle with a delay. This delay is correlated with a decrease in the levels of cyclin A, cyclin B1, and securin. In tax-expressing cells, the Cdc20-associated anaphase promoting complex (APC Cdc20 ), an E3 ubiquitin ligase that controls metaphase to anaphase transition, becomes active before cellular entry into mitosis as evidenced by premature cyclin B1 polyubiquitination and degradation during S͞G2. Consistent with the notion that Tax activates APC Cdc20 directly, Tax is found to coimmunoprecipitate with Cdc20 and Cdc27͞APC3. The APC Cdc20 activity prematurely activated by Tax remains sensitive to spindle checkpoint inhibition. Unscheduled activation of APC Cdc20 by Tax provides an explanation for the mitotic abnormalities in HTLV-I-infected cells and is likely to play an important role in the development of adult T cell leukemia.adult T cell leukemia ͉ cell cycle ͉ ubiquitination ͉ mitosis ͉ chromosome instability H uman T lymphotropic virus type I (HTLV-I) is the etiological agent of adult T cell leukemia͞lymphoma (ATL) and a neurological disorder called HTLV-I-associated myelopathy͞ tropical spastic paraparesis. Unlike cells of other leukemia, ATL cells are often aneuploid with complex chromosomal abnormalities including trisomy 3, trisomy 7, a partial deletion of 6q, and abnormalities of 14q11 (1). Morphologically, the nuclei of ATL cells are highly lobulated or convoluted, earning them the name of ''flower'' cells. Finally, atypical lymphocytes that are binucleated or contain cleaved͞cerebriform nuclei are readily seen in the blood smears of HTLV-I infected individuals (2-5). These pathological findings suggest that mitotic aberrations accompany HTLV-I viral replication and may play a role in the development of adult T cell leukemia.How HTLV-I infection progresses from clinical latency to T cell malignancy and HTLV-I-associated myelopathy͞tropical spastic paraparesis is not well understood, but involves the unique viral transactivator͞oncoprotein, Tax. Tax mediates potent activation of viral transcription and usurps regulatory mechanisms critical for cell growth and division to facilitate viral replication. The effects Tax exerts on cells are pleiotropic and include potent NF-B activation, cell cycle perturbation, and cell transformation (reviewed in ref. 6).We and others have shown that naïve cells that express tax for the first time exhibit severe cell cycle abnormalities (7-11). HeLa cells transduced with an adenovirus vector or a lentivirus vector carrying the tax gene experience a delay in mitotic entry and progression. They then progress through faulty mitosis, which leads immediately to severe karyotypic abnormalities and formation of micro-, bi-, or multinucleated cells. Human diploid fibr...

Induction of premature senescence may be a promising strategy for cancer treatment. However, biomarkers for senescent cancer cells are lacking. To identify such biomarkers, we performed comparative proteomic analysis of MCF7 human breast cancer cells undergoing cellular senescence in response to ionizing radiation (IR). IR-induced senescence was associated with up-regulation of cathepsin D (CD) and down-regulation of eukaryotic translation elongation factor 1B2 (eEF1B2), as confirmed by Western blot. The other elongation factor, eukaryotic translation elongation factor 1A1 (eEF1A1), was also down-regulated. IR-induced senescence was associated with similar changes of CD and eEF1 (eEF1A1 and eEF1B2) levels in the HCT116 colon cancer cell line and the H460 lung cancer cell line. Up-regulation of CD and down-regulation of eEF1 seemed to be specific to senescence, as they were observed during cellular senescence induced by hydrogen peroxide or anticancer drugs (camptothecin, etoposide, or 50 ng doxorubicin) but not during apoptosis induced by Taxol or 10 Mg doxorubicin or autophagy induced by tamoxifen. The same alterations in CD and eEF1A1 levels were observed during replicative senescence and Ras oncogene-induced senescence. Transient cell cycle arrest did not alter levels of eEF1 or CD. Chemical inhibition of CD (pepstatin A) and small interfering RNA-mediated knockdown of CD and eEF1 revealed that these factors participate in cell proliferation. Finally, the senescence-associated alteration in CD and eEF1 levels observed in cell lines was also observed in IR-exposed xenografted tumors. These findings show that CD and eEF1 are promising markers for the detection of cellular senescence induced by a variety of treatments. [Cancer Res 2009;69(11):4638-47]