Antagonistic effects of telomerase on cancer and aging in K5-mTert transgenic mice.

Many degenerative diseases that occur with aging, as well as premature aging syndromes, are characterized by presenting cells with critically short telomeres. Telomerase reintroduction is envisioned as a putative therapy for diseases characterized by telomere exhaustion. K5-mTert transgenic mice overexpress telomerase in a wide spectrum of tissues. These mice have a higher incidence of both induced and spontaneous tumors, resulting in increased mortality during the first year of life. Here, we show that in spite of this elevated tumor incidence and the initial lower survival, K5-mTert mice show an extension of the maximum lifespan from 1.5 to 3 months, depending on the transgenic line, which represents up to a 10% increase in the mean lifespan compared to wild-type littermates. This longer lifespan is coincidental with a lower incidence of certain age-related degenerative diseases, mainly those related to kidney function and germline integrity. Importantly, these effects of telomerase overexpression cannot be attributed to dramatic differences in telomere length in aged K5-Tert mice compared to wild-type mice, as shown by quantitative telomeric FISH. These findings indicate that telomerase overexpression extends the maximum lifespan of mice.

Novel roles for telomerase in aging.

Aging is a multifactorial and highly complex process. Telomeres, repetitive DNA elements at the end of linear chromosomes, and telomerase, the reverse transcriptase responsible for the synthesis and elongation of telomeres, are implicated in mammalian aging. Intact telomeres are essential for genome stability and chromosomal integrity, as well as for extended proliferative life span of cells. Lack of telomerase activity in human somatic tissues and concomitant telomere erosion correlate with age-related pathologies. Mouse models either lacking or overexpressing telomerase support the notion that short telomeres cause premature aging. Recent evidence suggests that telomerase might have other functions besides maintaining telomere length. Here, we propose a possible role for telomerase in delaying the aging process, which is independent of telomere length. The positive effects of telomerase on aging seem to come of the price of tumour promotion. These antagonistic roles of telomerase in aging and cancer may have important implications for putative telomerase based therapies.

Androgen receptor function is modulated by the tissue-specific AR45 variant.

A naturally occurring variant of the human androgen receptor (AR) named AR45 has been identified. It lacks the entire region encoded by exon 1 of the AR gene and is composed of the AR DNA-binding domain, hinge region and ligand-binding domain, preceded by a novel seven amino-acid long N-terminal extension. A survey of human tissues revealed that AR45 was expressed mainly in heart and skeletal muscle. In cotransfection experiments, AR45 inhibited AR function, an effect necessitating intact DNA- and ligand-binding properties. Overexpression of AR45 reduced the proliferation rate of the androgen-dependent LNCaP cells, in line with the repressive effects of AR45 on AR growth-promoting function. AR45 interacted with the AR N-terminal domain in two-hybrid assays, suggesting that AR inhibition was due to the formation of AR-AR45 heterodimers. Under conditions where the transcriptional coactivator TIF2 or the oncogene beta-catenin were overexpressed, AR45 stimulated androgen-dependent promoters in presence of dihydrotestosterone. AR45 activity was triggered additionally by the adrenal androgen androstenedione in presence of exogenous TIF2. Altogether, the data suggest an important role of AR45 in modulating AR function and add a novel level of complexity to the mode of action of androgens.

The role of DNA response elements as allosteric modulators of steroid receptor function.

Steroid receptors are ligand-activated transcription factors which control the expression of their target genes by binding to specific DNA elements. Consensus response elements have been delineated for the glucocorticoid, androgen, progesterone and mineralocorticoid receptors on one hand (steroid response element, SRE) and for the estrogen receptor on the other hand (estrogen response element, ERE). Small variations in these sequences not only affect the binding but may also have a dramatic impact on the transcriptional activity of steroid receptors. It has now become obvious that DNA response elements do not merely tether regulatory proteins to control regions of target genes but may additionally impart conformational changes onto the DNA-binding domain as well as to neighbouring domains of steroid receptors. This in turn will create unique platforms for selective recruitment of cofactors and possibly for induction of modifications in local chromatin architecture. An additional level of complexity is added by the frequent presence of multiple response elements in gene promoter regions. The allosteric effects of DNA response elements on steroid receptors may be essential for differential gene expression and this offers interesting perspectives for the identification of selective modulators.

Differential modulation of androgen receptor action by deoxyribonucleic acid response elements.

In addition to the steroid response elements (SREs), which are recognized by several steroid receptors, a second class of DNA elements exhibiting selectivity for the androgen receptor (AR) and named androgen response elements (AREs) has been identified. Here we provide evidence for the differential role of these element classes in modulating AR function. AR complexes attached to response elements representative of each class were purified. Limited protease digests of ARE- or SRE-bound AR complexes led to the generation of different patterns, in line with differential accessibilities. In transactivation assays, mutations in the AR dimerization interface of the DNA-binding domain had various effects, depending on the response elements tested. The R598D mutant displayed much enhanced activity on SREs, whereas far less effect was seen on the selective AREs. The A596T mutant had reduced activity on AREs but not on SREs. Ectopic expression of the coactivators transcriptional intermediary factor 2 (TIF2) and ARA55 stimulated AR activity to different extents, depending on the response element. When using cysteine-rich secretory protein 1 (CRISP-1) SRE as reference, the most significant difference was observed with Pem ARE-2. A differential response of each element class was furthermore observed in the presence of two enzymes involved in the sumoylation pathway. Ubiquitin-conjugating enzyme 9 (Ubc9) overexpression enhanced AR action conveyed by SREs, whereas little effect was seen on Pem ARE-1 and repression on Pem ARE-2. Protein inhibitor of activated STAT (PIAS)xalpha overexpression had little influence on SRE-mediated AR activity but was repressive when using AREs. Altogether, these results demonstrate that DNA response elements play an important modulatory role in transmitting AR action and may be determinative for specificity of gene expression in cell or tissue types.

OTEX, an androgen-regulated human member of the paired-like class of homeobox genes.

paired genes emerged early in evolution and code for homeobox transcription factors, having fundamental roles in various biological processes. We identified a novel human member of the paired-like class, which we named OTEX. A phylogenetic analysis revealed that OTEX belonged to the recently defined PEPP subfamily of paired-like homeobox genes. It was organized into three introns and, like the other PEPP genes, it was mapped to chromosome X. Its transcripts were detected mainly in the ovary, testis and epididymis, but also in the prostate and mammary gland. In the PC-3/ARwt prostate cell line, OTEX expression was stimulated dramatically following androgen treatment. Immunofluorescence studies revealed an exclusively nuclear localization of the OTEX protein. Mutation of the RARCRRHQRE amino acid sequence present at the C-terminus of the OTEX homeodomain resulted in a mainly cytoplasmic localization, indicating that this motif harboured the nuclear localization signal. No inherent transactivation function was seen for OTEX using the one-hybrid assay, and no homodimer formation was observed in the two-hybrid assay, suggesting that additional partners were needed for this activity. Taken together, the data show that OTEX represents a novel, androgen-regulated, paired-like homeobox protein, with possibly an important role in human reproduction.