Mechanisms of action of TGF-beta in cancer: evidence for Smad3 as a repressor of the hTERT gene

DNA methylation at individual CpG-sites of EPB41L3, HTERT and FAM19A4 are useful for detection of cervical high-grade squamous intraepithelial lesions (HSIL) or worse: Analysis of individual CpG-sites outperforms averaging

Global methylation analysis of gene promoters is promising for detection of high-grade squamous intraepithelial lesions or worse (HSIL+) in high-risk human papillomavirus (hrHPV)-positive women. However, diagnostic performance of methylation data at individual CpG-sites is limited. We explored methylation for predicting HSIL+ in self- and clinician-collected samples from Papua New Guinea. Methylation of EPB41L3 (1-6 CpG-sites), hTERT (1-10 CpG-sites) and FAM19A4 (1-5 CpG-sites) was assessed through pyrosequencing from 44 HPV+ samples (4 cancers, 19 HSIL, 4 low-grade squamous intraepithelial lesions (LSIL), 17 normal). New primers were designed for FAM19A4 directed to the first exon region not explored previously. In clinician-collected samples, methylation at CpG-sites 4 and 5 of EPB41L3 were the best HSIL predictors (AUC >0.83) and CpG-site 4 for cancer (0.925). Combination of EPB41L3 sites 2/4 plus FAM19A4 site 1 were the best HSIL+ markers [100% sensitivity, 63.2% specificity]. Methylation at CpG-site 5 of FAM19A4 was the best HSIL predictor (0.67) in self-collected samples, and CpG-sites 1 and 3 of FAM19A4 for cancer (0.77). Combined, FAM19A4 site 1 plus HPV 16/18 detection yielded sensitivity of 82.6% and specificity of 61.9%. In conclusion, methylation at individual CpG-sites of EPB41L3 and FAM19A4 outperformed global analysis and improved HSIL+ detection, warranting further investigation.

MAP4K4 and WT1 mediate SOX6-induced cellular senescence by synergistically activating the ATF2-TGFβ2-Smad2/3 signaling pathway in cervical cancer

SRY-box transcription factor 6 (SOX6) is a member of the SOX gene family and inhibits the proliferation of cervical cancer cells by inducing cell cycle arrest. However, the final cell fate and significance of these cell-cycle-arrested cervical cancer cells induced by SOX6 remains unclear. Here, we report that SOX6 inhibits the proliferation of cervical cancer cells by inducing cellular senescence, which is mainly mediated by promoting transforming growth factor beta 2 (TGFB2) gene expression and subsequently activating the TGFβ2-Smad2/3-p53-p21WAF1/CIP1-Rb pathway. SOX6 promotes TGFB2 gene expression through the MAP4K4-MAPK (JNK/ERK/p38)-ATF2 and WT1-ATF2 pathways, which is dependent on its high-mobility group (HMG) domain. In addition, the SOX6-induced senescent cervical cancer cells are resistant to cisplatin treatment. ABT-263 (navitoclax) and ABT-199 (venetoclax), two classic senolytics, can specifically eliminate the SOX6-induced senescent cervical cancer cells, and thus significantly improve the chemosensitivity of cisplatin-resistant cervical cancer cells. This study uncovers that the MAP4K4/WT1-ATF2-TGFβ2 axis mediates SOX6-induced cellular senescence, which is a promising therapeutic target in improving the chemosensitivity of cervical cancer.

Regulation and clinical potential of telomerase reverse transcriptase (TERT/hTERT) in breast cancer

Telomerase reverse transcriptase (TERT/hTERT) serves as the pivotal catalytic subunit of telomerase, a crucial enzyme responsible for telomere maintenance and human genome stability. The high activation of hTERT, observed in over 90% of tumors, plays a significant role in tumor initiation and progression. An in-depth exploration of hTERT activation mechanisms in cancer holds promise for advancing our understanding of the disease and developing more effective treatment strategies. In breast cancer, the expression of hTERT is regulated by epigenetic, transcriptional, post-translational modification mechanisms and DNA variation. Besides its canonical function in telomere maintenance, hTERT exerts non-canonical roles that contribute to disease progression through telomerase-independent mechanisms. This comprehensive review summarizes the regulatory mechanisms governing hTERT in breast cancer and elucidates the functional implications of its activation. Given the overexpression of hTERT in most breast cancer cells, the detection of hTERT and its associated molecules are potential for enhancing early screening and prognostic evaluation of breast cancer. Although still in its early stages, therapeutic approaches targeting hTERT and its regulatory molecules show promise as viable strategies for breast cancer treatment. These methods are also discussed in this paper. Video Abstract.

Low dose TGF-β1 can improve vohwinkel syndrome by promoting the proliferation of keratinocytes

Vohwinkel syndrome (VS) is a very rare autosomal dominant disorder that can cause disability and deformity in severe cases. Mutations of the LOR (loricrin) and GJB2 (Cx26) genes have been found in VS so far. Many studies have indicated that the differentiation and growth of epidermal keratinocytes are regulated by mutant Cx26, and it may explain the pathogenesis of VS. It has been found that transforming growth factor β1 (TGF-β1) expression was lower in G130V (OE1) and D66H (OE2) mutant keratinocytes in the VS model with GJB2 mutation as compared to normal keratinocytes (NC). TGF-β is a cytokine involved in the regulation of processes like cell proliferation and differentiation in different types of cells. At present, many in vitro studies focus on TGF- β 1 inhibition of keratinocyte growth.However, the relationship between TGF-β1 and VS remains unknown. This study aimed at elucidating the role and potential pathogenic mechanism of TGF-β in VS. The results indicated that the down-regulation expression of TGF-β1 in VS was linked to cell proliferation inhibition through p-Smad3/c-myc. In contrast, low-dose TGF-β1 treatment of VS keratinocytes can improve their proliferation inhibition and up-regulate the expression Cyclin D1. This suggests that low doses of TGF-β1 can improve the proliferation of VS and provide new insights into its treatment.

Loss of Growth Differentiation Factor 11 Shortens Telomere Length by Downregulating Telomerase Activity

Maintenance of telomere length is essential to delay replicative cellular senescence. It is controversial on whether growth differentiation factor 11 (GDF11) can reverse cellular senescence, and this work aims to establish the causality between GDF11 and the telomere maintenance unequivocally. Using CRISPR/Cas9 technique and a long-term in vitro culture model of cellular senescence, we show here that in vitro genetic deletion of GDF11 causes shortening of telomere length, downregulation of telomeric reverse transcriptase (TERT) and telomeric RNA component (TERC), the key enzyme and the RNA component for extension of the telomere, and reduction of telomerase activity. In contrast, both recombinant and overexpressed GDF11 restore the transcription of TERT in GDF11KO cells to the wild-type level. Furthermore, loss of GDF11-induced telomere shortening is likely caused by enhancing the nuclear entry of SMAD2 which inhibits the transcription of TERT and TERC. Our results provide the first proof-of-cause-and-effect evidence that endogenous GDF11 plays a causal role for proliferative cells to maintain telomere length, paving the way for potential rejuvenation of the proliferative cells, tissues, and organs.

GREM1 inhibits osteogenic differentiation, senescence and BMP transcription of adipose-derived stem cells

Purpose: Adipose-derived stem cells (ADSCs) are ideal for cell-based therapies to support bone regeneration. It is vital to understand the critical genes and molecular mechanisms involved in the functional regulation of ADSCs for enhancing bone regeneration. In the present study, we investigated the Gremlin 1 (GREM1) effect on ADSCs osteogenic differentiation and senescence.Materials and methods: The in vitro ADSCs osteogenic differentiation potential was evaluated by determining alkaline phosphatase (ALP) activity, mineralization ability, and the expression of osteogenic markers. Cell senescence is determined by SA-β-gal staining, telomerase assay, and the expression of aging markers.Results: GREM1 overexpression in ADSCs reduced ALP activity and mineralization, inhibited the expression of osteogenic related genes OCN, OPN, DSPP, DMP1, and BSP, and key transcription factors, RUNX2 and OSX. GREM1 knockdown in ADSCs enhanced ALP activity and mineralization, promoted the expression of OCN, OPN, DSPP, DMP1, BSP, RUNX2, and OSX. GREM1 overexpression in ADSCs reduced the percent SA-β-Gal positive cells, P16 and P53 expressions, and increased telomerase activity. GREM1 knockdown in ADSCs increased the percentage of SA-β-Gal positive cells, P16 and P53 expressions, and reduced telomerase activity. Furthermore, GREM1 reduced the mRNA expression levels of BMP2, BMP6, and BMP7.Conclusions: In summary, our findings suggested that GREM1 inhibited ADSCs senescence and osteogenic differentiation and antagonized BMP transcription.

The dichotomous role of TGF-β in controlling liver cancer cell survival and proliferation

Hepatocellular carcinoma (HCC) is the major form of primary liver cancer and one of the most prevalent and life-threatening malignancies globally. One of the hallmarks in HCC is the sustained cell survival and proliferative signals, which are determined by the balance between oncogenes and tumor suppressors. Transforming growth factor beta (TGF-β) is an effective growth inhibitor of epithelial cells including hepatocytes, through induction of cell cycle arrest, apoptosis, cellular senescence, or autophagy. The antitumorigenic effects of TGF-β are bypassed during liver tumorigenesis via multiple mechanisms. Furthermore, along with malignant progression, TGF-β switches to promote cancer cell survival and proliferation. This dichotomous nature of TGF-β is one of the barriers to therapeutic targeting in liver cancer. Thereafter, understanding the underlying molecular mechanisms is a prerequisite for discovering novel antitumor drugs that may specifically disable the growth-promoting branch of TGF-β signaling or restore its tumor-suppressive arm. This review summarizes how TGF-β inhibits or promotes liver cancer cell survival and proliferation, highlighting the functional switch mechanisms during the process.

TGF-beta receptor mediated telomerase inhibition, telomere shortening and breast cancer cell senescence

Human telomerase reverse transcriptase (hTERT) plays a central role in telomere lengthening for continuous cell proliferation, but it remains unclear how extracellular cues regulate telomerase lengthening of telomeres. Here we report that the cytokine bone morphogenetic protein-7 (BMP7) induces the hTERT gene repression in a BMPRII receptor- and Smad3-dependent manner in human breast cancer cells. Chonic exposure of human breast cancer cells to BMP7 results in short telomeres, cell senescence and apoptosis. Mutation of the BMPRII receptor, but not TGFbRII, ACTRIIA or ACTRIIB receptor, inhibits BMP7-induced repression of the hTERT gene promoter activity, leading to increased telomerase activity, lengthened telomeres and continued cell proliferation. Expression of hTERT prevents BMP7-induced breast cancer cell senescence and apoptosis. Thus, our data suggest that BMP7 induces breast cancer cell aging by a mechanism involving BMPRII receptor- and Smad3-mediated repression of the hTERT gene.

Liposomal trichostatin A: therapeutic potential in hormone-dependent and -independent breast cancer xenograft models

BACKGROUND

Trichostatin A (TSA) is one of the most potent histone deacetylase inhibitors (HDACi) in vitro but it lacks biological activity in vivo when injected intravenously owing to its fast metabolism.

MATERIALS AND METHODS

TSA was incorporated into Stealth® liposomes (TSA-lipo) at a high loading and its anticancer activity was evaluated in several types of breast cancer cells and xenografts.

RESULTS

In estrogen receptor α (ERα)-positive MCF-7 and T47-D cells, TSA induced a long-term degradation of cyclin A and a proteasome-dependent loss of ERα and cyclin D1, allowed derepression of p21WAF1/CIP1, HDAC1 and RhoB GTPase, concomitantly with blockade in G2/M of the cell cycle and apoptosis induction. In MDA-MB-231 (MDA) and SKBr-3 cells, TSA increased ERα mRNA and p21WAF1/CIP1 protein expression, but decreased cyclin A with a G2/M blockade and cleavage of polyADP-ribose polymerase (PARP). No significant restoration of any ER protein was noticed in any cells. TSA-lipo markedly inhibited tumor growth in MCF-7 and MDA cells xenografts following intravenous injection. Their anticancer effects were characterized by inhibition of Ki-67 labeling, the inhibition of tumor vasculature and an increase of p21WAF1/CIP1 in both tumors. In MCF-7 cell tumors, enhanced RhoB accumulation in the cytoplasm of epithelial cells was noticed, inversely to ERα that was strongly decreased.

CONCLUSION

Such anticancer activity of TSA-lipo is exp-lained by the protection provided by HDACi encapsulation and by the strong tumor accumulation of the nanocarriers as revealed by fluorescence confocal microscopy experi-ments. Together with its lack of toxicity, the enhanced stability of TSA-lipo in vivo justifies its development for therapeutic use in the treatment estradiol-dependent and -independent breast cancers.

How pregnancy at early age protects against breast cancer

Pregnancy at an early age has a strong protective effect against breast cancer in humans and rodents. Postulated mechanisms underlying this phenomenon include alterations in the relative dynamics of hormone and growth factor-initiated cell fate-determining signaling pathways within the hierarchically organized mammary gland epithelium. Recent studies in epithelial cell subpopulations isolated from mouse and human mammary glands have shown that early pregnancy decreases the proportion of hormone receptor-positive cells and causes pronounced changes in gene expression as well as decreased proliferation in stem/progenitor cells. The changes include downregulation of Wnt and transforming growth factor β (TGFβ) signaling. These new findings highlight the importance of cell-cell interactions within the mammary gland epithelium in modulating cancer risk and provide potential targets for breast cancer prevention strategies.

Human height genes and cancer

Body development requires the ability to control cell proliferation and metabolism, together with selective 'invasive' cell migration for organogenesis. These requirements are shared with cancer. Human height-associated loci have been recently identified by genome-wide SNP-association studies. Strikingly, most of the more than 100 genes found associated to height appear linked to neoplastic growth, and impose a higher risk for cancer. Height-associated genes drive the HH/PTCH and BMP/TGFβ pathways, with p53, c-Myc, ERα, HNF4A and SMADs as central network nodes. Genetic analysis of body-size-affecting diseases and evidence from genetically-modified animals support this model. The finding that cancer is deeply linked to normal, body-plan master genes may profoundly affect current paradigms on tumor development.

The MAPK pathway signals telomerase modulation in response to isothiocyanate-induced DNA damage of human liver cancer cells

4-methylthiobutyl isothiocyanate (MTBITC), an aliphatic, sulphuric compound from Brassica vegetables, possesses in vitro and in vivo antitumor activity. Recently we demonstrated the potent growth inhibitory potential of the DNA damaging agent MTBITC in human liver cancer cells. Here we now show that MTBITC down regulates telomerase which sensitizes cells to apoptosis induction. This is mediated by MAPK activation but independent from production of reactive oxygen species (ROS). Within one hour, MTBITC induced DNA damage in cancer cells correlating to a transient increase in hTERT mRNA expression which then turned into telomerase suppression, evident at mRNA as well as enzyme activity level. To clarify the role of MAPK for telomerase regulation, liver cancer cells were pre-treated with MAPK-specific inhibitors prior to MTBITC exposure. This clearly showed that transient elevation of hTERT mRNA expression was predominantly mediated by the MAPK family member JNK. In contrast, activated ERK1/2 and P38, but not JNK, signalled to telomerase abrogation and consequent apoptosis induction. DNA damage by MTBITC was also strongly abolished by MAPK inhibition. Oxidative stress, as analysed by DCF fluorescence assay, electron spin resonance spectroscopy and formation of 4-hydroxynonenal was found as not relevant for this process. Furthermore, N-acetylcysteine pre-treatment did not impact MTBITC-induced telomerase suppression or depolarization of the mitochondrial membrane potential as marker for apoptosis. Our data therefore imply that upon DNA damage by MTBITC, MAPK are essential for telomerase regulation and consequent growth impairment in liver tumor cells and this detail probably plays an important role in understanding the potential chemotherapeutic efficacy of ITC.

Genome-wide meta-analysis points to CTC1 and ZNF676 as genes regulating telomere homeostasis in humans

Leukocyte telomere length (LTL) is associated with a number of common age-related diseases and is a heritable trait. Previous genome-wide association studies (GWASs) identified two loci on chromosomes 3q26.2 (TERC) and 10q24.33 (OBFC1) that are associated with the inter-individual LTL variation. We performed a meta-analysis of 9190 individuals from six independent GWAS and validated our findings in 2226 individuals from four additional studies. We confirmed previously reported associations with OBFC1 (rs9419958 P = 9.1 × 10(-11)) and with the telomerase RNA component TERC (rs1317082, P = 1.1 × 10(-8)). We also identified two novel genomic regions associated with LTL variation that map near a conserved telomere maintenance complex component 1 (CTC1; rs3027234, P = 3.6 × 10(-8)) on chromosome17p13.1 and zinc finger protein 676 (ZNF676; rs412658, P = 3.3 × 10(-8)) on 19p12. The minor allele of rs3027234 was associated with both shorter LTL and lower expression of CTC1. Our findings are consistent with the recent observations that point mutations in CTC1 cause short telomeres in both Arabidopsis and humans affected by a rare Mendelian syndrome. Overall, our results provide novel insights into the genetic architecture of inter-individual LTL variation in the general population.

Tumor suppressors p53, p63TAα, p63TAy, p73α, and p73β use distinct pathways to repress telomerase expression

The promoter of the telomerase catalytic subunit (TERT) is subject to tight regulation and remains repressed in somatic cells to ensure their limited life span and to prevent tumor initiation. Here we report that the hTERT promoter is strongly repressed by p53 and the related family members p63 and p73. We found that p53-mediated repression was different in human and mouse cells and occurred through p53-dependent transcription inhibition of c-Myc or through E-box/E2F pathways, respectively. Although p63TAα-mediated repression occurred through SP1, p63TAy-mediated repression occurred through E2F signaling. Finally, p73α- and p73β-mediated repression occurred through NF-YB2. Our results show a complex multifactorial mechanism used by p53 and its family members to keep hTERT expression under tight control.

The Splicing Factor SRSF1 as a Marker for Endothelial Senescence

Aging is the major risk factor per se for the development of cardiovascular diseases. The senescence of the endothelial cells (ECs) that line the lumen of blood vessels is the cellular basis for these age-dependent vascular pathologies, including atherosclerosis and hypertension. During their lifespan, ECs may reach a stage of senescence by two different pathways; a replicative one derived from their preprogrammed finite number of cell divisions; and one induced by stress stimuli. Also, certain physiological stimuli, such as transforming growth factor-β, are able to modulate cellular senescence. Currently, the cellular aging process is being widely studied to identify novel molecular markers whose changes correlate with senescence. This review focuses on the regulation of alternative splicing mediated by the serine-arginine splicing factor 1 (SRSF1, or ASF/SF2) during endothelial senescence, a process that is associated with a differential subcellular localization of SRSF1, which typically exhibits a scattered distribution throughout the cytoplasm. Based on its senescence-dependent involvement in alternative splicing, we postulate that SRSF1 is a key marker of EC senescence, regulating the expression of alternative isoforms of target genes such as endoglin (ENG), vascular endothelial growth factor A (VEGFA), tissue factor (T3), or lamin A (LMNA) that integrate in a common molecular senescence program.

Hypomethylated CpG around the transcription start site enables TERT expression and HPV16 E6 regulates TERT methylation in cervical cancer cells

OBJECTIVE

The human papillomavirus (HPV) oncoprotein, E6, activates telomerase reverse transcriptase (TERT) expression and causes cellular immortalization. It remains unclear whether E6 affects TERT transcription by altering DNA methylation profiles. In this study, we explored the methylation status of the TERT promoter in cervical cancer cell lines and its variations after E6 was silenced by RNAi.

METHODS

Three kinds of cervical cell lines (HPV16 positive: CaSki and SiHa; HPV18 positive: HeLa), were taken to analyze the methylation status of the TERT promoter by methylation-specific polymerase chain reaction (MSP) and bisulfite sequencing (BS). Stealth RNAi was transiently transfected to these cell lines to silence the expression of HPV16/18 E6, and the subsequent changes of TERT mRNA levels and TERT promoter DNA methylation were examined.

RESULTS

Hypomethylation of the DNA around the TERT transcription start site (-156 to +162 bp) was functionally related to its transcription. After transfection with Stealth RNAi, the levels of HPV16/18 E6 and TERT mRNA were greatly decreased. The methylated CpG around the transcription start sites in CaSki and SiHa cells were statistically increased (respectively P=0.016, P=0.000). However, there was no significant difference in HeLa cells (P=0.128).

CONCLUSION

Hypomethylated CpG around the transcription start site enables the expression of TERT in cervical cancer cells. Our results show for the first time that HPV16 E6 can promote TERT transcription through demethylating the DNA sequence around the TERT transcription start site in cervical squamous cancer cells.

The role of activin in mammary gland development and oncogenesis

TGFβ contributes to mammary gland development and has paradoxical roles in breast cancer because it has both tumor suppressor and tumor promoter activity. Another member of the TGFβ superfamily, activin, also has roles in the developing mammary gland, but these functions, and the role of activin in breast cancer, are not well characterized. TGFβ and activin share the same intracellular signaling pathways, but divergence in their signaling pathways are suggested. The purpose of this review is to compare the spatial and temporal expression of TGFβ and activin during mammary gland development, with consideration given to their functions during each developmental period. We also review the contributions of TGFβ and activin to breast cancer resistance and susceptibility. Finally, we consider the systemic contributions of activin in regulating obesity and diabetes; and the impact this regulation has on breast cancer. Elevated levels of activin in serum during pregnancy and its influence on pregnancy associated breast cancer are also considered. We conclude that evidence demonstrates that activin has tumor suppressing potential, without definitive indication of tumor promoting activity in the mammary gland, making it a good target for development of therapeutics.

Leptin as a critical regulator of hepatocellular carcinoma development through modulation of human telomerase reverse transcriptase

Background

Numerous epidemiological studies have documented that obesity is associated with hepatocellular carcinoma (HCC). The aim of this study was to investigate the biological actions regulated by leptin, the obesity biomarker molecule, and its receptors in HCC and the correlation between leptin and human telomerase reverse transcriptase (hTERT), a known mediator of cellular immortalization.

Methods

We investigated the relationship between leptin, leptin receptors and hTERT mRNA expression in HCC and healthy liver tissue samples. In HepG2 cells, chromatin immunoprecipitation assay was used to study signal transducer and activator of transcription-3 (STAT3) and myc/mad/max transcription factors downstream of leptin which could be responsible for hTERT regulation. Flow cytometry was used for evaluation of cell cycle modifications and MMP1, 9 and 13 expression after treatment of HepG2 cells with leptin. Blocking of leptin's expression was achieved using siRNA against leptin and transfection with liposomes.

Results

We showed, for the first time, that leptin's expression is highly correlated with hTERT expression levels in HCC liver tissues. We also demonstrated in HepG2 cells that leptin-induced up-regulation of hTERT and TA was mediated through binding of STAT3 and Myc/Max/Mad network proteins on hTERT promoter. We also found that leptin could affect hepatocellular carcinoma progression and invasion through its interaction with cytokines and matrix mettaloproteinases (MMPs) in the tumorigenic microenvironment. Furthermore, we showed that histone modification contributes to leptin's gene regulation in HCC.

Conclusions

We propose that leptin is a key regulator of the malignant properties of hepatocellular carcinoma cells through modulation of hTERT, a critical player of oncogenesis.

Telomerase in the ovary

Telomerase, an enzyme complex that binds the chromosome ends (telomeres) and maintains telomere length and integrity, is present in germ cells, proliferative granulosa cells, germline stem cells, and neoplastic cells in the ovary, but it is absent in differentiated or aged cells. Activation of telomerase in the ovary underpins both benign and malignant cell proliferation in several compartments, including the germ cells, membrana granulosa, and the ovarian surface epithelium. The difference in telomerase operation between normal and abnormal cell proliferations may lie in the mechanisms of telomerase activation in a deregulated manner. Recent studies have implicated telomerase activity in ovarian cancer as well as oogenesis and fertility. Inhibition of telomerase and the shortening of telomeres are seen in occult ovarian insufficiency. Studies of how telomerase operates and regulates ovary development may provide insight into the development of both germ cells for ovarian reproductive function and neoplastic cells in ovarian cancer. The current review summarizes the roles of telomerase in the development of oocytes and proliferation of granulosa cells during folliculogenesis and in the process of tumorigenesis. It also describes the regulation of telomerase by estrogen in the ovary.

Regulation of telomerase activity by apparently opposing elements

Telomeres, the ends of chromosomes, undergo frequent remodeling events that are important in cell development, proliferation and differentiation, and neoplastic immortalization. It is not known how the cellular environment influences telomere remodeling, stability, and lengthening or shortening. Telomerase is a ribonucleoprotein complex that maintains and lengthens telomeres in the majority of cancers. Recent studies indicate that a number of factors, including hormones, cytokines, ligands of nuclear receptor, vitamins and herbal extracts have significantly influence telomerase activity and, in some instances, the remodeling of telomeres. This review summarizes the advances in understanding of the positive and negative regulation by extracellular factors of telomerase activity in cancer, stem cells and other systems in mammals.

Telomere/telomerase interplay in virus-driven and virus-independent lymphomagenesis: pathogenic and clinical implications

Telomerase is a ribonucleoprotein complex critically involved in extending and maintaining telomeres. Unlike the majority of somatic cells, in which hTERT and telomerase activity are generally silent, normal lymphocytes show transient physiological hTERT expression and telomerase activity according to their differentiation/activation status. During lymphomagenesis, induction of persistent telomerase expression and activity may occur before or after telomere shortening, as a consequence of the different mechanisms through which transforming factors/agents may activate telomerase. Available data indicate that the timing of telomerase activation may allow the distinction of two different lymphomagenetic models: (i) an early activation of telomerase via exogenous regulators of hTERT, along with an increased lymphocyte growth and a subsequent selection of cells with increased transforming potential may characterize several virus-related lymphoid malignancies; (ii) a progressive shortening of telomeres, leading to genetic instability which favors a subsequent activation of telomerase via endogenous regulators may occur in most virus-unrelated lymphoid tumors. These models may have clinically relevant implications, particularly for the tailoring of therapeutic strategies targeting telomerase.

Chromatin and epigenetic regulation of the telomerase reverse transcriptase gene

Telomerase expression and telomere maintenance are critical for long-term cell proliferation and survival, and they play important roles in development, aging, and cancer. Cumulating evidence has indicated that regulation of the rate-limiting subunit of human telomerase reverse transcriptase gene (hTERT) is a complex process in normal cells and many cancer cells. In addition to a number of transcriptional activators and repressors, the chromatin environment and epigenetic status of the endogenous hTERT locus are also pivotal for its regulation in normal human somatic cells and in tumorigenesis.

Activin inhibits telomerase activity in cancer

Activin is a pleiotropic cytokine with broad tissue distributions. Recent studies demonstrate that activin-A inhibits cancer cell proliferation with unknown mechanisms. In this report, we demonstrate that recombinant activin-A induces telomerase inhibition in cancer cells. In breast and cervical cancer cells, activin-A resulted in telomerase activity in a concentration-dependent manner. Significant inhibition was observed at 10 ng/ml of activin-A, with a near complete inhibition at 80 ng/ml. Consistently, activin-A induced repression of the telomerase reverse transcriptase (hTERT) gene, with the hTERT gene to be suppressed by 60-80% within 24h. In addition, activin-A induced a concomitant increase in Smad3 signaling and decrease of the hTERT gene promoter activity in a concentration-dependent fashion. These data suggest that activin-A triggered telomerase inhibition by down-regulating hTERT gene expression is involved in activin-A-induced inhibition of cancer cell proliferation.

Evidence for activation of the TGF-beta1 promoter by C/EBPbeta and its modulation by Smads

The transforming growth factor-beta1 (TGF-beta1) is a cytokine involved in many biological events inlcuding immunosuppression, angiogenesis, cell growth, and apoptosis. Expression of TGF-beta1 at the transcriptional level is controlled by a series of ubiquitous and specialized factors whose activities can be modulated by a variety of signaling events. Here we demonstrate that activity of the TGF-beta1 promoter is increased by C/EBPbeta, a DNA-binding transcription factor whose activity can be influenced by several immunomodulators, in astrocytes and microglial cells. Interestingly, expression of Smad3 and Smad4, the downstream regulators of the TGF-beta1-signaling pathway, impairs the activity of C/EBPbeta on the TGF-beta1 promoter. Further, we demonstrate that MH2, a common domain among Smads that has protein-binding activities, interacts with C/EBPbeta and decreases its association with a region of the TGF-beta1 promoter that is responsive to C/EBPbeta activation. Interestingly, the p65 subunit of nuclear factor-kappaB (NF-kappaB), which also interacts with C/EBPbeta, cooperates with MH2 and decreased DNA-binding and transcriptional activities of C/EBPbeta on the TGF-beta1 promoter. These observations indicate that an autoregulatory mechanism, involving the MH2 domain of Smads, modulates activation of the TGF-beta1 promoter by C/EBPbeta. Further, our results show that the interplay between NF-kappaB and C/EBPbeta has an impact on the ability of C/EBPbeta to stimulate TGF-beta1 transcription, hence, suggesting that the cross-communication of signaling pathways that modulate NF-kappaB and C/EBPbeta may dictate the level of TGF-beta1 promoter activity.

Telomerase regulation in hematological cancers: a matter of stemness?

Human telomerase is a nuclear ribonucleoprotein enzyme complex that catalyzes the synthesis and extension of telomeric DNA. This enzyme is highly expressed and active in most malignant tumors while it is usually not or transiently detectable in normal somatic cells, suggesting that it plays an important role in cellular immortalization and tumorigenesis. As most leukemic cells are generally telomerase-positive and have often shortened telomeres, our understanding of how telomerase is deregulated in these diseases could help to define novel therapies targeting the telomere/telomerase complex. Nonetheless, considering that normal hematopoietic stem cells and some of their progeny do express a functional telomerase, it is tempting to consider such an activity in leukemias as a sustained stemness feature and important to understand how telomere length and telomerase activity are regulated in the various forms of leukemias.

Bone morphogenetic protein-7 inhibits telomerase activity, telomere maintenance, and cervical tumor growth

Telomere maintenance is critical in tumor cell immortalization. Here, we report that the cytokine bone morphogenetic protein-7 (BMP7) inhibits telomerase activity that is required for telomere maintenance in cervical cancer cells. Application of human recombinant BMP7 triggers a repression of the human telomerase reverse transcriptase (hTERT) gene, shortening of telomeres, and hTERT repression-dependent cervical cancer cell death. Continuous treatment of mouse xenograft tumors with BMP7, or silencing the hTERT gene, results in sustained inhibition of telomerase activity, shortening of telomeres, and tumor growth arrest. Overexpression of hTERT lengthens telomeres and blocks BMP7-induced tumor growth arrest. Thus, BMP7 negatively regulates telomere maintenance, inducing cervical tumor growth arrest by a mechanism of inducing hTERT gene repression.

Estrogen deficiency leads to telomerase inhibition, telomere shortening and reduced cell proliferation in the adrenal gland of mice

Estrogen deficiency mediates aging, but the underlying mechanism remains to be fully determined. We report here that estrogen deficiency caused by targeted disruption of aromatase in mice results in significant inhibition of telomerase activity in the adrenal gland in vivo. Gene expression analysis showed that, in the absence of estrogen, telomerase reverse transcriptase (TERT) gene expression is reduced in association with compromised cell proliferation in the adrenal gland cortex and adrenal atrophy. Stem cells positive in c-kit are identified to populate in the parenchyma of adrenal cortex. Analysis of telomeres revealed that estrogen deficiency results in significantly shorter telomeres in the adrenal cortex than that in wild-type (WT) control mice. To further establish the causal effects of estrogen, we conducted an estrogen replacement therapy in these estrogen-deficient animals. Administration of estrogen for 3 weeks restores TERT gene expression, telomerase activity and cell proliferation in estrogen-deficient mice. Thus, our data show for the first time that estrogen deficiency causes inhibitions of TERT gene expression, telomerase activity, telomere maintenance, and cell proliferation in the adrenal gland of mice in vivo, suggesting that telomerase inhibition and telomere shortening may mediate cell proliferation arrest in the adrenal gland, thus contributing to estrogen deficiency-induced aging under physiological conditions.

17-Beta-estradiol inhibits transforming growth factor-beta signaling and function in breast cancer cells via activation of extracellular signal-regulated kinase through the G protein-coupled receptor 30

Breast cancer development and breast cancer progression involves the deregulation of growth factors leading to uncontrolled cellular proliferation, invasion and metastasis. Transforming growth factor (TGF)-beta plays a crucial role in breast cancer because it has the potential to act as either a tumor suppressor or a pro-oncogenic chemokine. A cross-communication between the TGF-beta signaling network and estrogens has been postulated, which is important for breast tumorigenesis. Here, we provide evidence that inhibition of TGF-beta signaling is associated with a rapid estrogen-dependent nongenomic action. Moreover, we were able to demonstrate that estrogens disrupt the TGF-beta signaling network as well as TGF-beta functions in breast cancer cells via the G protein-coupled receptor 30 (GPR30). Silencing of GPR30 in MCF-7 cells completely reduced the ability of 17-beta-estradiol (E2) to inhibit the TGF-beta pathway. Likewise, in GPR30-deficient MDA-MB-231 breast cancer cells, E2 achieved the ability to suppress TGF-beta signaling only after transfection with GPR30-encoding plasmids. It is most interesting that the antiestrogen fulvestrant (ICI 182,780), which possesses agonistic activity at the GPR30, also diminished TGF-beta signaling. Further experiments attempted to characterize the molecular mechanism by which activated GPR30 inhibits the TGF-beta pathway. Our results indicate that GPR30 induces the stimulation of the mitogen-activated protein kinases (MAPKs), which interferes with the activation of Smad proteins. Inhibition of MAPK activity prevented the ability of E2 from suppressing TGF-beta signaling. These findings are of great clinical relevance, because down-regulation of TGF-beta signaling is associated with the development of breast cancer resistance in response to antiestrogens.

Gene therapy of Cav1.2 channel with VIP and VIP receptor agonists and antagonists: a novel approach to designing promotility and antimotility agents

Recent findings show that the enteric neurotransmitter VIP enhances gene transcription of the alpha1C subunit of Cav1.2 (L-type) Ca2+ channels in the primary cultures of human colonic circular smooth muscle cells and circular smooth muscle strips. In this study, we investigated whether systemic infusion of VIP in intact animals enhances the gene transcription and protein expression of these channels to accelerate colonic transit. We also investigated whether similar systemic infusions of VPAC1/2 receptor antagonist retards colonic transit by repressing the constitutive gene expression of the alpha1C subunit. We found that the systemic infusion of VIP for 7 days by a surgically implanted osmotic pump enhances the gene and protein expression of the alpha1C subunit and circular muscle contractility in the proximal and the middle rat colons, but not in the distal colon. A similar systemic infusion of VPAC1/2 receptor antagonist represses the expression of the alpha1C subunit and circular smooth muscle contractility in the proximal and the middle colons. The VIP infusion accelerates colonic transit and pellet defecation by rats, whereas the infusion of VPAC1/2 receptor antagonist retards colonic transit and pellet defecation. VPAC1 receptors, but not VPAC2 receptors, mediate the above gene transcription-induced promotility effects of VIP. We conclude that VIP and VPAC(1) receptor agonists may serve as potential promotility agents in constipation-like conditions, whereas VPAC receptor antagonists may serve as potential antimotility agents in diarrhea-like conditions produced by enhanced motility function.