Erythropoietin in cancer: an update

Erythropoietin (EPO) has long been recognized as the major hematopoietic cytokine regulating normal erythropoiesis. Moreover, there is a growing interest in the non-erythropoietic, tissue-protective effects of EPO. Because of its potential to correct anemia, EPO has been increasingly prescribed to cancer patients. However, although recombinant human Epo (rHuEPO) significantly reduces the risk for red blood cell transfusions in cancer patients, recent clinical studies have reported decreased survival and disease control following rHuEPO treatment in patients with different cancer types. The issue of EPOR expression in tumor cells is critical in this respect. The expression of EPOR in tumor cells raises the possibility that exogenous rHuEPO may directly influence tumor growth or sensitivity to chemo-radiation therapy. In addition, EPOR expression in endothelial cells suggests what potential effects EPO may have on tumor capillaries, such as the stimulation of angiogenesis. However, as experimental studies reveal, the overall direct effect of EPO-EPOR signaling on cancer progression and therapy is not a straightforward one. The current paper provides an update on the biology of EPO, and discusses its utility in the treatment of cancer patients.     

化疗药物对人胃癌SGC-7901细胞系端粒酶活性影响

目的　研究常见化疗药物对人胃癌SGC 790 1细胞系端粒酶活性影响。方法　MTT (噻唑蓝 )法测定化疗药物顺铂、丝裂霉素、阿霉素、 5 氟尿嘧啶、氟铁龙 (脱氧氟尿苷 )对人胃癌SGC 790 1细胞系毒性作用的半数抑制(IC5 0 )浓度 ;用TRAP ELISA法测定 4 0×IC5 0浓度化疗药物作用于SGC 790 1细胞 4h、 2 8h端粒酶活性及IC5 0浓度IC5 0化疗药物作用于SGC 790 1细胞 2 4h、 72h、 12 0h细胞端粒酶活性。结果　高浓度 ,低浓度顺铂、丝裂霉素对SGC 790 1细胞端粒酶活性有完全抑制作用 ;而阿霉素、 5 氟尿嘧啶、氟铁龙对SGC 790 1细胞端粒酶活性有部分抑制作用。结论　阿霉素、 5 氟尿嘧啶、氟铁龙对SGC 790 1细胞端粒酶活性有轻度抑制作用 ;顺铂、丝裂霉素能完全抑制端粒酶活性 ,呈时间浓度效应     

Telomeres in cancer and ageing

Telomeres protect the chromosome ends from unscheduled DNA repair and degradation. Telomeres are heterochromatic domains composed of repetitive DNA (TTAGGG repeats) bound to an array of specialized proteins. The length of telomere repeats and the integrity of telomere-binding proteins are both important for telomere protection. Furthermore, telomere length and integrity are regulated by a number of epigenetic modifications, thus pointing to higher order control of telomere function. In this regard, we have recently discovered that telomeres are transcribed generating long, non-coding RNAs, which remain associated with the telomeric chromatin and are likely to have important roles in telomere regulation. In the past, we showed that telomere length and the catalytic component of telomerase, Tert, are critical determinants for the mobilization of stem cells. These effects of telomerase and telomere length on stem cell behaviour anticipate the premature ageing and cancer phenotypes of telomerase mutant mice. Recently, we have demonstrated the anti-ageing activity of telomerase by forcing telomerase expression in mice with augmented cancer resistance. Shelterin is the major protein complex bound to mammalian telomeres; however, its potential relevance for cancer and ageing remained unaddressed to date. To this end, we have generated mice conditionally deleted for the shelterin proteins TRF1, TPP1 and Rap1. The study of these mice demonstrates that telomere dysfunction, even if telomeres are of a normal length, is sufficient to produce premature tissue degeneration, acquisition of chromosomal aberrations and initiation of neoplastic lesions. These new mouse models, together with the telomerase-deficient mouse model, are valuable tools for understanding human pathologies produced by telomere dysfunction.     

端粒与端粒酶研究进展

细胞分裂中染色体因其末端（端粒）的DNA不能完全复制而短缩,使细胞逐渐失去增殖能力而衰老．端粒酶可延长染色体末端DNA,端粒酶的活化使细胞无限增殖．85％左右的恶性肿瘤端粒酶表达阳性,生殖细胞和无限繁殖的细胞系中端粒酶表达也呈阳性．文章综述了端粒的构成和功能、端粒酶在端粒合成中的作用,介绍了端粒酶活性的测定方法、细胞恶变与端粒酶激活的关系,并论及通过抑制端粒酶活性来治疗癌症的可能性．     

Increased epidermal tumors and increased skin wound healing in transgenic mice overexpressing the catalytic subunit of telomerase, mTERT, in basal keratinocytes

Telomerase transgenics are an important tool to assess the role of telomerase in cancer, as well as to evaluate the potential use of telomerase for gene therapy of age-associated diseases. Here, we have targeted the expression of the catalytic component of mouse telomerase, mTERT, to basal keratinocytes using the bovine keratin 5 promoter. These telomerase-transgenic mice are viable and show histologically normal stratified epithelia with high levels of telomerase activity and normal telomere length. Interestingly, the epidermis of these mice is highly responsive to the mitogenic effects of phorbol esters, and it is more susceptible than that of wild-type littermates to the development skin tumors upon chemical carcinogenesis. The epidermis of telomerase-transgenic mice also shows an increased wound-healing rate compared with wild-type littermates. These results suggest that, contrary to the general assumption, telomerase actively promotes proliferation in cells that have sufficiently long telomeres and unravel potential risks of gene therapy for age-associated diseases based on telomerase upregulation.     

Selective modulation of the erythropoietic and tissue-protective effects of erythropoietin: time to reach the full therapeutic potential of erythropoietin

Erythropoietin (EPO) has been used clinically both as an erythropoietic stimulating agent in the treatment of anemia and as a tissue-protective agent in diverse clinical settings including stroke, multiple sclerosis, acute myocardial infarction and others. However, use of EPO or EPO-analogues leads to simultaneous targeting of both the erythropoietic and tissue-protective properties of EPO, and this strategy has been associated with several problems. Specifically, the benefit of correction of cancer-related anemia can be offset by the tissue-protective effects of EPO, which may lead to stimulation of cancer cell proliferation. Conversely, the benefit of tissue-protection in patients with stroke or myocardial infarction can be offset by adverse effects associated with the erythropoietic effects of EPO such as elevation of red blood cell mass, hypertension and prothrombotic phenomena. The finding that the erythropoietic and tissue-protective properties of EPO are conferred via two distinct receptor systems raises the interesting possibility of discovering novel drugs that selectively stimulate either the erythropoietic or the tissue-protective activities of EPO. This article reviews the current status of the clinical use of EPO and EPO-analogues in the treatment of cancer-related anemia and for tissue protection, outlines the distinct molecular biology of the tissue-protective and erythropoietic effects of EPO and discusses strategies of selective targeting of these activities with the goal of exploiting the full therapeutic potential of EPO.     

Human telomerase RNA accumulation in Cajal bodies facilitates telomerase recruitment to telomeres and telomere elongation

Telomerase is required for telomere maintenance and is responsible for the immortal phenotype of cancer cells. How telomerase is assembled and reaches telomeres in the context of nuclear architecture is not understood. Recently, the telomerase RNA subunit (hTR) was shown to accumulate in Cajal bodies (CBs), subnuclear structures implicated in ribonucleoprotein maturation. However, the functional relevance of this localization for telomerase was unknown. hTR localization to CBs requires a short sequence motif called the CAB box. Here, we reconstitute telomerase in human cells and determine the effects of CAB box mutations on telomere biology. We demonstrate that mutant hTR, which fails to accumulate in CBs, is fully capable of forming catalytically active telomerase in vivo but is strongly impaired in telomere extension. The functional deficiency is accompanied by a decreased association of telomerase with telomeres. Collectively, these data identify subnuclear localization as an important regulatory mechanism for telomere length homeostasis in human cells.     

Inhibition of telomerase enhances apoptosis induced by sodium butyrate via mitochondrial pathway

Telomerase activation represents an early step in carcinogenesis. Increased telomerase activity in cervical cancer suggests a potential target for the development of novel therapeutic drugs. The aim of this study is to investigate the impact of telomerase activity on the biological features of HeLa cells and the possible mechanisms of enhanced apoptosis rate induced by sodium butyrate after telomerase inhibition. We introduced vectors encoding dominate negative (DN)-hTERT, wild-type (WT)-hTERT, or a control vector expressing only a drug-resistance marker into HeLa cells. Thus we assessed the biological effects of telomerase activity on telomere length, cell proliferation, chemosensitivity and radiosensitivity. In order to understand the mechanisms in which DN-hTERT enhances the apoptosis induced by sodium butyrate, we detected the release status of cytochrome c and apoptosis inducing factor (AIF) from mitochondria. Ectopic expression of DN-hTERT resulted in inhibition of telomerase activity, reduction of telomere length, decreased colony formation ability, and loss of tumorigenicity in nude mice. Moreover, DN-hTERT transfected HeLa cells with shortened telomeres were more susceptible to multiple chemotherapeutic agents and radiation. WT-hTERT transfected HeLa cells with longer telomeres exhibited resistance to radiation and chemotherapeutic agents. Our data demonstrate that elevated release level of cytochrome c and AIF from mitochondria might contribute to the enhanced apoptosis in DN-hTERT transfected HeLa cells after treatment with sodium butyrate. Inhibition of telomerase might serve as a promising adjunctive therapy combined with conventional therapy in cervical cancer. Both of them contributed equally to this work.     

N-(1-Pyrenyl) maleimide inhibits telomerase activity in a cell free system and induces apoptosis in Jurkat cells

Telomerase activity is repressed in normal human somatic cells, but is activated in most cancers, suggesting that telomerase may be an important target for cancer therapy. Agents that interact selectively with telomerase are anticipated to exert specific action on cancer cells. In this study, we evaluated maleimide derivatives for their potency and selectivity of telomerase inhibition. Among the several N-substituted derivatives of maleimide tested, N-(1-Pyrenyl) maleimide was shown to exert the greatest inhibition of telomerase in a cell free system, with an IC50 value of 0.25 μM. Importantly, we demonstrated that N-(1-pyrenyl) maleimide induces apoptosis in Jurkat T cells and displays the greatest differential cytotoxicity against hematopoietic cancer cells. These results suggest that N-(1-pyrenyl) maleimide is an attractive maleimide to be tested and developed as anti-cancer drug.     

Activity of the Human Telomerase Catalytic Subunit (hTERT) Gene Promoter Could Be Increased by the SV40 Enhancer

Telomerase is a ribonucleoprotein complex of which the function is to add telomeric repeats to chromosomal ends. Telomerase consists of two essential components, the telomerase RNA template (hTR) and the catalytic subunit (hTERT). hTERT is expressed only in cells and tissues positive for telomerase activity, i.e., tumor and fetal cells. The aim of this study is to test the increased telomerase promoter activity for cancer gene therapy in adenovirus vector. We cloned the hTERT promoter in place of the SV40 promoter in the pGL3-contol vector to be increased by the SV40 enhancer sequences, resulting in strong expression of luc+ only in telomerase positive cancer cells. Then we transfected the constructed plasmid into a normal human cell line and several cancer cell lines. Through these experiments, we identified the selective and increased expression of the luciferase gene controlled by the hTERT promoter and the SV40 enhancer in the telomerase positive cancer cell lines. To investigate the possibility of utilizing the hTERT promoter and the SV40 enhancer in targeted cancer gene therapy, we constructed an adenovirus vector expressing HSV-TK controlled by the hTERT promoter and the SV40 enhancer for the induction of specific telomerase positive cancer cell death. NSCLC cells infected by Ad-hT-TK-enh were more significantly suppressed and induced apoptosis than those infected by Ad-hT-TK. Telomerase is activated in 80～90% of cancers, so adenovirus with increasing telomerase promoter activity might be used for targeted cancer gene therapy using suicide genes. These results show that the hTERT promoter and the SV40 enhancer might be used for targeted cancer gene therapy.