Significance of NF‐κB activation in immortalization of nasopharyngeal epithelial cells

NF‐κB is a key regulator of inflammatory response and is frequently activated in human cancer including the undifferentiated nasopharyngeal carcinoma (NPC), which is common in Southern China including Hong Kong. Activation of NF‐κB is common in NPC and may contribute to NPC development. The role of NF‐κB activation in immortalization of nasopharyngeal epithelial (NPE) cells, which may represent an early event in NPC pathogenesis, is unknown. Examination of NF‐κB activation in immortalization of NPE cells is of particular interest as the site of NPC is often heavily infiltrated with inflammatory cellular components. We found that constitutive activation of NF‐κB signaling is a common phenotype in telomerase‐immortalized NPE cell lines. Our results suggest that NF‐κB activation promotes the growth of telomerase‐immortalized NPE cells, and suppression of NF‐κB activity inhibits their proliferation. Furthermore, we observed upregulation of c‐Myc, IL‐6 and Bmi‐1 in our immortalized NPE cells. Inhibition of NF‐κB downregulated expression of c‐Myc, IL‐6 and Bmi‐1, suggesting that they are downstream events of NF‐κB activation in immortalized NPE cells. We further delineated that EGFR/MEK/ERK/IKK/mTORC1 is the key upstream pathway of NF‐κB activation in immortalized NPE cells. Elucidation of events underlying immortalization of NPE cells may provide insights into early events in pathogenesis of NPC. The identification of NF‐κB activation and elucidation of its activation mechanism in immortalized NPE cells may reveal novel therapeutic targets for treatment and prevention of NPC.     

p16INK4a downregulation is involved in immortalization of primary human prostate epithelial cells induced by telomerase

Prostate cancer is a major cause of cancer death among male population. Therefore, development of appropriate model systems is critical for understanding the molecular basis of prostate cancer progression. In this study, introduction of human telomerase (hTERT) into normal human prostate epithelial cells (PrECs) renders them higher telomerase activity, elongated telomere length and an extended proliferative lifespan. The immortal mass culture of PrEC-hTERT cell line with stabilized telomere length has been established using hTERT transfection. However, activation of hTERT alone appears to be insufficient for immortalization of PrEC cells because methylation of p16(INK4a) promoter has been found to be involved in the immortalization process. p53 was functionally intact and no mutations of p53 gene were identified in the immortalized PrECs. In addition, the immortal PrECs show a near diploid complement of chromosomes albeit a few reciprocal and non-reciprocal translocations are identified. They are anchorage dependent and do not form tumors in immunosuppressed host animals. Therefore, premalignantly transformed human PrECs provide a valuable model for prostate cancer research.     

癌前鼻咽上皮细胞模型

研究鼻咽癌进展的实验模型系统可以为鼻咽癌发生的分子机制研究及潜在的临床干预措施提供有价值的信息。由于EB病毒仅感染人类及少数灵长类,目前尚缺乏有代表性的鼻咽癌动物模型。当前鼻咽癌早期发生的体外模型的建立主要采用使正常增殖的鼻咽上皮细胞转化为永生化细胞的方法。最早的两株永生化鼻咽上皮细胞是由外源表达SV40T及HPVE6／E7病毒癌基因诱导建立．并进行了验证。为了避免由病毒癌基因引起的一系列与鼻咽癌发生不相关的分子改变,我们利用在鼻咽癌细胞和组织中高表达的癌基因Bmi-1．介导建立并验证了两株永生化鼻咽上皮细胞。另外,由人端粒酶逆转录酶诱导产生的永生化鼻咽上皮细胞也已建立。与由病毒癌基因诱导产生的永生化细胞不同,这些永生化的鼻咽上皮细胞保留了正常的P53表达水平,除一些在鼻咽癌中存在的分子改变外。并未表现出其他的基因缺陷。因此,这些永生化的细胞可以用于由某些特定的分子遗传因素诱导的鼻咽癌进展的研究,特别是可以用于阐明EB病毒在鼻咽癌发展中所起的作用。     

5氮杂脱氧胞苷对鼻咽癌细胞RASSF1A基因甲基化和mRNA表达的影响

目的:研究5氮杂脱氧胞苷对鼻咽癌CNE2细胞中RASSF1A基因甲基化和mRNA表达的影响。方法:用不同浓度(0、5、10、20μmol/L)5氮杂脱氧胞苷处理CNE2细胞,采用甲基化特异性PCR(MSP)法对处理后细胞中RASSF1A基因甲基化状态进行检测;并用SYBR Green qReal Time-PCR法检测RASSF1A mRNA的表达。结果:阴性对照组CNE2细胞中,RASSF1A基因呈完全甲基化状态,当用5μmol/L 5氮杂脱氧胞苷处理后,CNE2细胞出现非甲基化产物,20μmol/L 5氮杂脱氧胞苷处理后,CNE2细胞甲基化状态完全被逆转,均为非甲基化产物。阴性对照组CNE2细胞RASSF1A基因呈低表达,经5～20μmol/L 5氮杂脱氧胞苷处理后,RASSF1A mRNA的相对表达量逐渐增加,10和20μmol/L 5氮杂脱氧胞苷处理组,RASSF1A mRNA表达水平均明显高于阴性对照组(P0.01);且20μmol/L处理组明显高于5μmol/L处理组(P0.01)。结论:CNE2细胞RASSF1A基因甲基化可以被5氮杂脱氧胞苷逆转,且5氮杂脱氧胞苷可促进RASSF1A mRNA的表达。     

EBV 诱导鼻咽上皮细胞逃避老化期过程中端粒酶活化和p16INK4A失活

目的 探讨EB病毒诱导人鼻咽上皮细胞逃避老化期的分子机制。方法 SA—β—Gal染色法观察人鼻咽上皮细胞逃避老化期；PCR—银染法、S—P免疫组化法分别检测端粒酶活性和p16^INK4A、p21^WAF1/CIPI和p53的表达情况。结果 EB病毒感染组细胞表达SA—β—Gal活性下降，并表达端粒酶活性，而p16^INK4A蛋白不表达，但p21^WAF1/CIPI和p53蛋白表达无明显变化。结论 人鼻咽上皮细胞逃避老化期过程中EB病毒激活端粒酶和抑制p16^INK4A蛋白表达。     

Inactivation of RASSF2A by promoter methylation correlates with lymph node metastasis in nasopharyngeal carcinoma

RASSF2 can bind directly to K-Ras and function as a negative effector of Ras protein. RASSF2A is the only isoform of RASSF2 that contains CpG islands in its promoter and it has been reported to be inactivated by its promoter methylation in several human cancers. In the present study, we investigated the correlation of RASSF2A expression with its promoter methylation in nasopharyngeal carcinoma (NPC). Expression of RASSF2A was down-regulated in 80% (4/5) of NPC cell lines. Decreased RASSF2A expression was also observed in NPC primary tumors compared with normal nasopharyngeal epithelia. Promoter methylation of RASSF2A could be detected in all the RASSF2A-silenced cell lines (4/5) of the NPC cell lines and 50.9% (27/53) of primary tumors, but not in any of the normal epithelia. RASSF2A-methylated cases showed a significantly lower level of RASSF2A expression than unmethylated cases. Loss of RASSF2A expression can be greatly restored by the methyltransferase inhibitor 5-aza-dC in NPC cell lines. In addition, patients with methylated RASSF2A presented a higher frequency of lymph node metastasis (p < 0.05). Ectopic expression of RASSF2A in RASSF2A-silenced and -methylated NPC cell line CNE2 shows that RASSF2A could inhibit cell cycle progression, colony formation and cell migration, which provided further evidence that RASSF2A is a candidate tumor suppressor gene. In conclusion, RASSF2A, a candidate tumor suppressor gene (TSG), is frequently inactivated by its promoter methylation and this aberrant methylation correlates with lymph node metastasis in NPC.     

缺氧调控端粒酶活性及抑制鼻咽癌细胞增殖实验研究

目的探讨缺氧及siRNA沉默缺氧诱导因子-1α(hypoxia inducible factor-1α,HIF-1α)后对鼻咽癌细胞中端粒酶催化亚单位(telomerase catalytic subunit,hTERT)、细胞周期和化疗耐药的影响。方法采用三气培养箱对鼻咽癌细胞5-8F和CNE2进行缺氧处理(1%O2),蛋白质印迹法检测不同乏氧时相(0~72h)HIF-1α和hTERT蛋白的表达。将HIF-1α基因特异性siRNA分别转染鼻咽癌细胞株5-8F和CNE2,筛选出沉默效率最高的siRNA,实验分为未处理组(常氧)、未处理组(缺氧)、Negative-siRNA(缺氧)和HIF-1α-siRNA(缺氧),荧光定量PCR及蛋白质印迹检测瞬时转染后hTERT及HIF-1α的表达。流式细胞术(flow cytometry,FCM)分析缺氧或沉默HIF-1α后对细胞周期的影响。MTT法检测缺氧或沉默HIF-1α后,鼻咽癌细胞对顺铂(DDP)和5-氟尿嘧啶(5-FU)的化疗敏感性。结果缺氧处理0~72h后鼻咽癌5-8F细胞HIF-1α(F=37.147,P<0.001)和hTERT(F=70.069,P<0.001)蛋白的表达上调,差异有统计学意义。HIF-1α-siRNA对5-8F细胞瞬时转染率>98%。HIF-1α-siRNA组hTERT mRNA表达量为0.37±0.05,显著低于未处理组(缺氧)的1.00±0.00和Negative-siRNA(缺氧)的0.95±0.01,F=360.339,P<0.001;hTERT蛋白表达量为(0.27±0.05),显著低于未处理组(缺氧)0.54±0.00和Negative-siRNA组(缺氧)0.53±0.01,F=24.010,P<0.001。未处理组(缺氧)G0/G1期细胞比例明显增加(45.63±2.01)%,显著高于未处理组(常氧)的(26.75±1.28)%,P<0.001。5-8F细胞未处理组(常氧)对5-FU的IC50分别为(17.30±3.31)μg/mL,未处理组(缺氧)为(32.04±12.75)μg/mL,Negative-siRNA组为(33.90±0.87)μg/mL,HIF-1α-siRNA组为(13.72±2.36)μg/mL,F=3.704,P<0.001。5-8F细胞缺氧组对DDP的化疗敏感性也降低,沉默HIF-1α后,5-8F细胞对DDP的化疗敏感性明显提高。除细胞周期外,CNE2与5-8F的结果均一致。结论缺氧促使鼻咽癌细胞发生G1/S阻滞及化疗耐药,可能与上调hTERT表达,进而上调端粒酶活性有关;沉默HIF-1α显著逆转缺氧诱导的肿瘤耐药并下调端粒酶活性。     

鼻咽癌及癌前病变组织中p16蛋白表达的研究

目的观察p16蛋白在鼻咽癌组织中的表达状态,探讨其与鼻咽癌的发生、发展关系。方法应用S-P免疫组化法检测p16蛋白在50例鼻咽癌、20例鼻咽粘膜慢性炎组织中的表达。结果鼻咽癌p16蛋白表达率为24.0%,显著低于鼻咽粘膜慢性炎组(P<0.01)。角化性鳞癌p16蛋白的表达率明显高于分化型非角化性癌和未分化癌(P<0.05)。20例淋巴结转移阳性组中p16蛋白表达率显著低于14例阴性组(P<0.05)。结论p16蛋白的缺失可能涉及鼻咽癌的发生、发展过程,且与鼻咽癌的转移、组织学分型有关。     

亚砷酸诱导人鼻咽癌细胞中p16基因表达的研究

目的 研究亚砷酸( As2O3)诱导鼻咽癌(nasopharyngeal carcinoma,NPC)CNE- 2Z细胞株中抑癌基因p16的表达.方法 体外培养的CNE-2Z细胞分别加入不同浓度的亚砷酸,并作用于不同时间.用终浓度为2μmol/L、1 μmol/L、0.5μmol/L的As2O3加入鼻咽癌CNE-2...     

Loss of cyclin D1 and p16 expression correlates with local recurrence in nasopharyngeal carcinoma following radiotherapy.

BACKGROUND: The cyclin D1/p16/Rb pathway plays a critical role in tumorigenesis and each component of this pathway may be affected in various malignancies. The purpose of this study was to investigate the expression and prognostic significance of these proteins in nasopharyngeal carcinoma (NPC). PATIENTS AND METHODS: Sixty-five patients undergoing radiotherapy for NPC were analyzed. The expression of cyclin D1, p16 and pRb was evaluated with immunohistochemical analysis of archived pretreatment tumor materials and expression of these proteins was correlated with clinicopathological parameters. RESULTS: Positive expression of cyclin D1 was observed in 43 of 65 NPCs (66%). p16 and pRb inactivation was identified in 42 of 65 (65%) and four of 65 (6%) tumors, respectively. All but seven tumors (58 of 65, 89%) contained at least one alternation in the cyclin D1/p16/Rb pathway. Loss of cyclin D1 as well as p16 was closely related to local recurrence after radiotherapy for NPC (P = 0.015 and 0.047). No association between pRb expression and clinicopathological outcome was apparent. CONCLUSIONS: The study's results suggest that the cyclin D1/p16/Rb pathway plays an important role in NPC tumorigenesis. We also find that cyclin D1 and p16 protein levels in NPC may be of use clinically as a predictor of local tumor control.     

Telomerase immortalization of human mammary epithelial cells derived from a BRCA2 mutation carrier

A novel human mammary epithelial cell line, HME348, was established from benign breast tissue from a 44-year-old germ-line BRCA2 mutation carrier with a history of stage 1 breast cancer. Mutation analysis showed that the patient had a known 6872del4 BRCA2 heterozygous mutation. The human mammary epithelial cells passaged in culture exhibited cellular replicative aging as evidenced by telomere shortening, lack of telomerase activity, and senescence. Ectopic expression of telomerase (hTERT) reconstituted telomerase activity in these cells and led to the immortalization of the cells. When grown on glass, the majority of immortalized HME348 cells expressed ESA and p63 with a small population also expressing EMA. In three-dimensional Matrigel culture, HME348 cells formed complex branching acini structures that expressed luminal (EMA, CK18) and myoepithelial (p63, CALLA, CK14) markers. Three clones derived from this culture were also p63(+)/ESA(+)/EMA(+/-) on glass but formed similar acinar structures with both luminal and myoepithelial cell differentiation in Matrigel confirming the mammary progenitor nature of these cells. Additionally, the experimentally immortalized HME348 cells formed acini in cleared mammary fat pads in vivo. As this is the first report establishing and characterizing a benign human mammary epithelial cell line derived from a BRCA2 patient without the use of viral oncogenes, these cells may be useful for the study of BRCA2 function in breast morphogenesis and carcinogenesis.     

PinX1 regulation of telomerase activity and apoptosis in nasopharyngeal carcinoma cells

Background

Human interacting protein X1 (PinX1) has been identified as a critical telomerase inhibitor and proposed to be a putative tumor suppressor gene. Loss of PinX1 has been found in a large variety of malignancies, however, its function in inhibiting telomerase activity of tumor cells is not well documented. Here we show that PinX1 is essential for down-regulation telomerase activity of nasopharyngeal carcinoma.

Methods

Expression vectors of human PinX1 (pEGFP-C3-PinX1) and its small interfering RNA (PinX1-FAM-siRNA) were constructed and transfected into NPC. Their effects on mRNA of telomerase catalytic subunit (hTERT), telomerase activity, cell proliferation, cell migration, wound healing, cell cycles and apoptosis were examined using semi-quantitative RT-PCR, stretch PCR, MTT assay, Transwell, scratch assay and flow cytometry, respectively.

Results

Transfection of pEGFP-C3-PinX1 and PinX1-FAM-siRNA increased and reduced PinX1 mRNA by 1.6-fold and 70%, respectively. Over-expression of PinX1 decreased hTERT mRNA by 21%, reduced telomerase activity, inhibited cell growth, migration and wound healing ability, arrested cells in G0/G1 phase, and increased apoptotic index. In contrast, down-regulation of PinX1 did not alter the above characteristics.

Conclusions

PinX1 may play important roles in NPC proliferation, migration and apoptosis and has application potential in tumor-targeted gene therapy.     

ALDH1A1基因表达沉默对鼻咽癌细胞的增殖抑制作用

目的：探讨干扰乙醛脱氢酶1A1（ALDH1A1）基因表达后对鼻咽癌5-8F和CNE2细胞生长、增殖的影响。方法：构建ALDH1A1 siRNA 表达质粒稳定转染鼻咽癌5-8F和CNE2细胞,Western blot 检测干扰ALDH1A1基因蛋白表达水平。MTT、平板克隆、裸鼠成瘤实验检测干扰ALDH1A1基因前后鼻咽癌5-8F和CNE2细胞的增殖、克隆及成瘤能力。结果：与空白组和阴性对照组相比,干扰ALDH1A1表达后5-8F和CNE2细胞增殖、克隆及肿瘤形成能力明显受到抑制。结论：干扰ALDH1A1基因表达,可抑制鼻咽癌细胞的生长、增殖、克隆及成瘤能力。     

E1A基因对鼻咽癌细胞放射敏感性影响的初步实验研究

目的 探讨E1A基因对鼻咽癌细胞放射增敏作用及相关机制.从而为提高鼻咽癌放射治疗疗效提供实验依据.方法 经腺病毒介导,将E1A基因导入人鼻咽癌细胞系CNE2细胞.经RT-PCR鉴定,获得含E1A的阳性克隆.将未转染的CNE2细胞、转染对照空载体Ad-B-gal的CNE2细胞和转染Ad-E1A的CNE2细胞用6 MV X线分别照射0、2、4、6、 8 Gy后进行成克隆分析并绘制细胞存活曲线,计算放射增敏比.流式细胞术和RT-PCR检测转染前后的细胞周期分布以及wtp53表达情况.结果 转染后阳性克隆细胞RT-PCR结果说明E1A已整合到细胞基因组中并且稳定表达.细胞存活曲线结果显示转染E1A的CNE2细胞放射增敏比分别为1.37(D_0值比)、1.95(D_q值比)、1.46(SF_2值比).未转染及空载体转染后的CNE2细胞照射后细胞存活曲线分析结果显示无差异,D0D_qSF2值分别为1.57 Gy及1.53 Gy、1.82 Gy及1.78 Gy、0.89及0.82.流式细胞术显示细胞周期出现G_2+M期阻滞,RT-PCR结果显示E1A基因能提高wtp53的表达.结论 E1A基因能显著提高人鼻咽癌细胞的放射敏感性,其作用机制可能与E1A基因提高叭p53基因的表达和引起G2+M期阻滞有关.     

鼻咽癌组织中RASSF1A基因甲基化的研究

目的观察RASSF1A基因在鼻咽癌组织和慢性鼻咽炎的甲基化情况。方法采用甲基化特异性PCR技术检测16例鼻咽低分化未角化癌和10例鼻咽黏膜慢性炎组织中RASSF1A基因的甲基化。结果RASSF1A基因的高甲基化率在鼻咽癌组织中为93．75％（15／16）,在慢性鼻咽炎组织中为0,两组病例的RASSF1A基因高甲基化率差别显著,P〈0．005。结论RASSF1A基因在鼻咽癌组织中呈高甲基化,可能是影响鼻咽癌发生发展的抑癌基因之一。     

端粒酶逆转录酶在脐静脉内皮细胞耐受曲古抑菌素A诱导凋亡中的作用

目的观察曲古抑菌素A（TSA）对脐静脉内皮细胞及官颈癌细胞凋亡、端粒酶逆转录酶（hTERT）表达的影响,并探讨hTERT在脐静脉内皮细胞耐受TSA中的作用。方法磺酰罗丹明B （RSB）法检测药物动力学特征;流式细胞仪检测周期改变和凋亡;RT-PCR检测hTERT和p21^Waf1基因表达变化;免疫荧光结合流式细胞术检测hTERT蛋白表达变化;转染hTERT质粒后,PCR-TRAP- ELISA法检测转染细胞端粒酶活性;AnnexinV／PI检测转染细胞在TSA作用下的早期凋亡。结果在大剂量TSA作用脐静脉内皮细胞后,增殖抑制、周期阻滞,但凋亡并不显著;HeLa细胞在相同剂量的TSA作用下凋亡明显。脐静脉内皮细胞经TSA诱导后,hTERT表达上调,p21^Waf1则无明显变化;而HeLa细胞p21^Waf1表达上升,hTERT表达下降。转染显性负突变hTERT的脐静脉内皮细胞,其端粒酶活性显著低于对照组。TSA作用转染不同质粒的脐静脉内皮细胞的凋亡率与对照组差异有统计学意义。结论脐静脉内皮细胞可以耐受大剂量TSA诱导的凋亡,hTERT表达上调可能是脐静脉内皮细胞耐受TSA诱导凋亡的重要机制之一。     

Epstein-Barr virus infection and persistence in nasopharyngeal epithelial cells

Epstein-Barr virus（EBV） infection is closely associated with undifferentiated nasopharyngeal carcinoma（NPC）, strongly implicating a role for EBV in NPC pathogenesis; conversely, EBV infection is rarely detected in normal nasopharyngeal epithelial tissues. In general, EBV does not show a strong tropism for infecting human epithelial cells, and EBV infection in oropharyngeal epithelial cells is believed to be lytic in nature. To establish life-long infection in humans, EBV has evolved efficient strategies to infect B cells and hijack their cellular machinery for latent infection. Lytic EBV infection in oropharyngeal epithelial cells, though an infrequent event, is believed to be a major source of infectious EBV particles for salivary transmission. The biological events associated with nasopharyngeal epithelial cells are only beginning to be understood with the advancement of EBV infection methods and the availability of nasopharyngeal epithelial cell models for EBV infection studies. EBV infection in human epithelial cells is a highly inefficient process compared to that in B cells, which express the complement receptor type 2（CR2） to mediate EBV infection. Although receptor（s） on the epithelial cell surface for EBV infection remain（s） to be identified, EBV infection in epithelial cells could be achieved via the interaction of glycoproteins on the viral envelope with surface integrins on epithelial cells, which might trigger membrane fusion to internalize EBV in cells. Normal nasopharyngeal epithelial cells are not permissive for latent EBV infection, and EBV infection in normal nasopharyngeal epithelial cells usually results in growth arrest. However, genetic alterations in premalignant nasopharyngeal epithelial cells, including p16 deletion and cyclin D1 overexpression, could override the growth inhibitory effect of EBV infection to support stable and latent EBV infection in nasopharyngeal epithelial cells. The EBV episome in NPC is clonal in nature, suggesting that NPC develops from a single     

Phenotypic alterations induced by the Hong Kong-prevalent Epstein-Barr virus-encoded LMP1 variant (2117-LMP1) in nasopharyngeal epithelial cells

Epstein-Barr virus (EBV) is closely associated with nasopharyngeal carcinoma (NPC), a common cancer in Hong Kong. The EBV-encoded LMP1 protein is believed to play an important role in cell transformation. We have previously identified a prevalent LMP1 variant (2117-LMP1) that is expressed in 86% of primary NPC in Hong Kong. In this study, the biologic phenotypes induced by 2117-LMP1 were compared with those of the prototypic B95.8-LMP1 in an immortalized nasopharyngeal epithelial cell line, NP69. The 2117-LMP1 could induce cell proliferation and resistance to apoptosis induced by growth factor deprivation. Expression of 2117-LMP1 also suppressed expression of p16, p21 and Bax but induced expression of CDK2 and A20. Compared with B95.8-LMP1, 2117-LMP1 could induce a higher migration ability in NP69 cells but was less efficient in inducing morphologic changes, anchorage-independent growth and cell invasion. Relatively weaker ability of 2117-LMP1 than B95.8-LMP1 in upregulation of vimentin, VEGF and MMP9 as well as in downregulation of E-cadherin was observed. 2117-LMP1 could activate higher level of NF-kappaB activity in HEK 293 cells than B95.8-LMP1. The present study supports a role of 2117-LMP1 in NPC development by enhancing cell proliferation, cell death inhibition and migration in premalignant nasopharyngeal epithelial cells. Furthermore, our study reveals significant functional differences between 2117-LMP1 and the prototypic B95.8-LMP1. Our results provide insights into the pathologic significance of this prevalent LMP1 variant, 2117-LMP1, in the development of NPC in the Hong Kong population.     

Telomerase activity is frequently found in metaplastic and malignant human nasopharyngeal tissues

Telomerase is a specialized ribonucleoprotein polymerase that directs the synthesis of telomere repeats at chromosome ends. Accumulating evidence has indicated that telomerase is stringently repressed in normal human somatic tissues but reactivated in cancers and immortal cells, suggesting that reactivation of telomerase plays an important role in carcinogenesis. In this study, the status of telomerase activity in diseased human nasopharyngeal lesions was determined by the telomeric repeat amplification protocol (TRAP). Fifty-four patients participated including 17 inflammation or hyperplasia, eight with squamous metaplasia, and 29 with different stages of carcinomas. Telomerase activity was detected in 1 of 17 (5.9%) inflammatory or lymphoid hyperplastic tissues, 3 of 8 (37.5%) squamous metaplastic, and 25 of 29 (86.2%) carcinoma tissues. The differences in telomerase expression in these groups is statistically significant (P < 0.001). Levels of telomerase activity correlated with tumour stage (P = 0.024). These results suggest that telomerase reactivation plays a role in the carcinogenesis of nasopharyngeal cancer. Since telomerase activity is found in the majority of nasopharyngeal cancers and a subset of metaplasia, this enzyme may be served as a reference to monitoring the status of abnormal nasopharyngeal tissues.