[Telomerase inhibitor]

Human normal somatic cells and tissues have undetectable or very weak telomerase activity and shorten telomere size at each cell division resulting in a limited proliferative life span. Human germ tissues and most tumor tissues have telomerase activity and maintain telomere size during cell proliferation resulting in unlimited growth. Telomerase is expected to be a new target for cancer chemotherapy. Cultured tumor cells are shown to die after losing telomerase activity.

Anti-Ca2+, Mg2+-dependent endonuclease antibody detects specifically a class of chromatin-bound endonuclease

A polyclonal antibody against purified bull seminal plasma Ca2+, Mg2+-dependent endonuclease was raised in a rabbit. The antibody specifically cross-reacted with chromatin-bound Ca2+, Mg2+-dependent endonucleases from bovine thymus, human placenta, and bovine, rat and mouse liver in addition to the bovine seminal enzyme. The antibody did not cross-react with other endonucleases examined, including the acid-endonucleases from bovine thymus and liver, porcine spleen DNase II, micrococcal nuclease, and bovine pancreas DNase I, a known Ca2+ and Mg2+ requiring endonuclease. The present results indicate that this antibody specifically recognizes a class of so-called Ca2+, Mg2+-dependent endonuclease, which is localized in cell nuclei of various tissues and is probably involved in chromatin degradation during apoptosis. The antibody will be used to study the functional role of this class of endonuclease.

Simple high-performance liquid chromatographic method for assaying cysteinesulfinic acid decarboxylase activity in rat tissue

A simple method is described for determining cysteinesulfinic acid decarboxylase activity in rat tissue. Enzyme preparations from the liver, kidney and brain were incubated with cysteinesulfinic acid substrate in the presence of pyridoxal 5-phosphate. The enzyme product, hypotaurine, was derivatized with o-phthalaldehyde and separated by reversed-phase high-performance liquid chromatography (Capsel Pack AG 120A C18 column) using a mobile phase of acetonitrile-water (20:80, v/v) containing 50 mM sodium phosphate buffer (pH 6.0) and detected using a fluorometer (excitation at 360 nm and emission at 455 nm). The method described is reproducible and sensitive enough to determine the activity of cysteinesulfinic acid decarboxylase activity in the liver, kidney and brain. This assay was subsequently used to evaluate the effect of dietary proteins whose sulfur amino acid contents differ. Consistent with reported data, compared to casein and whole egg protein, a dietary protein low in sulfur amino acid (soybean protein) increased cysteinesulfinic acid decarboxylase activity in the liver and kidney. This method is therefore applicable to studies on the dietary regulation of cysteinesulfinic acid decarboxylase in rat tissue.

Significance of telomerase activity in the diagnosis of small differentiated hepatocellular carcinoma

Precise diagnosis of well-differentiated hepatocellular carcinoma (HCC) is sometimes difficult to establish. Telomerase activity was examined by telomeric-repeat-amplification protocol (TRAP) in 37 HCC nodules smaller than 3 cm in diameter, including 24 fine-needle-aspiration biopsy specimens, 22 non-tumor chronic-liver-disease tissues (9 chronic hepatitis and 13 liver cirrhosis) and 3 normal liver tissues. Telomerase activity was assayed by serially diluted samples and quantitated by using an internal telomerase assay standard (ITAS). Telomerase activity was detected in all HCC and in 11 of 22 non-tumor chronic-liver-disease tissues. Normal liver samples had undetectable telomerase activity. Cut-off level of telomerase activity for its practical usage in HCC diagnosis was tentatively set for 0.6 microg liver protein/assay at 10-cell equivalent activity of a gastric-cancer cell line, MKN-1. This level was twice the highest activity in non-tumor chronic liver disease therefore, telomerase activity in all non-tumor liver samples was below this level. The telomerase-positive incidence exceeding this cut-off level was 73% (11/15) in well-differentiated HCC, 94% (16/17) in moderately differentiated HCC and 100% (5/5) in poorly differentiated HCC. Well-differentiated HCC showed low positivity by other diagnostic markers. 21% by AFP, 0% by PIVKA-II and 13% by angiography. The detection of telomerase activity may thus be a useful additional tool for precise and early diagnosis of small differentiated HCC, even when diagnosis is inconclusive by conventional techniques.

Assay method for femtogram order of Ca2+, Mg(2+)-dependent endonuclease

A sensitive method for the assay of Ca2+, Mg(2+)-dependent endonuclease was developed. The assay procedure is composed of two parts: (i) microscale endonuclease digestion of highly polymerized calf thymus DNA and (ii) the quantification of DNA breaks by measuring the activation of poly(ADP-ribose) polymerase, which is known to be activated proportionally to the number of nicks and ends of DNA added in the reaction mixture. This method was approximately 10(5)-fold more sensitive than a conventional DNase assay detecting acid-soluble DNA formation and, thus, the activity of 20 to 100 fg of purified bull seminal Ca2+, Mg(2+)-dependent endonuclease could be reliably measured. Ca2+ and Mg2+ requirements and the response to histone H2B of the endonuclease were also demonstrated by this method. Using this method, the assay of a very small amounts of Ca2+, Mg(2+)-dependent endonuclease in crude extracts of calf thymus chromatin was possible. This method may be applied to other types of endonucleases by modifying the mixture for endonuclease reaction.

A voltage- and K+-dependent K+ channel from a membrane fraction enriched in contractile vacuole of Dictyostelium discoideum

We obtained a membrane fraction enriched in the contractile vacuole by aqueous-polymer two-phase partitioning and its channel activities were analysed by incorporating it into artificial planar lipid bilayers. In asymmetrical KCl solutions (cis, 300 mM/100 mM, trans), we observed single-channel currents of a highly K(+)-selective channel with slope conductance of 102 pS and reversal potential of -20.4 mV, which corresponded to PK+/PCl- = 7. They showed bursts separated by infrequent quiescent periods. At 0 mV the mean open time was 2.0 ms. Among monovalent cations, Na+ and Li+ were impermeable, whereas Rb+ showed permeability equivalent to that of K+, although the unitary conductance was apparently reduced when the current flowed from the Rb+ containing side, suggesting that Rb+ is a permeant blocking ion. The open probability within bursts remained constant at approx.0.6 as long as the holding potential was positive on the cis side with respect to the trans side, but it decreased to 0 at negative potential. This channel was blocked by submillimolar concentrations of quinine and 30 mM TEA+. The open probability-voltage relationship showed a striking dependency on the KCl concentration on either side. This channel may play a role in water transport in this organelle.

Significance of telomerase activity in the diagnosis of small differentiated hepatocellular carcinoma

Precise diagnosis of well-differentiated hepatocellular carcinoma (HCC) is sometimes difficult to establish. Telomerase activity was examined by telomeric-repeat-amplification protocol (TRAP) in 37 HCC nodules smaller than 3 cm in diameter, including 24 fine-needle-aspiration biopsy specimens, 22 non-tumor chronic-liver-disease tissues (9 chronic hepatitis and 13 liver cirrhosis) and 3 normal liver tissues. Telomerase activity was assayed by serially diluted samples and quantitated by using an internal telomerase assay standard (ITAS). Telomerase activity was detected in all HCC and in 11 of 22 non-tumor chronic-liver-disease tissues. Normal liver samples had undetectable telomerase activity. Cut-off level of telomerase activity for its practical usage in HCC diagnosis was tentatively set for 0.6 microg liver protein/assay at 10-cell equivalent activity of a gastric-cancer cell line, MKN-1. This level was twice the highest activity in non-tumor chronic liver disease therefore, telomerase activity in all non-tumor liver samples was below this level. The telomerase-positive incidence exceeding this cut-off level was 73% (11/15) in well-differentiated HCC, 94% (16/17) in moderately differentiated HCC and 100% (5/5) in poorly differentiated HCC. Well-differentiated HCC showed low positivity by other diagnostic markers. 21% by AFP, 0% by PIVKA-II and 13% by angiography. The detection of telomerase activity may thus be a useful additional tool for precise and early diagnosis of small differentiated HCC, even when diagnosis is inconclusive by conventional techniques.

Mechanisms of thrombocytopenia induced by interferon therapy for chronic hepatitis B

To clarify the mechanisms of thrombocytopenia observed in patients with chronic hepatitis B treated with interferon. We studied six patients with chronic active hepatitis B who received intramuscular injections of natural interferon-alpha (3 or 5 million IU/ day) for 4 weeks. Peripheral blood platelet counts, bone marrow findings, and platelet kinetics, determined using 111In-labeled platelets, were analyzed. Platelets decreased significantly 1 week after the beginning of treatment and remained decreased until the completion of treatment. The number of nucleated cells and megakaryocytes in bone marrow decreased in three of five patients studied during treatment. The kinetic study showed platelet survival time to be 8.1 +/- 1.3 days (range, 5.8-10.0). One day after platelet injection, platelets accumulated predominantly in the splenic area in all patients, whereas hepatic accumulation was predominant 7 days after injection in three of the six patients. Thrombocytopenia during interferon treatment arises from the inhibition of stem cell proliferation and differentiation in the bone marrow and from the capture of platelets by the liver.

Cell cycle-dependent activation of telomerase in naturally synchronized culture of a true slime mold, Physarum polycephalum

Telomeres of Physarum plasmodia did not shorten with numerous repeats of nuclear division, and an apparent activity of telomerase was detected in this organism. In naturally synchronized culture of Physarum plasmodia, an evident activation of telomerase was observed at the late S-phase, just prior to the completion of in vivo DNA replication, and the low telomerase activity was detected throughout the cell cycle. In the nuclei isolated from different phases of synchronized plasmodia, a higher activity of telomerase was also observed at late S-phase. These results clearly show the existence of a cell cycle-dependent regulatory mechanism of telomerase activity in growing, naturally synchronized cells.

Further cholinergic aspects of carotid body chemotransduction of hypoxia in cats

From the 1930s into the 1970s, the role of acetylcholine (ACh) in the carotid body's chemotransduction of hypoxia was debated. Since the late 1970s, the issue has been pursued only intermittently or not at all. The purpose of this study was to test again with a new preparation the hypothesis that ACh is an excitatory neurotransmitter in the cat carotid body's chemotransduction of hypoxia. We tested the effect of the specific nicotinic blocker mecamylamine and the muscarinic blocker of all five muscarinic receptors, atropine. We further tested the effects of M1 and M2 muscarinic-receptor blockers. The carotid body region was selectively perfused with hypoxic Krebs-Ringer bicarbonate (KRB) solutions that were blocker free or contained varying doses of the blockers. Both mecamylamine and atropine reduced the response to hypoxic KRB in a dose-related manner. The M2 muscarinic-receptor blockers gallamine and AFDX 116 increased the response to hypoxic KRB, whereas the M1 muscarinic-receptor blocker pirenzepine reduced the response to hypoxic KRB. These data are consistent with an excitatory role for ACh in the carotid body chemotransduction of hypoxia in the cat.

ATP-sensitive anion channel from rat brain synaptosomal membranes incorporated into planar lipid bilayers

An anion channel was incorporated from rat brain synaptic plasma membrane fractions into planar lipid bilayers. The single-channel conductance was found to be 48.5 pS in choline-Cl solution (300 microM cis/100 microM trans). The anion selectivity of the channel was rather low (PCl/Pcholine = 1.7). The gating rate of the channel did not change with membrane potential over the range of -50 mV to 50 mV. Several drugs, which are known as inhibitors of anion channels, were found to be efficient inhibitors for the synaptosomal anion channel. 4-Acetoamino-4'-isothiocyanostilbene-2,2'-disulfonic acid, ethacrynic acid, indanyloxyacetic acid, and 5-nitro-2-(3-phenylpropylamino) benzoic acid inhibited the channel from the cis side of the membrane, corresponding to the cytoplasmic side of the plasma membrane. We found that the channel is regulated by intracellular ATP at millimolar concentrations. Other nucleotides, ADP and GTP, inhibited the channel as well. Glibenclamide, which is known as an inhibitor of an ATP-regulated potassium channel, inhibited the channel at micromolar concentrations from the trans side of the membrane. It is likely that the synaptosomal anion channel is a member of the ATP-binding cassette superfamily.

Effects of interferon alpha 2a on incidence of hepatocellular carcinoma in chronic active hepatitis without cirrhosis. Hepatitis Treatment Study Group

To determine the incidence of hepatocellular carcinoma among patients with chronic hepatitis C who received interferon (IFN) therapy, 63 patients with chronic hepatitis C who underwent IFN therapy (IFN alpha 2a 9 x 10(6) IU daily for 2 weeks and followed 9 x 10(6) IU three times weekly for 14 weeks) from January to December 1992, were studied. Selection criteria were as follows: within six months before IFN therapy patients were diagnosed with chronic active hepatitis without cirrhosis by hepatic histological examination, and were hepatitis C virus antibody positive. Furthermore, patients had records of follow-up liver function tests (once a month) for more than six months after IFN therapy completion, and of ultrasound scanning (once in three to four months) before and for at least more than six months after the therapy completion. An average period of observation was 2.7 years (0.6 to 3.8 years). Twenty five of 63 patients (39.7%) returned to normal values of serum ALT, whereas 38 of 63 (60.3%) still showed abnormal values at six months after IFN therapy completion. Nine of 63 (14.2%) and 6/63 (9.5%) developed cirrhosis and hepatocellular carcinoma, respectively. All patients who developed cirrhosis and hepatocellular carcinoma were from those (n = 38) that showed abnormal ALT values after therapy completion. The five of six patients that progressed to hepatocellular carcinoma were associated with cirrhosis. No patients who returned to normal ALT values developed hepatocellular carcinoma during the period of observation. These results suggest that IFN therapy is effective to prevent the development of hepatocellular carcinoma.

Thiadiazole derivatives: highly potent and selective inhibitors of human immunodeficiency virus type 1 (HIV-1) replications in vitro

We have recently reported that thiadiazole (TDA) derivatives are highly potent inhibitors of human immunodeficiency virus type 1 (HIV-1) replication. These compounds belong to the family of nonnucleoside reverse transcriptase inhibitors (NNRTIs). In an attempt to develop more effective and pharmacologically favorable compounds, novel TDA derivatives have been synthesized and examined for their anti-HIV-1 activity in vitro. Among them, RD4-2217 was found to be the most potent inhibitor of HIV-1 replication. It inhibited replication of the HTLV-IIIB strain in MT-4 cells at a concentration of 6 nM. RD4-2217 was also inhibitory to clinical isolates and zidovudine-resistant mutants of HIV-1. The combination of RD4-2217 with zidovudine or the protease inhibitor A-75925 synergistically inhibited HIV-1 replication. Studies on the emergence of drug-resistant mutants revealed that, although much higher concentrations (1-10 microM) were required, RD4-2217 completely suppressed the breakthrough of HIV-1 in the supernatants during long-term culturing of infected cells. Furthermore, RD4-2217 at low concentrations (10 or 100 nM), in combination with zidovudine, also completely inhibited viral breakthrough. In addition, RD4-2217 had lower lipophilicity and improved protein binding as compared to its congener RD4-2024 and loviride. These results suggest that RD4-2217, one of the TDA derivatives, is worth pursuing as a candidate drug for the treatment of HIV-1 infections.

A rapid, useful and quantitative method to measure telomerase activity by hybridization protection assay connected with a telomeric repeat amplification protocol

Telomerase, a ribonucleoprotein enzyme, is expected to be a new marker for cancer diagnosis. TRAP (the telomeric-repeat amplification protocol) developed by Kim et al. is a sensitive method to detect telomerase activity. Telomerase activity is detected by TRAP in most malignant cells in vivo and in vitro, but it is not found, or found only in very low amounts, in normal somatic cells and tissues. TRAP and its modified protocols are, however, not always suitable for measuring the activity of a large number of clinical samples to diagnose cancer, because they generally require a time-consuming detection step such as gel electrophoresis with radioactive materials. To improve the procedure for mass diagnosis, we applied a hybridization protection assay (HPA) to replace the detection step. HPA, which employs an acridinium-ester-labelled probe, is radioactivity-free, easy to handle without electrophoresis, quick, and applicable to a quantitative format. In this work we have established and demonstrated the advantages of TRAP/HPA. The telomerase activity of various primary and established cells, differentiating cancer cells, and normal and tumour colorectal and liver tissues was quantitatively analysed by TRAP/HPA. The results indicate that HPA combined with TRAP is a rapid and simple method, easy to handle and quantify, for the clinical diagnosis of cancer.

Reciprocal responses to dietary diacylglycerol of hepatic enzymes of fatty acid synthesis and oxidation in the rat

The activities of hepatic enzymes of fatty acid synthesis and oxidation were compared in rats fed on diacylglycerol and triacylglycerol. In the first trial, rats were fed on diacylglycerol or triacylglycerol (rapeseed oil) for 14 d. The diacylglycerol preparation contained 65.2 g and 32.6 g fatty acids/100 g total fatty acids as 1,3-species and 1,2-species respectively. Fatty acid compositions of these dietary lipids were similar. Dietary acylglycerols were added to experimental diets to provide the same amounts of fatty acids (93.9 g/kg diet). Dietary diacylglycerol compared with triacylglycerol significantly reduced the concentrations of serum and liver triacylglycerol. The activities of enzymes of fatty acid synthesis (fatty acid synthetase, glucose 6-phosphate dehydrogenase (EC 1.1.1.49) and malic enzyme (EC 1.1.1.40)) were significantly lower in rats fed on diacylglycerol than in those fed on triacylglycerol. In contrast, the rates of mitochondrial and peroxisomal oxidation of palmitoyl-CoA in liver homogenates were higher in rats fed on diacylglycerol than in those fed on triacylglycerol. In the second trial, varying amounts of dietary triacylglycerol were replaced by diacylglycerol while the dietary fatty acid content was maintained (93.9 g/kg diet). After 21 d of the feeding period the significant reductions in serum and liver triacylglycerol levels were confirmed in groups of rats fed on the diets in which diacylglycerol supplied more than 65.8 g fatty acids/kg diet (65.8 and 93.9 g/kg). Reductions in the activities of enzymes of fatty acid synthesis and increases in palmitoyl-CoA oxidation rates by both mitochondrial and peroxisomal pathways were also apparent when diacylglycerol replaced triacylglycerol in diets to supply more than 65.8 g fatty acid/kg. Increasing dietary levels of diacylglycerol also progressively increased the activities of enzymes involved in the beta-oxidation pathway (carnitine palmitoyltransferase (EC 2.3.1.21), acyl-CoA dehydrogenase (EC 1.3.99.3), acyl-CoA oxidase (EC 1.3.3.6), enoyl-CoA hydratase (EC 4.2.1.17), 3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35), 2,4-dienoyl-CoA reductase (EC 1.3.1.34) and delta 3, delta 2-enoyl-CoA isomerase (EC 5.3.3.8)) in the liver. These results suggest that alteration of fatty acid metabolism in the liver is a factor responsible for the serum triacylglycerol-lowering effect of dietary diacylglycerol.

Development and exacerbation of oral lichen planus during and after interferon therapy for hepatitis C

Oral lichen planus (OLP) is frequently seen in patients with hepatitis C virus (HCV) infection. To clarify the role of HCV in OLP pathogenesis, we investigated the occurrence and progression of oral lesions in chronic hepatitis C patients treated with interferon. Oral surgeons examined 24 hepatitis C patients (15 men, nine women; mean age 48.1 years) for oral lesions before, during and after interferon (IFN) treatment. OLP was observed in 16.7% (4/24). Two patients had OLP before treatment, one during and one after treatment. Those who developed OLP during or after treatment had neither improvement nor disappearance of OLP even when serum HCV RNA became negative. Leucoplakia was seen in four patients before treatment and oral cancer in one patient 6 months after completing treatment. OLP can occur, exacerbate and persist during IFN treatment for hepatitis C, even when serum HCV RNA becomes negative. The present study suggested that OLP pathogenesis in hepatitis C is due to host factors induced by HCV infection rather than direct HCV participation. Treating physicians should be aware of OLP occurrence or exacerbation by IFN treatment with hepatitis C patients, but IFN therapy is not necessarily contraindicated in these patients.

Telomerase in hepatocellular carcinogenesis

Despite the recent advances in diagnostic techniques of HCC, diagnosis of HCC is still difficult and ambiguous when HCC is small and of the well differentiated type. The results presented here demonstrated that strong telomerase activity was frequently detected in HCC irrespective of the stage or size of the nodules but neither in non-tumor diseased liver nor in normal liver. Telomerase activity determination can be a useful additional tool for the diagnosis of early well-differentiated HCC.

Activity of hepatic fatty acid oxidation enzymes in rats fed alpha-linolenic acid

The activity of hepatic fatty acid oxidation enzymes in rats fed linseed and perilla oils rich in alpha-linolenic acid (alpha-18:3) was compared to that in rats fed safflower oil rich in linoleic acid (18:2) and a saturated fat (palm oil). Palm and safflower oils were essentially devoid of alpha-18:3. The palmitoyl-CoA oxidation rates both in mitochondrial and peroxisomal pathways in liver homogenates were significantly higher in rats fed linseed oil than in those fed palm and safflower oils. Among rats fed diets containing palm oil, safflower oil, fat mixtures composed of safflower and perilla oils (2:1, w/w and 1:2, w/w), and perilla oil, mitochondrial and peroxisomal fatty oxidation rates increased with increasing dietary levels of perilla oil. Compared to palm and safflower oils, dietary alpha-18:3 either in the form of linseed or perilla oils profoundly increased the activity of carnitine palmitoyltransferase, acyl-CoA oxidase, 3-ketoacyl-CoA thiolase, and 2,4-dienoyl-CoA reductase. Smaller but significant increases by dietary alpha-18:3 of the activity of acyl-CoA dehydrogenase, enoyl-CoA hydratase, and delta 3, delta 2-enoyl-CoA isomerase were also observed. Unexpectedly, dietary alpha-18:3 greatly reduced the activity of 3-hydroxy-acyl-CoA dehydrogenase. Compared to palm oil, dietary polyunsaturated fats significantly reduced the activity of fatty acid synthetase and glucose-6-phosphate dehydrogenase to the same levels. The activity of pyruvate kinase was significantly higher in rats fed palm oil than in those fed polyunsaturated fats. The extent of reduction was more prominent with polyunsaturated fats containing alpha-18:3 than with safflower oil devoid of alpha-18:3. Thus, compared to linoleic acid and saturated fatty acids, dietary alpha-18:3 caused characteristic changes in the activity of hepatic enzymes in fatty acid and glucose metabolism in rats.

Telomerase activity in human breast cancer and benign breast lesions: diagnostic applications in clinical specimens, including fine needle aspirates

We analysed telomerase activity in normal, benign and malignant breast tissues and in fine needle aspirates by a PCR-based assay. The tissue samples we used in this assay consisted of 20 cryostat sections, 10 microns thick, from each breast biopsy. This method was used to obtain effective extraction from small samples and to confirm the histological identity of the specimen by microscopical examination of serial sections. Fifty-two of 71 breast carcinomas were positive for telomerase activity, and the intensity of this was strong in most cases, whereas all 6 samples of normal breast tissue and 17 of fibrocystic disease were negative and only 1 of 15 fibroadenomas was positive. Invasive ductal carcinomas were more frequently positive than invasive lobular carcinomas. There was no correlation of telomerase activity with tumour size or the occurrence of lymph node metastasis. Evaluation of our assay system showed that a signal of telomerase activity was detectable in extracts from single cryostat sections (< 1 mm2) of a cancer specimen and from as few as 4 cells of a human breast cancer cell line. On the basis of the above data, we applied this assay to fine needle aspirates of breast lesions. Ten of 15 aspirates which had been cytopathologically diagnosed as cancer were strongly positive, while 26 of 29 benign aspirates were totally negative and the remaining 3 showed only borderline activity. In 3 cases, the telomerase result could have helped establish a diagnosis when the cytological observations were inconclusive. Our results indicate that this sensitive assay could become a useful new modality for supplementing microscopic cytopathology in the detection of cancer cells in small tissue biopsies and fine needle aspirates.

Telomerase activity in normal human epithelial cells

Telomerase activity is found in most cancer tissues and many immortalized cell lines as well as in germ line cells but it is generally undetected in normal human somatic tissues. There is weak telomerase activity in some cell types of hematopoietic lineage in which a stem cell-like subpopulation may exist. Likewise, physiologically regenerating somatic tissues and organs such as skin, small intestine, and most other epithelia of the human body are supposed to contain similar cell lineages to maintain their renewal throughout the life span of individuals. It is therefore of interest whether telomerase activity is present in physiologically regenerating epithelial cells. Telomerase activity was detected, though very weakly, in cultured normal epidermal keratinocytes and at higher levels in a subpopulation that adhere rapidly on collagen IV-coated culture dishes. No telomerase activity was detected in a subpopulation that was less adherent on the coated dishes. The rapidly adherent subpopulation of keratinocytes was enriched in small proliferating cells with macrocolony forming potential. It was also passaged through more generations in culture, and expressed integrin beta 1 at higher levels than the less adherent subpopulation. Telomerase activity was similarly found in ectocervical keratinocytes as well as in simple endocervical epithelial cells. These findings provide the evidence of a telomerase-positive population among physiologically regenerating normal human epithelial cells. The identity of the telomerase-positive cells remains to be defined.