A persistent variant telomere sequence in a human pedigree.

The telomere sequence, TTAGGG, is conserved across all vertebrates and plays an essential role in suppressing the DNA damage response by binding a set of proteins termed shelterin. Changes in the telomere sequence impair shelterin binding, initiate a DNA damage response, and are toxic to cells. Here we identify a family with a variant in the telomere template sequence of telomerase, the enzyme responsible for telomere elongation, that led to a non-canonical telomere sequence. The variant is inherited across at least one generation and one family member reports no significant medical concerns despite ~9% of their telomeres converting to the novel sequence. The variant template disrupts telomerase repeat addition processivity and decreased the binding of the telomere-binding protein POT1. Despite these disruptions, the sequence is readily incorporated into cellular chromosomes. Incorporation of a variant sequence prevents POT1-mediated inhibition of telomerase suggesting that incorporation of a variant sequence may influence telomere addition. These findings demonstrate that telomeres can tolerate substantial degeneracy while remaining functional and provide insights as to how incorporation of a non-canonical telomere sequence might alter telomere length dynamics.

TPP1 promoter mutations cooperate with TERT promoter mutations to lengthen telomeres in melanoma.

Overcoming replicative senescence is an essential step during oncogenesis, and the reactivation of TERT through promoter mutations is a common mechanism. TERT promoter mutations are acquired in about 75% of melanomas but are not sufficient to maintain telomeres, suggesting that additional mutations are required. We identified a cluster of variants in the promoter of ACD encoding the shelterin component TPP1. ACD promoter variants are present in about 5% of cutaneous melanoma and co-occur with TERT promoter mutations. The two most common somatic variants create or modify binding sites for E-twenty-six (ETS) transcription factors, similar to mutations in the TERT promoter. The variants increase the expression of TPP1 and function together with TERT to synergistically lengthen telomeres. Our findings suggest that TPP1 promoter variants collaborate with TERT activation to enhance telomere maintenance and immortalization in melanoma.

Phenotypic Diversity Caused by Differential Expression of SFTPC-Cre-Transgenic Alleles.

Type II alveolar epithelial cells (AEC2s) play an essential role in the function and maintenance of the pulmonary epithelium. Several transgenic mice have been developed to study the function of these cells in vivo by using the human SFTPC promoter to drive expression of Cre recombinase. The precise activity of each of these transgenic alleles has not been studied, and previous reports suggest that their activity can depend on breeding strategies. We bred mice with a conditional allele of the essential telomere capping protein TRF2 with two different SFTPC-Cre-transgenic strains and observed opposite phenotypes (100% lethality vs. 100% viability). We characterized the Cre recombinase activity in these two transgenic lines and found that the contrasting phenotypes were driven by difference in embryonic expression of the two transgenes, likely due to position effects or differences in the transgenic constructs. We also tested if SFTPC-Cre activity was dependent on maternal or paternal inheritance. When paternally inherited, both SFTPC-Cre alleles produced offspring with constitutive reporter activity independent of the inheritance of the Cre allele, suggesting that Cre recombinase was expressed in the male germline before meiosis. Immunohistochemical analysis of the testis showed reporter activity during spermatogenesis. Analysis of single-cell RNA sequencing data from murine and human testis demonstrated SFTPC expression uniquely during human spermatogenesis, suggesting that use of the human promoter in these constructs is responsible for male germline activity. Our data highlight the importance of careful analysis of transgenic allele activity and identify an SFTPC-Cre allele that is useful for panepithelial targeting in the mouse.

Efficacy and safety of entecavir versus tenofovir treatment in chronic hepatitis B patients: A randomized controlled trial.

AIM: Entecavir (ETV) and tenofovir disoproxil fumarate (TDF) are considered among the most potent antiviral agents for the treatment of chronic hepatitis B infection. We aimed to compare treatment efficacy and safety of ETV and TDF in nucleoside-naïve chronic hepatitis B patients. METHODS: Inclusion criteria were compensated chronic hepatitis B patients who were either hepatitis B e antigen (HBeAg)-positive or HBeAg-negative. Exclusion criteria were co-infection with hepatitis C virus and/or HIV, concurrent malignancy, and decompensated cirrhosis. Virological, biochemical, and serological end-points at week 96 and 144 were compared. Of 400 patients, 200 patients received ETV and 200 received TDF. RESULTS: There were no significant differences between the two groups in baseline characteristics including age (41.6 ± 11.5 vs. 41.2 ± 11.6, mean baseline hepatitis B virus DNA (5.91 ± 1.79 vs. 5.94 ± 1.68 log10 IU/mL), mean baseline alanine aminotransferase (68.1 ± 64.1 vs. 76.8 ± 79.8 U/L), and cirrhosis (15.5% vs. 14.5%). At week 144 of treatment, 91 and 94% of the ETV and TDF groups, respectively, achieved undetectable hepatitis B virus DNA. In HBeAg-positive patients, HBeAg seroconversion could be achieved in 27.4% and 33.7% at week 144 for ETV and TDF groups, respectively. Quantitative hepatitis B surface antigen dropped significantly over 144 weeks of treatment period but only 1.0 to 1.5% experienced hepatitis B surface antigen loss. Safety profiles were consistent with previous reports of monotherapy. CONCLUSION: Both ETV and TDF showed potent antiviral activity against hepatitis B. Either ETV or TDF can be recommended as a treatment of choice for patients with chronic hepatitis B. Both drugs were safe and well tolerated.

Hepatocellular carcinoma screening and surveillance in 2293 chronic hepatitis B patients in an endemic area.

AIM: To determine the role of screening and surveillance of hepatocellular carcinoma (HCC) in treatment-naïve chronic hepatitis B (CHB) patients. METHODS: We recruited 2293 CHB patients (both males and females; aged 20-65 years). All patients were screened and underwent surveillance using abdominal ultrasonography (AUS) and serum alpha-fetoprotein (AFP) assay every 6 mo. The diagnosis, staging and treatment of HCC followed the American Association for the Study of Liver Diseases practice guidelines and the Barcelona Clinic Liver Cancer guidelines. The exclusion criteria included: decompensated cirrhosis; a history of any cancer in the last 5 years; previous antiviral treatment for CHB; concurrent infection with hepatitis C virus or human immunodeficiency virus; a Karnofsky Performance Status score < 60%; or any medical condition preventing eligibility to complete the protocol. The prevalence and incidence rates of HCC were determined; survival rates were calculated at 3-year post HCC diagnosis. The sensitivity and specificity were calculated on a per-patient basis. RESULTS: Among 2293 treatment-naïve CHB patients, seven cases had HCC at initial screening, giving a prevalence rate of 305 per 100000 persons; 3.3% were diagnosed with liver cirrhosis, all of which were Child-Pugh class A. With a median follow-up time of 42 (range, 3-48) mo, 10 additional cases were diagnosed with HCC, resulting in an incidence rate of 143 per 100000 persons per year. This burden was as high as that reported in other studies from East Asian countries. All HCC patients were aged ≥ 40 years. Most were at an early stage (Stage 0, A or B); 14/17 cases were successfully treated with surgical resection or radiofrequency ablation, with a high 3-year survival rate of 90%. Hemangioma was the most common focal liver lesion in CHB patients detected by AUS; the main causes of AFP elevation at the initial screening were cirrhosis, increased alanine aminotransferase level and HCC. AUS detected 16/17 HCC cases whereas AFP levels ≥ 20 µg/L at diagnosis were observed in only 7/17 patients, most with a tumor size > 5 cm. For HCC screening and surveillance, AUS had a sensitivity and specificity of 94% and 82%, respectively, whereas the sensitivity and specificity of AFP at a cut-off value of ≥ 20 µg/L were 41% and 98%, respectively. Combined use of AUS and AFP assay did not improve effectiveness. CONCLUSION: Implementation of active screening and surveillance using AUS to detect early-stage HCC in naïve CHB patients aged ≥ 40 years in an endemic area is of benefit.