In vitro culture systems of human myogenic cells contribute greatly to elucidation of the molecular mechanisms underlying terminal myogenic differentiation and symptoms of neuromuscular diseases. However, human myogenic cells have limited ability to proliferate in culture. We have established an improved immortalization protocol for human myogenic cells derived from healthy and diseased muscles; constitutive expression of mutated cyclin-dependent kinase 4, cyclin D1 and telomerase immortalized human myogenic cells. Normal diploid chromosomes were preserved after immortalization. The immortalized human myogenic cells divided as rapidly as primary human myogenic cells during the early passages, and underwent myogenic, osteogenic and adipogenic differentiation under appropriate culture conditions. The immortalized cells contributed to muscle differentiation upon xenotransplantation to immunodeficient mice under conditions of regeneration following muscle injury. We also succeeded in immortalizing cryopreserved human myogenic cells derived from Leigh disease patients following primary culture. Forced expression of the three genes shortened their cell cycle to o30 h, which is similar to the doubling time of primary cultured human myogenic cells during early passages. The immortalization protocol described here allowed human myogenic cells to recapture high proliferation activity without compromising their differentiation potential and normal diploidy.

Human keratinocytes and fibroblasts isolated from foreskin were transformed by transfection with recombinant human papillomavirus type 16 (HPV16) DNA. The transformed cells exhibited an extended (fibroblasts) or indefinite (keratinocytes) lifespan compared with that of normal controls. In addition, HS27, a human fibroblast cell line previously transfected with origin-defective simian virus 40, was successfully transfected. HPV16 sequences were stably maintained in the cells, and extensive amplification and rearrangements occurred with continuous culturing. Moreover, both fibroblasts and keratinocytes expressed several specific HPV16 mRNAs. Because HPV16-transfected cells had viral transcripts and because transfection with the vector alone did not extend the lifespan of the cells, it is likely that the virus was responsible for the indefinite lifespan. Transfected fibroblast and keratinocyte lines will be useful for investigating the molecular biology of HPV16 and the interactions between the viral DNA and the human genome. Moreover, transfected keratinocytes provide a model for analyzing the effects of HPV16 on the differentiation properties of human epithelial cells.

We report here that human esophageal keratinocyte stem cells are characterized by the expression of the lowaffinity neurotrophin receptor p75 NTR and differentially expressed cell adhesion molecules, the b1 and b4 integrins. The candidate stem cells could be fractionated from keratinocytes as a minor cell subset by means of immunocytochemical cell sorting based on the different levels of expression of these cell surface molecules. Flow cytometric analysis revealed that this minor cell subset retained a relatively slow-cycling phenotype in vitro. These cells expressed low levels of involucrin and cytokeratin 13, indicating that the p75 NTR -positive cell subset is immature relative to the other predominant subpopulations coexpressing b1 integrin at higher levels. The p75 NTR -positive cell subset was crucial for achieving longevity and the greatest output of keratinocytes comprising all distinguishable subpopulations in vitro. This process was associated with self-renewal and selfamplification of the p75 NTR -positive cell subset. These findings strongly implicate p75 NTR as a stem cell marker, which will be valuable for prospectively investigating stem cell regulation in association with different biological processes including neoplastic transformation of regenerative epithelia.

These cell lines will be useful tools for studying the repair and regeneration of dental and periodontal tissues and various diseases including odontogenic tumors.

In this study, we investigated the clinicopathologic significance of the low-affinity p75 neurotrophin receptor (p75NTR; which is expressed in the stem/progenitor cell fraction of normal esophageal epithelial cells) in 187 resected esophageal squamous cell carcinoma (ESCC) specimens and found that f50% of ESCC expressed p75NTR. Our investigation using ESCC cell lines showed that p75NTR was intensely expressed in the cells with high colony-forming capacity but they were sensitive to cell death on inhibition of p75NTR expression with transient transfection of small interfering RNA (siRNA). These findings suggest that p75NTR is necessary for survival and maintenance of ESCC tumors, providing us with a potential target for novel therapies. Purpose: p75NTR is expressed in a stem/progenitor cell fraction of human normal esophageal epithelial cells. In this study, we investigated the expression and biological role of p75NTR in ESCC.Experimental Design:The expression of p75NTR in 187 resected ESCC specimens was immunohistochemically investigated. The expression of p75NTR in 30 ESCC cell lines (KYSEs) was assessed by reverse transcription-PCR, immunocytochemistry, and flow cytometry. The p75NTR-bright and p75NTR-dim/negative cells were isolated from KYSE150 by magnetic beads and colony formation was investigated. The role of p75NTR in KYSEs was assessed by transient transfection of siRNA. Results: p75NTR was expressed in 92 of 187 (49.2%) tumors. In well-differentiated tumors, positive staining was apparent in the first one to two layers from infiltrative margin of the tumors where most of the cells were actively proliferating. In moderately differentiated tumors, p75NTR was expressed in wider range from the margin of the tumors whereas p75NTR was diffusely distributed in poorly differentiated tumors. p75NTR was expressed in all examined KYSEs and the mean proportion of the p75NTR-bright fraction was 30.1%.The size of p75NTR-positive colonies was larger than that of p75NTR-negative colonies derived from KYSE150 (P < 0.0001). The purified p75NTR-bright cells formed p75NTR-positive large colonies more frequently than the p75NTR-dim/negative cells (P < 0.0001). Down-regulation of p75NTR expression by siRNA resulted in marked growth inhibition with induction of apoptosis. Conclusions: Our findings suggest that p75NTR is necessary for survival and maintenance of ESCC tumors, providing us with a potential target for novel therapies.