obtaining a continuous source of normal cells or dna from a single individual has always been a rate limiting step in biomedical research. availability of lymphoblastoid cell lines (lcls) as a surrogate for isolated or cryopreserved peripheral blood lymphocytes has substantially accelerated the process of biological investigations. lcls can be established by in vitro infection of resting b cell...

High-risk human papillomavirus (hrHPV)-induced immortalization and malignant transformation are accompanied by DNA methylation of host genes. To determine when methylation is established during cell immortalization and whether it is hrHPV-type dependent, DNA methylation was studied in a large panel of HPVE6E7-immortalized keratinocyte cell lines. These cell lines displayed different growth beha...

Immortalization of primary cells is an early and important event in multistep tumorigenesis and is itself a multistep process. Adenovirus E1A 12S encodes an oncoprotein that can rescue cells from senescence and overcome apoptosis, leading to their immortalization. Five regions of 12S, located in both exons, are required for immortalization. Two regions in the first exon are necessary to activat...

Background: Microparticles (MPs) are small vesicles released from the cell membrane. Accordingly, these contain active molecules to mediate biological processes, including cell proliferation and cell cycle progression. The fusion of myeloma cell lines with immunized B lymphocytes is a critical step of hybridoma technology. MPs modulate lymphoproliferation, thereby facilitating B cell expansion ...

Abrogation of cellular senescence, resulting in immortalization, is a necessary step in the tumorigenic transformation of a cell. Four independent, spontaneously immortalized Li-Fraumeni syndrome (LFS) cell lines were used to analyze the gene expression changes that may have given these cell lines the growth advantage required to become immortal. A cellular senescence-like phenotype can be indu...

High-risk human papillomavirus (hrHPV) types induce immortalization of primary human epithelial cells. Previously we demonstrated that immortalization of human foreskin keratinocytes (HFKs) is HPV type dependent, as reflected by the presence or absence of a crisis period before reaching immortality. This study determined how the immortalization capacity of ten hrHPV types relates to DNA damage ...

The acquisition of immortalization is an early and carefully documented event in mouse mammary tumorigenesis. Activation of telomerase activity is one hypothesis to explain the acquisition of immortalization. We examined the activity of telomerase in well-defined immortalized, non-tumor cell populations of mouse mammary tissue in vivo. The results indicated that normal virgin and mid-pregnant m...

BACKGROUND Activation of telomerase is an early event in the development of breast and other cancers that may lead to cell immortalization, a critical and rate-limiting step in cancer progression. Breast epithelial cells from women with Li-Fraumeni syndrome (LFS) immortalize spontaneously and reproducibly in culture. We, therefore, tested whether immortalization of these cells could be prevente...

The hypothesis that induction of immortalization of rodent cells follows one-hit kinetics was tested by the determination of frequencies of immortalization of Syrian hamster embryo cells after treatment with benzo(a)pyrene, X-rays, or ethylnitrosourea. Contrary to expectation, immortalization did not occur in a single step. Full immortalization appeared to be a process which required at least t...

Linear EBV genomes undergo a transition to the circular form characteristic of latency by 16-20 h post-infection. This transition requires that the infected cells be activated to the G1 stage of the cell cycle. Cellular proliferation and expression of the activation marker CD23 were not required. Nevertheless, 36 h post-infection, only cells expressing CD23 contained covalently closed, circular...