Isolation of UV-resistant revertants from a xeroderma pigmentosum complementation group A cell line

Xeroderma pigmentosum (XP) is an autosomal recessive disease. Cells cultured from XP patients are hypersensitive to the lethal effects of UV light. Most XP cells are defective in an early stage in DNA repair of UV light-induced damage. The nature of the genetic defect of the XP syndrome has not been defined. To address this problem, we attempted to isolate UV-resistant cells from a cell line derived from an XP complementation group A (XPA) patient. By using a selection scheme capable of detecting one UV-resistant cell in a population of 10(8) cells, several UV-resistant clones were isolated at frequencies between 1 X 10(-7) and 2 X 10(-8). Here we describe the isolation and initial characterization of these phenotypic revertants.     

Molecular cloning of a new transforming gene from a chemically transformed human cell line

Molecular cloning of the transforming gene from a chemically transformed human osteosarcoma-derived cell line enables the gene to be mapped to chromosome 7 (7p11.4-7qter) and by this criterion and by direct hybridization to be shown to be unrelated to known oncogenes.     

A novel population of T-cell receptor alpha beta-bearing thymocytes which predominantly expresses a single V beta gene family

Recent studies have demonstrated that CD3 is expressed on a subset of thymocytes with a CD4-CD8- (double negative) phenotype. At least some of these cells bear the CD3-associated gamma delta T-cell receptor (TCR gamma delta). Here we describe a second subset of double negative thymocytes which expresses CD3-associated alpha beta receptors (TCR alpha beta). Surprisingly, these cells express predominantly the products of a single V beta gene family (V beta 8). These CD4-CD8-, TCR alpha beta+ cells appear relatively late in ontogeny (between birth and day 5 of life) and thus are unlikely to be the precursors to the TCR alpha beta-bearing cells (CD4+CD8- and CD4-CD8+) already present at birth. They can be selectively expanded in vitro by stimulation with a monoclonal antibody to V beta 8 (F23.1) in the presence of interleukin I (IL-1). We propose that this cell type is a unique T-cell population distinguishable from typical TCR alpha beta+ T cells by its CD4-CD8- phenotype and a restricted TCR V beta repertoire. Analysis of the unique phenotype of these cells suggests that they may represent the normal counterpart of the defective CD4-CD8- T cells found in the lpr autoimmune mouse.     

UV light-induced immunoglobulin heavy-chain class switch in a human lymphoblastoid cell line

During attempts to select nonsecretory variants from 0.467.3, and Epstein-Barr virus-transformed human lymphoblastoid cell line that secretes small amounts of IgM lambda, we exposed the cells to UV light. Cells that survived the irradiation were subcultured and their supernatants were screened for immunoglobulin production by an enzyme-linked immunosorbent assay (ELISA). Although stable nonsecretory variants were not isolated, we report here that an immunoglobulin class switch occurred in the UV-treated cell population. All survivors were found to produce large quantities of IgG lambda. Some cell cultures also produced the original IgM lambda. The UV-light-induced class switch was regularly reproducible with this target cell line.     

Controlled synthesis of HBsAg in a differentiated human liver carcinoma-derived cell line.

A significant aspect of primary hepatic carcinoma in man is the high positive correlation of hepatocellular carcinoma with infection with hepatitis B virus (HBV)1. Analysis of the relationship between HBV infection and oncogenesis is difficult because natural infection with HBV is limited to man and experimental infection has been achieved only in chimpanzees and gibbons. Furthermore, because HBV has not been successfully propagated in cell culture, basic study of virus-cell interaction of the aetiological agent of one of the most widespread infections of man has been impossible. Recently, however, a cell line (PLC/PRF/5) derived from a human hepatoma biopsy was described which produces the HRV surface antigen (HBsAg) and so provides a tool for the experimental investigation of HBV in viro. We now report the derivation and characterisation of two additional cell lines primary liver carcinomas. In contrast to the PLC/PRF/5 cell line, these cell lines retain the capacity to synthesise many human plasma proteins, including both albumin and alpha-fetoprotein (AFP). One of these lines also produces BHsAg. We also present evidence that HBsAg synthesis and secretion in this cell line are correlated with the growth state of the culture. This finding is in contrast to the continuous HBsAg production found in the PLC/PRF/5 cell line.     

Expression of a transfected human c-myc oncogene inhibits differentiation of a mouse erythroleukaemia cell line

The Friend-virus-derived mouse erythroleukaemia (MEL) cell lines represent transformed early erythroid precursors that can be induced to differentiate into more mature erythroid cells by a variety of agents including dimethyl sulphoxide (DMSO). There is a latent period of 12 hours after inducer is added, when 80-90% of the cells become irreversibly committed to the differentiation programme, undergoing several rounds of cell division before permanently ceasing to replicate. After DMSO induction, a biphasic decline in steady-state levels of c-myc and c-myb messenger RNAs occurs. Following the initial decrease in c-myc mRNA expression, the subsequent increase occurs in, and is restricted to, the G1 phase of the cell cycle. We sought to determine whether the down-regulation is a necessary step in chemically induced differentiation. Experiments reported here indicate that expression in MEL cells of a transfected human c-myc gene inhibits the terminal differentiation process.     

Biosynthesis of the major human red cell sialoglycoprotein, glycophorin A, in a continuous cell line

During biosynthesis of glycophorin A in K562 cells a precursor is rapidly transferred through the endoplasmic reticulum membrane with the COOH-terminal remaining in the cytoplasm. This is glycosylated within the cell and appears at the cell surface after about 30 min. The biosynthetic pathway resembles that described for viral membrane glycoproteins.