Suspension cultures of Chinese hamster cells (line CHO), which had stopped dividing and were arrested in G1 following growth to high cell concentrations in F-10 medium, could be induced to reinitiate DNA synthesis and to divide in synchrony upon addition of the appropriate amounts of isoleucine and glutamine. Both amino acids were required to initiate resumption of cell-cycle traverse. Deficiencies in other amino acids contained in F-10 medium did not result in accumulation of cells in G1, indicating a specific action produced by limiting quantities of isoleucine and glutamine. In the presence of sufficient glutamine, approximately 2 x 10-6 M isoleucine was required for all cells to initiate DNA synthesis in a population initially containing 1.5 x 105 cells/ml. Under similar conditions, about 4 x 10-6 M isoleucine was required for all G1-arrested cells to progress through cell division. In contrast, 1 x 10-4 M glutamine was necessary for maximum initiation of DNA synthesis in G1 cells, along with sufficient isoleucine. A technique for rapid production of G1-arrested cells is described in which cells from an exponentially growing population placed in F-10 medium deficient in both isoleucine and glutamine or isoleucine alone accumulated in G1 after 30 hr.

Suspension cultures of Chinese hamster cells (line CHO) were grown to stationary phase (approximately 8-9 X 10 5 cells/ml) in F-10 medium . Cells remained viable (95%) for at least 80 hr in stationary phase, and essentially all of the cells were in GI . Upon resuspension or dilution with fresh medium, the cells were induced to resume traverse of the life cycle in in synchrony, and the patterns of DNA synthesis and division were similar to those observed in cultures prepared by mitotic selection . Immediately after dilution, the rates of synthesis of RNA and protein increased threefold . This system provides a simple technique for production of large quantities of highly synchronized cells and may ultimately provide information on the biochemical mechanisms regulating cell-cycle traverse .

Exogenous propionate is incorporated in vivo by Escherichia coli as a primer to produce lipids with fatty acids of odd chain lengths. This provides a method for the specific labeling of the three terminal carbons in the fatty acyl chains of phospholipids. ' Data from reference 2. c Deuterochloroform solvent.

Induction of transforming growth factor alpha (TGF alpha) in human cell lines by 254 nm ultraviolet radiation (UVC) suggests that TGF alpha may have an autocrine role in UV-induced tumorigenesis. Binding of TGF alpha to epidermal growth factor receptor (EGFR) is an important initial step in transducing the signal for cell division. Experiments reported herein were designed to determine whether, in addition to inducing TGF alpha, UVC might also induce changes in the levels of EGFR on HeLa S3 cells [125I]EGF binding to HeLa S3 cells was inhibited 8 h after exposure to 7 J/m2 UVC radiation followed by increased [125I]EGF binding 16-32 h after irradiation. Scatchard analysis of EGF binding at 28 h indicated that irradiated cells had 60% more receptors with no differences in apparent binding affinities (56,300 +/- 5494 receptors versus 34,900 +/- 1899 receptors in sham-irradiated cells). Cell cycle analysis at 8 h post-UVC indicated that cells had slowed traverse of S-phase, but by 24 and 48 h, times at which increases in [125I]EGF were evident, cell cycle distributions were essentially back to normal. These results indicate that UVC modulates EGFR numbers in HeLa S3 cells and suggest that solar radiation may modulate EGFR numbers in keratinocytes or other cells in the skin. The presence of UV-induced growth factors such as TGF alpha and increased levels of EGFR may result in sustained cell proliferation by autocrine or paracrine mechanisms. These populations of cycling cells would then be at risk for subsequent mutational events that result in transformation to a tumorigenic state.

LP-BM5 murine leukemia virus (MuLV) induces an immunodeficiency syndrome (MAIDS) in C57BL/6 mice which resembles immunological abnormalities observed in early stages of human AIDS. In our study, MAIDS virus-infected mice were exposed to low doses of ultraviolet radiation (UVR) before and after virus inoculation and compared with MAIDS-infected but not UVR-exposed mice. In all tested parameters (blood IgM levels; mitogenic responses to PHA, ConA, LPS and anti-mu; MLR; antigenic response to SRBC; enlargement and histopathologic changes of the spleen) we observed the same trend: changes due to MAIDS infection were more pronounced in the UVR-exposed group than in the unexposed group. Statistically significant differences between these two groups were seen for mitogenic responses at two different time points after virus inoculation. These results demonstrate that in vivo UVR exposure enhances the immunosuppressive effects of a retroviral infection. UVR exposure may affect the progression of AIDS in a similar manner.