Differential regulation of JunB and JunD by adenovirus type 5 and 12 E1A proteins.

The genes of the Jun family encode components of the TPA-inducible transcription factor AP-1. These genes are induced by a wide variety of extracellular stimuli, such as growth factors, phorbol esters and activators of protein kinase A. We have previously shown that the adenovirus type 5 E1A protein (E1A5) induces c-jun and junB expression in a number of different cell types. In this paper we show that the third member of the Jun family, junD, is also strongly induced by E1A5. Multiple sequences in the junB and junD promoters are responsible for the effects of E1A5. By contrast, adenovirus type 12 E1A (E1A12), like retinoic acid (RA), strongly induces c-jun expression, while expression of junB and junD is not altered. Interestingly, E1A12 expression leads to complete differentiation of P19 EC cells, comparable to the effect of RA on these cells, while E1A5-expressing cells are only partially differentiated.

Cell cycle analysis during retinoic acid induced differentiation of a human embryonal carcinoma-derived cell line.

Several subclones of the human embryonal carcinoma (EC) cell line Tera-2 can be induced to differentiate in monolayer culture by retinoic acid (RA) to a flattened cell type with reduced growth rate. Using a method based on the transition probability model, we have analysed changes in cell cycle kinetics of Tera-2 cells during the differentiation process. Growth inhibition was shown to occur without a lag period and to be partly due to an increase in the duration of the S-phase, but with a relatively greater contribution from an increase in the duration of G1-phase. Since the fraction of the cell population in the G1-phase then doubled, cells accumulated in this part of the cycle. In contrast, the reduced proliferation rate of two murine EC cell lines, PC13 and P19, treated with RA occurs after a lag period of about two cell cycles and is mainly attributable to an increase in the duration of the S-phase. The results illustrate a differential response of human and murine EC cells to growth regulation by RA and again emphasize that although the stem cells of murine teratocarcinomas may provide a useful model, they are not identical to their human counterparts.

Screening for cytotoxicity in neuroblastoma cells. I. Dependence of growth inhibition on the presence of serum.

The growth-inhibitory effects of a variety of potentially toxic compounds on neuroblastoma cells in defined, serum-free medium were compared with those in serum-containing medium. For 13 of 21 compounds tested, concentrations between 2 and 10(5) times higher were required for 50% inhibition of growth in serum-containing medium. The ranking of substances for their potency in inhibiting growth was thereby different in the two different culture conditions. The presence of bovine serum albumin (BSA) in the medium had similar effects as serum on the dose-response curves.

Screening for cytotoxicity in neuroblastoma cells. II. Growth inhibition: cell death or impaired cell cycle progression?

Time-lapse films were made of neuroblastoma cells in chemically defined, serum-free medium in the presence of a variety of potentially toxic compounds. Using a simple method of analysis, based on the transition probability model and the increase in the number of cells per frame with time, growth inhibition in cell cultures could be specifically attributed to cell death or delayed progression through the cell cycle. For 4 of 8 compounds growth inhibition was the result of almost all cells showing an impaired rate of cell cycle progression while for 4 compounds there were equal or greater contributions from cell death and/or detachment.