Human cells arrest in S phase in response to adenovirus 12 E1A.

It has previously been shown that following viral infection, Ad5 E1A induces cell cycle progression of quiescent rodent cells, leading to DNA synthesis and mitosis. Here we have examined the effect of Ad12 E1A on the cell cycle characteristics of human cells. Human tumor (A549, KB, and HeLa) cells were infected with Ad12 d/620, a mutant virus which has a lesion in the E1B gene and essentially expresses only E1A. These infected cells progressed from being largely in G1 into S phase, where they arrested. Even up to 96 h postinfection (p.i.) the cells remained blocked in S phase. DNA synthesis did, however, proceed in Ad12 d/620-infected cells, giving rise to multiple copies of cellular DNA. Similar results were obtained when primary human skin fibroblasts were infected, although the polyploidy was less marked. The expression of cyclins A, B1, and E in the tumor cells increased appreciably in response to E1A. In contrast, there was a dramatic reduction in the levels of cyclin D1 and D3. Increases in cyclin D1 expression could be detected at very late times p.i. In those cell lines expressing low levels of cdc2 and cdk2 an appreciable increase in expression was seen soon after Ad12 E1A could be detected. The elevated levels of cyclins A, B1, and E were associated with increased protein kinase activity directed against histone H1. An increase in cyclin D1-associated kinase activity against Rb1 was also observed at late times. This deregulation of the cell cycle was not solely dependent on E1A inactivation of Rb, since similar effects were seen in Ad12 d/620-infected retinoblastoma (Y-79) cells, implicating p107 and p130 in E1A-mediated changes in cell cycle progression. We propose that the E1A-induced levels of cyclins A, B1, and E by Ad12 E1A in human cells may lead to an uncoupling of S phase from cell cycle progression.

The expression of MDM2 and other p53-regulated proteins in the tissues of the developing rat.

The expression of MDM2 was monitored in tissues taken from rats at different stages of development. Two major protein species of 90K and 130K were identified, although expression was not the same in all tissues. In most the level of the larger protein tended to decrease as the foetus developed, being relatively scarce after birth. The expression of the 90K product (usually considered to be the major MDM2 protein), however, increased as the animals developed, being most abundant in adult tissues, suggesting that the two proteins play quite different roles during development. p53 expression mirrored that of the smaller MDM2 protein in most, but not all, tissues. This is consistent with previous suggestions made on the basis of in vitro studies that expression of the latter protein is regulated by p53. In addition, the level of two other p53-regulated proteins, Bcl-2 and Bax, were examined. In most tissues expression of both proteins decreased as the foetus developed, being virtually undetectable in adults. These data strongly suggest that factors other than p53 exert the major influence over Bcl-2 and Bax expression, although levels of the 90K MDM2 protein are more likely to be regulated by p53. However, it was noted that the levels of MDM2 in the tissues of p53-null mice were comparable to those seen in the normal rat.

Enzyme polymorphisms in Ascaris lumbricoides in Bangladesh.

Fourteen enzymes of Ascaris lumbricoides were analysed electrophoretically on cellulose acetate plates; 8 stained well and 3 were found to be polymorphic. Allelic and genotypic frequencies at the 3 polymorphic enzyme loci, Mpi, Pgi and 6-Pgd, were determined in a sample of 117 worms from 8 children living in different houses in an urban slum in Bangladesh. Allele frequencies in samples of parasites from the different children were compared to test for the possibility of non-random distribution of parasite genotypes between people. No strong evidence of differences was found. Diploid genotype frequencies did not deviate significantly from those expected from the Hardy-Weinberg equilibrium. Significant linkage disequilibrium was observed in one of 3 pairs of enzyme loci tested, which might suggest that some genetic subdivision exists in the local A. lumbricoides population, although no strong interference should be made from this single result. Overall, the results suggest that the worms sampled formed part of a single population which appears to be randomly mating.