Synthesis of proteins and RNA of the 60S ribosomal subunit in HeLa cells recovering from valine deprivation

Cell cycle regulation of p70 S6 kinase and p42/p44 mitogen-activated protein kinases in Swiss mouse 3T3 fibroblasts

We show here using synchronized Swiss mouse 3T3 fibroblasts that p70 S6 kinase (p70S6k) and mitogen-activated protein kinases (p42mapk/p44mapk) are not only activated at the G0/G1 boundary, but also in cells progressing from M into G1. p70S6k activity increases 20-fold in G1 cells released from G0. Throughout G1, S, and G2 it decreases constantly, so that during M phase low kinase activity is measured. The kinase is reactivated 10-fold when cells released from a nocodazole-induced metaphase block enter G1 of the next cell cycle. p42mapk/p44mapk in G0 cells are activated transiently early in G1 and are reactivated late in mitosis after nocodazole release. p70S6k activity is dependent on permanent signaling from growth factors at all stages of the cell cycle. Immunofluorescence studies showed that p70S6k and its isoform p85S6k become concentrated in localized spots in the nucleus at certain stages in the cell cycle. Cell cycle-dependent changes in p70S6k activity are associated with alterations in the phosphorylation state of the protein. However, examination of the regulation of a p70S6k mutant in which the four carboxyl-terminal phosphorylation sites are changed to acidic amino acids suggests that a mechanism independent of these phosphorylation sites controls the activity of the enzyme during the cell cycle.

Effects of D-valine on pulmonary artery endothelial cell morphology and function in cell culture

The effects of D-valine on the cell culture of bovine pulmonary artery endothelial cells were studied using D-valine-modified Minimal Essential Medium (MEM). D-Valine-treated cultures (46-920 mg/l) were compared with replicate cells grown in L-valine (46 mg/l)-MEM. All media were supplemented with 15% fetal bovine serum (FBS). Endothelial cells were grown for 14 passages with split ratios varying from 1:3 to 1:6. Unlike cells grown in L-valine MEM, cells grown in D-valine MEM did not become contaminated by the growth fibroblasts in primary cultures. D-Valine-treated cells were found to grow in cobblestone array, exhibit contact inhibition and strongly express factor-VIII antigen (F-VIII). D-Valine-grown cells produced PGI2 in greater proportion to PGE2, both constitutively and when stimulated by bradykinin, on comparison with cells grown in L-valine. In addition, cells grown in L-valine, although able to express factor VIII, were not comparable to D-valine cells with respect to other parameters assayed (morphology and growth as a monolayer).