Doses cAMP control protein synthesis?

On the role of cyclic AMP in the cytotoxic effect of fluoride

The possible role of adenosine 3',5'-monophosphate (cAMP) in the cytotoxic effect of fluoride was investigated in fluoride sensitive mouse fibroblasts (LS) and a subline of LS resistant to 6 mM fluoride (FR6). In both cell lines, growth was inhibited by dibutyryl-cAMP, prostaglandin (PG)E2 and theophylline, FR6 being somewhat more sensitive to these agents than LS. FR6 had lower basal cAMP levels in the intact cells and lower basal adenylate cyclase activity in the homogenate preparation than LS, but the percentual response of intact cells or adenylate cyclase preparations to PGE1 or PGE2 was about the same in the two cell lines, and the sensitivity of the adenylate cyclase to fluoride was similar. No measurable increase in cAMP content was found in either LS or FR6 after exposure of the intact cells to various concentrations of fluoride for various times. The present results indicate that the development of fluoride resistance in these cells is not due to decreased sensitivity to cAMP, and probably not due to altered cAMP-formation in response to fluoride. The growth inhibitory and cytotoxic effects of fluoride in LS cells is probably not mediated through cAMP.

Identification and characterization of ribosomal proteins phosphorylated in vaccinia-virus-infected HeLa cells

Two-dimensional analysis of 32P-labelled ribosomal proteins revealed three proteins which are phosphorylated in vaccinia-virus-infected HeLa cells. All three proteins belong to the 40-S ribosomal subunits and were identified as S2, S6 and S16. The ribosomal protein S6 is phosphorylated also in uninfected HeLa cells. Phosphoserine was detected in all three proteins, phosphothreonine only in the protein S2. Phosphorylation of these ribosomal proteins in infected cells is dependent on the multiplicity of the viral infection and increases during the first six hours of infection. All three proteins are also phosphorylated in virus-infected cells treated with cycloheximide and in cells infected with ultraviolet-irradiated virus. This suggests that the phosphorylation reaction involves a vaccinia virion-associated protein kinase.