Anionic amino acid transport in ras- transformed fibroblasts

The sodium-dependent transport of anionic amino acids is suppressed in NIH3T3 cells that constitutively express ras oncogenes. In a model of NIH3T3 cells in which ras expression is triggered in the presence of dexamethasone, aspartate transport decreases gradually upon dexamethasone treatment and is almost completely suppressed after two days of incubation in the presence of the steroid. In the same cell model, lovastatin, an inhibitor of beta hydroxy-beta methyl-glutaryl-CoA-reductase and, hence, of farnesylation of p21ras, partially protects aspartate transport from the inhibition observed upon steroid treatment. Determinations of cell glutamate in ras-expressing and non expressing cells indicate that in both cell models glutamate decreases when extracellular medium is depleted of glutamine. However, this decrease is much faster in cells expressing ras (either constitutively or conditionally). It is proposed i) that cell production of oncogenic p21ras hinders sodium-dependent transport of anionic amino acids and ii) that the transport alteration impairs the maintenance of cell levels of glutamate in ras-expressing cells.