Effect of nutrient deprivation on ribosomal RNA and ribosomal protein mRNA in cultured mosquito cells

The effect of nutrient deprivation on RNA and protein synthesis in cultured Aedes albopictus mosquito cells was investigated by replacing the culture medium with phosphate-buffered saline. After a 2 h starvation treatment, incorporation of radio-labeled precursor into total RNA was inhibited by 50%, and after 4 h, incorporation of amino acids into protein was inhibited by 50%. To investigate directly the effects of starvation on rRNA synthesis, ribosomal subunits were prepared from treated cells by sucrose density gradient centrifugation. After 4 h in saline, incorporation of [H-3]uridine into ribosomal subunits had declined to baseline levels. Even after 8 h starvation, however, the effect was reversed by refeeding with complete medium, in which cells resumed rRNA synthesis and ribosomal subunit assembly. During 8 h starvation, total amounts of rRNA detected by northern blot remained stable. Ribosomal protein mRNA abundance was measured on northern blots, using probes corresponding to L8 and L31 ribosomal protein genes. The content of these ribosomal protein mRNAs was unchanged during starvation, or during treatment with actinomycin D. These results suggest that ribosomal protein mRNAs belong to a long-lived mRNA population, and suggest that post-transcriptional regulation of ribosomal protein synthesis is an important regulatory mechanism in growing mosquito cells. (C) 1998 Wiley-Liss, Inc.