INDUCTION OF CALRETICULIN EXPRESSION IN RESPONSE TO AMINO-ACID DEPRIVATION IN CHINESE-HAMSTER OVARY CELLS

The role of calreticulin as a stress-induced molecular chaperone prote in of the endoplasmic reticulum is becoming more apparent. We characte rize here the induction of calreticulin in response to complete amino acid deprivation in Chinese hamster ovary cells. Amino acid deprivatio n caused a 4-fold increase in calreticulin protein levels over a perio d of 4-10 h. In addition to an overall increase in protein levels, the glycosylation of calreticulin was increased. This glycosylation event was blocked by tunicamycin and was not required for the increase in c alreticulin protein levels. Immunofluorescence studies localized calre ticulin to the ER of CHO cells, and no significant change was observed after amino acid deprivation. Northern-blot analysis showed that calr eticulin mRNA levels were increased approx. 10-fold in response to com plete amino acid deprivation. The response was sensitive to actinomyci n D and alpha-amanitin, implying that regulation is primarily at the l evel of transcription. These results are similar to the large increase s in asparagine synthetase mRNA observed in response to amino acid dep rivation, but the amino acid-deprivation-response element identified t o be involved in asparagine synthetase induction is absent from the ca lreticulin promoter.