The role of calreticulin as a stress-induced molecular chaperone protein of the endoplasmic reticulum is becoming more apparent. We characterize here the induction of calreticulin in response to complete amino acid deprivation in Chinese hamster ovary cells. Amino acid deprivation caused a 4-fold increase in calreticulin protein levels over a period 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 calreticulin protein levels. Immunofluorescence studies localized calreticulin to the ER of CHO cells, and no significant change was observed after amino acid deprivation. Northern-blot analysis showed that calreticulin mRNA levels were increased approx. 10-fold in response to complete amino acid deprivation. The response was sensitive to actinomycin D and alpha-amanitin, implying that regulation is primarily at the level of transcription. These results are similar to the large increases in asparagine synthetase mRNA observed in response to amino acid deprivation, but the amino acid-deprivation-response element identified to be involved in asparagine synthetase induction is absent from the calreticulin promoter.
Aims: To determine whether intercellular signalling can occur between physically separated populations of Escherichia coli.
Methods and Results: Intercellular signalling between physically discrete populations of E. coli BL21 was analysed in bi‐partite Petri dishes. Transfer of a growth‐promoting signal resulted in induction of resistance to the antibiotic ampicillin. Optimal expression of the signal occurred when the signalling population was established as a bacterial lawn for 24 h. This represented an entry into the stationary phase of growth, as indicated by the expression profile of the RNA polymerase subunit σ38 (σS; sigma S). The growth‐promoting effect was also observed when E. coli DH5α (luxS–) was used as the signalling population. Preventing passage of air between the two populations resulted in a complete cessation of the growth‐promoting effect.
Conclusions: A growth‐promoting signal occurs between physically separated cultures of E. coli. The exact nature of the signal remains to be determined but does not involve the production of autoinducer‐2 from the luxS gene. Signal transmission is likely to involve airborne transfer of a signal species.
Significance and Impact of the Study: Intercellular signalling systems exist in bacteria that enable antibiotic resistance to be conferred between physically separated populations.
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