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Abstract

Translation is a sensitive process affected during stress response. Both heat shock and the induction of apoptosis are associated with a rapid and substantial inhibition of protein synthesis. By combining polysomal fractionation and microarray analysis it is possible to measure the state of translation in a cell and provide a picture of the communication between the transcriptome and the proteome. DNA-microarrays were used to determine the ability of mRNAs to be translated during heat shock and the induction of p53-mediated apoptosis in human cells. Changes of the transcriptome after thermal stress or etoposide treatment of HeLa cells were measured and correlated with changes on the association of mRNAs to polysomes. It was observed that increasing transcription always correlates with increasing translation, a phenomenon described in yeast as "potentiation". However, a stringent statistical analysis showed that most mRNAs are moved to or from polysomes without significant changes of transcriptional activity. During the response to heat shock 254 transcripts were recruited to polysomes and 238 dissociated from them with no changes in the transcript level. Only 50 genes were coordinately increased in both transcription and translation. During apoptosis induction, 258 mRNAs were recruited and 202 excluded from polysomes and only 6 were coordinately up-regulated. This indicates that a significant number of transcripts are subjected to translational control and result in an increase or decrease of the protein synthesis rate independently of the transcriptional activity. The analysis of the 5' UTRs (size distribution, AUG context) of the regulated mRNAs did not show any special feature that would allow an a priori prediction of a mechanism of translation. Comparison of both treatments revealed that they share very few genes in common, indicating that the control of translation is specific for each response. In this work, it has been shown that DNA-microarrays can effectively be used to study the interplay between transcriptome and proteome, and permit the identification of new candidates for translational control in different stress situations, stages of cell cycle, cancer, or infections. It has a big potential for the discovery of new targets for drug action and disease markers.