Expression of poly(A)-binding protein is upregulated during recovery from heat shock in HeLa cells

Induction of heat shock proteins (HSPs) helps cells to survive severe hyperthermal stress and removes toxic unfolded proteins. At the same time, the cap-dependent translation of global cellular mRNA is inhibited, due to the loss of function of eukaryotic initiation factor (eIF)4F complex. It has been previously reported that, following heat shock, HSP27 binds to the insoluble granules of eIF4G and impedes its association with cytoplasmic poly(A)-binding protein (PABP) 1 and eIF4E. In the studies reported here, in addition to heat shock, we have included results of our investigation on the association between eIF4G, PABP1 and HSP27 during recovery from heat shock, when cap-dependent mRNA translation resumes. We showed here that in the heat-shocked cells, the PABP1-eIF4G complex dissociated, and both polypeptides translocated with the HSP27 to the nucleus. During recovery after heat shock, PABP1 and eIF4G were redistributed into the cytoplasm and colocalized with each other. In addition, PABP1 expression was upregulated and its translation efficiency was increased during the recovery period, possibly to meet additional demands on the translation machinery. HSP27 remained associated with the eIF4G-PABP1 complex during recovery from heat shock. Therefore, our results raise the possibility that the association of HSP27 with eIF4G may not be sufficient to suppress cap-dependent translation during heat shock. In addition, we provide evidence that the terminal oligopyrimidine cis-element of PABP1 mRNA is responsible for the preferential increase of PABP1 mRNA translation in cells undergoing recovery from heat shock.