Virus infection triggers the cytoplasmic protein response (CPR)

Previously, we have shown that compatible virus infections, associated with virus replication in the cytoplasm, leads to a tight up-regulation of HSP70 in newly infected cells (Spatial and temporal changes in host gene expression after virus infection). We have investigated this further in Arabidopsis and shown that virus infection leads to specific induction of a subset of cytosolic HSP70s. Attempts to identify the specific inducers of this effect led to the identification of a novel phenomenon, which we have called the ‘cytoplasmic protein response’ or ‘CPR’ (Aparicio et al, 2005). The CPR is analogous to the much studied ‘unfolded protein response’ or ‘UPR’ in that the cell responds to the accumulation of unfolded proteins by the induction of a suite of chaperones, including HSP70. We believe that in this role HSP70 decides whether the protein can be repaired (refolded) or should be directed for degradation via the ubiquitination pathway.

Using chemical inducers of protein misfolding, we have confirmed that the CPR is a response to the accumulation of denatured proteins. We are investigating now whether the CPR and UPR are spatially distinct and what the regulatory pathways involving heat shock transcription factors (HSFs) that lead to HSP70 induction.