Interestingly, in GADD34 DC/DC MEFs, PKR mRNA strongly accumulated in response to poly I:C (Fig. 4D) , despite the absence of detectable IFN-ß production and PKR protein increase (Fig. 4B) . This continuous accumulation of PKR mRNA in response to poly I:C suggests the existence of alternative molecular mechanisms, capable of promoting PKR mRNA transcription and stabilization independently of autocrine IFN-b detection. Nevertheless in these conditions PKR expression, like IFN-b, was found to be dependent on the presence of GADD34 for its synthesis (Fig. 4B) .