Threonine 149 phosphorylation enhances ΔFosB transcriptional activity to control psychomotor responses to cocaine.

Stable changes in neuronal gene expression have been studied as mediators of addicted states. Of particular interest is the transcription factor Delta FosB, a truncated and stable FosB gene product whose expression in nucleus accumbens (NAc), a key reward region, is induced by chronic exposure to virtually all drugs of abuse and regulates their psychomotor and rewarding effects. Phosphorylation at Ser(27) contributes to Delta FosB's stability and accumulation following repeated exposure to drugs, and our recent work demonstrates that the protein kinase CaMKII alpha phosphorylates Delta FosB at Ser(27) and regulates its stability in vivo. Here, we identify two additional sites on Delta FosB that are phosphorylated in vitro by CaMKII alpha, Thr(149) and Thr(180), and demonstrate their regulation in vivo by chronic cocaine. We show that phosphomimetic mutation of Thr(149) (T149D) dramatically increases AP-1 transcriptional activity while alanine mutation does not affect transcriptional activity when compared with wild-type (WT) Delta FosB. Using in vivo viral-mediated gene transfer of Delta FosB-T149D or Delta FosB-T149A in mouse NAc, we determined that overexpression of Delta FosB-T149D in NAc leads to greater locomotor activity in response to an initial low dose of cocaine than does WT Delta FosB, while overexpression of Delta FosB-T149A does not produce the psychomotor sensitization to chronic low-dose cocaine seen after overexpression of WT Delta FosB and abrogates the sensitization seen in control animals at higher cocaine doses. We further demonstrate that mutation of Thr(149) does not affect the stability of Delta FosB overexpressed in mouse NAc, suggesting that the behavioral effects of these mutations are driven by their altered transcriptional properties.