Cocaine and the AP-1 transcription factor complex

Cocaine addiction in humans develops gradually with repeated administrations and persists long after cocaine has cleared the body The mechanisms underlying this persistent form of neuroplasticity are not understood and can involve both structural and biochemical mechanisms, The long time course for cocaine addiction in humans and for development of cocaine self-administration in animal models suggests the involvement of alterations in gene expression leading to altered signaling in the brain. In the striatum (Str) and nucleus accumbens (NAc) of rats, pretreatment with repeated cocaine administrations downregulates the induction of various immediate early genes (IEGs) by a subsequent acute challenge with cocaine. Some of these downregulated IEGs encode Fos-related components of the activator protein-1 (AP-I) complex, which is likely to regulate a number of genes important for neuronal function, Interestingly, repeated cocaine administration induces novel delta FosB-related proteins (called chronic Foe-related antigens (Fras)) in the NAc and Str that replace the downregulated isoforms of Fos, Unlike the acutely induced, short-lasting isoforms of Fos and FosB, the chronic Fras persist long after the last cocaine administration. The known form of delta FosB per se lacks the domain required to activate transcription. If the chronic Fras are similar in structure to delta FosB, then the induction of chronic Fras likely leads to a blockade of AP-l-dependent transcription resulting in altered gene expression. We are presently purifying the chronic Fras to obtain amino acid sequence in order to directly examine our hypothesis about the effects of repeated cocaine administration on AP-l-dependent transcription and gene expression in the brain.