Fig. 7.

Proposed model for involvement of Ap₄A hydrolase in transcription regulation. Upon immunological activation, Ap₄A hydrolase associates with importin beta and is translocated into the nucleus when Ap₄A levels are elevated. Ap₄A binds to Hint-1, dissociating it from MITF. With the repression removed, transcription factors are free to transcribe their target genes. The presence of Ap₄A hydrolase in the nucleus leads to hydrolysis of the accumulated Ap₄A into AMP and ATP, decreasing its levels to that found in resting cells. When Ap₄A levels decrease, Hint-1 reassociates with MITF.