Pro-Apoptotic Protein-BclGs Inhibits Ap-1 Activity Through Jab1

BclGs belongs to a member of BH3-only protein, which is structurally distant member of Bcl-2 protein family that trigger apoptosis. BclGs mRNA is uniquely expressed in testis. Apoptosis induction by BlcGs depends on the BH3 domain and is suppressed by coexpression of anti-apoptotic Bcl-xL protein. The molecular targets of BclGs so far remain unclear. Thus, we used the full length BclGs as "bait" in a yeast two-hybrid system to screen a human testis cDNA library. Several types of clones were identified, which interacted specifically with BclGs when tested for nutritional selection and P-galactosidase activity. One clone contained a cDNA insert with almost the entire coding sequence (amino acid 44-335) of human CSN5/JAB1, which is a coactivator of AP-1 transcription and the subunit 5 of CSN. Furthermore, we showed that BclGs specifically interacted with JAB1 by yeast two-hybrid and in vitro binding assay, and co-localized with it in the nucleus of Cos7 cells. By dual-reporter gene assay, BclGs inhibited AP-1 activity through JAB1. Correspondingly, it inhibited the endogenous phospho-c-Jun level through JAB1, and decreased the endogenous phospho-JNK level independent of MAPK pathways. At the same condition, BclGs also inhibited the phosphorylation of STAT3, and not influencing the phospho-STAT 1, 5 and 6. Interestingly, expression level of AKT was decreased, but the level of Lamin A/C was enhanced, and the degradation of Lamin A/C was not observed in COS7 cells. Taken together, it could be concluded that BclGs may inhibit JABl-controlled pathways and that the protein-protein interaction of BclGs-JABl may provide a molecular basis for key activities of BclGs. These results might elucidate a novel mechanism of BclGs signaling by specifically modulating the AP-1 pathway through JAB1 in early apoptosis.