RESUMEN
JNK, a member of the mitogen activated protein kinases (MAPKs) superfamily, plays a key role in cell death in many neurological disorders, but systemic inhibition of JNK has detrimental side effects. JNK can be regulated by two direct upstream kinases: MAPK kinase 4 (MKK4) and MAPK kinase 7 (MKK7). Here, we investigated the effect of GADD45ß-I, a recently designed cell-permeable inhibitor peptide for MKK7, on endoplasmic reticulum (ER) stress-induced cytotoxicity in neuronal HT22 cells. We found that treatment with the ER stress inducer tunicamycin (TM) increased the phosphorylation of JNK and MKK7 in HT22 cells, which was nullified by GADD45ß-I. GADD45ß-I significantly attenuated TM-induced toxicity via inhibiting apoptotic cell death, as evidenced by decreased number of TUNEL-positive cells and reduced caspase-3 activity. GADD45ß-I treatment also decreased expression of ER stress associated pro-apoptotic proteins and prevented morphological changes of the ER after TM exposure. In addition, inhibition of mitochondrial oxidative stress and preservation of intracellular ATP levels were observed in GADD45ß-I-treated cells. The experiments using siRNA transfection and Topflash reporter assay revealed a possible involvement of Wnt/ß-catenin pathway in GADD45ß-I-induced protection in HT22 cells. In summary, our results demonstrated that GADD45ß-I exerted protective effects against TM-induced cytotoxicity via regulating JNK-Wnt pathway. Targeting MKK7 could represent a new therapeutic strategy for the treatment of neurological diseases where ER stress associated neuronal injury are involved.
