Calcium/calmodulin-dependent protein kinase II (CaMKII) regulates tumour necrosis factor-related apoptosis inducing ligand (TRAIL)-mediated apoptosis of fibroblast-like synovial cells (FLS) by phosphorylation of Akt.

OBJECTIVE

We tried to determine whether calcium/calmodulin-dependent protein kinase II (CaMKII) regulates tumour necrosis factor-related apoptosis inducing ligand (TRAIL)-mediated apoptosis of fibroblast-like synovial cells (FLS).

METHODS

CaMKII expression in FLS was studied by both western blotting and real time reverse transcription polymerase chain reaction (RT-PCR). TRAIL-mediated apoptosis of FLS was quantified by disruption of mitochondrial transmembrane potential (DeltaPsim), Leu-Glu-His-Asp (IETD) ase activity and DNA degradation. Involvement of CaMKII and other kinases, including extracellular signal-regulated kinase (ERK), p38, c-Jun N-terminal kinase (JNK) and Akt during TRAIL-mediated apoptosis of FLS was estimated by the use of specific each kinase chemical inhibitor.

RESULTS

Predominant expression of delta and gamma isoform of CaMKII, especially delta isoform, was determined in cultured FLS. TRAIL rapidly induced apoptosis of FLS as well as the phosphorylation of extracellular signal-regulated kinase (ERK), p38, c-Jun N-terminal kinase (JNK) and Akt. Chemical kinase inhibitor toward CaMKII and Akt significantly augmented TRAIL-mediated apoptosis of FLS whereas those toward ERK, p38 and JNK did not. Notably, CaMKII chemical inhibitor abrogated TRAIL-induced phosphorylation of Akt. Elevation of Leu-Glu-His-Asp (IETD) ase activity was associated with the apoptotic phenomena, which was almost suppressed by IETD competitive peptides.

CONCLUSION

Our results suggest a first observation that CaMKII regulates TRAIL-mediated apoptosis of FLS through Akt, standing an upstream of caspase-8-dependent cascades. Furthermore, CaMKII is suggested to be a new therapeutic target molecule of rheumatoid arthritis (RA).