Previous studies have demonstrated that c-Jun NH2-terminal protein kinase (JNK) plays a crucial role in neuronal apoptosis. Here, we report that indirubin-3'-oxime, a known effective inhibitor of cyclin-dependent kinases (CDKs) and glycogen synthase kinase 3-beta (GSK-3β), has a significant inhibitory effect on JNK. Kinase assay showed that indirubin-3'-oxime directly inhibited the activity of all three isoforms of JNK (JNK1, and JNK3) in vitro, with half inhibition dose (IC50) of 0.8µM, 1.4µM, and 1.0µM, respectively. In cerebellar granule neurons (CGNs), indirubin-3'-oxime blocked c-Jun phosphorylation induced by potassium withdrawal and prevented CGNs from apoptosis in a dose dependent manner. However, inhibitors of CDKs and GSK-3βwere ineffective in reducing c-Jun phosphorylation both in vitro and in vivo, suggesting that indirubin-3'-oxime prevents c-Jun phosphorylation independent of its inhibition on CDKs and GSK-3β. Our studies give further supports for JNK-targeting strategy in preventing neuronal apoptosis.

Kringle 5 (K5), a proteolytic fragment of plasminogen, has been proved to be an angiogenic inhibitor. Previously, we have evaluated the effect of K5 on the vascular leakage and neovascularization in a rat model of oxygen-induced retinopathy. In this study, we expressed K5 and a deletion mutant of K5 (K5 mutant) in a prokaryocyte expression system and purified them by affinity chromatography. K5 mutant was generated by deleting 11 amino acids from K5 while retaining the three disulfide bonds. The anti-angiogenic activity of intact K5 and K5 mutant were compared in endothelial cells and retinal neovascularization rat model. K5 mutant inhibited the proliferation of primary human retinal capillary endothelial cells (HRCEC) in a concentration-dependent manner, with an apparent EC50 of approximate 35nmol/L, which is twofold more potent than intact K5. In the even higher concentration range, K5 mutant did not inhibit pericytes from the same origin of HRCEC, which suggested an endothelial cell-specific inhibition. K5 mutant had no effect on normal liver cells and Bel7402 hepatoma cells even at high concentration range either. Intravitreal injection of the K5 and mutant in the oxygen-induced retinopathy rat model both resulted in significantly fewer neovascular tufts and nonperfusion area than controls with PBS injection, as shown by fluorescein angiography. Furthermore, K5 mutant exhibited more strong inhibition effect on neovascularization than intact K5 by quantification of vascular cells. These results suggest that this K5 deletion mutant is a more potent angiogenic inhibitor than intact K5 and may have therapeutic potential in the treatment of those disorders with neovascularization, such as solid tumor, diabetic retinopathy, age-related macular degeneration, rheumatoid arthritis, and hyperplasia of prostate.