Protein phosphorylation reportedly involved in signal transd

Protein phosphorylation reportedly involved in signal transduction pathways. The gnrh agonist of IPO is regulated by protein kinases and phosphatases in the wounding signaling pathway of sweet potato [40]. However, the interplay among protein kinase, phosphatase, and H2O2 has not been explored yet. To answer this question, SB, a p38 MAPK inhibitor, and OKA, a protein phosphatase inhibitor, were used. When sweet potato was treated with OKA, OKA inhibited the protein phosphatase activity and blocked the signal transduction inducing IPO expression [40]. Herein, these inhibitors were added in turn. IPO expression induced by SB was blocked by pretreatment with OKA (Fig. 7B). These results indicate that wounding may first repress p38-like MAPK protein kinase activity and then activate protein phosphatases to induce IPO expression (Fig. 7B). Moreover, OKA blocks the wounding- and H2O2- induced IPO expression (Fig. 7A). To summarize, wounding induces the production of H2O2, which represses protein kinase activity. The declined protein kinase activity would activate p38-like MAPK protein phosphatase, and eventually induce IPO expression. The MAPK cascade is one of the earliest signaling events in eukaryotic signaling cascades. The activation of MAPKs occurs by MAPKKs, which are phosphorylated through MAPKKKs. In tobacco, the transcription and activity of MAPKs are rapidly induced by wounding within 1 min [65]. In addition, MEK2, a tobacco MAPKK, is necessary for the activation of MAPKs after wounding [20]. The expression of IPO is regulated by MAPKK in the wounding signaling pathway of sweet potato [23,24,40]. To determine the connections between MAPKK and p38-like MAPK, PD, SB, and H2O2 were used. The expression of IPO is activated by wounding, H2O2 and SB (Fig. 8). In addition, the amount of pp38-like MAPK was decreased by wounding and SB (Fig. 1, Fig. 3). When PD, a MAPKK inhibitor, was used, the induction of IPO gene by wounding, SB and H2O2 was blocked in sweet potato (Fig. 8). These results may imply that wounding first represses p38-like MAPK protein kinase activity, and MAPKK is then activated. Conclusively, sweet potato after wounding decreases the amount of phosphorylated p38-like MAPK, which activates H2O2 production. Then, H2O2 mediates the generation of dephosphorylated protein via protein phosphatase. Finally, the IbMEK1/IbMAPK cascade is promoted to induce IPO expression. This IPO transduction pathway via p38-like MAPK mechanism was cytosolic calcium-independent (Fig. 9).
Materials and methods
Authors’ contributions
Competing interests
Acknowledgment
Introduction Benzimidazole-based compounds are widely used anthelmintic drugs that are high effective against a wide range of helminth species and possess low mammalian toxicity [25]. The molecular mechanism of action of benzimidazoles is related to microtubule inhibition, which results in the disruption of the microtubule structure and interference with the microtubule-mediated transport of secretory vesicles in the absorptive tissues of helminths [21], [26], [28]. This leads to the immobilization and death of the parasite [33]. Given that microtubules play key roles in the proliferation, trafficking, and migration of eukaryotic cells and tumor cells, compounds interfering with the microtubule structure have been used for cancer chemotherapies [11], [35]. Indeed, several studies reveal that the microtubule disrupting properties of benzimidazole derivatives such as albendazole (ABZ) and flubendazole (FUZ) could be repositioned for cancer therapies [5], [9], [23], [36], [38], [45], [50]. The antitumor properties of benzimidazoles have been demonstrated in vitro and in animal models. ABZ was found to effective against hepatocellular carcinoma cells [38], epothilone/paclitaxel-resistant leukemic cells [23], paclitaxel-resistant ovarian carcinoma cells, metastatic melanoma [9], and small-cell lung cancer cell lines [36]. FUZ has shown antiproliferative potential in neuroblastomas, leukemic cells, and myeloma cells [34], [45]. FUZ binds to tubulin at a site distinct from vinblastine and potentiated the effect of vinblastine and vincristine in a leukemia xenograft model [45]. Although microtubule-targeting agents induce mitotic arrest, several studies reveal that non-mitotic effects of microtubule-targeting agents play prominent roles in inducing apoptosis of cancer cells [12], [27], [40]. Some studies have revealed that microtubule-targeting agents induce apoptosis of cancer cells through the mitochondria- or death receptor (TNF-α superfamily)-mediated death pathways [3], [8], [16]. Notably, a benzimidazole derivative induces apoptosis of breast cancer cells via the JNK-mediated upregulation of death receptor 5 [8]. Although benzimidazoles are found to suppress the growth of leukemic cell lines [23], [45], the dependence of its anti-leukemic activity on non-mitotic effect has not been addressed yet. In view of the findings that benzimidazole-based compound markedly induces the death of human leukemia U937 cells [45], we thus investigated the mechanistic pathway responsible for ABZ-induced death of human leukemia U937 cells.