Novel Antifungal Compound Z-705 Specifically Inhibits Protein Kinase C of Filamentous Fungi.

The cell wall integrity signaling (CWIS) pathway is involved in fungal cell wall biogenesis. This pathway is composed of sensor proteins, protein kinase C (PKC), and the mitogen-activated protein kinase (MAPK) pathway, and it controls the transcription of many cell wall-related genes. PKC plays a pivotal role in this pathway; deficiencies in PkcA in the model filamentous fungus and in MgPkc1p in the rice blast fungus are lethal. This suggests that PKC in filamentous fungi is a potential target for antifungal agents. In the present study, to search for MgPkc1p inhibitors, we carried out screening by three-dimensional (3D) structural modeling and performed growth inhibition tests for on agar plates. From approximately 800,000 candidate compounds, we selected Z-705 and evaluated its inhibitory activity against chimeric PKC expressed in cells in which the kinase domain of native PKC was replaced with those of PKCs of filamentous fungi. Transcriptional analysis of , which encodes a downstream factor of PKC in , and phosphorylation analysis of the mitogen-activated protein kinase (MAPK) Mpk1p, which is activated downstream of PKC, revealed that Z-705 specifically inhibited PKCs of filamentous fungi. Moreover, the inhibitory activity of Z-705 was similar to that of a well-known PKC inhibitor, staurosporine. Interestingly, Z-705 inhibited melanization induced by cell wall stress in We discuss the relationships between PKC and melanin biosynthesis. A candidate inhibitor of filamentous fungal protein kinase C (PKC), Z-705, was identified by screening. A screening system to evaluate the effects of fungal PKC inhibitors was constructed in Using this system, we found that Z-705 is highly selective for filamentous fungal PKC in comparison with PKC. Analysis of the mRNA level, which is regulated by Mps1p mitogen-activated protein kinase (MAPK) via PKC, in the rice blast fungus revealed that Z-705 had a PKC inhibitory effect comparable to that of staurosporine. Micafungin induced hyphal melanization in , and this melanization, which is required for pathogenicity of , was inhibited by PKC inhibition by both Z-705 and staurosporine. The mRNA levels of , , and , which are essential for melanization in , were suppressed by both PKC inhibitors.