The juvenile hormone analogue methoprene up-regulates the Ha-RNA-binding protein

RNA-binding proteins (RBPs) associate with RNA in cells to form ribonucleoprotein (RNP) complexes. The RBPs are involved in various aspects of RNA metabolism, but their roles in the juvenile hormone (JH) signaling pathway are not well known. An RNA-binding protein (Ha-RBP) was obtained from Helicoverpa armigera, a lepidopteran insect, which could be up-regulated by the juvenile hormone analogue methoprene at the mRNA level. Immunohistochemistry showed that Ha-RBP was mainly distributed in cells where protein synthesis was active, and its knockdown decreased the protein levels of JH-responsive genes. Immunocytochemistry showed that Ha-RBP was located in both the nucleus and the cytoplasm of normal cells, and methoprene could promote the translocation of Ha-RBP from the nucleus to the cytoplasm. This process was mediated by the JH receptor candidate HaMet but not by the ultraspiracle protein (USP). The knockdown of HaMet by RNAi decreased the expression of Ha-RBP and blocked its translocation from the nucleus to the cytoplasm. Together these findings indicate that Ha-RBP is involved in the juvenile hormone signaling pathway and Met mediates JH signaling by regulating Ha-RBP translocation from nucleus to cytoplasm, which may allow Ha-RBP to modify protein translation.