An immunological role of a PKC alpha binding protein (PICK1) expressed in the hemocytes of the beet armyworm, Spodoptera exigua

Protein kinase C (PKC) regulates various intracellular processes and its activity is tightly controlled by various factors, such as secondary messengers and binding proteins. A cDNA of a PKC alpha binding protein (also called PICK1: protein interacting with C kinase 1) was cloned in hemocytes of the beet armyworm, Spodoptera exigua (Noctuidae: Lepidoptera). It encodes 475 amino acid residues with putative PDZ and BAR domains interacting with other proteins or ligands. The PICK1 gene of S. exigua (Se-PICK1) was expressed in all developmental stages. In the larval stage, it was highly expressed in hemocyte and brain tissues. A quantitative RT-PCR indicated that its expression was significantly up-regulated by a bacterial challenge. RNA interference of Se-PICK1 in the fifth instar larvae with 100 ng of a specific double-stranded RNA could effectively knockdown its expression after 48 h post-injection in hemocytes. The suppressed expression of Se-PICK1 significantly impaired the larvae of S. exigua to induce hemocyte-spreading behavior and to form hemocyte nodules in response to bacterial infection. This is the first report of an immunological role of PICK1, which has been identified in various insect and mammalian genomes.