Cytoskeleton Protein BmACT1 Is Potential for the Autophagic Function and Nuclear Localization of BmAtg4b in .

Homologs of Autophagy-related (Atg) protein 4 are reported to cleave LC3 protein and facilitate autophagy occurrence differently in mammals, whereas their functions have not been investigated in insects. Three homologs, including and its short form as well as exist in . Herein, the autophagic functions of BmAtg4a and BmAtg4b were investigated. qPCR detection found that and both peaked during larval-pupal metamorphosis when autophagy occurs robustly. Immunofluorescent staining showed that BmAtg4a was predominantly localized at the cytoplasm, while BmAtg4b had notable nuclear localization. Overexpression of and both slightly promoted basal autophagy but inhibited the autophagy induced by the infection of nucleopolyhedrovirus (BmNPV) and, thereby, its proliferation. In comparison, knockout of or significantly upregulated BmNPV-induced autophagy and its replication in BmN cells. Results of Co-immunoprecipitation associated with mass spectrum showed that the cytoskeleton protein actin A2 (BmACT2) and actin A1 (BmACT1) bound with BmAtg4a and BmAtg4b especially. Knockout of and inhibited BmAtg4b- and BmAtg4a-induced autophagy, respectively; moreover, knockout of reduced the ratio of cells with nuclear BmAtg4b. Of note, BmAtg4a and BmAtg4b had physical interaction, and they had an inhibitory effect on mutual autophagic function. In this work, we provide new insights into the autophagy machinery in insects as well as its function in the proliferation of BmNPV.