title: Baculovirus IE2 Stimulates the Expression of Heat Shock Proteins in Insect and Mammalian Cells to Facilitate Its Proper Functioning.
abstract: Baculoviruses have gained popularity as pest control agents and for protein production in insect systems. These viruses are also becoming popular for gene expression, tissue engineering and gene therapy in mammalian systems. Baculovirus infection triggers a heat shock response, and this response is crucial for its successful infection of host insect cells. However, the viral protein(s) or factor(s) that trigger this response are not yet clear. Previously, we revealed that IE2-an early gene product of the baculovirus-could form unique nuclear bodies for the strong trans-activation of various promoters in mammalian cells. Here, we purified IE2 nuclear bodies from Vero E6 cells and investigated the associated proteins by using mass spectrometry. Heat shock proteins (HSPs) were found to be one of the major IE2-associated proteins. Our experiments show that HSPs are greatly induced by IE2 and are crucial for the trans-activation function of IE2. Interestingly, blocking both heat shock protein expression and the proteasome pathway preserved the IE2 protein and its nuclear body structure, and revived its function. These observations reveal that HSPs do not function directly to assist the formation of the nuclear body structure, but may rather protect IE2 from proteasome degradation. Aside from functional studies in mammalian cells, we also show that HSPs were stimulated and required to determine IE2 protein levels, in insect cells infected with baculovirus. Upon inhibiting the expression of heat shock proteins, baculovirus IE2 was substantially suppressed, resulting in a significantly suppressed viral titer. Thus, we demonstrate a unique feature in that IE2 can function in both insect and non-host mammalian cells to stimulate HSPs, which may be associated with IE2 stabilization and lead to the protection of the its strong gene activation function in mammalian cells. On the other hand, during viral infection in insect cells, IE2 could also strongly stimulate HSPs and ultimately affect viral replication.
authors: Molecular and Biological Agricultural Sciences, Taiwan International Graduate Program, Academia Sinica, Taipei, Taiwan, and National Chung Hsing University, Taichung, Taiwan.|Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.|Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan.
authors: Hsuan
authors: H
authors: Tung
authors: Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.|Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan.
authors: Sung-Chan
authors: SC
authors: Wei
authors: Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.
authors: Huei-Ru
authors: HR
authors: Lo
authors: Molecular and Biological Agricultural Sciences, Taiwan International Graduate Program, Academia Sinica, Taipei, Taiwan, and National Chung Hsing University, Taichung, Taiwan.|Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.|Biotechnology Center, National Chung Hsing University, Taichung, Taiwan.
authors: Yu-Chan
authors: YC
authors: Chao
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001559:Benzhydryl Compounds / Q000494:pharmacology; D002522:Chlorocebus aethiops; D020869:Gene Expression Profiling; D015967:Gene Expression Regulation, Viral; D017930:Genes, Reporter; D006360:Heat-Shock Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D054884:Host-Pathogen Interactions; D017874:Immediate-Early Proteins / Q000502:physiology*; D007181:Inclusion Bodies, Viral; D045586:Intranuclear Inclusion Bodies; D007976:Leupeptins / Q000494:pharmacology; D008969:Molecular Sequence Data; D017924:Nucleopolyhedroviruses / Q000235:genetics / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011760:Pyrrolidinones / Q000494:pharmacology; D034622:RNA Interference; D061987:Sf9 Cells; D018411:Spodoptera; D015534:Trans-Activators / Q000502:physiology*; D015854:Up-Regulation; D014709:Vero Cells; D014779:Virus Replication
chemical_list: D001559:Benzhydryl Compounds; D006360:Heat-Shock Proteins; D017874:Immediate-Early Proteins; C410027:KNK 437; D007976:Leupeptins; D011760:Pyrrolidinones; D015534:Trans-Activators; C072773:IE2 protein, polyhedrosis virus; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde