Functional analysis of inhibitor of apoptosis 1 of the silkworm Bombyx mori.
Recent advances in genome-wide surveys have revealed a number of lepidopteran insect homologs of mammalian and Drosophila genes that are responsible for apoptosis regulation. However, the underlying molecular mechanisms for apoptosis regulation in lepidopteran insect cells remain poorly understood. In the present study, we demonstrated that the transfection of Bombyx mori BM-N cells with dsRNA against the B. mori cellular iap1 gene (cbm-iap1) induces severe apoptosis that is accompanied by an increase of caspase-3-like protease activity. In these apoptotic cells, the cleaved form of the endogenous initiator caspase Dronc (Bm-Dronc) was detected, indicating that cBm-IAP1 protein depletion by RNAi silencing resulted in the activation of Bm-Dronc. In transient expression assays in BM-N cells, cBm-IAP1 suppressed the apoptosis triggered by Bm-Dronc overexpression and depressed the elevation of caspase-3-like protease activity, but also increased the cleaved form of Bm-Dronc protein. cBm-IAP1 also suppressed the caspase-3-like protease activity stimulated by Bm-caspase-1 overexpression. Co-immunoprecipitation experiments demonstrated that cBm-IAP1 strongly interacts with Bm-Dronc, but only has weak affinity for Bm-caspase-1. Transient expression analyses showed that truncated cBm-IAP1 proteins defective in the BIR1, BIR2 or RING domain were unable to suppress Bm-Dronc-induced apoptosis. In addition, BM-N cells expressing truncated cBm-IAP1 proteins underwent apoptosis, suggesting that intact cBm-IAP1, which has anti-apoptotic activity, was replaced or displaced by the overexpressed truncated cBm-IAP1 proteins, which are incapable of interfering with the apoptotic caspase cascade. Taken together, the present results demonstrate that cBm-IAP1 is a vital negative regulator of apoptosis in BM-N cells and functions by preventing the activation and/or activity of Bm-Dronc and Bm-caspase-1.
Laboratory of Sericulture and Entomoresources, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
Rina
R
Hamajima
Laboratory of Sericulture and Entomoresources, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
Asako
A
Iwamoto
Laboratory of Sericulture and Entomoresources, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
Moe
M
Tomizaki
Laboratory of Sericulture and Entomoresources, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
Ikue
I
Suganuma
Laboratory of Sericulture and Entomoresources, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
Koji
K
Kitaguchi
Laboratory of Sericulture and Entomoresources, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
Michihiro
M
Kobayashi
Laboratory of Sericulture and Entomoresources, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
Hayato
H
Yamada
Laboratory of Sericulture and Entomoresources, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan. Electronic address: mochiko@agr.nagoya-u.ac.jp.
Motoko
M
Ikeda
D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D012831:Bombyx / Q000235:genetics / Q000502:physiology*; D020169:Caspases / Q000235:genetics* / Q000378:metabolism; D051034:Inhibitor of Apoptosis Proteins / Q000235:genetics* / Q000378:metabolism; D019476:Insect Proteins / Q000235:genetics* / Q000378:metabolism
D051034:Inhibitor of Apoptosis Proteins; D019476:Insect Proteins; D020169:Caspases
Apoptosis; Bombyx mori; IAP; Inhibitor of apoptosis; Initiator caspase Dronc; Lepidopteran caspase-1