Iridovirus Bcl-2 protein inhibits apoptosis in the early stage of viral infection.
The grouper iridovirus (GIV) belongs to the family Iridoviridae, whose genome contains an antiapoptotic B-cell lymphoma (Bcl)-2-like gene. This study was carried-out to understand whether GIV blocks apoptosis in its host. UV-irradiated grouper kidney (GK) cells underwent apoptosis. However, a DNA fragmentation assay of UV-exposed GK cells after GIV infection revealed an inhibition of apoptosis. The UV- or heat-inactivated GIV failed to inhibit apoptosis, implying that a gene or protein of the viral particle might contribute to an apoptosis inhibitory function. The DNA ladder assay for GIV-infected GK cells after UV irradiation confirmed that apoptosis inhibition was an early process which occurred as early as 5 min post-infection. A GIV-Bcl sequence comparison showed distant sequence similarities to that of human and four viruses; however, all possessed the putative Bcl-2 homology (BH) domains of BH1, BH2, BH3, and BH4, as well as a transmembrane domain. Northern blot hybridization showed that GIV-Bcl transcription began at 2 h post-infection, and the mRNA level significantly increased in the presence of cycloheximide or aphidicolin, indicating that this GIV-Bcl is an immediate-early gene. This was consistent with the Western blot results, which also revealed that the virion carries the Bcl protein. We observed the localization of GIV-Bcl on the mitochondrial membrane and other defined intracellular areas. By immunostaining, it was proven that GIV-Bcl-expressing cells effectively inhibited apoptosis. Taken together, these results demonstrate that GIV inhibits the promotion of apoptosis by GK cells, which is mediated by the immediate early expressed viral Bcl gene.
Lin
Pei-Wen
PW
Molecular Genetics Laboratory, Rm. 336, Institute of Cellular and Organismic Biology, Academia Sinica, 128 Academia Road Section 2, Nankang, Taipei, Taiwan, ROC.
Huang
Yi-Jen
YJ
John
Joseph Abraham Christopher
JA
Chang
Ya-Nan
YN
Yuan
Chung-Hsiang
CH
Chen
Wen-Ya
WY
Yeh
Chiao-Hwa
CH
Shen
San-Tai
ST
Lin
Fu-Pang
FP
Tsui
Wen-Huei
WH
Chang
Chi-Yao
CY
D000595:Amino Acid Sequence; D000818:Animals; D016590:Aphidicolin / Q000494:pharmacology; D017209:Apoptosis / Q000528:radiation effects; D001483:Base Sequence; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D053938:DNA Fragmentation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019254:Genes, bcl-2; D017994:Iridovirus / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D010473:Perciformes; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry / Q000378:metabolism*; D014466:Ultraviolet Rays
D004791:Enzyme Inhibitors; D011500:Protein Synthesis Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D016590:Aphidicolin; D003513:Cycloheximide