CRISPR/Cas9-mediated knockout of HIF-1α gene in epithelioma papulosum cyprini (EPC) cells inhibited apoptosis and viral hemorrhagic septicemia virus (VHSV) growth

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Hypoxia-inducible factor-1 (HIF-1) is a heterodimer of HIF-1α and HIF-1β, and its key role in the regulation of cellular responses to hypoxia has been well-demonstrated. The participation of HIF-1α in apoptosis has been reported in mammals, however, a little information is available on the role of HIF-1α in the progression of apoptosis in fish. In this study, to know the role of HIF-1α in the apoptosis of fish cells, we produced HIF-1α knockout Epithelioma papulosum cyprini (EPC) cells using a CRISPR/Cas9 vector, and a single cell clone showing a heterozygous insertion/deletion (indel) mutation (one nucleotide insertion and one nucleotide deletion in HIF-1α gene) was chosen for further experiments. To confirm the knockout of HIF-1α, cells were transfected with a hypoxia reporting vector containing hypoxic response elements (HREs). EPC cells transfected with the reporting plasmids showed significantly increased luminescence by exposure to cobalt chloride, a prolyl hydroxylases inhibitor. On the other hand, HIF-1α knockout EPC cells showed a non-responsiveness to a cobalt chloride exposure, suggesting that functional HIF-1α protein was not produced in the HIF-1α knockout EPC cells. Apoptosis progression induced by camptothecin and viral hemorrhagic septicemia virus (VHSV) infection was severely inhibited by HIF-1α knockout, and the replication of VHSV was significantly retarded in HIF-1α knockout EPC cells. These results suggest that HIF-1α in EPC cells acts as a pro-apoptotic factor in the progression of apoptosis triggered by a DNA damaging agent and rhabdoviral infection.