The β4 subunit of Cav1.2 channels is required for an optimal interferon response in cardiac muscle cells

Abstract

The auxiliary β₄ subunit of the cardiac Ca_v1.2 channel plays a poorly understood role in gene transcription. Here, we characterized the regulatory effects of the β₄ subunit in H9c2 rat cardiac cells on the abundances of Ifnb mRNA [which encodes interferon-β (IFN-β)] and of the IFN-β-related genes Ddx58, Ifitm3, Irf7, Stat2, Ifih1, and Mx1, as well as on the abundances of the antiviral proteins DDX58, IRF7, STAT2, and IFITM3. Knocking down the β₄ subunit in H9c2 cells reduced the expression of IFN-β-stimulated genes. In response to inhibition of the kinase JAK1, the abundances of β₄ subunit mRNA and protein were decreased. β₄ subunit abundance was increased, and it translocated to the nucleus, in cells treated with IFN-β, infected with dengue virus (DENV), or transfected with poly(I:C), a synthetic analog of double-stranded RNA. Cells that surrounded the virus-infected cells showed translocation of β₄ subunit proteins to nuclei in response to spreading infection. We showed that the β₄ subunit interacted with the transcriptional regulator IRF7 and that the activity of an Irf7 promoter-driven reporter was increased in cells overexpressing the β₄ subunit. Last, overexpressing β₄ in undifferentiated and differentiated H9c2 cells reduced DENV infection and decreased the abundance of the viral proteins NS1, NS3, and E-protein. DENV infection and poly(I:C) also increased the concentration of intracellular Ca²⁺ in these cells. These findings suggest that the β₄ subunit plays a role in promoting the expression of IFN-related genes, thereby reducing viral infection.