Aoi IKEGAMI

ABSTRACT The chimeric protein p210 BCR‐ABL is a major causative factor of chronic myeloid leukemia (CML). Previously, we found that p210 BCR‐ABL translocates from the cytosol to the mitochondria upon mitochondrial damage via the interaction of its pleckstrin homology domain (p210‐PH) with cardiolipin (CL), a mitochondria‐specific phospholipid. However, the precise pathological functions of this event are unknown. Here, using multivalent peptide library screens, we identified a tetravalent peptide, WDD‐R4‐tet, which binds to the CL‐binding region of p210‐PH and inhibits the translocation of p210 BCR‐ABL to the mitochondria. Notably, WDD‐R4‐tet induced the apoptosis of CML cells by specifically suppressing the expression of cellular inhibitor of apoptosis 1 and 2 (cIAP1/2), ubiquitin ligases with anti‐apoptotic functions, leading to the activation of caspases. Other compounds that inhibited cIAP1/2 also efficiently inhibited the proliferation of CML cells. Thus, WDD‐R4‐tet might be a novel therapeutic agent for CML, which functions by inhibiting novel cell‐survival signaling pathways generated on the mitochondrial outer membrane of CML cells.

Ca2+/calmodulin-dependent protein kinase II (CaMKII) is one of hundreds of host-cell factors involved in the propagation of type A influenza virus (IAV), although its mechanism of action is unknown. Here, we identified CaMKII inhibitory peptide M3 by targeting its kinase domain using affinity-based screening of a tailored random peptide library. M3 inhibited IAV cytopathicity and propagation in cells by specifically inhibiting the acute-phase activation of retinoic acid-inducible gene I (RIG-I), which is uniquely regulated by CaMKII. Downstream of the RIG-I pathway activated TBK1 and then IRF3, which induced small but sufficient amounts of transcripts of the genes for IFN α/β to provide the capped 5'-ends that were used preferentially as primers to synthesize viral mRNAs by the cap-snatching mechanism. Importantly, knockout of RIG-I in cells almost completely inhibited the expression of IFN mRNAs and subsequent viral NP mRNA early in infection (up to 6 h after infection), which then protected cells from cytopathicity 24 h after infection. Thus, CaMKII-dependent acute-phase activation of RIG-I promoted IAV propagation, whereas the canonical RIG-I pathway stimulated antiviral activity by inducing large amounts of mRNA for IFNs and then for antiviral proteins later in infection. Co-administration of M3 with IAV infection rescued mice from the lethality and greatly reduced proinflammatory cytokine mRNA expression in the lung, indicating that M3 is highly effective against IAV in vivo. Thus, regulation of the CaMKII-dependent non-canonical RIG-I pathway may provide a novel host-factor-directed antiviral therapy.IMPORTANCEThe recent emergence of IAV strains resistant to commonly used therapeutic agents that target viral proteins has exacerbated the need for innovative strategies. Here, we originally identified CaMKII-inhibitory peptide M3, which efficiently inhibits IAV-lethality in vitro and in vivo. M3 specifically inhibited the acute-phase activation of RIG-I, which is a novel pathway to promote IAV propagation. Thus, this pathway acts in an opposite manner compared with the canonical RIG-I pathway, which plays essential roles in antiviral innate immune response later in infection. The CaMKII-dependent non-canonical RIG-I pathway can be a promising and novel drug target for the treatment of infections.