CACNB4 and infection: The absence of cytoplasmic CAB4-GFP during these infections, along with the presence of cytoplasmic CAB2 and CAB2ΔvopC, point to the necessity of the VtrABC signaling cascade, the regulatory apparatus of the T3SS2, and associated virulence factors disrupted in CAB4 but intact in CAB2 and CAB2ΔvopC in mediating endosomal escape, as well as T3SS2 expression (4, 37).