Involved in the formation of the dorsoventral pattern. It inhibits nuclear translocation of the dorsal morphogen in the dorsal region of the embryo. Acts as a negative regulator of the NF-kappa-B (rel) signaling pathway. Cact is degraded by IKKbeta, this is essential for NF-kappa-B (rel) activation. Phosphorylated isoform A binds to dorsal (dl); inhibits dl translocation to the nucleus and therefore from binding to DNA. In vitro, interacts with IKKbeta. Interacts with cactin and kappa-B-Ras. Expressed in ovary (at protein level). Expressed during embryogenesis (at protein level). Isoform A is expressed in ovaries and 0-1 hour embryos. After 2-3 hours unphosphorylated zygotic protein is expressed. Between 4-8 hours phosphorylated zygotic protein is expressed. After 12 hours the amount of unphosphorylated zygotic protein increases until, by the end of embryogenesis, it is the most abundant form of cactus. Activated IKKbeta phosphorylates cact. Belongs to the NF-kappa-B inhibitor family.