Phosphorylation is shown to be having a regulatory role in the function of claudin-3 and claudin-4, for example, activated PKA (D’Souza et al., 2005) or PKC (D’Souza et al., 2007) phosphorylates claudin-3 and claudin-4 and enhance the paracellular permeability in ovarian cancer cells through the mislocalization of claudins. The gene discussed is CLDN4; the disease is ovarian cancer.