ANXA5 and cancer: IL-24 elevates cAMP levels in a concentration-dependent manner, resulting in PKA activation, and increases the phosphorylation of PKA substrates (Figure 2A,B) Cell viability and annexin V analysis shows that cancer cell killing by IL-24 is dependent on PKA, as chemical inhibition of PKA by H-89 abrogates the pro-apoptotic activity of IL-24 on cancer cells (Figure 3A,B).