XIAP and cancer: UA has also been suggested to inhibit proliferation signaling pathways including Ras/MAPK, PI3K/Akt, and STAT3 [19,20,33], downregulate the apoptosis inhibitor X-linked inhibitor of apoptotic protein (XIAP) [15], and suppress the transcription factor Sp1 [18] (which is a poor prognostic factor for many cancers [34]).