IRES-mediated translational control of AMAP1 expression during differentiation of monocyte U937 cells

Global control of mRNA translation plays key roles in cell regulation, including growth, differentiation and apoptosis. Human monocyte-like U937 cells differentiate into macrophage-like cells upon 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment, a process which is known to be accompanied with a large decrease in general protein synthesis. Here, we found that protein levels of AMAP1 (also called ASAP1 or DDEF1), a GTPase-activating protein for Arf GTPases, increase several fold during U937 cell differentiation. This increase was not accompanied with a notable increase in the AMAP1 gene transcript, nor seemed to be due to 5’-Cap-dependent mRNA translational activities in differentiated U937 cells. We identified the 5’-untranslated region (5’-UTR) of AMAP1 mRNA, and found that this 5’-UTR exhibits significant internal ribosome entry site (IRES)-dependent translational activity in differentiated U937 cells, but not in undifferentiated cells. Our results indicate that monocyte differentiation involves enh...