NME/NDPK family
proteins are involved in the control of intracellular
nucleotide homeostasis as well as in both physiological and pathological cellular processes, such as proliferation, differentiation, development, apoptosis, and
metastasis dissemination, through mechanisms still largely unknown. One family member, NME1/NDPK-A, is a
metastasis suppressor, yet the primary physiological functions of this
protein are still missing. The purpose of this study was to identify new NME1/NDPK-A-dependent
biological functions and pathways regulated by this gene in the liver. We analyzed the
proteomes of wild-type and transgenic NME1-null mouse livers by combining two-dimensional gel electrophoresis and mass spectrometry (matrix-assisted
laser desorption/ionization time of flight and liquid chromatography-tandem mass spectrometry). We found that the levels of three
proteins, namely,
phenylalanine hydroxylase,
annexin IV, and
elongation factor 1 Bα (EF-1Bα), were strongly reduced in the cytosolic fraction of NME1(-/-) mouse livers when compared to the wild type. This was confirmed by immunoblotting analysis. No concomitant reduction in the corresponding messenger RNAs or of total
protein level was observed, however, suggesting that NME1 controls
annexin IV and EF-1Bα amounts by post-translational mechanisms. NME1 deletion induced a change in the subcellular location of
annexin IV in hepatocytes resulting in enrichment of this
protein at the plasma membrane. We also observed a redistribution of EF-1Bα in NME1(-/-) hepatocytes to an intracytoplasmic compartment that colocalized with a marker of the reticulum endoplasmic. Finally, we found reduced expression of
annexin IV coincident with decreased NME1 expression in a panel of different
carcinoma cell lines. Taken together, our data suggest for the first time that NME1 might regulate the subcellular trafficking of
annexin IV and EF-1Bα. The potential role of these
proteins in metastatic dissemination is discussed.