Abstract
Compartmentalization is vital for biological systems at multiple levels, including biochemical reactions in metabolism. Organelle-based compartments such as mitochondria and peroxisomes sequester the responsible enzymes and increase the efficiency of metabolism while simultaneously protecting the cell from dangerous intermediates, such as radical oxygen species. Recent studies show intracellular nucleotides, such as ATP and GTP, are heterogeneously distributed in cells with high concentrations at the lamellipodial and filopodial projections, or leading edge. However, the intracellular distribution of purine nucleotide enzymes remains unclear. Here, we report the enhanced localization of GTP-biosynthetic enzymes, including inosine monophosphate dehydrogenase (IMPDH isotype 1 and 2), GMP synthase (GMPS), guanylate kinase (GUK1) and nucleoside diphosphate kinase-A (NDPK-A) at the leading edge in renal cell carcinoma cells. They show significant co-localization at the membrane subdomain, and their co-localization pattern at the membrane is distinct from that of the cell body. While other purine nucleotide biosynthetic enzymes also show significant localization at the leading edge, their co-localization pattern with IMPDH is divergent. In contrast, a key glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), predominantly localized in the cytoplasm. Mechanistically, we found that plasma membrane localization of IMPDH isozymes requires active actin polymerization. Our results demonstrate the formation of a discrete metabolic compartment for localized purine biosynthesis at the leading edge, which may promote localized nucleotide metabolism for cell migration and metastasis in cancers.
Keywords:
GMPS; GUK1; IMPDH; Metabolic compartmentalization; Salvage purine synthesis; de novo purine synthesis.