DPMS is Essential for Tumor Angiogenesis

Abstract

Dolichol phosphate mannose synthase (DPMS) an inverting GT‐A folded enzyme and classified as GT2 by CAZy (carbohydrate active enZyme; http://www.cazy.org). It catalyzes the transfer reaction Dol‐P + GDP‐Man < == > Dol‐P‐Man + GDP in endoplasmic reticulum (ER) for the synthesis of dolichol‐linked tetra‐decasaccharide [Glc3Man9GlcNAc2‐PP‐Dol; lipid linked oligosaccharide (LLO)], a pre‐requisite for the glycosylation of asparagine‐linked (N‐linked) glycoproteins. N‐Glycosylation provides structural and functional stability, and adds flexibility to glycoproteins. The gene for DPMS has been cloned from many species, i.e., from archaea to human. The amino acid sequence identifies the presence of a metal binding (i.e., DAD) signature and a cAMP‐dependent protein phosphorylation (PKA) motif. Phosphorylation enhances the DPMS catalytic activity and consequently increases the synthesis and turnover of LLO. In capillary endothelial cells, it means increased proliferation, i.e., angiogenesis. Angiogenesis is a hallmark for breast cancer progression. Therefore, we have hypothesized that overexpression of DPMS in capillary endothelial cells could mimic the cAMP signaling and independently increase angiogenesis. To test the hypothesis, we have used a cell line that stably overexpresses DPMS and evaluated the role of D(+)mannose on their proliferation by MTT assay. Capillary endothelial cells harboring the DPMS overexpressing plasmid exhibited increased expression of DPMS when examined by immunofluorescence microscopy, western blotting, and QPCR. There was increased expression of cell surface N‐glycans as judged by Texas‐Red conjugated WGA‐binding. The cell proliferation as well as the cellular mitotic activity were also enhanced. To evaluate if mannose is required for the observed effect, we have monitored the cellular proliferation as a function of mannose concentration and the time of incubation by MTT assay. The results indicate mannose supplementation did not support the growth of neither the DPMS overexpressing cells nor the control cells. Triple negative human breast cancer cells also showed a similar result. We therefore conclude DPMS overexpression induces angiogenesis. Mechanistically it is not due to upregulation of mannose transport. The environmental factors increasing intracellular cAMP level increase DPMS catalytic activity metabolically or through gene expression and enhance angiogenesis for breast tumor progression. DPMS, thus could be an excellent target for developing a new generation glycotherapy against breast cancer.Support or Funding InformationInstitutionalThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.