Galectin-1 (Gal1) co-opts VEGFR2 (KDR) signaling pathways through the formation of lectin-glycan lattices on highly branched complex N-glycans

CROCI DO; SALATINO M; ILARREGUI JM; DOMAICA C; CERLIANI JP; MASCANFRONI ID; DERGAN DYLON SL; STUPIRSKI JC; SUNDBLAD V; TOSCANO MA; RABINOVICH GA

Buenos Aires

Congreso; First French-Argentine Immunology Congress; 2010

Sociedad Argentina de Inmunología

In previous studies we demonstrated that galectin-1 (Gal1) links tumor hypoxia and VEGF-mediated angiogenesis. The present study was conducted to investigate signaling pathways associated with this pro-angiogenic function and to identify potential glyco-receptors mediating these effects. We first examined the ‘glycosylation signature’ of ECs in resting conditions or exposed to proliferative, tolerogenic or inflammatory stimuli. In contrast to ECs stimulated with pro-inflammatory (TNF), TH1-(IFN-g) or TH-17(IL-17) stimuli, ECs exposed to tolerogenic  (IL-10 or TGF-b or proliferative (bFGF) signals exhibited a substantial up-regulation of cell surface N- glycans that are critical for galectin-1 signaling, an effect which was consistent with galectin-1 binding to ECs (p<0.01). Screening of the phosphorylation status of a spectrum of growth factor receptors using signaling arrays revealed a 2-fold increase in phosphorylation of KDR, Akt and Erk1/2 upon exposure to Gal1, a pattern comparable to that induced by VEGF. Pharmacological inhibition of Akt or Erk1/2 signaling abrogated Gal1-induced EC proliferation  (p<0.01), migration (p<0.01) and angiogenesis (p<0.05). siRNA-mediated silencingof KDR completely  prevented Akt and ERK1/2 phosphorylation induced by either Gal1 or  VEGF-A. Interruption of N-acetylglucosaminyltransferase V (GnT5)-mediated N-glycan  branching prevented Gal1 but not VEGF-A signaling. Co-immunoprecipitation revealed specific  association of Gal1 with KDR through Nglycan- dependent interactions. Consistently, KDR  blockade or interruption of N-glycan elongation  prevented Gal1-induced EC migration (p<0.01)  and morphogenesis (p<0.05), whereas blockade of VEGFR1, VEGFR3, NRP-1 or VEGF-A had no effect. Collectively, our results suggest that signaling complexes established between lectins and specific glycans might serve as alternative or compensatory pathways by mimicking ‘cognate  ligands’, thus preserving critical cellular processes such as angiogenesis.