Differential regulation of fibroblast growth factor receptor 1 trafficking and function by extracellular galectins

Abstract

Fibroblast growth factor receptors (FGFRs) are integral membrane proteins that transmit signals through the plasma membrane. FGFRs signaling needs to be precisely adjusted as aberrant FGFRs function is associated with development of human cancers or severe metabolic diseases. The subcellular localization, trafficking and function of FGFRs rely on the formation of multiprotein complexes. In this study we revealed galectins, lectin family members implicated in cancer development and progression, as novel FGFR1 binding proteins. We demonstrated that galectin-1 and galectin-3 directly bind to the sugar chains of the glycosylated extracellular part of FGFR1. Although both galectins compete for the same binding sites on FGFR1, these proteins elicit different impact on FGFR1 function and cellular trafficking. Galectin-1 mimics fibroblast growth factor as it efficiently activates FGFR1 and receptor-downstream signaling pathways that result in cell proliferation and apoptotic evasion. In contrast, galectin-3 induces extensive clustering of FGFR1 on the cell surface that inhibits constitutive internalization of FGFR1. Our data point on the interplay between extracellular galectins and FGFRs in the regulation of cell fate.

FGFR1 clustering with engineered tetravalent antibody improves the efficiency and modifies the mechanism of receptor internalization

“…Recently, we have reported that galectin family members, galectin‐1 and galectin‐3, interact with the sugar chains of the glycosylated extracellular domain of FGFR1, regulating activity and trafficking of the receptor [31]. Using competitive BLI, we studied the effect of B‐Fc and T‐Fc binding on the receptor interaction with galectin‐1 and galectin‐3.…”

“…To study which CIE route mediates the endocytosis of T‐Fc, we employed siRNA‐mediated knockdown of key CIE‐specific proteins. We downregulated expression of dynamin‐2, which is involved in CME and in several CIE routes, galectin‐3, FGFR1‐binding protein mediating the clathrin‐independent carriers (CLIC) pathway, and ROCK1 and ROCK2 proteins involved in RhoA‐dependent CIE [31,51]. As a control, we knocked down a μ2 subunit of the adaptin‐2 complex (AP2μ2), an CME adaptor [53,54].…”

“…Recombinant PDGFRβ and VEGFR2 were from R&D Systems. Recombinant galectin‐1, galectin‐3, and FGF1 were obtained as described previously [31,50].…”

“…The mechanisms involved in FGFR1 internalization are only partially understood [29]. It was demonstrated that FGFR1 is subjected to constitutive, low‐rate internalization, however, FGFR1 dimerization caused by ligand binding largely accelerates uptake of the receptor [30–33]. The efficiency and mechanism of FGFR1 internalization depend on the type of an applied ligand [29,34–39].…”

“…We have recently uncoupled FGFR1 dimerization from the receptor activation and have demonstrated that dimerization of FGFR1, but not receptor autophosphorylation, triggers CME of FGFR1 [5,6]. A number of proteins involved in CME of FGFR1 in response to FGF binding were identified,however, the exact role of a number of these factors in the receptor internalization is still largely mysterious [31,40–44]. Besides CME, clathrin‐independent endocytosis (CIE) may participate in FGFR1 internalization [34,45,46].…”