FGFR2b signaling regulates ex vivo submandibular gland epithelial cell proliferation and branching morphogenesis

Abstract

Branching morphogenesis of mouse submandibular glands is regulated by multiple growth factors. Here, we report that ex vivo branching of intact submandibular glands decreases when either FGFR2 expression is downregulated or soluble recombinant FGFR2b competes out the endogenous growth factors. However, a combination of neutralizing antibodies to FGF1, FGF7 and FGF10 is required to inhibit branching in the intact gland, suggesting that multiple FGF isoforms are required for branching. Exogenous FGFs added to submandibular epithelial rudiments cultured without mesenchyme induce distinct morphologies. FGF7 induces epithelial budding, whereas FGF10 induces duct elongation, and both are inhibited by FGFR or ERK1/2 signaling inhibitors. However, a PI3-kinase inhibitor also decreases FGF7-mediated epithelial budding, suggesting that multiple signaling pathways exist. We immunolocalized FGF receptors and analyzed changes in FGFR, FGF and MMP gene expression to identify the mechanisms of FGF-mediated morphogenesis. FGFR1b and FGFR2b are present throughout the epithelium,although FGFR1b is more highly expressed around the periphery of the buds and the duct tips. FGF7 signaling increases FGFR1b and FGF1expression, and MMP2 activity, when compared with FGF10, resulting in increased cell proliferation and expansion of the epithelial bud, whereas FGF10 stimulates localized proliferation at the tip of the duct. FGF7- and FGF10-mediated morphogenesis is inhibited by an MMP inhibitor and a neutralizing antibody to FGF1, suggesting that both FGF1 and MMPs are essential downstream mediators of epithelial morphogenesis. Taken together,our data suggests that FGFR2b signaling involves a regulatory network of FGFR1b/FGF1/MMP2 expression that mediates budding and duct elongation during branching morphogenesis.

The ADAM17–amphiregulin–EGFR Axis in Mammary Development and Cancer

“…On the other hand, no mammary phenotype has been described in FGF7-deficient mice, possibly due to the compensatory effects of other FGFs, and it remains unclear whether other FGF receptors or specific receptor isoforms are involved. Nevertheless, contrary to the implications associated with their name, stromal FGFs and their epithelial receptors play key roles in Drosophila tracheal branching and in mammalian lung, salivary gland and kidney branching, suggesting that similar mechanisms may also affect mammary branching [3,89,90]. Indeed, considerable data suggest that FGF signaling can affect cell migration through chemotaxis as well as cell proliferation.…”

FGF signaling segregates biliary cell‐lineage from chick hepatoblasts cooperatively with BMP4 and ECM components in vitro

“…2). FGF7 has been reported to induce the expression of Fgfr1b in the branching processes of the mouse submandibular gland in vitro (Hoffman et al, 2002;Steinberg et al 2005), suggesting that bFGF administration to the hepatic epithelium in vitro could increase the transcription of Fgfr1 and Fgfr2. To verify this possibility, we analyzed the expression of Fgfr1 or Fgfr2 by semi-quantitative RT-PCR in the hepatic epithelium cultured in the presence and absence of bFGF.…”

Homodimerization Controls the Fibroblast Growth Factor 9 Subfamily's Receptor Binding and Heparan Sulfate-Dependent Diffusion in the Extracellular Matrix

“…This results in the establishment of a bidirectional signaling loop between the epithelium and mesenchyme that is essential for organogenesis and tissue homeostasis. It is well established that FGF7 and FGF10, which are expressed exclusively in the mesenchyme, activate specifically FGFR2b to mediate mesenchymal-to-epithelial signaling in the lung, prostate, and lacrimal, mammary, and salivary glands (19,29,35,36,59). Several lines of genetic and biochemical evidence suggest that the members of the FGF9 subfamily, which includes FGF9, FGF16, and FGF20, convey the reciprocal signaling from the epithelium to the mesenchyme.…”