Interrogation of a lacrimo-auriculo-dento-digital syndrome protein reveals novel modes of fibroblast growth factor 10 (FGF10) function

Abstract

Heterozygous mutations in the gene encoding fibroblast growth factor 10 (FGF10) or its cognate receptor, FGF-receptor 2 IIIb (FGFR2-IIIb) result in two human syndromes -LADD (lacrimo-auriculo-dento-digital) and ALSG (Aplasia of lacrimal and salivary glands). To date, the partial loss-of-FGF10 function in these patients has been attributed solely to perturbed paracrine signalling functions between FGF10-producing mesenchymal cells and FGF10-responsive epithelial cells. However, the functioning of a LADD-causing G138E FGF10 mutation, which falls outside its receptor interaction interface, has remained enigmatic. In this study, we interrogated this mutation in the context of FGF10's protein sequence and threedimensional structure, and followed the subcellular fate of tagged proteins containing this or other combinatorial FGF10 mutations, in vitro. We report that FGF10 harbours two putative nuclear localization sequences, termed NLS1 and NLS2, which individually or co-operatively promote nuclear translocation of FGF10. Furthermore, FGF10 localizes to a subset of dense fibrillar components of the nucleolus. G138E falls within NLS1 and abrogates FGF10's nuclear translocation whilst attenuating its progression along the secretory pathway. Our findings suggest that in addition to its paracrine roles, FGF10 may normally play intracrine role/s within FGF10-producing cells. Thus, G138E may disrupt both paracrine and intracrine function/s of FGF10 through attenuated secretion and nuclear translocation, respectively. ABSTRACTHeterozygous mutations in the gene encoding fibroblast growth factor 10 (FGF10) or its cognate receptor, FGF-receptor 2 IIIb (FGFR2-IIIb) result in two human syndromes -LADD (lacrimo-auriculo-dento-digital) and ALSG (Aplasia of lacrimal and salivary glands). To date, the partial loss-of-FGF10 function in these patients has been attributed solely to perturbed paracrine signalling functions between FGF10-producing mesenchymal cells and FGF10-responsive epithelial cells.However, the functioning of a LADD-causing G138E FGF10 mutation, which falls outside its receptor interaction interface, has remained enigmatic. In this study, we interrogated this mutation in the context of FGF10's protein sequence and threedimensional structure, and followed the subcellular fate of tagged proteins containing this or other combinatorial FGF10 mutations, in vitro. We report that FGF10 harbours two putative nuclear localization sequences, termed NLS1 and NLS2, which individually or co-operatively promote nuclear translocation of FGF10. Furthermore, FGF10 localizes to a subset of dense fibrillar components of the nucleolus. G138E falls within NLS1 and abrogates FGF10's nuclear translocation whilst attenuating its progression along the secretory pathway. Our findings suggest that in addition to its paracrine roles, FGF10 may normally play intracrine role/s within FGF10-producing cells. Thus, G138E may disrupt both paracrine and intracrine function/s of FGF10 through attenuated secretion and nuclear translocation, respectively....

Fibroblast growth factor 10 is a negative regulator of postnatal neurogenesis in the mouse hypothalamus

“…The receptors for FGF2 – FgfR1-IIIc and FgfR2-IIIc isoforms – are expressed by β-tanycytes ( Kaminskas et al, 2019 ), but the cognate receptor for FGF10 – FgfR2-IIIb – is absent from the hypothalamus altogether ( Hajihosseini et al, 2008 ). Second, the recent discovery that FGF10 harbours nuclear localization motifs that facilitate its nuclear/nucleolar targeting has opened up the possibility that FGF10 can also function non-canonically to drive cell-autonomous gene-regulatory effects within Fgf10+ cells themselves ( Mikolajczak et al, 2016 ). Therefore, in the absence of its receptor from the hypothalamus, a cell-intrinsic receptor-independent role for Fgf10 in β-tanycytes is plausible.…”

Characterisation of endogenous players in fibroblast growth factor‐regulated functions of hypothalamic tanycytes and energy‐balance nuclei

“…shows that FGFs may also function non-canonically; for example, by trafficking to the nucleus/nucleolus, either alone, or in complex with FGFRs, to induce nuclear cell signalling or to carry out gene-regulating functions via chromatin and RNA-binding properties. [48][49][50] and FGF14, respectively, regulate the stabilisation of microtubules 51 and proper functioning of voltage-gated sodium and potassium ion channels 52,53 and so these intracellular FGFs could regulate axonal integrity and transport as well conductivity within neurones of the arcuate (Figure 4F,G) and other hypothalamic nuclei.…”

Regulation of FGF10 Signaling in Development and Disease

“…Mutated FGF10 failed to translocate into the nucleus. This might attenuate FGF10 intracrine functions, possibly explaining the phenotype observed in LADD or ALSG patients ( Mikolajczak et al, 2016 ).…”