Browsing by Subject "FGF"

Growth factors and their receptors coordinate neuronal differentiation during development, yet their roles in the embyronal tumor neuroblastoma, where differentiation is a validated treatment strategy, remain unclear. The neuroblastoma tumor stroma is thought to suppress neuroblast growth via release of soluble differentiating factors. Here we identify critical components of the differentiating stroma secretome and describe preclinical testing of a novel therapeutic strategy based on their mechanism of action.

Expression of heparan sulfate proteoglycans (HSPGs), including TβRIII, GPC1, GPC3, SDC3, and SDC4, is decreased in neuroblastoma, high in the stroma, and suppresses tumor growth. High expression of TβRIII, GPC1, and SDC3 is associated with improved patient prognosis. HSPGs signal via heparan sulfate binding to FGFR1 and FGF2, which leads to phosphorylation of FGFR1 and Erk MAPK, and upregulation of the transcription factor inhibitor of DNA binding 1 (Id1). Surface expression and treatment with soluble HSPGs promotes neuroblast differentiation via this signaling complex. Expression of individual HSPGs positively correlates with Id1 expression in neuroblastoma patient samples and multivariate regression demonstrates that expression of HSPGs as a group positively correlates with Id1 expression, underscoring the clinical relevance of this pathway. HSPGs also enhance differentiation from FGF2 released by the stroma and FGF2 is identified as a potential serum prognostic biomarker in neuroblastoma patients.

The anticoagulant heparin has similar differentiating effects to HSPGs, decreasing neuroblast proliferation and reducing tumor growth while extending survival in an orthotopic xenograft model of neuroblastoma. Dissection of individual sulfation sites identifies 2-O-, 3-O-de-sulfated heparin (ODSH) as a differentiating agent that suppresses orthotopic xenograft growth and metastasis in two models while avoiding anticoagulation. These studies form the preclinical rationale for a multicenter clinical trial currently being proposed.

In conclusion, these studies translate mechanistic insights in neuroblast HSPG function to identify heparins as differentiating agents for clinical development in neuroblastoma, while demonstrating that tumor stroma biology can inform design of targeted molecular therapeutics.

Fibroblast growth factor homologous factors (FHFs) are non-canonical members of the fibroblast growth factor family (FGF11-14) that were initially discovered to bind and regulate neuronal and cardiac voltage-gated Na+ channels. Loss-of-function mutations that disrupt interaction between FHFs and Na+ channels cause spinocerebellar ataxias and cardiac arrhythmias such as Brugada syndrome. Although recent studies in brain of FHF knockout mice suggested novel functions for FHFs beyond ion channel modulation, it is unclear whether FHFs in the heart serve additional roles beyond regulating cardiac excitability. In this study, we performed a proteomic screen to identify novel interacting proteins for FGF13 in mouse heart. Mass spectrometry analysis revealed an interaction between FGF13 and a complex of cavin proteins that regulate caveolae, membrane invaginations that organize protective signaling pathways and provide a reservoir to buffer membrane stress. FGF13 controls the relative distribution of cavin 1 between the plasma membrane and cytosol and thereby acts as a negative regulator of caveolae. In inducible, cardiac-specific Fgf13 knockout mice, cavin 1 redistributed to the plasma membrane and stabilized the caveolar structural protein caveolin 3, leading to an increased density of caveolae. In a transverse aortic constriction model of pressure overload, this increased caveolar abundance enhanced cardioprotective signaling through the caveolar-organized PI3 kinase pathway, preserving cardiac function and reducing fibrosis. Additionally, the increased caveolar reserve provided mechanoprotection, as indicated by reduced membrane rupture in response to hypo-osmotic stress. Thus, our results establish FGF13 as a novel regulator of caveolae-mediated mechanoprotection and adaptive hypertrophic signaling, and suggest that inhibition of FHFs in the adult heart may have cardioprotective benefits in the setting of maladaptive hypertrophy.