OBJECTIVES Fibroblast growth factors (FGFs) represent potent effectors and play essential roles in both normal development and many pathological processes. Little is known about their possible implication in retinoblastoma growth. We sought to examine FGF high- and low-affinity receptor (FGFR) expression, activation of FGFR1 by acidic FGF (FGF-1), and proliferative effects on Y79 cells. METHODS Expression of FGFR1 to FGFR4 was screened in Y79 cells by means of immunochemical and reverse transcriptase polymerase chain reaction techniques. Tyrosine phosphorylation of FGFR1 induced by FGF was examined by immunoprecipitation after stimulation with FGF-1 in the presence or absence of heparin. Retinoblastoma proliferation was monitored by radiolabeled thymidine incorporation or a vital dye-based assay, after addition of FGF-1 with or without inclusion of a specific FGFR1 neutralizing antibody or FGFR1 antisense oligonucleotides. Low-affinity heparan sulfate proteoglycan coreceptors were blocked through sodium chlorate or heparinase treatment of Y79 cells. RESULTS Y79 retinoblastoma expressed all 4 FGFRs, at both the protein and messenger RNA levels. The FGFR1 was differentially phosphorylated in a time- and heparin-dependent manner by FGF-1. Proliferation of Y79 cells induced by FGF-1 was entirely mediated by FGFR1, since inclusion of specific neutralizing antibodies or antisense oligonucleotides completely prevented tumor cell multiplication. Finally, FGF-1-induced proliferation was dependent on the presence and sulfation of heparan sulfate proteoglycan. CONCLUSIONS Y79 retinoblastoma expresses all 4 FGFRs, but FGFR1 activation entirely accounts for FGF-1-driven cell proliferation. CLINICAL RELEVANCE These studies demonstrate a role for the FGF-1/FGFR1 pathway in retinoblastoma proliferation, and may contribute to developing therapeutic strategies to limit retinoblastoma growth.

Fibroblast growth factors (FGFs) are important regulators of retinal development and survival. We examined the expression and distribution of FGF9 and its preferred receptors FGFR2IIIc and FGFR3IIIc in this tissue. FGF9 transcripts in whole rat retina were detected by RT‐PCR but were not present in purified cultured Müller glia. Transcripts appeared as 3.2‐kb and 4.0‐kb bands on Northern blots, and Western blotting of whole retina revealed FGF9‐immunoreactive bands at 30 and 55 kDa. FGF9 mRNA demonstrated a biphasic expression profile, elevated at birth and adulthood, but relatively decreased during terminal retinal differentiation (4–14 days postnatal). Antibody labeling broadly reflected these findings: staining in vivo was observed mainly in the inner retina (and outer plexiform layer in adults) whereas FGF9 was not detectable in cultured Müller glia. In adults, FGF9 in situ hybridization also showed a detectable signal in inner retina. FGFR2IIIc and FGFR3IIIc were detected by RT‐PCR, and Western blotting showed both FGFRs existed as multiple forms between ∼100–200 kDa. FGFR2 and FGFR3 antibodies showed prominent labeling in the inner retina, especially in proliferating cultured Müller glia. Exogenous FGF9 elicited a dose‐dependent increase in Müller glial proliferation in vitro. These data suggest a role for FGF9 in retinal differentiation and maturation, possibly representing a neuronally derived factor acting upon glial (and other) cells. © 2004 Wiley‐Liss, Inc.