Binding of pigment epithelium-derived factor (PEDF) to retinoblastoma cells and cerebellar granule neurons - Evidence for a PEDF receptor

Pigment epithelium-derived factor (PEDF);has neuronal differentiation and s urvival;activity on retinoblastoma and cerebellar granule (CG) cells. Here, we investigated the presence of PEDF receptors on retinoblastoma Y-79 and CG cells. PEDF radiolabeled with I-125 remained biologically active and was used for radioligand binding analysis. The binding was saturable and speci fic to a single class of receptors on both cells and with similar affinitie s (K-d = 1.7-3.6 nM, B-max = 10.5-2.7 x 10(5) sites/Y-79 cell; and K-d = 3. 2 nM, B-max = 1.1 x 10(3) sites/CG cell). A polyclonal antiserum to PEDF, p reviously shown to block the PEDF neurotrophic activity, prevented the I-12 5-PEDF binding. We designed two peptides from a region previously shown to confer the neurotrophic property to human PEDF, synthetic peptides 34-mer ( positions 44-77) and 44-mer (positions 78-121). Only peptide 44-mer compete d for the binding to Y-79 cell receptors (EC50 = 5 nM) and exhibited neuron al differentiating activity. PEDF affinity column chromatography of membran e proteins from both cell types revealed a PEDF-binding protein of similar to 80 kDa. These results are the first demonstration of at PEDF-binding pro tein with characteristics of a PEDF receptor and suggest that the region co mprising amino acid positions 78-121 of PEDF might be involved in ligand-re ceptor interactions.