Activity of a novel PDGF β-receptor enhancer during the cell cycle and upon differentiation of neuroblastoma

PDGF acts as an autocrine and paracrine factor in certain tumors through upregulation of the PDGF β-receptor expression. In order to elucidate the control mechanism for the receptor expression, we have isolated an enhancer from two P1 clones that together contain a 102 kb NotI region covering the entire human PDGFRB gene. They were partially digested with TspI and cloned into the PDGFRB enhancer trap vector to make a library for identification of enhancers. The digested DNA containing enhancer was identified by expression of GFP when transfected in PDGF β-receptor expressing cells. One of the enhancer clones was further examined by making several deletion mutants in a luciferase vector. This enhancer was most active in neuroblastoma cells, IMR32 and BE2, but less active in hemangioma and in smooth muscle cell lines. Chip assay revealed that SP1, AP2, and GATA2 bound the enhancer in BE2 cells. Their interaction occurred dependently of the cell cycle and synchronously with their binding to the promoter. Transfection of GATA2 alone or with Ets, which binds adjacent to GATA, resulted in differentiation of BE2 cells in parallel with increased PDGF β-receptor expression. Furthermore, over-expression of the PDGF β-receptor in BE2 cells induced neurite extension.