Nrl and Sp nuclear proteins mediate transcription of rod-specific cGMP-phosphodiesterase β-subunit gene -: Involvement of multiple response elements

cGMP-phosphodiesterase (PDE) is the key effector in rod photoreceptor signal transduction. Mutations in the gene encoding its catalytic, beta -subunit (beta -PDE) cause retinal degenerations leading to blindness. We report that the short -93 to +53 sequence in the upstream region of this gene is sufficient for beta -PDE transcription in both Y79 human retinoblastoma cells and Xenopus embryo heads maintained ex vivo. This sequence also functions as a minimal rod-specific promoter in transgenic Xenopus tadpoles. The Nrl transcription factor binds in vitro to the beta Ap1/NRE regulatory element located within this region and transactivates it when overexpressed in non-retinal 293 embryonic kidney cells. We also found a G/C-rich activator element, beta /GC, important for promoter activity in Y79 retinoblastoma cells and Xenopus embryos. Both the ubiquitous Sp1 and the central nervous system-specific Sp4 transcription factors are expressed in retina and interact with this element in vitro. Electrophoretic mobilities of beta /GC-Y79 nuclear protein complexes are altered by antibodies against Sp1 and Sp4. Thus, our results implicate Nr1, Sp1, and Sp4 in transcriptional regulation of the rod-specific minimal beta -PDE promoter. We also conclude that Xenopus laevis is an efficient system for analyzing the human beta -PDE promoter and may be used to study other human retinal genes ex vivo and in vivo.