Sp4 is expressed in retinal neurons, activates transcription of photoreceptor-specific genes, and synergizes with Crx.
To investigate the molecular mechanisms of photoreceptor-specific gene transcription, we examined the role of the neuronal-enriched Sp4 nuclear protein in transcription from the rod-specific beta-PDE and rod opsin gene promoters and compared it to the ubiquitous members of the Sp family, Sp1 and Sp3. Sp4 activates both the rod opsin and beta-PDE promoters, whereas Sp1 activates only the rod opsin promoter and Sp3 activates neither promoter. Interestingly, Sp1 and Sp3 competitively repress Sp4-mediated activation of the beta-PDE promoter. In addition, Sp4, Sp1, and Sp3 each show functional synergy with the photoreceptor-enriched Crx transcriptional regulator on the rod opsin promoter but not the beta-PDE promoter, although Sp4-mediated activation was the most significant. Sp4, Sp1, and Sp3 bind Crx in co-immunoprecipitation experiments, and their zinc finger domains as well as the Crx homedomain are necessary and sufficient for these interactions. Chromatin immunoprecipitation showed that the rod opsin and beta-PDE promoters are targets of both Sp4 and Crx, which further supports Sp4-Crx interactions in vivo in the context of retinal chromatin environment. In situ hybridization and immunohistochemistry demonstrated that Sp4 is abundantly expressed in various neurons of all retinal layers, and thus co-localizes or overlaps with multiple retina-restricted and -enriched genes, its putative targets. Our results indicate that photoreceptor-specific gene transcription is controlled by the combinatorial action of Sp4 and Crx. The other Sp family members may be involved in photoreceptor-specific transcription directly or through their competition with Sp4. These data suggest the potential importance of Sp4 in retinal neurobiology and pathology.
Lerner
Leonid E
LE
Jules Stein Eye Institute, UCLA School of Medicine, Los Angeles, California 90095, USA. leonid.lerner@uphs.upenn.edu
Peng
Guang-Hua
GH
Gribanova
Yekaterina E
YE
Chen
Shiming
S
Farber
Debora B
DB
D000818:Animals; D002417:Cattle; D002460:Cell Line; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6; D004268:DNA-Binding Proteins / Q000502:physiology; D004357:Drug Synergism; D015870:Gene Expression; D005786:Gene Expression Regulation; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D006801:Humans; D017403:In Situ Hybridization; D051379:Mice; D009474:Neurons / Q000737:chemistry*; D010727:Phosphoric Diester Hydrolases / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D012160:Retina / Q000737:chemistry / Q000166:cytology*; D017948:Retinal Rod Photoreceptor Cells / Q000737:chemistry*; D012175:Retinoblastoma; D017299:Rod Opsins / Q000235:genetics; D016329:Sp1 Transcription Factor / Q000502:physiology; D051705:Sp3 Transcription Factor; D051706:Sp4 Transcription Factor; D014018:Tissue Distribution; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics* / Q000502:physiology*; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured; D016335:Zinc Fingers
D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D012333:RNA, Messenger; D017299:Rod Opsins; C497121:SP3 protein, human; C497124:SP4 protein, human; D016329:Sp1 Transcription Factor; C497122:Sp3 protein, mouse; D051706:Sp4 Transcription Factor; C497125:Sp4 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; C109288:cone rod homeobox protein; D051705:Sp3 Transcription Factor; D010727:Phosphoric Diester Hydrolases; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6; C517431:PDE6B protein, human; C517438:Pde6b protein, mouse