Gap junctional communication modulates gene transcription by altering the recruitment of Sp1 and Sp3 to connexin-response elements in osteoblast promoters.
Loss-of-function mutations of gap junction proteins, connexins, represent a mechanism of disease in a variety of tissues. We have shown that recessive (gene deletion) or dominant (connexin45 overexpression) disruption of connexin43 function results in osteoblast dysfunction and abnormal expression of osteoblast genes, including down-regulation of osteocalcin transcription. To elucidate the molecular mechanisms of gap junction-sensitive transcriptional regulation, we systematically analyzed the rat osteocalcin promoter for sensitivity to gap junctional intercellular communication. We identified an Sp1/Sp3 containing complex that assembles on a minimal element in the -70 to -57 region of the osteocalcin promoter in a gap junction-dependent manner. This CT-rich connexin-response element is necessary and sufficient to confer gap junction sensitivity to the osteocalcin proximal promoter. Repression of osteocalcin transcription occurs as a result of displacement of the stimulatory Sp1 by the inhibitory Sp3 on the promoter when gap junctional communication is perturbed. Modulation of Sp1/Sp3 recruitment also occurs on the collagen Ialpha1 promoter and translates into gap junction-sensitive transcriptional control of collagen Ialpha1 gene expression. Thus, regulation of Sp1/Sp3 recruitment to the promoter may represent a potential general mechanism for transcriptional control of target genes by signals passing through gap junctions.
Stains
Joseph P
JP
Division of Bone and Mineral Diseases, Washington University School of Medicine and Barnes-Jewish Hospital, St. Louis, Missouri 63110, USA.
Lecanda
Fernando
F
Screen
Joanne
J
Towler
Dwight A
DA
Civitelli
Roberto
R
D000818:Animals; D002450:Cell Communication / Q000235:genetics*; D024042:Collagen Type I / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D017629:Gap Junctions / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism; D015675:Osteocalcin / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics*; D051381:Rats; D016329:Sp1 Transcription Factor / Q000235:genetics*; D051705:Sp3 Transcription Factor; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D024042:Collagen Type I; D004268:DNA-Binding Proteins; D016329:Sp1 Transcription Factor; C497123:Sp3 protein, rat; D014157:Transcription Factors; D015675:Osteocalcin; D051705:Sp3 Transcription Factor