Disorders with similar clinical phenotypes reveal underlying genetic interaction: SATB2 acts as an activator of the UPF3B gene.
Two syndromic cognitive impairment disorders have very similar craniofacial dysmorphisms. One is caused by mutations of SATB2, a transcription regulator and the other by heterozygous mutations leading to premature stop codons in UPF3B, encoding a member of the nonsense-mediated mRNA decay complex. Here we demonstrate that the products of these two causative genes function in the same pathway. We show that the SATB2 nonsense mutation in our patient leads to a truncated protein that localizes to the nucleus, forms a dimer with wild-type SATB2 and interferes with its normal activity. This suggests that the SATB2 nonsense mutation has a dominant negative effect. The patient's leukocytes had significantly decreased UPF3B mRNA compared to controls. This effect was replicated both in vitro, where siRNA knockdown of SATB2 in HEK293 cells resulted in decreased UPF3B expression, and in vivo, where embryonic tissue of Satb2 knockout mice showed significantly decreased Upf3b expression. Furthermore, chromatin immunoprecipitation demonstrates that SATB2 binds to the UPF3B promoter, and a luciferase reporter assay confirmed that SATB2 expression significantly activates gene transcription using the UPF3B promoter. These findings indicate that SATB2 activates UPF3B expression through binding to its promoter. This study emphasizes the value of recognizing disorders with similar clinical phenotypes to explore underlying mechanisms of genetic interaction.
Biomedical Science Program, Faculty of Graduate School, Chulalongkorn University, Bangkok, Thailand.
Petcharat
P
Leoyklang
Kanya
K
Suphapeetiporn
Chalurmpon
C
Srichomthong
Siraprapa
S
Tongkobpetch
Stefanie
S
Fietze
Heidi
H
Dorward
Andrew R
AR
Cullinane
William A
WA
Gahl
Marjan
M
Huizing
Vorasuk
V
Shotelersuk
D000818:Animals; D019556:COS Cells; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D003072:Cognition Disorders / Q000235:genetics*; D019465:Craniofacial Abnormalities / Q000235:genetics*; D057809:HEK293 Cells; D006801:Humans; D036961:Matrix Attachment Region Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D010641:Phenotype; D011401:Promoter Regions, Genetic; D016601:RNA-Binding Proteins / Q000235:genetics*; D013577:Syndrome; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
D036961:Matrix Attachment Region Binding Proteins; D016601:RNA-Binding Proteins; C521297:SATB2 protein, human; C501473:SATB2 protein, mouse; D014157:Transcription Factors; C435488:UPF3B protein, human; C585775:UPF3B protein, mouse