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Published on: August 20, 2019
Loss of CBP acetyltransferase activity by PHD finger mutations in Rubinstein-Taybi syndrome
Eric Kalkhoven1, Jeroen H Roelfsema, Hans Teunissen
1Department of Molecular Cell Biology, MGC Centre for Biomedical Genetics, Leiden University Medical Centre, Wassenaarseweg 72, 2333 AL Leiden, The Netherlands.
Insights
Mutations in the CREB binding protein (CBP) gene, specifically its PHD finger, cause Rubinstein-Taybi syndrome (RTS). These mutations reduce CBP
Area of Science:
- Genetics
- Molecular Biology
- Developmental Biology
Background:
- Rubinstein-Taybi syndrome (RTS) is a developmental disorder linked to the CREB binding protein (CBP) gene.
- CBP functions as a transcriptional coactivator and possesses histone acetyltransferase (HAT) activity crucial for gene expression.
- The HAT domain's plant homeodomain (PHD) finger is vital for CBP's enzymatic function.
Purpose of the Study:
- To investigate the role of PHD finger integrity in CBP function and its association with RTS.
- To identify mutations in the CBP gene, particularly within the HAT domain, in RTS patients.
Main Methods:
- Mutational analysis of the CBP gene in 39 RTS patients.
- In vitro functional assays to assess the HAT activity of mutated CBP.
- Analysis of endogenous CBP HAT activity in patient-derived lymphoblastoid cells.
Main Results:
- Eight novel heterozygous mutations in the CBP HAT domain were identified, including two affecting the PHD finger.
- RTS-associated PHD finger mutants exhibited significantly reduced in vitro HAT activity and impaired coactivator function for CREB.
- Patient cells with a PHD finger deletion showed a ~50% reduction in endogenous CBP HAT activity.
Conclusions:
- The PHD finger is functionally critical for CBP's HAT activity in vivo.
- Reduced CBP HAT activity, caused by PHD finger disruption, is sufficient to cause Rubinstein-Taybi syndrome.
- These findings highlight the molecular mechanisms underlying RTS and the importance of CBP's enzymatic function in development.
Abstract:
Disruption of one copy of the human CREB binding protein (CBP or CREBBP) gene leads to the Rubinstein-Taybi syndrome (RTS), a developmental disorder characterized by retarded growth and mental functions, broad thumbs, broad big toes and typical facial abnormalities. The CREB binding protein (CBP) is an essential transcriptional coactivator for many different transcription factors. CBP has the intrinsic ability to acetylate histones and other proteins, which is regarded as an important step in transcription activation. In vitro studies have shown that this enzymatic activity critically depends on the integrity of a plant homeodomain (PHD)-type zinc finger in the HAT domain of CBP. We therefore investigated whether PHD finger mutations are present in RTS patients. Mutational analysis of 39 patients revealed eight novel heterozygous mutations in the HAT domain of CBP, one of which alters a conserved PHD finger amino acid (E1278K), while a second mutation deletes exon 22, which encodes the central region of the PHD finger. Functional analysis of these RTS-associated PHD finger mutants showed that they lacked in vitro acetyltransferase activity towards histones and CBP itself and displayed reduced coactivator function for the transcription factor CREB. Importantly, in EBV-transformed lymphoblastoid cells from the exon 22 deletion patient we found approximately 50% less endogenous CBP HAT activity. These findings therefore underscore the functional importance of the PHD finger in vivo and imply that reduction of CBP HAT activity, as exemplified here by disruption of the PHD finger, is sufficient to cause RTS.
