The major research interest of the Wang lab is the regulation of gene transcription and its role in cell proliferation and human disease. Our studies focus on the function of the general transcription factor complex TFIID and how mutations in its TAF subunits contribute to cancer or other human genetic disorders. The Wang lab uses molecular, biochemical and structural approaches to investigate the normal function of TAFs in gene transcription and how debilitating mutations may contribute to cancer, cognitive impairment, and neurodegeneration. Our long-term goal is to understand how misregulation of gene transcription promotes human disease and to assess the potential of the TAF subunits of TFIID as druggable targets or diagnostic markers for improving human health.
Unraveling the TAF1-7 module of TFIID in Cell Proliferation and Human Cancer
The expression of protein encoding genes is essential for the proper execution of all cellular processes. Abnormal gene expression patterns are a feature of cancer and commonly are the result of mutations in transcription factors. TAF1 is the largest subunit of the general transcription factor complex TFIID and possesses histone acetyltransferase (HAT) activity. TAF1 HAT activity maps to a conserved central domain and is critical for transcription of a subset of cell cycle genes. Interestingly, direct binding of TAF7, another TFIID subunit, can block the HAT activity of TAF1. Our studies suggest that phosphorylation of TAF7 at S264 causes its release from TFIID, alleviating its inhibitory effect on TAF1. Therefore, the TAF1-TAF7 complex has emerged as a dynamic module within TFIID that is important for proper cell cycle progression.
Genetic and biochemical evidence implicate misregulation of TAF1 in tumorigenesis. A survey of uterine serous carcinoma (USC) by whole-exome sequencing revealed that approximately 13% of USC tumors analyzed carried TAF1 mutations at positions strictly conserved during evolution. TAF1 is required for the expression of cyclin D1, a proto-oncogene frequently overexpressed in various cancers. TAF1 also enhances cell cycle progression by promoting degradation of the tumor suppressor protein p53. Therefore, our goal is to elucidate the TAF1 dependent molecular mechanisms and signaling pathways controlling cell proliferation and to use this information to uncover new targets for anti-cancer drugs.
Core promoter DNA binding activity of TAF1
TFIID is the first general transcription factor to bind to the core promoter DNA of protein encoding genes. This binding event initiates the assembly of a functional pre-initiation complex that transcribes DNA into RNA. TFIID subunits, TAF1, TAF2, TAF6 and TAF9, are well-documented to directly contact core promoter DNA. Specifically, TAF1 binds to the initiator (Inr), the site of transcription initiation. Our research aims to define the TAF1 domain(s) that interfaces with core promoter DNA and the mechanism that conveys DNA sequence specificity.
In collaboration with Dr. Ning Zheng, we solved the structure of a TAF1-TAF7 complex, by X-ray crystallography, and discovered a winged helix (WH) fold embedded in the TAF1 HAT domain. Although the TAF1 WH contains amino acids essential for TAF1 to contact promoter DNA, the TAF1 fragment displayed little sequence specificity suggesting the involvement of other determining factors. Sequence analysis of the TAF1 protein revealed an evolutionarily conserved Zn knuckle motif, which is absent from our TAF1 fragment. TAF1 also interacts with TAF2, another TFIID subunit that directly binds to the Inr. Therefore, we want to determine whether the Zn knuckle or presence of TAF2 provides additional points of contact with DNA that may dictate DNA sequence specificity.
Genetics of Human Disorders: Role of TAF1 and TAF2 mutations
Intellectual disability (ID) is a developmental disability characterized by limited cognitive and adaptive function, defined by an IQ < 70. It is estimated that ID affects 1-2% of the general population before age 18. Whole genome and exome sequencing of individuals diagnosed with ID and their unaffected family members has uncovered de novo mutations in the TAF1 and TAF2 subunits of TFIID that co-segregate with ID. X-linked dystonia-parkinsonism (XDP) is a neurodegenerative disorder indigenous to the Panay Island of the Phillipines. Genome sequencing of 166 XDP patients revealed that nearly all affected individuals harbor seven disease-specific genetic changes, three of which map to the TAF1 gene. The significant of the TAF1 mutations to ID and XDP is further substantiated by a report that ranked TAF1 as the 53rd most constrained human gene among the top 1000. We have begun to introduce disease-associated mutations into the TAF1 and TAF2 proteins in order to investigate the functional consequences of these changes using molecular and cellular biology, biochemistry and structural techniques.