Dr Walden Ai:
University of Massachusetts
Ph.D. Institute of Genetics, Chinese Academy of Sciences
Office: (803) 253-5850
Lab: (803) 216-3405
Fax: (803) 216-3428
My major research interest is the study of a transcriptional factor called Kruppel-like factor 4 (KLF4), a C2H2 zinc-finger-containing nuclear factor implicated in the control of cell proliferation and differentiation. Expression of KLF4 is upregulated upon DNA damage. In this process, KLF4 is a critical mediator of the checkpoint functions of p53 by inducing G1/S and G2/M cell cycle arrest. Recently data also showed that KLF4 has an antiapoptotic effect upon DNA damage. However, the molecular mechanism is not fully elucidated. In vivo studies have demonstrated that KLF4 is required for terminal differentiation of goblet cells in the colon, a process that is regulated by the Notch signaling pathway. Recently data also indicated a new function of KLF4 in embryonic stem cell self renewal. The following experiments are designed to understand the molecular mechanism of how KLF4 is involved in DNA damage response, to study how KLF4 is regulated by the Notch signaling pathway, and to test the role of KLF4 in stem cell biology and cancer development.
Study the role of KLF4 in DNA damage response pathway
We have identified Tip60, a member of the MYST family of HATs that was initially identified as a cellular protein that interacts with HIV protein Tat, as a KLF4-interacting protein by yeast two-hybrid screening. Since Tip60 is one component of a multiple subunit complex that is involved in DNA damage repair and apoptosis, the interaction between KLF4 and Tip60 provides a possible mechanism by which KLF4 and Tip60 cooperatively regulate cell cycle arrest and apoptosis. The interaction domains in both proteins will be identified and the significance of these domains will be tested in order to dissect their specific roles in cell cycle arrest and apoptosis. In addition, the role of p53 will be further studied in this context since the interactions between KLF4 and p53, between p53 and Tip60 have been reported. Finally the posttranslational modifications including phosphorylation, ubiquitination, and acetylation of KLF4 after DNA damage will be examined, and the significance of the modifications will be evaluated.
Study the mechanisms of how KLF4 is regulated by the Notch signaling pathway
The Notch signaling pathway has been shown to play a positive or a negative role in tumor development depending on the cellular context. The in vivo link between Notch and KLF4 raises a possibility that KLF4 mediates the function of the Notch signaling pathway in cancer development. Our preliminary studies indicate that KLF4 gene expression is inhibited by the Notch signaling pathway both in vivo using a ?-secretase inhibitor that inhibits the Notch signaling pathway and in vitro using a constitutively active Notch 1 (ICN1). Further studies identified a Notch responsive element in the KLF4 promoter. The physiological relevance of the transcriptional factor will be assessed by in vivo methods that likely involve the generation of transgenic and/or knockout mouse models. The detailed mechanism such as the singling pathways that are involved will be delineated by in vitro assays with cell lines by using ?secretase inhibitors and ICN1 and different inhibitors that inhibit different signaling pathways.
Study the role of KLF4 expression in stem cells or progenitor cells in the development of cancer
Recently it has been reported that overexpression of four nuclear factors including Oct4, c-Myc, Sox2 and KLF4 transformed differentiated fibroblasts into embryonic stem cell like cells, indicating an important role of KLF4 in stem cell biology. Since KLF4 also has a function to promote embryonic stem cell self renewal, we hypothesize that KLF4 is expressed in stem cell or progenitor cell population, and change of KLF4 gene expression in stem cells or progenitor cells plays an important role in cancer development that has been linked to cancer stem cells. We have already generated a KLF4/EGFP transgenic mice model using a modified BAC (bacterial artificial chromosome) clone as the transgene. Since BAC construct contains big pieces of fragment in both 5 and 3 regions of KLF4 gene and EGFP has been inserted into the KLF4 start codon, this model will most likely allow us to monitor endogenous expression of KLF4 by chasing expression of EGFP. Using the same strategy, we have also generated a KLF4/CRE transgenic mouse model. By crossing these mice with a reporter mouse line such as Rosa 26R beta Geo or EGFP mice, KLF4 expressing cells will be traced by X-gal staining or green fluorescence of EGFP after tamoxifen induction. By using both KLF4/EGFP and KLF4/CRE transgenic mouse models, KLF4 gene expression in stem cells in adult tissues including skin, small intestine, colon, and bone marrow is being examined. Further studies will be conducted to evaluate a role of KLF4 expression in stem cells in cancer development.
Search PubMed for publications by Dr Walden Ai
- Ai W, Zheng H, Yang X, Liu Y, Wang TC, Tip60 functions as a potential corepressor of KLF4 in regulation of HDC promoter activity. 2007. Nucleic Acids Res. 2007; 35(18):6137-49. Epub 2007 Sep 7.
- Tu S, Chi AL, Lim S, Cui G, Dubeykovskaya Z, Ai W, Fleming JV, Takaishi S, Wang TC. Gastrin regulates the TFF2 promoter through gastrin-responsive cis-acting elements and multiple signaling pathways. Am J Physiol Gastrointest Liver Physiol. 2007 Mar1; [Epub ahead of print]
- Cui G, Takaishi S, Ai W, Betz KS, Florholmen J, Koh TJ, Houghton J, Pritchard DM, Wang TC. Gastrin-induced apoptosis contributes to carcinogenesis in the stomach. Lab Invest. 2006 Oct; 86(10):1037-51.
- Ai W, Takaishi S, Wang TC, Fleming JV. Regulation of L-histidine decarboxylase and its role in carcinogenesis. Prog Nucleic Acid Res Mol Biol. 2006; 81:231-70.
- Ai W, Liu Y, Wang TC. Yin Yang 1(YY1) represses histiding decarboxylase (HDC) gene expression with SREBP-1a in part through an upstream Sp1 site. Am. J. Physiol. Gastrointest Liver Physiol, 2006 June, 290(6): G1096-1104.
- Sinclair NF, Ai W, Bi, MX, Raychowdhury R. Koh TJ, and McLaughlin J. Gastrin Regulates the heparin Binding Epidermal-like Growth Factor Promoter Via a PKC/EGFR Dependent Mechanism. Am. J. Physiol. Gastrointest Liver Physiol. 2004 June; 286(6): G992-9.
- Ai W, Liu Y, Langlois M, Wang TC. Kruppel-like factor 4 (KLF4) represses histidine decarboxylase (HDC) gene expression through an upstream Sp1 site and downstream gastrin responsive elements. J Biol Chem. 2004, Vol. 279(10): 8684-8693.
- McLaughlin JT, Ai W, Sinclair NF, Colucci R, Raychowdhury R, Koh TJ, Wang TC. PACAP and Gastrin regulate the Histidine Decarboxylase Promoter via Distinct Mechanisms. Am. J. Physiol. Gastrointest Liver Physiol, 2004 Jan; 286(1):G51-9.
- Tsang C.K., Bertram PG, Ai W, Drenan R and Zheng XF. Chromatin-mediated Regulation of Nucleolar Structure, RNA Polymerase I Localization and rDNA Transcription by Target of Rapamycin (TOR), EMBO J, 2003 Nov 17, 22(22):6045-56.
- Ai W, Bertram PG, Tsang CK, Chan TF, Zheng XF. Regulation of Subtelomeric Silencing during Stress Response. Mol. Cell, 2002 Dec 20; 10(6):1295-305
- Bertram PG, Choi JH, Carvalho J, Chan TF, Ai W, and Zheng XF. Convergence of TOR-Nitrogen and Snf1-Glucose Signaling Pathways onto Gln3. Mol Cell Biol. 2002 Feb; 22(4):1246-52.
- Chan TF, Bertram PG, Ai W, Zheng XF. Regulation of APG14 expression by the GATA-type transcription factor Gln3p. J Biol Chem. 2001 Mar 2; 276(9):6463-7.
- Bertram PG, Choi JH, Carvalho J, Ai W, Zeng C, Chan TF, Zheng XF. Tripartite regulation of Gln3p by TOR, Ure2p, and phosphatases. J Biol Chem. 2000, 275(46): 35727-33
- Ai W, Narahari J. and Roman A. Yin yang 1 negatively regulates the differentiation-specific E1 promoter of human papillomavirus type 6. J Virol. 2000, 74(11): 5198-5205
- Ai W, Toussaint E and Roman A. CCAAT displacement protein binds to and negatively regulates human papillomavirus type 6 E6, E7, and E1 promoters. J Virol. 1999, 73(5): 4220-4229
- Ai W, Gong J, and Yu L. MAP kinase activation by mu opioid receptor involves phosphatidylinositol 3-kinase but not the cAMP/PKA pathway. FEBS Letters, 1999, 456: 196-200