Wnt signaling, cancer, gene expression, development; intestine; stem cells; LEF and TCF transcription factors
The goal of research in the Waterman laboratory is to understand how
the Wnt signaling pathway regulates target genes through the actions
of LEF/TCF transcription factors. Dysfunctional Wnt signals
misregulate gene expression and cause cancer and most of our work on
LEF/TCFs is within the context of the final step of this dysregulated
pathway. LEF/TCF proteins bind to Wnt Response Elements in target
genes and recruit ß-catenin for gene activation or repressors for gene
silencing. There are two main areas of research: 1) Regulation of
LEF/TCF expression, and 2) Structure and activities of LEF/TCFs. Our
work in these two areas has led to new insights on LEF/TCF structure,
Wnt response element recognition, signals from the tumor
microenvironment and chromatin regulators that modify the types and
amounts of LEF/TCFs. In almost every aspect LEF/TCF expression and/or
function has been distorted in cancer.
Regulation of LEF/TCF Transcription
Transcription: The LEF1 locus has two promoters for RNA polymerase II transcription, where each promoter produces a differently acting form of LEF-1. One promoter is activated in Wnt-linked cancers (P1), the other promoter is silenced (P2). We aim to identify the regulatory elements, transcription factors and signaling pathways that create this pattern, as the activated-silenced pattern produces only Wnt-promoting forms of LEF-1. We are also working to define common themes of transcription regulation of all four mammalian LEF/TCFs for a more comprehensive view of expression of this family is modulated during development and disease.
Translation: LEF1 mRNA produced from P1 contains two Internal
Ribosome Entry Sites in its long 5 UTR. We have discovered a
cancer-relevant signaling pathway that regulates IRES activity and
LEF-1 protein production. Current efforts are focused on a new method
to isolate LEF1 mRNA/protein complexes for mass spectrometry analysis
and IRES-factor discovery.
Structure and Activities of LEF/TCFs
A new DNA binding domain: We have discovered a second DNA binding
domain in the C-terminus of TCFs. Previously known as the CRARF
region, we refer to it as the C-clamp because of four invariant and
essential cysteines. The C-clamp is a new type of DNA binding domain
and appears to be critical for TCF-mediated growth control. We aim to
define the role of this domain in carcinogenesis and obtain structural
and gene targeting information to develop ways to interfere with its
Nuclear export of TCFs: Another major effort in the laboratory is a focus on subcellular trafficking of LEF/TCFs. Our early research identified nuclear localization activities and receptors that ushered LEF/TCFs into the nucleus. More recently, we have discovered that certain mammalian TCFs engage in nuclear/cytoplasmic shuttling an activity that is active and distorted in cancer. We have discovered a Wnt-linked kinase cascade that can control this shuttling, linking TCF trafficking to extracellular signals that may be aberrant in the tumor microenvironment. The Wnt-linked signal has elements of canonical and non-canonical signaling, and we are working to define these novel elements as well as the molecular changes in LEF/TCFs when export is triggered.