Telephone: (919) 962-2271 (Office);
(919) 962-2272 (Lab)

E-mail: peifer@unc.edu

Office: 521 Fordham Hall

Mailing Address:
CB# 3280, Coker Hall
The University of North Carolina at Chapel Hill
Chapel Hill, North Carolina 27599-3280

Hooker Distinguished Professor
(Initial appointment 1992)
Member, Lineberger Cancer Center
Ph.D., Harvard University (1988)
B.A., Saint Olaf College (1980)

Selected References | Teaching | Curriculum Vitae
Current Lab Members and their projects | Accomplishments of Former Grad students
Undergraduate Research | Lab Alumni | Selected recent talks by lab members

Biomedical science has twin goals; to explain the many amazing properties of our own bodies and those of other animals, and to use this information to reveal the causes of disease and to suggest possible treatments. We work at the interface between cell and developmental biology, focusing on the epithelial tissues that form the basic architectural unit of our bodies and of those of other animals. Epithelial tissues like skin, lung, colon, and breast are affected in many cancers. To explore underlying causes of epithelial tumors and to understand the basic cellular machinery that links cell adhesion, signal transduction and cytoskeletal regulation, we focus on the Armadillo/ß-catenin protein. It is mutated in colon and other cancers, and it is also critical for normal embryonic development. Cancer results from alterations in normal cell behaviors. Drosophila Armadillo and its vertebrate homolog ß-catenin play key roles both in cell-cell adherens junctions, initiating the formation of epithelial tissues, and as transducers of Wingless/Wnt family cell-cell signals. We study these processes in the fruit fly Drosophila, combining classical and molecular genetics with cell biology and biochemistry, and thus capitalizing on the speed of this model system and its synergy with vertebrate cell biology (for a review click here), and supplement this with work on cultured Drosophila cells and cultured colon cancer cells.

We demonstrated that Armadillo is a key component of cell-cell adherens junctions, where it joins transmembrane cadherins to alpha-catenin and the actin cytoskeleton. Armadillo and adherens junctions are essential for maintaining epithelial organization, for cell polarity, and for normal embryonic development. Metastasis of epithelial tumors requires inactivation of this cell-cell adhesion machinery. Armadillo plays a separate role in transduction of the Wingless cell-cell signal. In this role, it forms a heterodimer with the TCF DNA-binding protein, creating a bipartite transcription factor that regulates Wingless target genes. Armadillo's role in signal transduction is regulated by regulating Armadillo protein stability. In cells not receiving signal, Armadillo protein is destroyed outside of adherens junctions. Wingless signal prevents Armadillo from being destroyed, and it accumulates in the cytoplasm of nucleus of these cells (for a pretty picture of this, click here). The machinery for targeting Armadillo for destruction includes both the tumor suppressor protein APC and the Serine/Threonine protein kinase Zeste white-3 (also known as GSK-3ß).  Many colon and other tumors result in part from inappropriate activation of ß-catenin signaling, via mutations in APC that render it unable to destroy ß-catenin or mutations in ß-catenin that make it indestructible. We generated similar mutations in Armadillo and found that they make it constitutively active in transduction of Wingless signal. These data helped serve as the foundation of our current model for regulation of Wnt signaling in normal cells and its disruption in cancer, diagrammed above.

We are currently exploring the cellular and biochemical mechanisms regulating cell adhesion and transduction of Wnt cell-cell signals, and are identifying and examining the function of other components of adherens junctions and the Wnt signal transduction pathway. Our goal is to understand these processes at the biochemical level. Armadillo/ß-catenin and their interactors are potential drug targets, via small molecule inhibitors of ß-catenin action in carcinogenesis.

APC2 (Red) is enriched in dividing neural stem cells, and both it and Armadillo (Green) accumulate asymmetrically in dividing neuroblasts.

Our current work on Wnt signaling focuses on using both fruit flies and cultured colon cancer cell lines to explore the mechanisms of action of the key tumor suppressor APC. In collaboration with Hans Clevers lab, we identified second APC genes in both Drosophila and in mammals. While our collaborators in the Clevers lab characterized the second mouse APC, we have focused on fly APC2. Working together with Amy Bejsovec's lab, we found that APC2 plays a key role in regulating Wingless signaling in the embryonic epidermis, and have begun to examine the mechanism by which this occurs. In addition, we have used our antibody to APC2 to look at its subcellular distribution. These data demonstrated that in addition to regulating Arm levels, APC2 also regulates the cytoskleton. We found that APC2 helps mediate the attachment of the mitotic spindle to the actin cortex. This role in spindle positioning may help explain why APC mutant tumors exhibit defects in chromosome segregation. We have also begun to examine the role of APC proteins in neural stem cells and brain development. We tested the hypothesis that APC may mediate spindle orientation in neural stem cells and also help mediate cell adhesion during axon outgrowth.

Armadillo-GFP localization to cell-cell junctions during dorsal closure in a living embryo.

In studying adhesion, our challenge is to alter our static model of adhesion to explain the remarkable cellular events of morphogenesis that shape the embryonic body plan. To do so, we must understand the dynamic regulation of cell adhesion and the interactions between adhesion and the cytoskeleton. We are visualizing these processes in live animals using GFP-fusions including a fully functional Armadillo-GFP fusion protein and various GFP fusions that track that track other adhesion and cytoskeletal regulatory proteins as well as the actin and microtubule cytoskeletons. This allows us to examine adherens junctions and the cytoskeleton during dynamic events of morphogenesis, such as dorsal closure. A set of still pictures depicting this is displayed at the left, and a movie can be seen by clicking here. In searching for regulators of adhesion and the cytoskeleton, we have focused on the non-receptor tyrosine kinase Abelson (Abl). Mutations in Abl cause two forms of human leukemia. We have found that Abl regulates adhesion and the connection to the actin cytoskeleton. We are currently exploring the role of Abl in the complex events of morphogenesis and examining the function of Enabled, an Abl target. We have expanded our focus to include the functions of a number of additional proteins that act in adherens junctions and/or regulate its connections to the cytoskeleton. These include the small GTPases Rho, the Rho effector Diaphanous, and the junctional protein Canoe/Afadin.

In addition to their role in adhesion, cell junctions also regulate cell polarity. We have begun to explore how different junctional proteins help establish and elaborate cell polarity.

To learn more about our work, check out some selected publications from our lab, or find out more about the people in the lab, with brief descriptions of their projects and contact information. It's an exciting time to be working at the interface between cell and developmental biology, and we are always looking for talented and enthusiastic graduate students and postdocs to add to our group.

The anti-Armadillo antibody is now available from the Developmental Studies Hybridoma Bank, an NIH funded facility that produces antibodies for the research community at cost. They will sell you anti-Armadillo 7A1 mouse monoclonal antibody at $10/ml. You can reach them by phone at 319-335-3826 or by email at dshb@uiowa.edu. Perhaps the easiest way to reach them is at their home page at http://dshb.biology.uiowa.edu/.

If you need more information about the use of the antibody, feel free to contact us. We use it at 1:40 in situ on embryos, 1:20 for immunoprecipitations, and at 1:400 on Westerns.

Good luck with your experiments.

Armadillo protein is normally found in the adherens junctions surrounding each cell. However, in cells which have received Wingless signal, Armadillo protein also accumulates in the cytoplasm and the nucleus, where we suspect it may be involved in activating transcription of target genes. Panel A shows an embryo double labeled with anti-Armadillo antibody (red) and anti-Engrailed antibody (green). Engrailed is a transcription factor and marks the nucleus. Some nuclei are yellow, showing co-localization of Armadillo and Engrailed in the nuclei of cells receiving Wingless signal. Panels B and C are the single labeled images.