Khavari Lab Research Interests

Research Description

In stratified epithelium, proliferative basal cells adherent to the underlying basement membrane undergo cell cycle arrest then outward migration and terminal differentiation. The control of this transition from epithelial stem cell to differentiated corneocyte, which is abnormal in epidermal cancers, is not well understood. Our laboratory is currently pursuing 2 lines of effort: 1) studies of the gene regulatory mechanisms controlling epithelial growth and carcinogenesis 2) development of new molecular therapeutics for the treatment of skin and systemic disease.

Regulation of epithelial growth and carcinogenesis

Stratified epithelium displays two broad programs of gene expression: 1) a basal layer undifferentiated program that mediates proliferation and adhesion to the underlying basement membrane and 2) a suprabasal program expressed in growth arrested cells that mediates terminal differentiation. We have recently demonstrated that the transition between these mutually exclusive states involves spatially regulated activation of NF-kB/Rel family gene regulatory proteins. NF-kB proteins are induced in a range of conditions involving cellular stress and injury; stratified epithelial tissues must respond to such frequent environmental stresses while maintaining a precise balance between cellular proliferation and cell loss via desquamation. Using murine genetic models we have shown that NF-kB proteins trigger cellular growth arrest and prevent default apoptosis during early epithelial differentiation. Without NF-kB RelA, epidermal cells fail to exit the proliferative compartment, illuminating a new, non-redundant function for NF-kB in epithelial homeostasis. In addition to NF-kB, we have characterized other dominant regulators of epithelial growth, including Ras signaling proteins. We have demonstrated that Ras, acting in part via the MEK/Raf/MAPK cascade, maintains epithelial cells in the undifferentiated, proliferative state. Disruption of epidermal Ras function leads to loss of self-renewal and default differentiation, confirming that Ras plays a central role in the undifferentiated basal program. In order to study interactions between dominant regulators such as NF-kB and Ras, we have developed multiplex serial gene transfer (MSGT) in which alterations in 8 or more signaling networks can be rapidly made in normal cells and tissue. Using MSGT, we have begun to study how cells integrate complex input from multiple gene regulatory pathways in normal epithelial growth control and neoplasia. These new genetic approaches have permitted the molecular reconstruction of events sufficient to trigger invasive human epidermal neoplasia and have provided a model in which to study genes important in epithelial cancer, such as squamous cell carcinoma. This capacity to regenerate human skin tissue with defined genetic alterations has also facilitated development of human tissue models of basal cell carcinoma and malignant melanoma. These models are being used to systematically elucidate proteins required for cutaneous carcinogenesis and to test their potential role as therapeutic targets. Complementing these studies, we have pursued a genome-wide screening approach using array-based transcript profiling to characterize genes expressed in different epidermal cancers and at specific steps in the transition from epithelial stem cell to growth arrested terminally differentiating cell. From these latter efforts, we have identified a host of previously uncharacterized genes altered in carcinogenesis that also appear part of precisely controlled genetic programs that accompany the growth arrest and differentiation process in epithelium. In combination, all of these studies are providing a broad perspective on the genetic controls of epithelial cell proliferation and are linking this information to human epithelial cancers.

Molecular therapeutics for epithelial tissue

Epithelial tissues in general and skin in particular offer an attractive site for development of new approaches in molecular therapeutics. A family of human genetic skin diseases is characterized by defective epithelial gene expression. Among the most severe of these are subtypes of epidermolysis bullosa (EB) and lamellar ichthyosis (LI). We have developed approaches for high efficiency gene transfer to EB and LI patient skin tissue that are corrective at biochemical, histologic, clinical and functional levels. In addition to EB subtypes [LAMB3, BPAG2, COL7A1 genes] and LI [TGM1 gene], we have undertaken corrective similar efforts with a number of other genetic skin disorders, including X-linked ichthyosis [STS] and xeroderma pigmentosum [XPC]. We have extended these studies to develop new vectors capable of sustainable therapeutic gene delivery to epidermis as a basis for initiating clinical trials in humans. In addition to these efforts at molecular correction of genetic skin disorders, we have also developed new approaches for genetic vaccination and systemic gene delivery via the skin. Moreover, using an array of nonviral and viral vectors, we have developed new approaches to regulated delivery of therapeutic polypeptides to the bloodstream via cutaneous gene transfer. As a complement to gene-based therapeutics, we have developed new ways to introduce proteins and small molecule pharmacotherapeutics through the epidermal permeability barrier using conserved transporter domains. These efforts are aimed to advance progress in the application of molecular therapeutics to epithelial tissues.

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