The primary function of the epidermis is to provide a protective barrier from the environment; strong but adaptable cell-cell adhesion is required for the normal execution of this function. Cell-cell adhesion in epidermis is mediated through two distinct structures known as adherens junctions and desmosomes, each of which has numerous molecular components. Little is presently known about the regulatory and functional inter-relationships among the different adhesion molecules and structures. An understanding of the regulation and precise mechanisms of epidermal cell-cell adhesion has important consequences for normal epidermal morphogenesis, a process that continues throughout life to regenerate this multilayered tissue. Furthermore, a variety of cutaneous disorders, including pemphigus, Hailey-Hailey disease, and Darier's disease involve defects in epidermal cell-cell adhesion that are not presently understood. The broad goal of the present proposal is to determine the function of and regulatory relationships among the different cell-cell adhesion molecules during epidermal stratification. The homotypic adhesion molecule E- cadherin,which is a component of the adherens junction, has previously been shown to be required for normal stratification; furthermore, in the absence of both E-cadherin and P-cadherin function, intercellular junctions do not form and stratification does not occur. Further studies are proposed to determine the specific effects of compromised cadherin function on adhesion mechanisms and stratification and differentiation parameters. The hypothesis that E-cadherin exerts its regulatory effects on intercellular junction organization through protein kinase C activation will be tested. The functional inter-relationships among the cadherins and the desmogleins and desmocollins (major transmembrane glycoproteins of the desmosome, which are in the cadherin superfamily of adhesion molecules) will be explored. Finally, the relationship between stratification and the normal orderly pattern of epidermal differentiation will be examined. Human keratinocyte culture at the air-liquid interface, which faithfully mimicks in vivo patterns of keratinization, will be used as a model system. Modulation of the calcium ion concentration allows intercellular junction organization and stratification to be initiated at a precise point in time. Specific inhibitory antibodies will be used to inhibit individual adhesion molecules, thus permitting evaluation of their functions. These studies will help to define the roles of the individual adhesion molecules and structures during stratification; furthermore, this approach will evaluate whether there is any overlap in specific function among distinct adhesion molecules and structures or whether each has a totally separate and unique role.