Hominoid apes (gorilla, chimpanzee, orangutan, gibbon), Old World monkeys (rhesus, cynomolgus), New World monkeys (owl, cebus), and a prosimian (lemur) express involucrin-like proteins in cultured keratinocytes. Primate involucrins can be precipitated with trichloroacetic acid, resolubilized at pH 8, and subsequently retain aqueous solubility in 67% ethanol. Polyacrylamide gel electrophoresis of keratinocyte extracts after this rapid partial purification has revealed in each species tested one (chimpanzee, orangutan, gibbon) or two (gorilla, rhesus, owl, cebus) antigenically crossreactive proteins that migrate in the vicinity of human involucrin. In the species examined further (gorilla, chimpanzee, rhesus), poly(A)+ mRNA isolated from the cultures directed the cell-free translation of polypeptides with mobilities similar to those extracted from the cells. From five cynomolgus monkeys, three different electrophoretic profiles were obtained, suggesting the existence of different alleles. Quantitative comparisons by a sensitive enzyme-linked immunosorbent assay indicated that certain primate involucrins have a higher density of antigenic determinants than the human protein, whereas others lack some determinant(s). In contrast to those from other species, all of which showed substantial crossreactivity, the lemur protein was minimally immunoreactive by immunoblotting and not clearly detected by solid-phase assay. The electrophoretic and antigenic differences displayed throughout the primate order suggest that this protein has been subject to relatively rapid evolution.

Epidermal keratinocyte differentiation on the body surface is a carefully choreographed process that leads to assembly of a barrier that is essential for life. Perturbation of keratinocyte differentiation leads to disease. Activator protein 1 (AP1) transcription factors are key controllers of this process. We have shown that inhibiting AP1 transcription factor activity in the suprabasal murine epidermis, by expression of dominant-negative c-jun (TAM67), produces a phenotype type that resembles human keratoderma. However, little is understood regarding the structural and molecular changes that drive this phenotype. In the present study we show that TAM67-positive epidermis displays altered cornified envelope, filaggrin-type keratohyalin granule, keratin filament, desmosome formation and lamellar body secretion leading to reduced barrier integrity. To understand the molecular changes underlying this process, we performed proteomic and RNA array analysis. Proteomic study of the corneocyte cross-linked proteome reveals a reduction in incorporation of cutaneous keratins, filaggrin, filaggrin2, late cornified envelope precursor proteins, hair keratins and hair keratin-associated proteins. This is coupled with increased incorporation of desmosome linker, small proline-rich, S100, transglutaminase and inflammation-associated proteins. Incorporation of most cutaneous keratins (Krt1, Krt5 and Krt10) is reduced, but incorporation of hyperproliferation-associated epidermal keratins (Krt6a, Krt6b and Krt16) is increased. RNA array analysis reveals reduced expression of mRNA encoding differentiation-associated cutaneous keratins, hair keratins and associated proteins, late cornified envelope precursors and filaggrin-related proteins; and increased expression of mRNA encoding small proline-rich proteins, protease inhibitors (serpins), S100 proteins, defensins and hyperproliferation-associated keratins. These findings suggest that AP1 factor inactivation in the suprabasal epidermal layers reduces expression of AP1 factor-responsive genes expressed in late differentiation and is associated with a compensatory increase in expression of early differentiation genes.