The cornified envelope is assembled from transglutaminase cross-linked proteins and lipids in the outermost epidermal layers and is essential for skin barrier function. Involucrin, envoplakin, and periplakin form the protein scaffold on which the envelope assembles. To examine their combined function, we generated mice deficient in all three genes. The triple knockouts have delayed embryonic barrier formation and postnatal hyperkeratosis (abnormal accumulation of cornified cells) resulting from impaired desquamation. Cornified envelopes form but are ultrastructurally abnormal, with reduced lipid content and decreased mechanical integrity. Expression of proteases is reduced and the protease inhibitor, serpina1b, is highly upregulated, resulting in defective filaggrin processing and delayed degradation of desmoglein 1 and corneodesmosin. There is infiltration of CD4+ T cells and a reduction in resident γδ+ T cells, reminiscent of atopic dermatitis. Thus, combined loss of the cornified envelope proteins not only impairs the epidermal barrier, but also changes the composition of T cell subpopulations in the skin.

Lung cancer is a significant disease with survival rates remaining poor despite numerous therapeutic advances during the last 30 years. Understanding lung cancer pathogenesis through murine modeling may improve future human therapies, and new data indicate that mutations within different endogenous stem cells situated throughout airways can drive cancer formation. Airway stem cells maintain prototumorigenic characteristics, including high proliferative capacity, multipotent differentiation, and a long lifespan relative to other cells. These cells localize to proximal airway submucosal glands/intercartilagenous rings, neuroepithelial bodies, and terminal bronchioles/bronchoalveolar duct junctions. Recent studies suggest that endogenous stem cell signaling and differentiation pathways are maintained within distinct cancer types, and that destabilization of this signaling machinery may initiate region-specific lung cancers. A better understanding of this relationship among stem cell regulation, cellular mutation, and lung cancer oncogenesis is critical for developing the next wave of lung cancer therapies.

Periplakin forms part of the scaffold onto which the epidermal cornified envelope is assembled. The NH2-terminal 133 amino acids mediate association with the plasma membrane and bind a novel protein, kazrin. Kazrin is highly conserved and lacks homology to any known protein. There are four alternatively spliced transcripts, encoding three proteins with different NH2 termini. Kazrin is expressed in all layers of stratified squamous epithelia; it becomes membrane associated in the suprabasal layers, coincident with up-regulation of periplakin, and is incorporated into the cornified envelope of cultured keratinocytes. Kazrin colocalizes with periplakin and desmoplakin at desmosomes and with periplakin at the interdesmosomal plasma membrane, but its subcellular distribution is independent of periplakin. On transfection, all three kazrin isoforms have similar subcellular distributions. We conclude that kazrin is a novel component of desmosomes that associates with periplakin.

Cancers are a heterogeneous mix of cells, some of which exhibit cancer stem cell-like characteristics including ATP-dependent drug efflux and elevated tumorigenic potential. To determine whether aerodigestive squamous cell carcinomas (SCCs) contain a subpopulation of cancer stem cell-like cells, we performed Hoechst dye efflux assays using four independent cell lines. Results revealed the presence of a rare, drug effluxing stem cell-like side population (SP) of cells within all cell lines tested (SCC-SP cells). These cells resembled previously characterised epithelial stem cells, and SCC-SP cell abundance was positively correlated with overall cellular density and individual cell quiescence. Serial SCC-SP fractionation and passaging increased their relative abundance within the total cell population. Purified SCC-SP cells also exhibited increased clonogenic potential in secondary cultures and enhanced tumorigenicity in vivo. Despite this, SCC-SP cells remained chemotherapeutically sensitive upon ATP-dependent transporter inhibition. Overall, these findings suggest that the existence of ATP transporter-dependent cancer stem-like cells may be relatively common, particularly within established tumours. Future chemotherapeutic strategies should therefore consider coupling identification and targeting of this potential stem cell-like population with standard treatment methodologies.

Kazrin is an evolutionarily conserved protein that is upregulated during keratinocyte terminal differentiation. Kazrin localizes to desmosomes and binds the epidermal cornified envelope protein periplakin. Kazrin overexpression in human epidermal keratinocytes caused profound changes in cell shape, reduced filamentous actin, reorganized keratin filaments, and impaired assembly of intercellular junctions. These effects were attributable to decreased Rho activity in kazrin-overexpressing cells. Kazrin overexpression also stimulated terminal differentiation and reduced clonal growth in culture. Knockdown of kazrin decreased expression of differentiation markers and stimulated proliferation without changing total Rho activity. We conclude that kazrin is a dual regulator of intercellular adhesion and differentiation in keratinocytes and regulates these processes by Rho-dependent and -independent mechanisms.Supplementary material available online at