ß-Catenin determines upper airway progenitor cell fate and preinvasive squamous lung cancer progression by modulating epithelial-mesenchymal transition.

Human lung cancers, including squamous cell carcinoma (SCC) are a leading cause of death and, whilst evidence suggests that basal stem cells drive SCC initiation and progression, the mechanisms regulating these processes remain unknown. In this study we show that ß-catenin signalling regulates basal progenitor cell fate and subsequent SCC progression. In a cohort of preinvasive SCCs we established that elevated basal cell ß-catenin signalling is positively associated with increased disease severity, epithelial proliferation and reduced intercellular adhesiveness. We demonstrate that transgene-mediated ß-catenin inhibition within keratin 14-expressing basal cells delayed normal airway repair while basal cell-specific ß-catenin activation increased cell proliferation, directed differentiation and promoted elements of early epithelial-mesenchymal transition (EMT), including increased Snail transcription and reduced E-cadherin expression. These observations are recapitulated in normal human bronchial epithelial cells in vitro following both pharmacological ß-catenin activation and E-cadherin inhibition, and mirrored our findings in preinvasive SCCs. Overall, the data show that airway basal cell ß-catenin determines cell fate and its mis-expression is associated with the development of human lung cancer.

KazrinE is a desmosome-associated liprin that colocalises with acetylated microtubules.

Kazrin is a widely expressed, evolutionarily conserved cytoplasmic protein that binds the cytolinker protein periplakin. Multiple functions of kazrin have been reported, including regulation of desmosome assembly, embryonic tissue morphogenesis and epidermal differentiation. Here, we identify kazrinE as a kazrin isoform that contains a liprin-homology domain (LHD) and forms complexes with kazrinA, kazrinB and kazrinC. As predicted from the presence of the LHD, kazrinE can associate with the leukocyte common antigen-related (LAR) protein tyrosine phosphatase in a phosphorylation-dependent manner. When overexpressed in epidermal keratinocytes, kazrinE induces changes in cell shape and stimulates terminal differentiation. Like the other kazrin isoforms, kazrinE localises to the nucleus and desmosomes. However, in addition, kazrinE associates with stabilised microtubules via its LHD. During terminal differentiation, the keratinocyte microtubule network undergoes extensive reorganisation; in differentiating keratinocytes, endogenous kazrinE colocalises with microtubules, but periplakin does not. We speculate that the kazrinE-microtubule interaction contributes to the mechanism by which kazrin regulates desmosome formation and epidermal differentiation.

Kazrin regulates keratinocyte cytoskeletal networks, intercellular junctions and differentiation.

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.

Lung cancer and lung stem cells: strange bedfellows?

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.

Mice deficient in involucrin, envoplakin, and periplakin have a defective epidermal barrier.

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 gammadelta+ 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.

Kazrin, a novel periplakin-interacting protein associated with desmosomes and the keratinocyte plasma membrane.

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.