AP1 transcription factors in epidermal differentiation and skin cancer.

AP1 (jun/fos) transcription factors (c-jun, junB, junD, c-fos, FosB, Fra-1, and Fra-2) are key regulators of epidermal keratinocyte survival and differentiation and important drivers of cancer development. Understanding the role of these factors in epidermis is complicated by the fact that each protein is expressed, at different levels, in multiple cells layers in differentiating epidermis, and because AP1 transcription factors regulate competing processes (i.e.

Lysophosphatidic acid promotes cell migration through STIM1- and Orai1-mediated Ca2+(i) mobilization and NFAT2 activation.

Lysophosphatidic acid (LPA) enhances cell migration and promotes wound healing in vivo, but the intracellular signaling pathways regulating these processes remain incompletely understood. Here we investigated the involvement of agonist-induced Ca(2+) entry and STIM1 and Orai1 proteins in regulating nuclear factor of activated T cell (NFAT) signaling and LPA-induced keratinocyte cell motility. As monitored by Fluo-4 imaging, stimulation with 10 μM LPA in 60 μM Ca(2+)(o) evoked Ca(2+)(i) transients owing to store release, whereas addition of LPA in physiological 1.

TIG3 tumor suppressor-dependent organelle redistribution and apoptosis in skin cancer cells.

TIG3 is a tumor suppressor protein that limits keratinocyte survival during normal differentiation. It is also important in cancer, as TIG3 level is reduced in tumors and in skin cancer cell lines, suggesting that loss of expression may be required for cancer cell survival. An important goal is identifying how TIG3 limits cell survival.

Lithium regulates keratinocyte proliferation via glycogen synthase kinase 3 and NFAT2 (nuclear factor of activated T cells 2).

Certain environmental factors including drugs exacerbate or precipitate psoriasis. Lithium is the commonest cause of drug-induced psoriasis but underlying mechanisms are currently unknown. Lithium inhibits glycogen synthase kinase 3 (GSK-3).

Type I transglutaminase accumulation in the endoplasmic reticulum may be an underlying cause of autosomal recessive congenital ichthyosis.

Type I transglutaminase (TG1) is an enzyme that is responsible for assembly of the keratinocyte cornified envelope. Although TG1 mutation is an underlying cause of autosomal recessive congenital ichthyosis, a debilitating skin disease, the pathogenic mechanism is not completely understood. In the present study we show that TG1 is an endoplasmic reticulum (ER) membrane-associated protein that is trafficked through the ER for ultimate delivery to the plasma membrane.

TIG3: a regulator of type I transglutaminase activity in epidermis.

Keratinocytes undergo a process of terminal cell differentiation that results in the construction of a multilayered epithelium designed to produce a structure that functions to protect the body from dehydration, abrasion and infection. These protective properties are due to the production of a crosslinked layer of protein called the cornified envelope. Type I transglutaminase (TG1), an enzyme that catalyzes the formation of epsilon-(gamma-glutamyl)lysine bonds, is the key protein responsible for generation of the crosslinks.

Localization of the TIG3 transglutaminase interaction domain and demonstration that the amino-terminal region is required for TIG3 function as a keratinocyte differentiation regulator.

Tazarotene-induced gene 3 (TIG3) regulates keratinocyte terminal differentiation by activating type I transglutaminase (TG1). TIG3 consists of an amino-terminal (N-terminal) segment, that encodes several conserved motifs, and a carboxy-terminal (C-terminal) membrane-anchoring domain. By producing a series of truncation mutants that remove segments of the N-terminal region, and monitoring the ability of each mutant to co-precipitate TG1, function as a TG1 substrate, or functionally localize with TG1 in cells, we show that the TIG3 domain that interacts with TG1 is located within a TIG3 segment spanning amino acids 112-164.

Expression of lysosome-associated membrane protein 1 (Lamp-1) and galectins in human keratinocytes is regulated by differentiation.

Lysosomes and their components are suspected to be involved in epidermal differentiation. In this study, lysosomal enzyme activities, expression of the lysosome-associated membrane protein 1 (Lamp-1) and expression of the epidermal galectins-1, -3 and -7 were investigated in human keratinocytes cultured at different cell densities (subconfluence, confluence and postconfluence) in order to induce differentiation. Detected by Western blot and immunofluorescence, Lamp-1 expression is transiently upregulated at culture confluence, but reduced at postconfluence.

Effects of the cyclin-dependent kinase inhibitor CYC202 (R-roscovitine) on the physiology of cultured human keratinocytes.

CYC202 (R-roscovitine) is a potent cyclin-dependent kinase inhibitor, investigated as a potential anti-cancer agent. The knowledge of the action of this pharmacological agent on normal human cells is still limited. In this study, we have explored the effects of the cyclin-dependent kinase inhibitor CYC202 on normal human epidermal keratinocytes.

Cholesterol depletion upregulates involucrin expression in epidermal keratinocytes through activation of p38.

Cholesterol has been recently suggested to regulate the early steps of keratinocyte differentiation through lipid rafts. In many cell types, depletion of cholesterol activates signaling proteins like epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER2), or extracellular signal-regulated kinase (ERK) known to affect cell differentiation. In this study, we explored the effects of cholesterol depletion on the phenotype of cultured keratinocytes, using a treatment with methyl-beta-cyclodextrin (MbetaCD) to extract cholesterol and a treatment with lovastatin to inhibit cholesterol neosynthesis.

Calcium entry into keratinocytes induces exocytosis of lysosomes.

During the final steps of epidermal differentiation, extracellular calcium ions enter keratinocytes and induce transglutaminase activity and cornified envelope formation. In other cell types, entry of calcium mediated by ionophores has been reported to induce exocytosis of lysosomes. In this study, we investigated whether lysosomes of keratinocytes might exhibit a similar behaviour.