Protein Kinase Cα Puts the Handcuffs on Epidermal Keratinocyte Proliferation

As the predominant cellular receptor for phorbol esters, protein kinase C (PKC) is assumed to play a role in epidermal carcinogenesis. Nevertheless, determining its exact role in keratinocytes has been difficult because of the existence of multiple PKC isoforms and the inherent weaknesses in methodologies used to investigate their function. In this issue, Jerome-Morais et al. describe their use of multiple in vitro, in situ, overexpression, and knockdown approaches to demonstrate that PKCα induces keratinocyte growth arrest

A Hypothesis Concerning a Potential Involvement of Ceramide in Apoptosis and Acantholysis Induced by Pemphigus Autoantibodies

Autoimmune diseases affect more than 50 million Americans, resulting in significant healthcare costs. Most autoimmune diseases occur sporadically; however, endemic pemphigus foliaceus (EPF) is an autoimmune skin disease localized to specific geographic loci. EPF, and the related diseases pemphigus vulgaris (PV) and pemphigus foliaceus (PF), are characterized by skin lesions and autoantibodies to molecules found on epidermal keratinocytes. A variant of EPF in patients from El Bagre, Colombia, South America, has recently been reported to be distinct from previously described loci in Brazil and Tunisia epidemiologically and immunologically. As in PF and EPF, El Bagre EPF patients exhibit autoantibodies towards desmoglein-1, a cell adhesion molecule critical for maintaining epidermal integrity. An association of El Bagre EPF with sun exposure has been detected, and ultraviolet irradiation also exacerbates symptoms in PV, PF and EPF. Our hypothesis is that: (1) the autoantibodies generate pathology through an alteration in ceramide metabolism in targeted keratinocytes, resulting in apoptosis and/or cell death and acantholysis, but only when the cell's ability to metabolize ceramide is exceeded, and (2) apoptosis in response to this altered ceramide metabolism is initiated and/or exacerbated by other agents that increase ceramide levels, such as cytokines, ultraviolet irradiation, and senescence

8-Cl-Adenosine enhances 1,25-dihydroxyvitamin D(3)-induced growth inhibition without affecting 1,25-dihydroxyvitamin D(3)-stimulated differentiation of primary mouse epidermal keratinocytes

BACKGROUND: Epidermal keratinocytes continuously proliferate and differentiate to form the mechanical and water permeability barrier that makes terrestrial life possible. In certain skin diseases, these processes become dysregulated, resulting in abnormal barrier formation. In particular, skin diseases such as psoriasis, actinic keratosis and basal and squamous cell carcinomas are characterized by hyperproliferation and aberrant or absent differentiation of epidermal keratinocytes. We previously demonstrated that 8-Cl-adenosine (8-Cl-Ado) can induce keratinocyte growth arrest without inducing differentiation. RESULTS: To determine if this agent might be useful in treating hyperproliferative skin disorders, we investigated whether 8-Cl-Ado could enhance the ability of 1,25-dihydroxyvitamin D(3 )[1,25(OH)(2)D(3)], a known keratinocyte differentiating agent and a clinical treatment for psoriasis, to inhibit keratinocyte growth. We found that low concentrations of 8-Cl-Ado and 1,25(OH)(2)D(3 )appeared to act additively to reduce proliferation of primary mouse epidermal keratinocytes. However, another agent (transforming growth factor-beta) that triggers growth arrest without inducing differentiation also coincidentally inhibits differentiation elicited by other agents; inhibition of differentiation is suboptimal for treating skin disorders, as differentiation is often already reduced. Thus, we determined whether 8-Cl-Ado also decreased keratinocyte differentiation induced by 1,25(OH)(2)D(3), as measured using the early and late differentiation markers, keratin 1 protein levels and transglutaminase activity, respectively. 8-Cl-Ado did not affect 1,25(OH)(2)D(3)-stimulated keratin 1 protein expression or transglutaminase activity. CONCLUSIONS: Our results suggest that 8-Cl-Ado might be useful in combination with differentiating agents for the treatment of hyperproliferative disorders of the skin

Effects of the Selective Protein Kinase C Inhibitor, Ro 31-7549, on the Proliferation of Cultured Mouse Epidermal Keratinocytes

We have investigated the effects of Ro 31-7549, a selective protein kinase C (PKC) inhibitor, on DNA synthesis and proliferation in two primary mouse epidermal keratinocyte culture systems. In differentiating keratinocytes incubated in medium containing 10% serum and high calcium (approximately 0.5 mM), Ro 31-7549 blocked the inhibitory effect of the phorbol ester 12-0-tetradecanoyl-13-acetate (TPA) (a PKC activator) on keratinocyte DNA synthesis at 24 h [50% maximal response concentration (EC50) = 1 μM], consistent with inhibition of PKC-mediated differentiation. Continuous treatment of the differentiative culture system with the PKC inhibitor resulted in a marked (fourfold) stimulation of [3H]thymidine incorporation at day 7 of exposure, with an EC50 of 0.25 μM. The potencies of these effects of Ro 31-7549 are comparable to that reported for inhibition of TPA-induced platelet 47-kD protein phosphorylation [50% inhibitory concentration (IC50) = 4.4 μM]. The time course of [3H]thymidine incorporation indicated that Ro 31-7549 did not directly stimulate DNA synthesis but instead prevented the loss of proliferative capacity associated with continued culture in this medium. Maximal stimulation (2.6 times) of DNA synthesis was observed on day 4, whereas DNA synthesis at day 1 was unaffected. In a highly proliferative culture system using serum-free medium containing 25 μM calcium, TPA dose-dependently inhibited proliferation with an IC50 of approximately 0.3 nM. This antiproliferative effect of TPA was largely reversed by 0.1 M Ro 31-7549. In the proliferative culture system, 0.75 M Ro 31-7549 also essentially reversed the inhibition of proliferation caused by switching to high (1.0 mM) calcium. These results suggest that the loss of proliferative capacity in differentiating epidermal keratinocyte cultures maybe mediated, at least in part, by PKC

Aquaporin-3 Re-Expression Induces Differentiation in a Phospholipase D2-Dependent Manner in Aquaporin-3-Knockout Mouse Keratinocytes

Aquaporin-3 (AQP3) is a water and glycerol channel expressed in epidermal keratinocytes. Despite many studies, controversy remains about the role of AQP3 in keratinocyte differentiation. Previously, our laboratory has shown co-localization of AQP3 and phospholipase D2 (PLD2) in caveolin-rich membrane microdomains. We hypothesized that AQP3 transports glycerol and “funnels” this primary alcohol to PLD2 to form a pro-differentiative signal, such that the action of AQP3 to induce differentiation should require PLD2. To test this idea, we re-expressed AQP3 in mouse keratinocytes derived from AQP3-knockout mice. The re-expression of AQP3, which increased [3H]glycerol uptake, also induced mRNA and protein expression of epidermal differentiation markers such as keratin 1, keratin 10, and loricrin, with or without the induction of differentiation by an elevated extracellular calcium concentration. Re-expression of AQP3 had no effect on the expression of the proliferation markers keratin 5 and cyclin D1. Furthermore, a selective inhibitor of PLD2, CAY10594, and a lipase-dead (LD) PLD2 mutant, but not a LD PLD1 mutant, significantly inhibited AQP3 re-expression–induced differentiation marker expression with calcium elevation, suggesting a role for PLD2 in this process. Thus, our results indicate that AQP3 has a pro-differentiative role in epidermal keratinocytes and that PLD2 activity is necessary for this effect

Satisfaction of staff of Swiss insurance companies with medical appraisals: a cross sectional study

<p>Abstract</p> <p>Background</p> <p>A high quality of timely delivered medical appraisals is crucial for social and other insurances to judge possible occupational reintegration measures for patients with medical conditions who are in danger to lose their job. However, little is known about the satisfaction of staff of insurance companies with medical appraisals that they have commissioned.</p> <p>Our questionnaire survey prospectively included all medical appraisals arriving at Swiss insurances from FEB to APR 2008. We assessed the satisfaction of the commissioner with medical appraisals performed by medical assessors. In addition, we evaluated the contribution of several factors to overall satisfaction. The unit of sample was the medical appraisal.</p> <p>Findings</p> <p>We analysed 3165 medical appraisals, 2444 (77%) of them from the public disability insurance, 678 (22%) from private accident, liability and loss of income insurances and 43 (1%) from other insurances. Overall satisfaction of staff of insurance companies in Switzerland was high, but satisfaction of the disability insurance with appraisals was generally lower compared to satisfaction of private insurances. The staff of the disability insurance judged time for preparation as too long in 30%. For staff of private insurance companies 20% of appraisals were not "worth its price". Well-grounded and comprehensible conclusions were the single most important factor for high overall satisfaction (OR 10.1; 95%-CI: 1.1-89.3).</p> <p>Conclusions</p> <p>From the viewpoint of staff of insurance companies, a relevant part of medical appraisals arrives too late. Medical assessors have to take the specific needs of insurances into account, to perform more appraisals with sound conclusions in due time.</p