SiRNA-Mediated Selective Inhibition of Mutant Keratin mRNAs Responsible for the Skin Disorder Pachyonychia Congenita

RNA interference offers a novel approach for treating genetic disorders including the rare monogenic skin disorder pachyonychia congenita (PC). PC is caused by mutations in keratin 6a (K6a), K6b, K16, and K17 genes, including small deletions and single nucleotide changes. Transfection experiments of a fusion gene consisting of K6a and a yellow fluorescent reporter (YFP) resulted in normal keratin filament formation in transfected cells as assayed by fluorescence microscopy. Similar constructs containing a single nucleotide change (N171K) or a three-nucleotide deletion (N171del) showed keratin aggregate formation. Mutant-specific small inhibitory RNAs (siRNAs) effectively targeted these sites. These studies suggest that siRNAs can discriminate single nucleotide mutations and further suggest that "designer siRNAs" may allow effective treatment of a host of genetic disorders including PC.

A disease- and phosphorylation-related nonmechanical function for keratin 8

Keratin 8 (K8) variants predispose to human liver injury via poorly understood mechanisms. We generated transgenic mice that overexpress the human disease-associated K8 Gly61-to-Cys (G61C) variant and showed that G61C predisposes to liver injury and apoptosis and dramatically inhibits K8 phosphorylation at serine 73 (S73) via stress-activated kinases. This led us to generate mice that overexpress K8 S73-to-Ala (S73A), which mimicked the susceptibility of K8 G61C mice to injury, thereby providing a molecular link between K8 phosphorylation and disease-associated mutation. Upon apoptotic stimulation, G61C and S73A hepatocytes have persistent and increased nonkeratin proapoptotic substrate phosphorylation by stress-activated kinases, compared with wild-type hepatocytes, in association with an inability to phosphorylate K8 S73. Our findings provide the first direct link between patient-related human keratin variants and liver disease predisposition. The highly abundant cytoskeletal protein K8, and possibly other keratins with the conserved S73-containing phosphoepitope, can protect tissue from injury by serving as a phosphate “sponge” for stress-activated kinases and thereby provide a novel nonmechanical function for intermediate filament proteins.

Retinoic acid disintegrated desmosomes and hemidesmosomes in stratified oral keratinocytes

BACKGROUND

Although it is known that retinoic acid (RA) regulates the cellular differentiation of skin keratinocytes, the effects of RA on the anchoring junction have not been clarified. The effects of all-trans RA on cell-cell and cell-matrix connections of gingival epithelial (GE)1 cells in a multilayered culture were investigated.

METHODS

Ultrastructures of GE1 cells were observed and immunohistochemistry was used to detect keratin 4, keratin 13, and desmoglein expression. Reverse transcription-polymerase chain reaction was performed to detect expression of desmosome and hemidesmosome-associating adhesion molecules, keratin 13, and keratin14.

RESULTS

Retinoic acid caused immunohistochemical diminution of keratin 4, keratin 13, and desmoglein. Ultrastructurally, RA induced drastic loss of typical desmosomes and complete loss of hemidesmosomes. RA significantly decreased the transcript levels of keratin 13, keratin 14, desmoglein 1, and desmocollin 1 in a dose-dependent manner. The 230-kD bullous pemphigoid antigen (BPAG1) gene expression was also reduced by RA, whereas transcript levels of integrin alpha6, integrin beta4, the 180-kD bullous pemphigoid antigen (BPAG2), and laminin 5 were not affected.

CONCLUSION

These results indicated that RA disintegrated not only desmosomes by depriving the cells of desmoglein 1, desmocollin 1, keratin 13, and keratin 4, but also hemidesmosomes by reducing the expression of BPAG1 and keratin 14 in basal keratinocytes.

Conformational Changes in the Rod Domain of Human Keratin 8 following Heterotypic Association with Keratin 18 and Its Implication for Filament Stability†

Keratin intermediate filaments are heteropolymers of type I and type II polypeptides that constitute the bulk of the epithelial cytoskeleton. We microinjected seven keratin monoclonal antibodies into human epithelial cells, and two of them, only A45-B/B3 and LP3K, caused the formation of keratin aggregates. The keratin filaments in human epithelial cells were also disrupted by a monovalent A45-B/B3 Fab fragment, suggesting that the binding of the antibody, rather than cross-linking, collapses the filaments. Immunoblotting and ELISA experiments suggested that the antibody reacted weakly with recombinant K8 but did not react with recombinant K18 at all. However, the antibody reactivity increased substantially when a mixture of the two keratin polypeptides, either recombinant or derived from MCF-7, was used. The epitopes of 15 monoclonal antibodies recognizing human K8 were characterized by their reactivity with recombinant fragments of K8. Reactivity of antibody A45-B/B3 with fragments of K8 in the presence of K18 revealed that the antibody recognizes an epitope in the rod domain of K8, between residues 313 and 332, on the amino-terminal side of the stutter in helix 2B, which is involved in heterotypic association. The data suggest that this region of K8 undergoes a conformational change following interaction with the complementary K18 either to expose the epitope or to increase its affinity for the antibody. Taken together, the data highlight the role of this epitope in heterotypic association and in filament stabilization.

The effect of the PDE-4 inhibitor (cipamfylline) in two human models of irritant contact dermatitis

BACKGROUND

New therapeutic approaches have to be considered in the treatment of irritant contact dermatitis (ICD). Recently, phosphodiesterase 4 (PDE-4) inhibitors have been introduced as nonsteroidal, antiinflammatory agents. These agents inhibit the secretion of the cytokines thought to be involved in the pathogenesis of ICD. We investigated the effect of a new selective PDE-4 inhibitor (cipamfylline) in human models using single and repeated exposures to an irritant in a blind, randomized pilot study with healthy volunteers. We compared the effect of cipamfylline ointment with a strong corticosteroid (betamethasone-17-valerate) and with a placebo ointment.

METHODS

Ten volunteers were patch tested at four investigation sites with sodium dodecyl sulphate (1%) for 24 h. In a model that simulates chronic damage, 11 volunteers were patch tested with sodium dodecyl sulphate (0.2%) for 4 h daily for four consecutive days. The investigation sites were treated once a day with the above-mentioned agents. One site was left untreated. We used erythema scoring, measurements of transepidermal water loss (TEWL) and several immunohistochemical markers for epidermal proliferation and differentiation.

RESULTS

Repeated application revealed that betamethasone-17-valerate caused a statistically significant reduction in erythema and TEWL compared to cipamfylline and placebo. We also observed a significant suppression of proliferating cells and cytokeratin 16 expression at sites treated with betamethasone compared to the other sites. In the model for acute ICD, no significant differences were seen between the investigated sites.

CONCLUSIONS

Our results show that betamethasone-17-valerate may modulate the response in ICD. In this human model of ICD we could not confirm the efficacy of cipamfylline. Clinical studies are needed before the effect of PDE-4 inhibitors in ICD can be refuted with certainty.

Cytostatic action of enamel matrix derivative (EMDOGAIN) on human oral squamous cell carcinoma-derived SCC25 epithelial cells

During surgical treatment of periodontal disease, enamel matrix derivative (EMD) is topically applied as a substitute for extracellular matrix in order to facilitate regeneration of damaged periodontal tissue. However, the mechanism for EMD action is poorly understood. We have now examined the effects of EMD on the proliferation of oral epithelial (SCC25) cells in vitro. After 3 days of treatments, EMD (25 100 microg/ml) dose-dependently inhibited cell division and concomitantly arrested cell cycle at the G1 phase. Prior to this inhibition, EMD significantly up-regulated p21WAF1/cip1, a cyclin-dependent kinase inhibitor, induced G1-arrest, and inhibited DNA synthesis. In addition, EMD down-regulated expression of cytokeratin-18 (CK18) protein, which was most due to decreased production, but less to increased degradation. However, EMD did not discernibly increase the number of apoptotic cells over 8 days of treatment. These findings indicate (1) that EMD acts as a cytostatic agent, rather than a cytotoxic agent, on epithelial cells, and (2) that this anti-proliferative action is probably due to p21WAF1/cip1-mediated G1-arrest. Furthermore, our in vitro cellular data clearly verify and provide an explanation for the clinical observation that EMD application suppresses the down-growth of junctional epithelium onto dental root surfaces, a process that frequently interferes with the formation of new connective tissue attachments.

The role of anti-epithelial cell antibodies in the pathogenesis of bilateral radiation pneumonitis caused by unilateral thoracic irradiation

Two cases of bilateral radiation pneumonitis associated with unilateral thoracic irradiation against lung cancer are described. Both patients died of respiratory failure and autopsy was performed. Histologically, bilateral diffuse alveolar damage was demonstrated in both cases, associated with marked organization of hyaline membrane in one case (case 1). In addition, numerous hyperplastic type II pneumocytes which strongly expressed cytokeratins 8, 18 and 19 were observed. In both patients' sera, antibodies against cytokeratin 8, 18 and 19 were demonstrated by a Western immunoblot. The possible association between autoantibodies to cytokeratins and diffuse alveolar damage observed in patients with bilateral radiation pneumonitis are discussed.

The effect of sodium lauryl sulphate on the expression of cytokeratin mRNA in hamster cheek pouch epithelium

The effect of sodium lauryl sulphate (SLS) on cytokeratin (CK) gene expression in hamster cheek pouch epithelium was studied with a hybridohistochemical technique. Using specific human anti-sense RNA probes, the plausible hamster mRNA counterparts for these human CK mRNAs were localized by detection of heterologous hybrids. In comparison with normal epithelium, the expression and distribution pattern of CK mRNAs in the hamster cheek pouch were obviously changed after application of SLS. There was a decreased expression of CK mRNAs in the hyperplastic basal layer, and increased expression in the hypertrophic granular layer. Strikingly, hybridization with the human CK 18 cRNA probe revealed an additionally expressed CK mRNA in the SLS-treated epithelium that was not found in the untreated epithelium. The present study indicates that cRNA probes for human CK mRNAs can be used successfully, not only to distinguish between different hamster CK mRNAs but also to investigate changes in CK gene expression upon the induction of non-neoplastic and neoplastic alterations in the hamster cheek pouch model. This may help elucidate the molecular changes involved in epithelial pathologies.

Retinoic acid alters the keratinization of cultured rat sublingual keratinocytes in vitro

A multilayered, continuously proliferating keratinocyte cell culture has been produced from rat sublingual epithelium. The rate of growth of the cultures was stable throughout long-term culture. Retinoic acid (3.3 microM) inhibited the keratinization of these cultures. Morphological changes included total loss of tonofilaments within 7 days, decrease in desmosomes, an increase in intercellular spaces, absence of thickened plasma membranes, and elongated and more numerous cytoplasmic projections. Exposure to retinoic acid (3.3 microM) for 33 days did not affect the growth rates of the cultures, as estimated from the protein and DNA content per flask. Retinoic acid (3.3 microM) reduced the polyacrylamide gel electrophoresis protein profile within 3 days of treatment and produced reductions in the incorporation of amino acids into keratins of molecular weights 62,000 and 60,000 within 24 h. All five keratin polypeptides showed a reduced incorporation rate after treatment for 3 days. This inhibition was reversible. Protein synthesis of nonkeratins was not detectably affected by retinoid treatment.

Topical and systemic effects of retinoids on horn-filled utriculus size in the rhino mouse. A model to quantify "antikeratinizing" effects of retinoids

A method was developed to quantify the "antikeratinizing" effects of various retinoids (all-trans-retinoic acid, 13-cis-retinoic acid, motretinide, etretinate) in rhino mouse skin, which contains many keratinized pilosebaceous structures or horn-filled utriculi. Mean utriculus diameters in whole mount epidermis were determined and dose-response relationships were constructed after topical or oral administration of test retinoids. All-trans-retinoic acid was 3.7x, 12.5x, and 50x more potent than 13-cis-retinoic acid, etretinate, and motretinide, respectively, after topical administration. Administered orally, all-trans-retinoic acid was 2.3x more potent than 13-cis-retinoic acid. At 5 mg/kg, each retinoid produced a significant reduction in utriculus size. The rhino mouse model represents a novel and useful assay to quantify antikeratinizing activity and potency differences of biologically active retinoids.

Effects of retinoic acid on embryonic chick skin

The influence of vitamin A on differentiating epithelia was examined in explants of skin from 14-day chick embryos exposed to retinoic acid (RA) in low, moderate, and high doses. The changes observed in RA-treated cultures are both dose- and time-dependent and are reversible when explants are transferred to control medium. The periderm sloughs prematurely and horizontal stratification is lost. Keratinization is inhibited and fewer desmosomes and tonofilaments are seen. Surface epidermal cells develop microvilli, bulge upwards, and detach. Golgi elements, rough endoplasmic reticulum, and polyribosomes are unusually prominent. Mucin granules form and gland-like structures develop with intercellular canaliculi characterized by tight junctions, brush borders, and dense secretory contents. On the basis of present evidence there are several possible mechanisms by which RA could alter epidermal differentiation. RA-induced gaps in the basal lamina allow direct contact between epidermal basal cells and fibroblasts and collagen fibers which could result in inappropriate dermal signals reaching the epidermis. In younger embryos the entire epidermis, including the mitotically inactive surface cells, appears to respond to RA, and this could imply an epigenetic modulation of cell phenotype. Finally, after the formation of a stratum corneum in older embryos only the relatively undifferentiated basal layer shows a metaplastic response, indicating that RA could be acting directly on the genome.