E. B. Lane

Plectin deficiency results in muscular dystrophy with epidermolysis bullosa.

We report that mutation in the gene for plectin, a cytoskeleton–membrane anchorage protein, is a cause of autosomal recessive muscular dystrophy associated with skin blistering (epidermolysis bullosa simplex). The evidence comes from absence of plectin by antibody staining in affected individuals from four families, supportive genetic analysis (localization of the human plectin gene to chromosome 8q24.13–qter and evidence for disease segregation with markers in this region) and finally the identification of a homozygous frameshift mutation detected in plectin cDNA. Absence of the large multifunctional cytoskeleton protein plectin can simultaneously account for structural failure in both muscle and skin.

Mutations in the plakophilin 1 gene result in ectodermal dysplasia/skin fragility syndrome

Members of the armadillo protein gene family, which includes plakoglobin and β-catenin, have important functions in cytoskeleton/cell membrane interactions1,2. These proteins may act as linker molecules at adherens junctions and desmosomes at the plasma membrane3; in addition, they may have pivotal roles in signal transduction pathways and significant effects on cell behaviour during development4–7. Here, we describe the first human mutations in one of these dual function proteins, plakophilin 1 (band-6 protein; refs 8–10). The affected individual has a complete absence of immunostaining for plakophilin 1 in the skin and is a compound heterozygote for autosomal-recessively inherited premature termination codons of translation on both alleles of the plakophilin 1 gene (PKP1). Clinically, there are features of both cutaneous fragility and congenital ectodermal dysplasia affecting skin, hair and nails. There is no evidence of significant abnormalities in other epithelia or tissues. Desmosomes in the skin are small and poorly formed with widening of keratinocyte intercellular spaces and perturbed desmosome/keratin intermediate filament interactions. The molecular findings and clinical observations in this patient attest to the dual importance of plakophilin 1 in both cutaneous cell–cell adhesion and epidermal morphogenesis.

Use of monoclonal antibodies for the histopathological diagnosis of human malignancy

This paper describes the use of a panel of seven monoclonal antibodies (selected so as to include reagents reactive with both epithelial and lymphoid cells) for distinguishing between anaplastic carcinoma and high grade lymphoma. Details are given of the immunohistological reactions of these antibodies against a wide range of both normal and malignant tissues and of a number of practical instances in which use of the antibody panel enabled a diagnosis to be made when routine histological examination had been inconclusive.

Keratins and skin disorders

The association of keratin mutations with genetic skin fragility disorders is now one of the best‐established examples of cytoskeleton disorders. It has served as a paradigm for many other diseases and has been highly informative for the study of intermediate filaments and their associated components, in helping to understand the functions of this large family of structural proteins. The keratin diseases have shown unequivocally that, at least in the case of the epidermal keratins, a major function of intermediate filaments is to provide physical resilience for epithelial cells. This review article reflects on the variety of phenotypes arising from mutations in keratins and the reasons for this variation. Copyright

Disruption of the keratin filament network during epithelial cell division.

The behaviour of keratin filaments during cell division was examined in a wide range of epithelial lines from several species. Almost half of them show keratin disruption as described previously: by immunofluorescence, filaments are replaced during mitosis by a ‘speckled’ pattern of discrete cytoplasmic dots. In the electron microscope these ‘speckles’ are seen as granules around the cell periphery, just below the actin cortical mesh, with no detectable 10 nm filament structure inside them and no keratin filament bundles in the rest of the cytoplasm. A time course of the filament reorganization was constructed from double immunofluorescence data; filaments are disrupted in prophase, and the filament network is intact again by cytokinesis. The phenomenon is restricted to cells rich in keratin filaments, such as keratinocytes; it is unrelated to the co‐existence of vimentin in many of these cells, and vimentin is generally maintained as filaments while the keratin is restructured. Some resistance to the effect may be conferred by an extended cycle time. Filament reorganization takes place within minutes, so that a reversible mechanism seems more likely than one involving de novo protein synthesis, at this metabolically quiet stage of the cell cycle.

Modulation of cell proliferation by cytokeratins K10 and K16

ABSTRACT The members of the large keratin family of cytoskeletal proteins are expressed in a carefully regulated tissue- and differentiation-specific manner. Although these proteins are thought to be involved in imparting mechanical integrity to epithelial cells, the functional significance of their complex differential expression is still unclear. Here we provide new data suggesting that the expression of particular keratins may influence cell proliferation. Specifically, we demonstrate that the ectopic expression of K10 inhibits the proliferation of human keratinocytes in culture, while K16 expression appears to promote the proliferation of these cells. Other keratins, such as K13 or K14, do not significantly alter this parameter. K10-induced inhibition is reversed by the coexpression of K16 but not that of K14. These results are coherent with the observed expression pattern of these proteins in the epidermis: basal, proliferative keratinocytes express K14; when they terminally differentiate, keratinocytes switch off K14 and start K10 expression, whereas in response to hyperproliferative stimuli, K16 replaces K10. The characteristics of this process indicate that K10 and K16 act on the retinoblastoma (Rb) pathway, as (i) K10-induced inhibition is hampered by cotransfection with viral oncoproteins which interfere with pRb but not with p53; (ii) K10-mediated cell growth arrest is rescued by the coexpression of specific cyclins, cyclin-dependent kinases (CDKs), or cyclin-CDK complexes; (iii) K10-induced inhibition does not take place in Rb-deficient cells but is restored in these cells by cotransfection with pRb or p107 but not p130; (iv) K16 efficiently rescues the cell growth arrest induced by pRb in HaCaT cells but not that induced by p107 or p130; and (v) pRb phosphorylation and cyclin D1 expression are reduced in K10-transfected cells and increased in K16-transfected cells. Finally, using K10 deletion mutants, we map this inhibitory function to the nonhelical terminal domains of K10, hypervariable regions in which keratin-specific functions are thought to reside, and demonstrate that the presence of one of these domains is sufficient to promote cell growth arrest.

An immunocytochemical study of fetal cells at the maternal-placental interface using monoclonal antibodies to keratins, vimentin and desmin

SummaryThe expression of keratin, vimentin and desmin intermediate filaments by cells in the placenta, amniochorion and placental bed at different stages of pregnancy was studied by use of a panel of monoclonal antibodies. All trophoblast subsets express keratin but not vimentin or desmin intermediate filaments at all stages of pregnancy. Differentiation of the various forms of trophoblast probably does not involve qualitative alterations to the keratin pattern of embryonic trophoblast. Amniotic epithelium co-expressed keratin and variable amounts of vimentin while a subset of fetal mesenchyme cells of the amniochorion and chorionic villi were immunolabelled by antibodies to keratin, to vimentin and to desmin, suggesting simultaneous triple co-expression of three intermediate filaments. This finding suggests the identification of a cell population that is analogous to parietal endoderm in some eutherian animals.

Monospecific monoclonal antibodies to keratin 1 carboxy terminal (synthetic peptide) and to keratin 10 as markers of epidermal differentiation

Summary Monospecific antibodies to individual keratin polypeptides can be used to examine the tissue and cellular coexpression of members of keratin pairs. Monospecific monoclonal and polyclonal antibodies have been raised to keratins 1 and 10 using both crude cytoskeletal extracts and synthetic peptides. The tissue distribution of these keratins has been determined against a panel of freshly frozen normal tissues from humans, rodents and pigs, Epidermal expression has been examined in psoriatic plaques, and healing wounds, as examples of epidermal hyperproliferation. Cultured keratinocytes in monolayer(low calcium), stratified (high calcium), and complex cultures, transformed keratinocytes, and tumour cell lines, have been examined for the in vitro expression of these keratins. The sensitivity and precise localization of reactivity with these monospecific antibodies gives a highly accurate picture of individual cell expression. There is confirmation of coexpression of keratins 1 and 10 in epidermal and mucosal sites, and with keratin 16 in hyperproliferative states. These monospecific antibodies provide an important means of examining keratin expression in epidermal tumours and keratinizing disorders, and of seeking keratin mutations in cell lines and in skin diseases.

Expression of individual lamins in basal cell carcinomas of the skin

In this study we used a unique collection of type specific anti-lamin antibodies to study lamin expression patterns in normal human skin and in skin derived from patients with basal cell carcinomas (BCCs). Lamin expression in serial sections from frozen tissue samples was investigated by single and double indirect immunofluorescence. In normal skin, lamin A was expressed in dermal fibroblasts and in suprabasal epithelial cells but was absent from all basal epithelial cells. Lamin C was expressed in dermal fibroblasts, suprabasal epithelial cells and a majority of basal epithelial cells. However, lamin C was not expressed in quiescent basal epithelial cells. Lamin B1was expressed in all epithelial cells but was not expressed in dermal fibroblasts. Finally, lamin B2was expressed in all epithelial cells but was not expressed in dermal fibroblasts. Finally, lamin B2was expressed in all cell types in normal skin. Lamin expression was also investigated in a collection of 16 BCCs taken from a variety of body sites. Based upon patterns of lamin expression the BCCs were classified into four groups: A-negative (10/16 tumours), C-negative (5/16 tumours), A/C-negative (1/16 tumours) and A/B2-negative (1/16 tumours). Lamin expression was also compared to cell proliferation index by staining serial sections with the proliferation marker Ki67. 9/10 of the lamin A negative tumours were highly proliferative, whereas 4/5 of the lamin C negative tumours were slow growing. Thus as a general rule absence of lamin A was correlated with rapid growth within the tumour, while absence of lamin C was correlated with slow growth within the tumour. Our data supports the hypothesis that lamin A has a negative influence on cell proliferation and its down regulation may be a requisite of tumour progression.

Psoriasis: maintenance of an intact monolayer basal cell differentiation compartment in spite of hyperproliferation

Frozen sections of punch biopsies from normal epidermis and psoriatic involved and uninvolved epidermis have been examined immunocytochemically using a panel of anti‐keratin monoclonal antibodies with various specificities in the skin. Since psoriasis is thought to involve hyperproliferative expansion of the basal compartment from one to about three cell layers in thickness, the samples were screened with antibodies to intermediate filament determinants associated with basal cells, suprabasal cells and hyperproliferating keratinocyte‐derived cell lines, respectively. The basal—suprabasal division was observed to be intact, with only one layer of basal cells demarcated by the specific antibodies used under all circumstances. this suggests that (a) psoriatic ‘basal cell hyperproliferation’ may not specifically involve the basal cell compartment containing the stem cells, but rather a population of amplifying transit cells which are predominantly suprabasal, and that (b) while keratinocyte differentiation begins as the cells lose contact with the basal lamina, the first stages at least of differentiation are not dependent on the loss of the capacity to divide.