Spontaneous losses of control of cytokeratin gene expression in transformed, non-epithelial human cells occurring at different levels of regulation

The single-cell atlas of cultured human endometrial stromal cells

OBJECTIVE

To systematically analyze the cell composition and transcriptome of primary human endometrial stromal cells (HESCs) and transformed human endometrial stromal cells (THESCs).

DESIGN

The primary HESCs from 3 different donors and 1 immortalized THESC were collected from the human endometrium at the midsecretory phase and cultured in vitro.

SETTING

Academic research laboratory.

PATIENT(S)

None.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Single-cell ribonucleic acid sequencing analysis.

RESULT(S)

We found the individual differences among the primary HESCs and bigger changes between the primary HESCs and THESCs. Cell clustering with or without integration identified cell clusters belonging to mature, proliferative, and active fibroblasts that were conserved across all samples at different stages of the cell cycles with intensive cell communication signals. All primary HESCs and THESCs can be correlated with some subpopulations of fibroblasts in the human endometrium.

CONCLUSION(S)

Our study indicated that the primary HESCs and THESCs displayed conserved cell characters and distinct cell clusters. Mature, proliferative, and active fibroblasts at different stages or cell cycles were detected across all samples and presented with a complex cell communication network. The cultured HESCs and THESCs retained the features of some subpopulations within the human endometrium.

Histogenesis of Merkel Cell Carcinoma: A Comprehensive Review

Merkel cell carcinoma (MCC) is a primary neuroendocrine carcinoma of the skin. This neoplasia features aggressive behavior, resulting in a 5-year overall survival rate of 40%. In 2008, Feng et al. identified Merkel cell polyomavirus (MCPyV) integration into the host genome as the main event leading to MCC oncogenesis. However, despite identification of this crucial viral oncogenic trigger, the nature of the cell in which MCC oncogenesis occurs is actually unknown. In fact, several hypotheses have been proposed. Despite the large similarity in phenotype features between MCC tumor cells and physiological Merkel cells (MCs), a specialized subpopulation of the epidermis acting as mechanoreceptor of the skin, several points argue against the hypothesis that MCC derives directly from MCs. Alternatively, MCPyV integration could occur in another cell type and induce acquisition of an MC-like phenotype. Accordingly, an epithelial as well as a fibroblastic or B-cell origin of MCC has been proposed mainly based on phenotype similarities shared by MCC and these potential ancestries. The aim of this present review is to provide a comprehensive review of the current knowledge of the histogenesis of MCC.

Reviewing the current evidence supporting early B-cells as the cellular origin of Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a highly malignant skin cancer characterized by early metastases and poor survival. Although MCC is a rare malignancy, its incidence is rapidly increasing in the U.S. and Europe. The discovery of the Merkel cell polyomavirus (MCPyV) has enormously impacted our understanding of its etiopathogenesis and biology. MCCs are characterized by trilinear differentiation, comprising the expression of neuroendocrine, epithelial and B-lymphoid lineage markers. To date, it is generally accepted that the initial assumption of MCC originating from Merkel cells (MCs) is unlikely. This is owed to their post-mitotic character, absence of MCPyV in MCs and discrepant protein expression pattern in comparison to MCC. Evidence from mouse models suggests that epidermal/dermal stem cells might be of cellular origin in MCC. The recently formulated hypothesis of MCC originating from early B-cells is based on morphology, the consistent expression of early B-cell lineage markers and the finding of clonal immunoglobulin chain rearrangement in MCC cells. In this review we elaborate on the cellular ancestry of MCC, the identification of which could pave the way for novel and more effective therapeutic regimens.

Circulating tumor cells expressing cancer stem cell marker CD44 as a diagnostic biomarker in patients with gastric cancer

Epithelial cell adhesion molecule (EpCAM) is a marker for circulating tumor cells (CTCs) in various types of cancer, while cluster of differentiation 44 (CD44) is a marker for gastric cancer (GC) stem cells. To evaluate the clinical significance of CD44⁺ CTCs in patients with GC in the present study, the number of EpCAM⁺CD44⁺ and EpCAM⁺CD44^- cells were detected in the peripheral blood of 26 GC patients and 12 healthy volunteers using flow cytometry. The number (mean ± standard deviation) of EpCAM⁺CD44⁺ cells in the GC patients and healthy volunteers was 69.9±52.0 and 0.91±2.10, respectively (P=0.0001), while that of EpCAM⁺CD44^- cells was 59.1±88.0 and 9.83±9.91, respectively (P=0.0313). The sensitivity and specificity of EpCAM⁺CD44⁺ cell detection for the identification of GC patients were 92.3 and 100%, respectively. By contrast, the values of EpCAM⁺CD44^- cell detection were 76.9 and 83.3%, respectively. The number of EpCAM⁺CD44⁺ cells in the GC patients was correlated with the disease stage (P=0.0423), the depth of the tumor (P=0.0314) and venous invasion (P=0.0184) in the resected tumor specimens, while the number of EpCAM⁺CD44^- cells did not correlate with any clinicopathological factors. The number of EpCAM⁺CD44⁺ cells significantly decreased following surgical resection of the tumor or induction of systemic chemotherapy. Additionally, atypical cells with a high nuclear to cytoplasmic ratio were morphologically detected in the sorted EpCAM⁺CD44⁺ cells. These results suggested that CD44⁺ CTCs, but not CD44^- CTCs, reflect the malignant status of the primary tumor in patients with GC, providing a candidate biomarker for diagnosis and treatment response.

Downregulation of cytokeratin 18 is associated with paclitaxel‑resistance and tumor aggressiveness in prostate cancer

Paclitaxel frequently serves as the first-line chemotherapeutic agent for castration-resistant prostate cancer (PCa) patients. However, acquired paclitaxel-resistance almost always occurs after initial responses, and the mechanisms by which this occurs remain largely unknown. The goal of the present study was to identify differentially expressed protein(s) associated with paclitaxel-resistance and further explore the potential mechanisms involved in drug resistance. By comparing the nuclear matrix protein (NMP) patterns of DU145-TxR cells, the previously established stable paclitaxel-resistant PCa cells, with that of the parental DU145 cells using two-dimensional electrophoresis, we found that cytokeratin 18 (CK18) is downregulated in DU145-TxR cells. The downregulation of CK18 in DU145-TxR cells at mRNA, NMP and total cellular protein levels was validated by real-time RT-PCR, immunoblotting and immunofluorescence, indicating that the downregulation of CK18 was a global effect in DU145-TxR cells due to paclitaxel-resistance. Furthermore, in vivo assay of xenograft transplantation confirmed the higher tumorigenicity of DU145-TxR cells, suggesting that these paclitaxel-resistant PCa cells possessed potent cancer stem cell (CSC)-like properties and eventually developed paclitaxel-resistance. Moreover, we determined by immunohistochemistry that CK18 expression in PCa tissues was inversely correlated with tumor grade in a statistically significant fashion, indicating a potential association of the downregulation of CK18 with tumor aggressiveness. Therefore, further study to define the potential role of CK18 may lead to novel therapy strategies as well as clinically useful biomarker for PCa patients.

Merkel cell carcinoma: is this a true carcinoma?

Recent years have brought an enhanced understanding of Merkel cell carcinoma (MCC) biology, especially with regard to the Merkel cell polyoma virus as a causative agent. Differences between Merkel cell polyomavirus-positive and Merkel cell polyomavirus-negative MCC in morphology; gene expression, miRNA profiles and prognosis have been reported. Origin of MCC is controversial. Presence of neurosecretory granules has suggested that these carcinomas originate from one of the neurocrest derivatives, most probably Merkel cells; the name Merkel cell carcinoma is now widely accepted. Expression of PGP 9.5, chromogranin A and several neuropeptides, initially regarded as specific markers for neural and neuroendocrine cells, has recently been shown in a subset of lymphomas. MCC commonly expresses terminal deoxynucleotidyl transferase and PAX5. Their co-expression under physiologic circumstances is restricted to pro/pre-B cells and pre-B cells. These findings lead to the hypothesis by zur Hausen et al. that MCC originates from early B cells. This review was intended to critically appraise zur Hausen's hypothesis and discuss the possibility that MCC is a heterogenous entity with distinct subtypes.

Pleomorphic spindle cell dermal neoplasm with dot-like keratin reactivity: keratin-positive AFX or carcinoma?

Atypical fibroxanthoma (AFX) is an uncommon cutaneous neoplasm of pleomorphic myofibroblast-like cells. Diagnosis requires exclusion of other undifferentiated spindle and pleomorphic cell neoplasms by immunohistochemistry. We report two patients with p63-non-reactive spindle cell neoplasms which resembled AFX but demonstrated anomalous dot-like immunolabeling with antibodies to high molecular weight keratin and keratin 5. One case recurred locally, suggesting such lesions may behave aggressively. Whether these lesions represent keratin-positive dermal sarcomas or poorly differentiated carcinomas is debatable. Regardless of exact classification, our experience suggests such cases should be managed as high-risk non-melanoma skin cancers.

Keratin Expression Patterns in Stromal Cells of Benign Sclerosing Lesions of the Breast: A Potential Diagnostic Pitfall

Context

Metaplastic carcinomas arising in association with benign sclerosing lesions (BSLs) are rare malignancies in which a neoplastic spindle cell proliferation can be recognized extending beyond the boundaries of the complex sclerosing lesion or papilloma. However, in cases in which the metaplastic carcinoma is of the low-grade fibromatosis-like type or is a low-grade adenosquamous carcinoma, distinction from the background BSL can be a significant challenge. Cytokeratin (CK) and/or p63 immunostains are helpful in confirming the diagnosis of metaplastic carcinoma, but the expression patterns of these markers in the stromal cells of BSLs have not been well characterized.

Objective

To characterize the expression patterns of CKs and p63 in BSLs.

Design

We evaluated the spindle cell component of 55 BSLs using CK 5/6, CK 903, CK MNF116, and p63.

Results

A total of 45 cases (81%) showed no staining for CKs or p63 in benign stromal cells. CK 5/6, CK 903, and p63 were positive in one case each. CK MNF116 stained spindle cells within 10 BSLs. No cases showed spindle cell reactivity for all 4 markers. Positive cases demonstrated very focal, weak staining of spindle cells; only 1 case showed focal, moderate CK staining. Spindle cell positivity was not associated with lesion type, growth pattern, spindle cell atypia, or mitoses.

Conclusions

These findings suggest that although the presence or absence of expression of CK 5/6, CK 903, and p63 may be useful to distinguish BSL from metaplastic carcinomas arising in this setting, CK MNF116 positivity may be a diagnostic pitfall.

Cells of origin in skin cancer

Adult skin stem cells do not protect their genome by asymmetric chromosome segregation; thus, they are prone to accumulating oncogenic mutations.

The assessment of the in vivo to in vitro cellular transition of human umbilical cord multipotent stromal cells

INTRODUCTION

Human umbilical cord stroma is a rich source of primitive multipotent stromal cells (hUC-MSCs). However, the methods for hUC-MSC isolation and propagation remain controversial and vary among laboratories. Our group previously demonstrated that two cell types emerge upon enzymatic isolation of hUC-MSCs, which subsequently undergo a transition towards a fibroblastoid phenotype in later passages. The aim of this study was to further analyse cultured hUC-MSCs by evaluating the cytoskeletal and cell adhesion proteins and by comparing the remodelling of those proteins in umbilical cord sections to determine the cell alterations due to enzymatic and explant methods.

METHODS

Tissue sections and cultured cells isolated by enzymatic or explant methods were analysed morphologically and by labelling cytokeratin, vimentin, alpha-smooth muscle actin, E-cadherin and N-cadherin profiles.

RESULTS

The present observations confirmed that wide, flat cells (type-1) share myofibroblastic features, appear exclusively in enzymatically isolated early cultures; gradually diminish or are replaced by fibroblastoid cells (type-2) in later passages. In contrast, the explant method does not result in the existence of type-1 cells in vitro. Among the tested CK subtypes, CK18 expression is upregulated, whereas CK19 expression is downregulated upon culturing after both protocols. Vimentin and α-SMA, as the major intermediate filaments of hUC-MSCs were found unaltered throughout the culturing period regardless of the cell isolation technique used.

DISCUSSION

The data presented confirm and further elucidate the previously observed phenotypic change in hUC-MSCs as illustrated by alterations in structural proteins during enzymatic isolation and subsequent culturing of cells compared with in situ equivalents.

Merkel cell carcinoma - recent advances in the biology, diagnostics and treatment

Merkel cell carcinoma (MCC) is an uncommon primary cutaneous carcinoma with neuroendocrine differentiation. Since recent discovery of MCCs strong association with Merkel cell polyomavirus (MCPyV), there has been a rapid increase in the understanding of the carcinomas genetics, molecular biology and pathogenesis. In our study, we reviewed recent advances and controversies concerning MCC histogenesis, epidemiology, diagnostic and prognostic markers. We analyzed the association of MCPyV with MCC and the possible new targets for therapy. We also examined English-based literature regarding MCC pathogenesis published between 2008 and 2013, which lead to a deeper understanding of the topic. Our study showed that the association of MCPyV strongly influences the course of MCC. Additionally, it has been shown that a immunological response to MCPyV may in the future give hope to identify new therapeutic strategies in treatment of this fatal malignancy. This article is part of a Directed Issue entitled: Rare Cancers.

Immunohistochemistry of soft tissue tumours - review with emphasis on 10 markers

Immunohistochemistry is an integral component in the proper analysis of soft tissue tumours, and a simple panel of six markers is useful in practical triage: CD34, desmin, epithelial membrane antigen (EMA), keratin cocktail AE1/AE3, S100 protein and alpha smooth muscle actin (SMA). These markers frequently assist in the differential diagnosis of fibroblastic, myoid, nerve sheath and perineurial cell tumours, synovial and epithelioid sarcoma and others. However, they all are multispecific, so that one has to be cognizant of their distribution in normal and neoplastic tissues. Four additional useful markers for specific tumour types are discussed here: CD31 and ERG for vascular endothelial tumours, and KIT and DOG1/Ano-1 for gastrointestinal stromal tumours (GISTs). However, hardly any marker is totally monospecific for any one type of tumour. Furthermore, variably lineage-specific markers do not usually distinguish between benign and malignant proliferations, so that this distinction has to be made on histological grounds. Immunohistochemical evaluation is most useful, efficient and cost-effective when used in the context of careful histological evaluation by an experienced pathologist, aware of all diagnostic entities and their histological spectra. Additional diagnostic steps that must be considered in difficult cases include clinicoradiological correlation and additional sampling of remaining wet tissue, if possible.

Early B-cell differentiation in Merkel cell carcinomas: clues to cellular ancestry

Merkel cell carcinoma (MCC) is a highly malignant neuroendocrine nonmelanoma skin cancer, which is associated with the Merkel cell polyoma virus (MCPyV). Recently, expression of the terminal deoxynucleotidyl transferase (TdT) and the paired box gene 5 (PAX 5) has been consistently reported in the majority of MCCs. We tested 21 MCCs for the expression of MCPyV, TdT, PAX5, IgG, IgM, IgA, kappa, and lambda by immunohistochemistry and assessed IgH and Igk rearrangement in all 21 MCCs. All of the MCCs revealed specific expression of PAX5 and 72.8% of the MCCs expressed TdT. In addition, most of the MCCs revealed specific expression of one or more Ig subclasses and kappa or lambda. One MCC did reveal monoclonal IgH and Igk rearrangement next to two other MCCs showing Igk rearrangement. As coexpression of TdT and PAX5 under physiologic circumstances is restricted to pro/pre- and pre-B cells we propose, on the basis of our results, that the cell of origin of MCCs is a pro/pre- or pre-B cell rather than the postmitotic Merkel cells. MCPyV infection and transformation of pro-/pre-B cells are likely to induce the expression of simple cytokeratins as has been shown for SV40 in other nonepithelial cells. This model of cellular ancestry of MCCs might impact therapy and possibly helps to understand why approximately 20% of MCCs are MCPyV-negative.

Immunoreactivity for calretinin and keratins in desmoid fibromatosis and other myofibroblastic tumors: a diagnostic pitfall

Calretinin is an intracellular calcium-binding EF-hand protein of the calmodulin superfamily. It plays a role in diverse cellular functions, including message targeting and intracellular calcium signaling. It is expressed in the mesothelium, mast cells, some neural cells, and fat cells, among others. Because of its relative specificity for mesothelial neoplasms, calretinin is widely used as one of the primary immunohistochemical markers for malignant mesothelioma and in differentiating it from adenocarcinoma. On the basis of our sporadic observation on calretinin immunoreactivity in desmoid fibromatosis, we systematically evaluated calretinin, keratin cocktail (AE1/AE3), and WT1 immunoreactivity in 268 fibroblastic/myofibroblastic neoplasms. Calretinin was observed in 75% (44/58) of desmoid fibromatosis, 50% (21/42) of proliferative fasciitis, 23% (8/35) of nodular fasciitis, 33% (13/40) of benign fibrous histiocytoma, 35% (22/62) of malignant fibrous histiocytoma, and 13% (4/31) of solitary fibrous tumors but not in normal connective tissue fibroblasts at various sites. Keratin AE1/AE3 immunoreactivity was also commonly (6/13) present in the large ganglion-like cells of proliferative fasciitis and sometimes in nodular fasciitis (3/35), solitary fibrous tumor (3/27), and malignant fibrous histiocytoma (9/62). Nuclear immunoreactivity for WT1 or keratin 5 positivity was not detected in myofibroblastic tumors. On the basis of these observations, it can be concluded that calretinin and focal keratin immunoreactivity is fairly common in benign and malignant fibroblastic and myofibroblastic lesions. Calretinin-positive and keratin-positive spindle cells in desmoid and nodular fasciitis or calretinin-positive ganglion-like cells in proliferative fasciitis should not be confused with elements of epithelioid or sarcomatoid mesothelioma. These diagnostic pitfalls can be avoided with careful observation of morphology, quantitative differences in keratin expression, and use of additional immunohistochemical markers such keratin 5 and WT1 to verify true epithelial and mesothelial differentiation typical of mesothelioma.

Unique amino acid signatures that are evolutionarily conserved distinguish simple-type, epidermal and hair keratins

Keratins (Ks) consist of central α-helical rod domains that are flanked by non-α-helical head and tail domains. The cellular abundance of keratins, coupled with their selective cell expression patterns, suggests that they diversified to fulfill tissue-specific functions although the primary structure differences between them have not been comprehensively compared. We analyzed keratin sequences from many species: K1, K2, K5, K9, K10, K14 were studied as representatives of epidermal keratins, and compared with K7, K8, K18, K19, K20 and K31, K35, K81, K85, K86, which represent simple-type (single-layered or glandular) epithelial and hair keratins, respectively. We show that keratin domains have striking differences in their amino acids. There are many cysteines in hair keratins but only a small number in epidermal keratins and rare or none in simple-type keratins. The heads and/or tails of epidermal keratins are glycine and phenylalanine rich but alanine poor, whereas parallel domains of hair keratins are abundant in prolines, and those of simple-type epithelial keratins are enriched in acidic and/or basic residues. The observed differences between simple-type, epidermal and hair keratins are highly conserved throughout evolution. Cysteines and histidines, which are infrequent keratin amino acids, are involved in de novo mutations that are markedly overrepresented in keratins. Hence, keratins have evolutionarily conserved and domain-selectively enriched amino acids including glycine and phenylalanine (epidermal), cysteine and proline (hair), and basic and acidic (simple-type epithelial), which reflect unique functions related to structural flexibility, rigidity and solubility, respectively. Our findings also support the importance of human keratin 'mutation hotspot' residues and their wild-type counterparts.

Five different phenotypes of endothelial cell cultures from the bovine corpus luteum: present outcome and role of potential dendritic cells in luteolysis

Progress in understanding the background of structural luteolysis depends on insights into the physiological function of innate immunity (INIM), in particular the presence of dendritic cells (DCs) in the corpus luteum (CL). For this reason, the cultures of five endothelial cell-like phenotypes derived from the bovine CL and their long-lasting analysis (morphology, function, and origin) become important. Types 1 and 2 represent microvascular endothelial cells with cytokeratin (CK) expression, assumed to be danger-sensing cells. Types 3 and 4 express features of common endothelial cells. Type 5 indicates a steroidogenic cell type, which could be derived from steroidogenic CK(+) cells in the CL of development after loss of CK expression. Type 5 is a promising candidate to become a mature DC. It might act with the microvascular CK(+) cell/type 1 like a luteovascular unit, which connects INIM with adaptive/cell-mediated immunity (ADIM) in structural luteolysis.

Upregulation of plakophilin-2 and its acquisition to adherens junctions identifies a novel molecular ensemble of cell-cell-attachment characteristic for transformed mesenchymal cells

In contrast to the desmosome-containing epithelial and carcinoma cells, normal and malignantly transformed cells derived from mesenchymal tissues and tumors are connected only by adherens junctions (AJs) containing N-cadherins and/or cadherin-11, anchored in a cytoplasmic plaque assembled by alpha- and beta-catenin, plakoglobin, proteins p120 and p0071. Here, we report that the AJs of many malignantly transformed cell lines are characterized by the additional presence of plakophilin-2 (Pkp2), a protein hitherto known only as a major component of desmosomal plaques, i.e., AJs of epithelia and carcinomatous cells. This massive acquisition of Pkp2 and its integration into AJ plaques of a large number of transformed cell lines is demonstrated with biochemical and immunolocalization techniques. Upregulation of Pkp2 and its integration into AJs has also been noted in some soft tissue tumors insitu and some highly proliferative colonies of cultured mesenchymal stem cells. As Pkp2 has recently been identified as a functionally important major regulatory organizer in AJs and related junctions in epithelial cells and cardiomyocytes, we hypothesize that the integration of Pkp2 into AJs of "soft tissue tumor" cells also can serve functions in the upregulation of proliferation, the promotion of malignant growth in general as well as the close-packing of diverse kinds of cells and the metastatic behavior of such tumors. We propose to examine its presence in transformed mesenchymal cells and related tumors and to use it as an additional diagnostic criterion.

Cordial connections: molecular ensembles and structures of adhering junctions connecting interstitial cells of cardiac valves in situ and in cell culture

Remarkable efforts have recently been made in the tissue engineering of heart valves to improve the results of valve transplantations and replacements, including the design of artificial valves. However, knowledge of the cell and molecular biology of valves and, specifically, of valvular interstitial cells (VICs) remains limited. Therefore, our aim has been to determine and localize the molecules forming the adhering junctions (AJs) that connect VICs in situ and in cell culture. Using biochemical and immunolocalization methods at the light- and electron-microscopic levels, we have identified, in man, cow, sheep and rat, the components of VIC-connecting AJs in situ and in cell culture. These AJs contain, in addition to the transmembrane glycoproteins N-cadherin and cadherin-11, the typical plaque proteins alpha- and beta-catenin as well as plakoglobin and p120, together with minor amounts of protein p0071, i.e. a total of five plaque proteins of the armadillo family. While we can exclude the occurrence of desmogleins, desmocollins and desmoplakin, we have noted with surprise that AJs of VICs in cell cultures, but not those growing in the valve tissue, contain substantial amounts of the desmosomal plaque protein, plakophilin-2. Clusters of AJs occur not only on the main VIC cell bodies but are also found widely dispersed on their long filopodia thus forming, in the tissue, a meshwork that, together with filopodial attachments to paracrystalline collagen fiber bundles, establishes a three-dimensional suprastructure, the role of which is discussed with respect to valve formation, regeneration and function.

Heterogeneity of mesenchymal stromal cell preparations

As an archetype of human adult stem cells that can readily be harvested, enriched and expanded in vitro, mesenchymal stromal cells (MSC) have been reported to be of significance for regenerative medicine. The literature is replete with reports on their developmental potentials in pre-clinical model systems. Different preparative protocols have been shown to yield MSC-like cell cultures or even cell lines, from starting materials as diverse as bone marrow, fat tissue, fetal cord blood and peripheral blood. However, MSC are still ill-defined by physical, phenotypic and functional properties. The quality of preparations from different laboratories varies tremendously and the cell products are notoriously heterogeneous. The source and freshness of the starting material, culture media used, presence of animal sera, cytokines, cell density, number of passages upon culture, etc., all have a significant impact on the (1) cell type components and heterogeneity of the initial population, (2) differential expansion of specific subsets, with different potentials of the end products, and (3) long-term functional fate of MSC as well as other types of progenitor cells that are co-cultivated with them. Consequently, there is an urgent need for the development of reliable reagents, common guidelines and standards for MSC preparations and of precise molecular and cellular markers to define subpopulations with diverse pathways of differentiation and divergent potentials.

The human keratins: biology and pathology

The keratins are the typical intermediate filament proteins of epithelia, showing an outstanding degree of molecular diversity. Heteropolymeric filaments are formed by pairing of type I and type II molecules. In humans 54 functional keratin genes exist. They are expressed in highly specific patterns related to the epithelial type and stage of cellular differentiation. About half of all keratins—including numerous keratins characterized only recently—are restricted to the various compartments of hair follicles. As part of the epithelial cytoskeleton, keratins are important for the mechanical stability and integrity of epithelial cells and tissues. Moreover, some keratins also have regulatory functions and are involved in intracellular signaling pathways, e.g. protection from stress, wound healing, and apoptosis. Applying the new consensus nomenclature, this article summarizes, for all human keratins, their cell type and tissue distribution and their functional significance in relation to transgenic mouse models and human hereditary keratin diseases. Furthermore, since keratins also exhibit characteristic expression patterns in human tumors, several of them (notably K5, K7, K8/K18, K19, and K20) have great importance in immunohistochemical tumor diagnosis of carcinomas, in particular of unclear metastases and in precise classification and subtyping. Future research might open further fields of clinical application for this remarkable protein family.

Cytokeratin expression in hematological neoplasms: a tissue microarray study on 866 lymphoma and leukemia cases

Aberrant expression of cytokeratins (CK) is known to occasionally occur in malignant lymphomas. The monoclonal mouse-anti-human CK cocktail CK22 recognizes keratin polypeptides with a wide range of molecular weights and can be applied in diagnostic panels for tumors of unknown origin. Using tissue microarray technology, we tested 1059 lymphoma and acute leukemia cases, covering the most common disease entities, for aberrant CK expression, using CK22. In total, 866 of the arrayed cases were evaluable (80%), and 13 positive cases (1.5%) were found: 1 out of 230 Hodgkin lymphomas (0.4%), 1 plasma cell myeloma, 2 out of 326 diffuse large B-cell lymphomas (0.6%), 5 out of 18 mantle cell lymphomas (26%), 3 out of 70 small cell lymphomas/chronic lymphocytic leukemias (4%) and 1 out of 27 peripheral T-cell lymphomas, not otherwise specified (4%). Immunostaining was finely granular in most cases, and the total amount of positively staining cells exceeded 10% only in the cases of Hodgkin lymphoma and plasmocytoma. All CK22-positive cases, except for one mantle cell lymphoma, expressed the specific simple epithelial CK8 but not the basal/stratified epithelial CK5/6. Aberrant CK expression can be encountered in a small subset of otherwise characteristic B- and T-cell lymphomas, but not in acute leukemias, which should be considered in difficult differential diagnostic settings.

Squamous differentiation and cytokeratin expression in an osteosarcoma: a case report and review of the literature

Cytokeratin expression has been documented in a variety of sarcomas including synovial sarcomas, epithelioid sarcomas, Ewing's sarcomas and, rarely, osteosarcomas. In osteosarcomas immunohistochemically shown to expression cytokeratins, a component of epithelioid cells is generally present. These epithelioid cytokeratin positive cells raise the possibility of metastatic disease with prognostic and therapeutic implications differing from primary osteosarcoma. The cytokeratin-expressing cells of the cases reported in the literature have not shown definitive squamous differentiation with keratin pearl formation. We report a case of osteosarcoma in which islands of malignant squamous cells were present showing keratin pearl formation and expression of cytokeratins.

Processus and recessus adhaerentes: giant adherens cell junction systems connect and attract human mesenchymal stem cells

Substrate-adherent cultured cells derived from human bone marrow or umbilical cord blood ("mesenchymal stem cells") are of special interest for regenerative medicine. We report that such cells, which can display considerable heterogeneity with respect to their cytoskeletal protein complement, are often interconnected by special tentacle-like cell processes contacting one or several other cells. These processus adhaerentes, studded with many (usually small) puncta adhaerentia and varying greatly in length (up to more than 400 microm long), either contact each other in the intercellular space ("ET touches") or insert in a tight-fitting manner into deep plasma membrane invaginations (recessus adhaerentes), thus forming a novel kind of long (up to 50 microm) continuous cuff-like junction (manubria adhaerentia). The cell processes contain an actin microfilament core that is stabilized with ezrin, alpha-actinin, and myosin and accompanied by microtubules, and their adhering junctions are characterized by a molecular complement comprising the transmembrane glycoproteins N-cadherin and cadherin-11, in combination with the cytoplasmic plaque proteins alpha- and beta-catenin, together with p120(ctn), plakoglobin, and afadin. The processes are also highly dynamic and rapidly foreshorten as cell colonies approach a denser state of cell packing. These structures are obviously able to establish cell-cell connections, even over long distances, and can form deep-rooted and tight cell-cell adhesions. The possible relationship to similar cell processes in the embryonic primary mesenchyme and their potential in cell sorting and tissue formation processes in the body are discussed.

Keratin expression in schwannoma; a study of 115 retroperitoneal and 22 peripheral schwannomas

Schwannomas have been variably observed to be glial fibrillary acid protein (GFAP) and occasionally keratin positive, with antibodies reacting with multiple keratins (pankeratins, keratin cocktail (CK), but specific keratin polypeptides (K) have not been examined for in schwannoma. Since we observed CK positivity in retroperitoneal schwannomas, we wanted to study a large group of retroperitoneal and peripheral schwannomas with GFAP, CK and Ks to explore the frequency and biologic background of this finding. We immunohistochemically evaluated a large number of retroperitoneal (n=115) and peripheral schwannomas (n=22) for GFAP, 16 individual K and AE1/AE3 keratin cocktail. The great majority (104/115, 90%) of retroperitoneal schwannomas were positive for GFAP, and 72/104 (69%) cases were positive for AE1/AE3, often extensively. Both markers highlighted the cellular Antoni A areas, particularly adjacent to the capsule, myxoid or degenerative areas, and perivascularly. Most cases 87/104 (84%) stained for both AE1/AE3 and GFAP at least focally. No tumors stained for keratins that were GFAP negative. None of the immunostains for individual K showed positivity comparable to that obtained with AE1/AE3 CK. However, 62% were focally positive for high molecular weight K1 and 8/61 (13%) for K7. None of the retroperitoneal schwannomas were positive for other keratins including K2, 4, 5, 8, 9, 10 and K14-20. Peripheral schwannomas showed GFAP-positivity in only three of 22 cases (14%), and all were negative for keratins, both cocktail and individual K. We conclude that crossreactivity of AE1/AE3 with other intermediate filament proteins, such as GFAP, as previously observed in brain and glioma tissue, probably accounts for the extensive keratin-positivity seen in some retroperitoneal schwannomas. However, focal expression of K1 and K7 cannot be ruled out. Keratin-positive schwannomas should not be confused with other keratin-positive tumors, such as sarcomatoid carcinoma, mesothelioma, and synovial sarcoma.

Placental Cadherin and the Basal Epithelial Phenotype of BRCA1-Related Breast Cancer

PURPOSE

BRCA1-related breast cancer frequently has a basal epithelial phenotype, and P-cadherin is a basal marker. We undertook a detailed evaluation of the relationship among P-cadherin, prognostic markers in breast cancer, and outcome.

EXPERIMENTAL DESIGN

This study was restricted to 292 cases of first primary invasive breast cancer diagnosed in Ashkenazi Jewish women between 1980 and 1995. All available blocks were stained for P-cadherin, and 261 were included in the final statistical analyses, including 27 germ line BRCA1 mutation carriers and 8 BRCA2 mutation carriers. Descriptive analyses were done followed by survival analyses and a Poisson regression analysis.

RESULTS

P-cadherin was present in 80 of the 261 breast cancers (31%) and was more frequently present in tumors that have a basal epithelial phenotype [i.e., high-grade, estrogen receptor- and KIP1 (p27(Kip1))-negative tumors, with expression of cytokeratin 5/6, cyclin E, TP53, and presence of BRCA1 mutations and vascular nests (all P < 0.001)]. In a univariate survival model, expression of P-cadherin was associated with a relative risk (RR) of death from breast cancer at a 10-year follow-up of 2.9 (95% confidence interval, 1.8-4.7; P < 0.0001) and was a predictor of poor univariate survival in both lymph node-negative and -positive breast cancers. In a multivariate analysis, the effect of P-cadherin levels was not independent of other basal-related markers. Multivariable interaction modeling showed that P-cadherin positivity was highly predictive of a poor prognosis in small, node-negative breast cancers (RR, 7.1; P = 0.006).

CONCLUSIONS

P-cadherin is a marker for basal-like breast cancers and is strongly associated with the presence of a BRCA1 mutation. It is an adverse prognostic factor, particularly in small, node-negative breast cancers.

A Theileria annulata DNA binding protein localized to the host cell nucleus alters the phenotype of a bovine macrophage cell line

The apicomplexan parasite Theileria annulata is the only intracellular eukaryote that is known to induce the proliferation of mammalian cells. However, as the parasite undergoes stage differentiation, host cell proliferation is inhibited, and the leukocyte is eventually destroyed. We have isolated a parasite gene (SuAT1) encoding an AT hook DNA binding polypeptide that has a predicted signal peptide, PEST motifs, nuclear localization signals, and domains which indicate interaction with regulatory components of the higher eukaryotic cell cycle. The polypeptide is localized to the nuclei of macroschizont-infected cells and was detected at significant levels in cells that were undergoing parasite stage differentiation. Transfection of an uninfected transformed bovine macrophage cell line, BoMac, demonstrated that SuAT1 can modulate cellular morphology and alter the expression pattern of a cytoskeletal polypeptide in a manner similar to that found during the infection of leukocytes by the parasite. Our findings indicate that Theileria parasite molecules that are transported to the leukocyte nucleus have the potential to modulate the phenotype of infected cells.

Are primary cultures realistic models of prostate cancer?

Primary cultures fill a unique niche among the repertoire of in vitro model systems available to investigate the biology of the normal and malignant human prostate. This review summarizes some of the properties of primary cultures, with special emphasis on two questions: are primary cultures from adenocarcinomas really comprised of cancer rather than normal cells, and do primary cultures faithfully retain characteristics of cells of origin?

Down-Regulated Expression of Cytokeratin 18 Promotes Progression of Human Breast Cancer

PURPOSE

Cytokeratins (CKs) have been recognized for >20 years as structural marker proteins specific for epithelial cells. Recent expression profiling analyses indicate, however, that CK down-regulation may occur in breast cancer.

EXPERIMENTAL DESIGN

Here we evaluated the expression pattern of CK18 by immunohistochemical analysis of primary breast carcinomas (n = 1458) spotted on a high-density tissue microarray. The findings were correlated to histopathological risk factors and clinical outcome.

RESULTS

Down-regulation of CK18 (as compared to normal breast tissue) was observed in 25.4% of the tumors with a lower rate in lobular carcinomas (17.0%) than in ductal carcinomas (25.4%) or other histological entities (32.5%). CK down-regulation was significantly correlated to advanced tumor stage and high grade but not to axillary lymph node status. Kaplan-Meier survival analysis revealed CK18 as a prognostic indicator of overall survival (P = 0.015) and cancer-specific survival (P = 0.005).

CONCLUSIONS

Down-regulation of the luminal CK18 is not rare and a clinically relevant event in breast cancer. This finding has important implications for the use of CK18 as epithelial tumor marker. The correlations with clinical follow-up suggest that CK18 might suppress tumor progression.

Occurrence and comparison of the expressed keratins in cultured human fibroblasts, endothelial cells and their sarcomas

We investigated keratin (K) expression in cultured fibroblasts, endothelial cells and their sarcomas by using two-dimensional gel electrophoresis and electron microscopy techniques. Although the fibroblast and endothelial cell lines were derived from mesenchyme, we confirmed Ks in both cell lines. The K in two cultured cell lines consisted of K14 and K16, together with vimentin. In addition to the above Ks, K5 and K8/K17 were comprised in each cell line, respectively. On the other hand, the cultured fibrosarcomas contained K8 and K18 in addition to the Ks present in the cultured fibroblasts, except K17. Moreover, cultured angiosarcomas showed the same Ks expression as those of the cultured fibrosarcomas, except vimentin. However, electron microscopy showed that the extremely thin fiber-like substances existed or at least did not form filamentous structures in four cultured cell types.

Intracellular distribution of intermediate filaments in vimentin-positive gastric carcinomas: confocal laser scanning microscopy using formalin-fixed paraffin-embedded specimens

Intermediate filaments are known as cytoskeletal elements. Recently, additional vimentin expression has been reported in some carcinomas; however, the function of such expression remains unclear. We studied the intracellular distribution of low-molecular weight cytokeratin and vimentin by immunohistochemistry in 17 vimentin-positive gastric carcinomas using confocal laser scanning microscopy. All materials were formalin-fixed and paraffin-embedded. Low-molecular weight cytokeratin expression showed a membranous pattern with a prominent deposition just below the cytoplasmic membrane in both tubular and solid components of the carcinomas. This unique membranous deposition was frequently absent in diffuse components. On the other hand, vimentin expression showed a fibrillary pattern in all components and also showed a unique basal distribution in the tubular components. We also recognized an aggregate pattern of the intermediate filament expression in diffuse components. We conclude that the significance of vimentin expression in carcinoma cells cannot be explained as a simple substitution for low-molecular weight cytokeratin because the distribution of vimentin and low-molecular weight cytokeratin is different.

Expression of cytokeratin 20 in mucinous bronchioloalveolar carcinoma

Mucinous bronchioloalveolar carcinomas (BACs) can closely mimic metastatic adenocarcinoma to the lung both clinically and morphologically. Several studies have demonstrated that the differential expression of cytokeratin 7 (CK7) and cytokeratin 20 (CK20) is a valuable diagnostic tool in differentiating primary pulmonary adenocarcinomas (PPAs) (usually CK7 positive/CK20 negative) from metastatic colonic adenocarcinoma (usually CK7 negative/CK20 positive). The present study is designed to correlate the histologic subtypes of PPA with expression of 7 and 20. A total of 113 cases of bonafide PPA were selected and classified according to the 1999 World Health Organization criteria as adenocarcinoma, NOS (n = 80), nonmucinous BAC (n = 14), and mucinous BAC (n = 19). Representive sections of all the tumors were immunohistochemically analyzed for CK7 and CK20 expression. To evaluate the diagnostic utility of CK7 and CK20 expression, 6 cases of colonic adenocarcinoma metastatic to the lung were tested with the same antibodies and compared with mucinous BAC. Results were expressed in a semiquantitative fashion based on the percentage of positive tumor cells: <10%, focal; 10% to 25%, 1+; 26% to 75%, 2+; > or =76%, 3+. All 113 PPAs exhibited strong, diffuse CK7 expression. With respect to CK20 expression, 17 of the 19 cases (89.4%) of mucinous BAC showed moderate to strong expression of this protein, whereas only 10 cases of conventional adenocarcinomas and 4 cases of nonmucinous BAC exhibited expression. All 6 examples of metastatic colonic adenocarcinomas were negative for CK7 and strongly positive for CK20. In summary, mucinous BAC is distinct from other PPAs by virtue of its CK20 expression. Although the CK7/CK20 immunoprofile is a valuable diagnostic marker for differentiating primary lung adenocarcinoma from metastatic colonic adenocarcinoma, caution should be exercised when dealing with mucinous BAC.

Patterns of nestin and other intermediate filament expression distinguish between gastrointestinal stromal tumors, leiomyomas and schwannomas

The KIT-positive specific gastrointestinal stromal tumors (GISTs), leiomyomas, and schwannomas are the three most common types of primary mesenchymal tumors of the gastrointestinal (GI) tract. The intermediate filaments are abundant cytoskeletal proteins commonly used as cell differentiation markers in diagnostic immunohistochemistry. Their patterns have not been fully characterized in GI mesenchymal tumors, and could offer differential diagnostically useful parameters. Very recently, nestin, a class VI intermediate filament expressed in neuroectodermal stem cells and skeletal muscle progenitor cells, has been shown in GISTs and suggested as a marker for these tumors. In this study we immunohistochemically examined the expression of nestin and other intermediate filament proteins, including desmin, keratins (Ks), glial fibrillary acidic protein (GFAP), neurofilament, and vimentin in GISTs of different sites, esophageal leiomyomas and GI schwannomas. Nestin was nearly consistently present in GISTs of different locations whether spindle cell or epithelioid, and benign or malignant. It was also detected in 23 of 24 (96%) GI schwannomas, whereas leiomyomas were uniformly negative. Vimentin was present in both GISTs and schwannomas, whereas it was typically absent in leiomyomas (25% positive, usually focally). Desmin was present in all leiomyomas, whereas only 3% of GISTs (4 of 140) were positive, and all schwannomas were negative. K18 was detected in a minority of GISTs, leiomyomas, and schwannomas. Malignant GISTs were more commonly keratin positive than the benign ones; there was 18% K18 positivity in malignant gastric and small intestinal GISTs, but 9% K18 positivity in benign gastric and small intestinal GISTs. Moreover, K8, albeit to a lesser degree, was detected in a minority of GISTs, but K7, K14, K19 and K20 were not detected. GFAP was present in the majority of schwannomas, whereas all GISTs were negative; some leiomyomas had weak cytoplasmic positivity. These results document distinctive patterns of intermediate filament proteins in GI mesenchymal tumors. Nestin is confirmed to be consistently expressed in GISTs but it is also present in most GI schwannomas; GFAP is helpful when separating GISTs and schwannomas, since only the latter are positive. The potential presence of K8 and K18 in GISTs should not lead to the misdiagnosis of carcinoma on biopsy.

Mapping of the keratin polypeptides in meningiomas of different types: an immunohistochemical analysis of 463 cases

Keratins are known to be expressed in some meningiomas, and they have been consistently reported in secretory meningiomas. However, the expression of individual keratin polypeptides has not yet been systematically explored, and such a study could provide important information for the differential diagnosis of meningioma and other tumors, particularly metastatic carcinomas. In this study we analyzed the keratin polypeptide patterns of 463 meningiomas of different types using well-characterized monoclonal antibodies specific to 11 individual keratins and 3 additional antibodies that recognize more than 1 keratin. Archnoid tissues from autopsies were examined for comparison. Secretory meningiomas showed consistent positivity for all simple epithelial keratins K7, K8, K18, and K19, usually limited to the slender spindle cells lining the gland-like lumina. Other keratins variably detected in a minority of gland-like structures were K5/6, K14, K16, and K17. Among other meningiomas, keratin 18 was commonly present in a significant number of tumor cells in different subtypes (30% to 80% of cases), often extensively. The K18 positivity of meningiomas paralleled that observed in normal arachnoids, which were negative for K7, K8, K19, and AE1. Only rare meningiomas, other than the secretory ones, had significant positivity for K7, K8, K19, and other keratins than K18. The concentric spindle cells around psammoma bodies and few other spindle cell foci were often focally positive for K7 and to lesser degree for K8, K14, and K19. The complex pattern of keratins in meningiomas has to be considered in the differential diagnosis of meningioma and metastatic carcinoma. In this context, antibodies to K7, K8, and K19 and the antibodies AE1 and AE3 are useful, because they only rarely label significant numbers of meningioma cells but are positive in a great majority of carcinomas. Careful histologic analysis is necessary to differentiate anaplastic meningiomas and metastatic carcinomas, which have overlapping patterns of several keratins except K20, which was never present in any type of meningioma.

Spindle cell (sarcomatoid) carcinomas of the larynx: a clinicopathologic study of 187 cases

Laryngeal spindle cell (sarcomatoid) carcinomas are uncommon tumors, frequently misdiagnosed as reactive lesions or mesenchymal malignancies. The records of 187 patients with tumors diagnosed as laryngeal spindle cell (sarcomatoid) carcinoma were retrieved from the files of the Otorhinolaryngic Tumor Registry of the Armed Forces Institute of Pathology. There were 174 men and 13 women, 35-92 years of age (average, 65.6 years). Nearly all patients experienced hoarseness (n = 165 [88%] patients) for a mean duration of 11.0 months. Patients admitted to smoking (n = 162 [87%] patients) and/or alcohol use (n = 90 [48%] patients). Most tumors were glottic (n = 132 [71%]), T1 (n = 111 [59%]), 1 and polypoid (n = 185 [99%]), with a mean tumor size of 1.8 cm. Histologically, squamous cell carcinoma (n = 157 [84%]) was noted, ulcerated, and blended with the spindle cell component, which was most frequently arranged in a storiform pattern (n = 92 [49%] tumors). Foci of benign or malignant cartilage and/or bone (n = 13 [7%]) were noted in the spindle cell component. All patients were treated with surgery (n = 90 [48%] patients) or surgery with radiation (n = 97 [52%] patients). Recurrences developed in 85 (45%) patients. Overall, T1 glottic tumors managed by complete surgical eradication had the best outcome (mean follow-up, 7.8 years).

Transdifferentiation of neoplastic cells

Transdifferentiation is a process in which a stable cell's phenotype changes to that of a distinctly different cell type. It occurs during certain physiological processes and leads to transition of tumor cell phenotypes. The latter process includes neoplastic epithelial-epithelial transition, neoplastic epithelial-mesenchymal transition, neoplastic mesenchymal-epithelial transition and transition between non-neural and neural neoplastic cell. This phonomenon is exemplified in some origin-debated tumors, such as carcinosarcoma, pleomorphic adenoma, synovial sarcoma, Ewing's/pPNET, and malignant fibrohistiocytoma. We propose that differentiation disturbance of cancer cells should include not only undifferentiation and dedifferentiation, but also transdifferentiation as well. Tumor cell transdifferentiation may be influenced or determined by cellular genetic instabilities, proliferation and apoptosis, as well as by extracellular matrix and growth factors.

Bromodeoxyuridine increases keratin 19 protein expression at a posttranscriptional level in two human lung tumor cell lines

Keratins form the largest subfamily of intermediate filament proteins and show strict lineage- and differentiation-associated expression in epithelial cells. Little is known about the mechanisms that control keratin protein synthesis in these cells. We have examined the effect of the differentiation-modulating agent, 5'-bromo-2'-deoxyuridine (BrdU), on keratin 19 (K19) expression in two human lung carcinoma cell lines, DLKP and A549. Treatment of both cell lines with 10 microM BrdU for 7 d induced the expression of K19 protein in keratin-negative DLKP cells, and significantly increased K19 protein expression in A549 cells. K19 messenger ribonucleic acids (mRNAs) were detected by Northern blot and reverse transcriptase-polymerase chain reaction analyses in both cell lines, but no increase in K19 mRNA levels was detected in either cell line, even with treatment with BrdU for up to 21 d. This suggests that K19 protein synthesis is normally blocked at a posttranscriptional level in DLKP cells, and BrdU can somehow reverse this block, resulting in the induction of K19 protein synthesis. Treatment of HL60, a leukemic cell line, with BrdU, resulted in noninduction of K19 protein synthesis, and no K19 mRNA transcripts were detected before and after BrdU treatment, possibly suggesting that BrdU is acting in an epithelial-specific manner to reverse a block in K19 protein synthesis in DLKP keratin-negative lung cancer cells. Therefore, DLKP (and A549) may be useful cellular models to investigate if this represents a regulatory step in early lung development or a mechanism whereby tumor cells possess the ability to down-regulate the expression of a more-differentiated phenotype.

Keratin 1 expression in endothelia and mesenchymal tumors: an immunohistochemical analysis of normal and neoplastic tissues

Keratin polypeptides of the nonhair type, numbered 1 through 20 in the Moll catalog, are selectively expressed in normal and neoplastic tissues. Keratin 1 (K1), the highest-molecular-weight keratin (67 kd), was generally considered specific for keratinizing squamous epithelia. However, recent studies have shown that it is an integral component of the multiprotein kininogen receptor of endothelial cells. A library of formalin-fixed, paraffin-embedded tissue samples was evaluated immunohistochemically (avidin-biotin peroxidase complex method) for K1 expression using a specific monoclonal antibody (Novocastra clone 34betaB4). The study group included a wide variety of normal tissues and 541 tumors of epithelial or mesenchymal derivation. The specificity of the antibody to K1 was verified in normal epithelial tissues, where the staining was essentially limited to the epidermis and Hassal corpuscles of the thymus and focally to other squamous epithelia. Among carcinomas, it was essentially limited to keratinizing squamous carcinomas. It was also regularly found in endothelial cells of normal capillaries, veins, and arteries. Capillary, cavernous, and venous hemangiomas often had endothelia with K1 positivity. Among the malignant vascular tumors, epithelioid hemangioendotheliomas were consistently positive (8 of 8). However, angiosarcomas had more variable expression (59 of 81 were positive), with well-differentiated tumors generally having greater reactivity than poorly differentiated examples. Mesenchymal tumors with K1 expression included schwannomas (10 of 16), epithelioid sarcomas (26 of 37), and synovial sarcomas (19 of 68). In the last 2 tumor types, K1 reactivity was detected in both epithelioid and spindled neoplastic populations. In addition to its specificity for keratinizing squamous epithelia, K1 can be immunohistochemically detected in normal vascular endothelial cells and a spectrum of vascular tumors. However, its expression in poorly differentiated vascular tumors is variable, suggesting that this marker is poorly conserved in highly transformed endothelia. The unexpected K1 immunoreactivity in nonvascular soft tissue tumors, such as synovial sarcoma, epithelioid sarcoma, and schwannomas, requires further study.

Influenza A virus infection of human middle ear cells in vitro

HYPOTHESIS

Human-derived normal middle ear mucosal cells can be harvested and cultured and will support influenza A virus (INF A) infection.

STUDY DESIGN

Protocols for the collection and in vitro culture of middle ear mucosal cells were developed and used to investigate the effects of INF A infection as it relates to the pathogenesis of otitis media.

MATERIALS AND METHODS

Middle ear mucosa was harvested during surgeries that opened the normal middle ear. Middle ear mucosal cells were plated and grown in collagen-coated dishes. Cells were characterized before and after INF A exposure using phase-contrast and immunofluorescence microscopy as well as reverse transcriptase-polymerase chain reaction (RT-PCR) for cytokeratin 18 gene expression and INF A.

RESULTS

Primary cultures of human middle ear epithelial cells were established. Prolonged growth of middle ear cells yielded a second cell type that failed to stain for cytokeratin on immunofluorescence but continued to produce positive RT-PCR results on cytokeratin 18 analysis. After INF A exposure, cytological changes and immunofluorescence staining showed cellular infection. RT-PCR analysis using INF A-specific primers showed positive results for up to 72 hours after viral exposure.

CONCLUSIONS

Primary cultures of human middle ear mucosal cells have been established. Two distinctly different cell culture systems have been developed: 1) middle ear epithelial cells and 2) either dedifferentiated epithelial cells or fibroblasts. Exposure of both cell types to INF A demonstrates that each can support cellular infection and viral replication. These models should be useful for studies of the pathogenesis of virus-mediated otitis media.

Bone marrow micrometastases and gastrointestinal cancer detection and significance

Accurate staging of cancer is important, as the presence or absence of systemic spread determines treatment. The sensitivity of current imaging and biochemical techniques is suboptimal for the detection of minimal residual disease and latent metastases. This results in understaging and potential undertreatment. To improve detection of disseminated epithelial malignancy, immunohistochemical and molecular methods have been employed that search for epithelial cell-specific proteins in nonepithelial tissue. Bone marrow is mesenchymal tissue (that does not normally express epithelial cell components) and represents an accessible window for detection of micrometastatic carcinoma cells. Detection methods for epithelial cell components (cytokeratins, epithelial membrane antigen, carcinoembryonic antigen) include immunohistochemistry, flow cytometry, reverse transcriptase polymerase chain reaction (rt-PCR), and enzyme linked immunoassay (ELISA). Micrometastatic cells in bone marrow are viable, capable of proliferation, resistant to immune attack, and insensitive to s-phase chemotherapeutic agents. Patients with carcinomas of the lung, breast, prostate, or gastrointestinal tract and in whom bone marrow micrometastases are detected have a foreshortened interval to recurrence and impaired survival. Detection of micrometastases deserves serious consideration in treatment protocols, and standardization of methods is now required.

Homozygous nonsense mutation in helix 2 of K14 causes severe recessive epidermolysis bullosa simplex

We have studied a consanguineous family containing two children with severe, generalized epidermolysis bullosa simplex (EBS). Electron microscopy of skin biopsies from the affected individuals showed that basal keratinocytes were devoid of tonofilament bundles, although some single intermediate filament were visible. Genetic linkage analysis with the microsatellite probe D12S96 excluded the type II keratin gene cluster in this family. However, homozygosity by descent was observed with the polymorphic probes KRT9, KRT10 Ava II, and D17S1787 in both affected children, consistent with a recessive defect in a type I keratin. Immunoreactivity to keratin K5 and K15 was normal, but monoclonal antibodies LL001 and RCK107 against K14 showed no staining, suggesting a deficiency of K14 in these individuals. mRNA extracted from biopsy material was amplified by RT-PCR to obtain full-length K14 cDNA. Direct automated sequencing identified a homozygous nonsense mutation, W305X. A Hinf I restriction enzyme site is created by this nucleotide transition, which was used to confirm the presence of the mutation in this kindred and exclude it from 100 normal chromosomes. This is the fourth kindred with severe recessive EBS for whom a mutation has been found in the K14 gene. In this instance, the premature termination codon is the farthest downstream of the reported cases, occurring in the helix 2 domain and so giving a much longer translation product. Nevertheless, the heterozygous carriers are unaffected by the disease and display no epidermal fragility. We postulate that translation of the potentially dominant-negative truncated K14 might be down-regulated due to instability of the mutant mRNA, as observed in previous cases with similar mutations.

Sarcomatoid carcinoma of the urinary bladder: a clinicopathologic and immunohistochemical analysis of 14 patients

Sarcomatoid carcinoma of the urinary bladder is a rare entity, in which both the histogenesis and biological behavior remain controversial. We herein describe the clinicopathologic and immunohistochemical profiles of sarcomatoid carcinomas and discuss the significance of cell adhesion molecules in the development of this peculiar neoplasm. The authors examined formalin-fixed and paraffin-embedded tissue samples from 14 patients with sarcomatoid carcinoma of the urinary bladder. An immunohistochemical analysis was performed by using antibodies against epithelial and mesenchymal antigens as well as adhesion molecules. Most patients suffered from an advanced stage of the tumor, extending to the muscular layer (7 cases) or to the perivesical tissues (5 cases). Microscopically, all 14 tumors were composed predominantly of a carcomatoid component and an obviously carcinomatous component. The sarcomatoid component was composed of a mixture of spindle cells, round cells, and pleomorphic giant cells. The carcinomatous components consisted of papillary or nonpapillary high-grade transitional cell carcinoma (TCC). The zones of gradual transition between the carcinomatous and the sarcomatous elements were focally apparent in each tumor. The findings of an immunohistochemical examination indicated that both carcinomatous and sarcomatoid components expressed epithelial antigens (pankeratin or EMA), even though the staining pattern varied from case to case. As for cell adhesion molecules, the carcinomatous components were positive for E-cadherin (8 of 12), CD44s (8 of 12), and CD44v6 (6 of 12). Although the sarcomatoid components were also positive for E-cadherin (5 of 12), CD44s (4 of 12), and CD44v6 (3 of 12), these rates were lower than those in the carcinomatous components. Six patients died of their disease between 5 and 36 months after the diagnosis was made. The recognition of sarcomatoid carcinomas has important therapeutic and prognostic implications. It seems appropriate to treat these neoplasms in the same manner as conventional high-grade TCCs with similar degrees of invasion. We consider that sarcomatoid carcinomas should be regarded as a high-grade carcinoma that shows a prominent pseudosarcomatous dedifferentiation. The sarcomatoid component of sarcomatoid carcinomas may result from either anaplastic changes or dedifferentiation related to the process of losing cell adhesion molecules.

Epithelioid sarcoma: an immunohistochemical analysis of 112 classical and variant cases and a discussion of the differential diagnosis

Epithelioid sarcoma (ES) is a distinctive soft tissue neoplasm with a predilection for the distal extremities of young adults. This tumor typically contains nodular aggregates of epithelioid and spindle cells with zonal necrosis. The neoplastic cells are generally reported to coexpress keratin and vimentin and are often stated to be positive for CD34. However, there is no large series with extensive immunohistochemical data, there are few data with regard to expression of different keratin subtypes, and there are no large series discussing the epithelioid sarcoma subtypes. In the current study, we immunohistochemically evaluated 88 typical and 24 variant (8 angiomatoid, 9 large cell/rhabdoid, and 7 "fibroma-like") ESs. Nearly all ESs with typical histology (94%) were positive for keratin 8 (K8), whereas 72% were positive for K19, 48% for intermediate- and high-molecular-weight keratins (34betaEH12), and 22% for K7; reactivity with the latter two antibodies was usually seen in only a minority of tumor cells. Vimentin reactivity was present in all cases, EMA in 96% of cases and muscle-specific actin and CD34 were noted in 41% and 52% of the cases, respectively. A few ESs (7%) showed focal cytoplasmic CD31 reactivity, but none exhibited a distinctive membrane staining pattern, and examples tested for FVIIIRAg were negative. The angiomatoid, fibroma-like, and large cell-rhabdoid ES variants had immunohistochemical profiles similar to the classic cases, supporting a common pathogenesis. Although not consistently expressed in ES, the presence of CD34 is helpful in distinguishing this entity from primary and metastatic carcinomas and other sarcomas such as malignant rhabdoid tumor.

Desmosomal plakophilin 2 as a differentiation marker in normal and malignant tissues

Plakophilin 2 (PKP2) is a widespread protein which shows a remarkable dual location: On the one hand, it appears as a constitutive karyoplasmic protein and on the other it is a desmosomal plaque component of most, probably all, desmosome-possessing tissues and cell culture lines. Here we report on its desmosomal occurrence as revealed by immunocytochemical results obtained with three PKP2-specific murine monoclonal antibodies (mAbs) PP2-62, PP2-86 and PP2-150. These mAbs detect PKP2 in characteristic desmosomes of most normal cells, including simple and stratified epithelia as well as non-epithelial tissues such as myocardium and lymph node follicles. In addition, however, several normal tissues consistently display a differentiation-related PKP2 distribution, for example an absence of immunostaining in the "keratinizing" local specializations of the thymic epithelial reticulum, i.e. Hassall's corpuscles, and the restriction of PKP2 to the stratum basale of most stratified squamous epithelia, in contrast to its absence in upper strata, which contain PKP1- or PKP3-rich desmosomes instead. Taking advantage of the reactivity of mAb PP2-150 with formalin-fixed, paraffin-embedded material, a series of human carcinomas (n = 37) has also been analyzed. The results suggest that mAbs to PKP2 may serve as markers for the identification and characterization of carcinomas derived from--or corresponding to--simple or complex epithelia. Thus consistent PKP2 immunostaining has been observed in all 18 cases of adenocarcinomas tested, but more variable and heterogeneous staining has been noted in squamous cell carcinomas, depending on the specific tumor type. The potential value of such mAbs for cell typing in normal and embryonic tissues and for detecting cell subpopulations with different degrees of differentiation is discussed with respect to their possible application in tumor diagnosis.

Lessons from keratin 18 knockout mice: formation of novel keratin filaments, secondary loss of keratin 7 and accumulation of liver-specific keratin 8-positive aggregates

Here, we report on the analysis of keratin 18 null mice. Unlike the ablation of K8, which together with K18 is expressed in embryonic and simple adult epithelia, K18 null mice are viable, fertile, and show a normal lifespan. In young K18 null mice, hepatocytes were completely devoid of keratin filaments. Nevertheless, typical desmosomes were formed and maintained. Old K18 null mice, however, developed a distinctive liver pathology with abnormal hepatocytes containing K8-positive aggregates. These stained positively for ubiquitin and MM120-1 and were identified as Mallory bodies, one hallmark of human alcoholic hepatitis. This is the first demonstration that the ablation of one keratin leads to the accumulation of its single partner. Another striking finding was the absence or drastic down regulation of K7 in several tissues despite its ongoing transcription. Moreover, K18 null mice revealed new insights in the filament-forming capacity of the tail-less K19 in vivo. Due to the unexpected secondary loss of K7, only K8/19 are expressed in the uterine epithelium of K18 null mice. Immunoelectron microscopy of this tissue demonstrated the presence of typical K8/19 IF, thus highlighting in vivo that K19 is a fully competent partner for K8.

Value of electron microscopy and immunohistochemistry in the diagnosis of soft tissue tumors

Light microscopy alone is often insufficient to type a soft tissue tumor. In this study 142 consecutive soft tissue tumors (benign or malignant), for which both electron microscopy (EM) and immunohistochemistry (IHC) had been performed, were reviewed to assess the contribution of these two modalities to making the final diagnosis. A tentative diagnosis (58 cases) or differential diagnosis (84 cases) was made following light microscopical examination. Ultrastructural and immunohistochemical features were then reviewed. Overall, EM more often contributed to diagnosing the tumor type than IHC (80 vs. 65%), with a statistically significant difference (p = .001). This was most apparent in high-grade sarcomas (grade III); the contribution of the two modalities was similar in benign and low-grade malignant tumors. IHC more often than EM (33% vs 22%) did not provide information to aid in typing of the tumor. However in 47% of the cases in which one of the two modalities was noncontributory, the other technique was helpful in reaching a diagnosis. These findings suggest that both IHC and EM are necessary to properly evaluate soft tissue tumors.