Basal cell carcinomas display extensive abnormalities in the hemidesmosome anchoring fibril complex

Structural variations of collagen in normal and pathological tissues: role of electron microscopy

The spectrum of ultrastructural appearances assumed by collagen in normal and pathological tissues is illustrated using techniques of thin section transmission electron microscopy and computer-assisted analysis. The normal fibrillar collagen types are described in order to provide a basis for comparing other normal and abnormal forms. In normal tissues, the anchoring fibril and basal lamina (basement membrane) represent tissue structures largely containing collagen but differing significantly in organisation from normal types I to III fibrillar collagen. In pathological tissue, deviations from normal fine structure are reflected in abnormal aggregates of collagen fibrils (amianthoid and skeinoid fibres) and abnormalities in fibril diameter and cross-sectional profile. Fibrous and segment long-spacing collagen represent two further organisational variants of collagen, the former found widely in pathological tissues, the latter very rarely. Much remains to be discovered about these abnormal collagen variants-their mode of formation, the cells that produce them, and their roles. They also present a challenge for the collagen biologist formulating hypotheses of collagen fibril assembly and molecular organisation.

Investigation into the mechanism of the loss of laminin 5 (alpha3beta3gamma2) expression in prostate cancer

Laminin 5 is a pivotal hemidesmosomal protein involved in cell stability, migration, and anchoring filament formation. Protein and gene expression of the alpha3, beta3, and gamma2 chains of laminin 5 were investigated in normal and invasive prostate carcinoma using immunohistochemistry, Northern analysis, and in situ hybridization. Laser capture microdissection of normal and carcinomatous glands, in conjunction with RNA amplification and reverse Northern analysis, were used to confirm the gene expression data. Protein and mRNA expression of all three laminin 5 chains were detected in the basal cells of normal glands. In contrast, invasive prostate carcinoma showed a loss of beta3 and gamma2 protein expression with variable expression of alpha3 chains. Despite the loss of protein expression, there was retention of beta3 and gamma2 mRNA expression as detected by in situ hybridization, Northern and reverse Northern analysis. Our findings imply that an altered mechanism of translation of beta3 or gamma2 mRNAs into functional proteins contributes to failure of anchoring filaments and hemidesmosomal formation. The resultant hemidesmosome instability or loss would suggest a less stable epithelial-stromal junction, increased invasion and migration of malignant cells, and disruption of normal integrin signaling pathways.

Adhesion Molecules as Diagnostic Tools in Tumor Pathology

Adhesion molecules are transmembrane glycoproteins mediating cell-cell and cell extracellular matrix interactions. They control a number of fundamental biological processes including cell migration, differentiation, proliferation, and apoptosis. In the last decade there has been an increasing interest in the exploitation of these molecules as diagnostic and/or prognostic markers in tumor pathology. For example, a large number of studies have shown that loss of E-cadherin expression correlates with high tumor grade and advanced tumor stage in a number of malignancies. The analysis of adhesion molecule profile in a routine clinical setting needs further investigation in prospective multicenter studies. Int J Surg Pathol 8(3):191-200, 2000

Integrin alpha6beta4 as a suppressor and a predictive marker for peritoneal dissemination in human gastric cancer

BACKGROUND & AIMS

Because alterations of integrin expression in cancers contribute to cancer cell biology, we analyzed the association between the potential for peritoneal dissemination and integrin expression.

METHODS

The dissemination potential of 10 human gastric cancer cell lines in mice with severe combined immunodeficiency (SCID) was compared with the expression of various integrins. The relationship between integrin expression and peritoneal dissemination was also investigated in surgically resected gastric cancer cases.

RESULTS

The level of integrin beta4 subunit expression was inversely correlated with dissemination potential. Introduction of a full-length complementary DNA (cDNA) for beta4 subunit into cancer cells showing negligible beta4 subunit expression markedly suppressed peritoneal dissemination and inhibition of endogenous integrin alpha6beta4 by introduction of a cytoplasmic domain-deleted beta4 subunit cDNA into cells showing high expression of beta4 subunit promoted peritoneal dissemination. Apoptosis, which was histologically evident in peritoneal nodules of SCID mice, was induced in the cells with high beta4 subunit expression by attachment to laminin and stimulation with growth factors in vitro. An immunohistochemical study of specimens from 120 cases of primary gastric cancer showed that patients with beta4 subunit-positive tumors exhibited peritoneal dissemination only infrequently (P < 0.0001) and had a better outcome (P < 0.01).

CONCLUSIONS

These results indicate that integrin alpha6beta4 is both a suppressor and a predictive marker for peritoneal dissemination in gastric cancer.

Altered integrin expression and the malignant phenotype: the contribution of multiple integrated integrin receptors

The integrins are a family of cell surface adhesion receptors that mediate adhesion to either components of the extracellular matrix or to other cells. The beta1 family of integrins represent the major class of cell substrate receptors with specificities primarily for collagens, laminins, and fibronectins. The role of the integrin family of cell surface adhesion receptors in normal mammary gland morphogenesis and the contributions of altered integrin receptor expression to the invasive and metastatic phenotype have been the primary focus of our lab, as well as a number of other laboratories. The alpha2beta1 integrin is expressed at high levels by normal differentiated epithelial cells including those of the normal breast. Using breast cancer as a model, we evaluated changes in integrin expression in malignancy. We and other investigators made the key observation that alpha2beta1 integrin expression is decreased in adenocarcinoma of the breast in a manner that correlates with the stage of differentiation. Studies of other adenocarcinomas have yielded similar results. When the alpha2beta1 integrin was reexpressed in a poorly differentiated mammary carcinoma that expressed no detectable alpha2 integrin subunit, a dramatic reversion of malignant phenotype to a differentiated epithelial phenotype was observed, indicating a critical role for alpha2beta1 expression in mammary gland differentiation. Other laboratories using monoclonal antibodies to competitively inhibit alpha2beta1 integrin adhesion or oncogenic transformation using c-erb2 have confirmed the important role of that alpha2beta1 integrin in mammary gland morphogenesis. Re-expression of the alpha2beta1 integrin also results in upregulation of both the alpha6 and beta4 integrin subunits. To determine the contribution of enhanced alpha6 and beta4 integrin expression to the abrogation of the malignant phenotype by alpha2beta1 integrin expression, we have now separately re-expressed the human alpha6 or beta4 integrin subunit in the breast cancer model.

Decreased mRNA expression of several basement membrane components in basal cell carcinoma

The biologic factors that control the behavior of basal cell carcinoma are poorly understood. This study was undertaken to elucidate the mechanisms responsible for the altered protein levels of several basement membrane components found in basal cell carcinoma. RNA was isolated from papulonodular basal cell carcinoma, normal human epidermal keratinocytes, and normal human skin, reverse transcribed to cDNA and amplified by the polymerase chain reaction utilizing primers specific for the 230 kDa bullous pemphigoid antigen (BPAG1), the 180 kDa bullous pemphigoid antigen (BPAG2), the alpha6 and beta4 chains of the alpha6beta4 integrin complex, and the beta3 chain of laminin 5. Southern blots probed with internal oligonucleotides confirmed that each polymerase chain reaction was specific for the basement membrane component amplified. The mRNA expressions of basement membrane components were indistinguishable between normal human epidermal keratinocytes and normal human skin, and subsequent experiments used normal human epidermal keratinocytes as controls. Quantitation of polymerase chain reaction products indicated that all basement membrane specific mRNA were significantly decreased in basal cell carcinoma as compared with normal human epidermal keratinocytes. The mean polymerase chain reaction product intensities were significantly less in the basal cell carcinoma as compared with the normal human epidermal keratinocytes at the following levels: p < 0.001 for alpha6 and beta4 integrins and the beta3 chain of laminin 5; p < 0.01 for BPAG1; and p < 0.05 for BPAG2. Our results demonstrate that decreased protein levels of basement membrane components in basal cell carcinoma are due at least partially to a downregulation of basement membrane mRNA species. We speculate that these alterations may lead to a structurally incompetent basement membrane that facilitates the basal cell carcinoma ability to invade tissues.

Basal cell carcinoma with thickened basement membrane: a variant that resembles some benign adnexal neoplasms

Because cutaneous basal cell carcinoma (BCC) is such a common malignancy, its unusual histologic manifestations are important. We identified a variant of BCC in which thickened basement membranes surround aggregations of neoplastic epithelial cells. Thickened basement membranes of similar appearance have previously been observed in benign cutaneous adnexal neoplasms, in basaloid monomorphic adenomas of the salivary gland and in other benign conditions, such as folliculocentric basaloid proliferation. We identified nine BCCs that otherwise met standard criteria, but which also had thick basement membranes surrounding some of the aggregations, and examined them by routine and histochemical staining. The cases included BCC with nodular, micronodular, and infiltrating patterns. Two neoplasms were composed largely of clear cells, suggesting, together with the thickened membranes, outer root sheath differentiation. CD34, which labels keratinocytes of the outer root sheath, marked only the epithelial cells of one of these cases. The thickened membranes were stained by periodic-acid Schiff with and without diastase (PAS-D) and by antibodies to type IV collagen and laminin, with slightly different staining patterns. Intraepithelial droplets within aggregations stained with PAS-D and type IV collagen antibodies. Thickened basement membranes therefore can occur in most of the common growth patterns of BCC. The absence of CD34 staining of epithelial cells in most cases makes it problematic at this time to prove that the thickened membranes indicate trichilemmal differentiation. BCC with thick basement membranes can closely mimic benign neoplasms, such as cylindroma and trichilemmoma, from which they can be distinguished in routinely stained sections. The presence of a continuous thick basement membrane around aggregates of epithelial cells does not in and of itself distinguish between benign and malignant cutaneous epithelial neoplasms.

The integrin alpha 6 beta 4 and the biology of carcinoma

The integrin family of adhesion receptors plays a major role in epithelial organization and function. Moreover, the altered expression and function of specific integrins most likely contributes significantly to carcinoma progression. The integrin alpha 6 beta 4, the focus of this review, is a receptor for several members of the laminin family and is preferentially expressed at the basal surface of most epithelia, where it contributes to basement membrane interactions. Mounting evidence suggests that the alpha 6 beta 4 integrin plays a key role in carcinoma cell biology. Several histopathological studies have established a correlation between alpha 6 beta 4 integrin expression and tumor progression. The importance of alpha 6 beta 4 expression in tumors in underscored by the findings that invading fronts of several carcinomas are enriched in the expression of alpha 6 beta 4 integrin ligands, such as laminin-1 and laminin-5. The participation of the alpha 6 beta 4 integrin in invasion is supported further by in vitro functional studies using carcinoma cells that have been transfected with the beta 4 cDNA. The mechanisms by which alpha 6 beta 4 contributes to tumor progression are probably related to its mechanical and signaling properties and are currently under intense study.

Epiligrin is decreased in papulonodular basal cell carcinoma tumor nest basement membranes and the extracellular matrix of transformed human epithelial cells

Patients with anti-epiligrin cicatricial pemphigoid have anti-basement membrane autoantibodies that immunoprecipitate a set of disulfide-linked human keratinocyte polypeptides that co-migrate in sodium dodecyl sulfate polyacrylamide gel electrophoresis with the same complex identified by monoclonal anti-epiligrin (P1E1) and monoclonal anti-nicein/kalinin (GB3) antibodies. In an attempt to further compare the reactivity of patient autoantibodies, P1E1 and GB3, these reagents were tested against the tumor nest basement membranes of 7 papulonodular basal cell carcinomas. These studies found that all of these reagents showed markedly decreased or no reactivity against this substrate. Though their concordant lack of reactivity failed to distinguish these antibodies, these studies did identify a significant defect in papulonodular basal cell carcinoma tumor nest basement membranes. Similarly, integrin subunits alpha 6, beta 4, alpha 3, and alpha 2 as well as bullous pemphigoid antigens 1 and 2 (all potential receptors for the extracellular matrix ligands epiligrin and nicein/kalinin) were also reduced in these tumor nest basement membranes. These findings signify an extensive impairment in the lamina lucida of this neoplasm's basement membrane. Related comparative studies of normal human keratinocytes and transformed human epithelial cell lines (specifically, A-431 and HaCat cells) showed that epiligrin production is markedly decreased in the latter. Decreased expression of epiligrin and nicein/kalinin in papulonodular basal cell carcinoma tumor nest basement membranes in vivo and transformed epithelial cells in vitro indicate that this complex is a transformation-sensitive cell adhesion ligand.