Hemidesmosomal dimensions and frequency in experimental oral carcinogenesis: a stereological investigation

Role of Hemidesmosomes in Oral Carcinogenesis: A Systematic Review

BACKGROUND

Oral cancers have limited diagnostic tools to aid clinical management. Current evidence indicates that alterations in hemidesmosomes, the adhesion complexes primarily involved in epithelial attachment to the basement membrane, are correlated to cancer phenotype for multiple cancers. This systematic review aimed to assess the experimental evidence for hemidesmosomal alterations, specifically in relation to oral potentially malignant disorders and oral squamous cell carcinomas.

METHODS

We conducted a systemic review to summarise the available literature on hemidesmosomal components and their role in oral pre-cancer and cancer. Relevant studies were retrieved from a comprehensive search of Scopus, Ovid MEDLINE, Ovid Embase and Web of Science.

RESULTS

26 articles met the inclusion criteria, of which 19 were in vitro studies, 4 in vivo studies, 1 in vitro and in vivo study, and 2 in vitro and cohort studies. Among them, 15 studies discussed individual alpha-6 and/or beta-4 subunits, 12 studies discussed the alpha-6 beta-4 heterodimers, 6 studies discussed the entire hemidesmosome complex, 5 studies discussed bullous pemphigoid-180, 3 studies discussed plectin, 3 studies discussed bullous pemphigoid antigen-1 and 1 study discussed tetraspanin.

CONCLUSION

Heterogeneity in cell type, experimental models, and methods were observed. Alterations in hemidesmosomal components were shown to contribute to oral pre-cancer and cancer. We conclude that there is sufficient evidence for hemidesmosomes and their components to be potential biomarkers for evaluating oral carcinogenesis.

Preliminary assessment of the epithelial nuclear-cytoplasmic ratio and nuclear volume density in human palatal lesions

We have analysed both the nuclear-cytoplasmic (N/C) ratio and nuclear volume densities (VVN) in defined strata from human hard palate lesions with and without malignant potential to determine the prognostic reliability and/or validity of this parameter. Measurements of cellular and nuclear areas of basal and spinous cells from normal (N) and pathological palatal epithelium were made on histological sections using an image analyser. The lesions comprised fibrous hyperplasia (FH), traumatic inflammation (INF), benign hyperkeratosis (HK), squamous cell papilloma (PP), dysplastic epithelium adjacent to invasive carcinoma (CE) and islands of invasive squamous cell carcinoma (CI). In basal cells, no significant differences were detected in comparisons of N/C and VVN between all pathological groups and the N control group. The mean value for CE was lower than that obtained for N. In spinous cells, the only statistically significant comparison was between IF and FH for both N/C and VVN. Both parameters were lower in CE than in N. Of all groups analysed except CI, the CE group is the only one likely to possess an increased malignant potential. The N/C ratio therefore seems to be of no value as a predictor of malignancy in palatal epithelial lesions.

Basement membrane and tumor invasion: ultrastructural observations in the basement membrane of rat bladder with invasive transitional cell carcinoma induced by N-butyl-N-(4-hydroxybutyl)nitrosamine

This study describes ultrastructural alterations in the basement membrane (BM) of rat bladder with invasive transitional cell carcinoma (TCC) induced by N-butyl-N-(4-hydroxybutyl)nitrosamine. Various alterations including thickening, degradation and neosynthesis were found in the bladder BM of one rat with invasive TCC. Focal destruction of both the BM lamina zones was found in addition to partially degraded BMs showing focal degradation and loss of only the BM lamina rara. Neosynthesis of complete BM including the lamina rara and lamina densa was observed surrounding the nests of carcinoma cells deep in the stroma, while neosynthesis of incomplete BM including only a lamina densa-like structure was also found around carcinoma cells which had just crossed the BM into the adjacent stroma from the original tumor masses. There was an increased hemidesmosomal frequency in some areas of thickened BM, and focal loss of hemidesmosome in the areas of degraded BM. It is suggested that BM degradation may take place in two steps, and that BM neosynthesis may also be a two-step process in invasive TCC of rat bladder.

Basement membrane and carcinogenesis: ultrastructural observations in the basement membrane of the bladder epithelium in rats treated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN)

This study investigated the structural alterations in the basement membrane (BM) of the bladder epithelium in rats treated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) using transmission electron microscopy. Following administration of BBN, thickening of the BM of the bladder epithelium was observed and remained almost constant from 4 to 20 weeks, although the pathological changes in the rat bladder epithelium induced by BBN altered over the same period of 20 weeks. The reason for this phenomenon can be explained by the increased interfacial area between the basal epithelial cells and the BM of the rat bladder epithelium due to an increase in the number and size of the microvilli on the basal cell surfaces adjacent to the BM. Our results also showed that the frequency of hemidesmosomes increased progressively during the period of carcinogenesis, especially in the lesions of noninvasive transitional cell carcinoma (TCC) in the rat bladder. It is suggested that the neosynthesis of BM components can be carried out both by benign hyperplastic cells and by noninvasive TCC cells of rat bladder. The alterations in the BM thickness may be affected by the changes in the number and size of the microvilli occurring on the basal cell surfaces adjacent to the BM. Both an increased frequency of hemidesmosomes and the neosynthesis of BM are closely related to cell proliferation during carcinogenesis.

Integrin alpha 6/beta 4 complex is located in hemidesmosomes, suggesting a major role in epidermal cell-basement membrane adhesion

The alpha 6/beta 4 complex is a member of the integrin family of adhesion receptors. It is found on a variety of epithelial cell types, but is most strongly expressed on stratified squamous epithelia. Fluorescent antibody staining of human epidermis suggests that the beta 4 subunit is strongly localized to the basal region showing a similar distribution to that of the 230-kD bullous pemphigoid antigen. The alpha 6 subunit is also strongly localized to the basal region but in addition is present over the entire surfaces of basal cells and some cells in the immediate suprabasal region. By contrast staining for beta 1, alpha 2, and alpha 3 subunits was very weak basally, but strong on all other surfaces of basal epidermal cells. These results suggest that different integrin complexes play differing roles in cell-cell and cell-matrix adhesion in the epidermis. Immunoelectron microscopy showed that the alpha 6/beta 4 complex at the basal epidermal surface is strongly localized to hemidesmosomes. This result provides the first well-characterized monoclonal antibody markers for hemidesmosomes and suggests that the alpha 6/beta 4 complex plays a major role in epidermal cell-basement membrane adhesion. We suggest that the cytoplasmic domains of these transmembrane glycoproteins may contribute to the structure of hemidesmosomal plaques. Immunoultrastructural localization of the BP antigen suggests that it may be involved in bridging between hemidesmosomal plaques and keratin intermediate filaments of the cytoskeleton.

What's new in the ultrastructure of tumor invasion in vivo?

An important point emerging from the literature on tumor invasion in vivo is the great variability of nearly all aspects studied. It seems that there is neither one particular morphologic change which renders a cell invasive, nor one particular mechanism by which a cell crosses the boundaries of its original tissue compartment to occupy another. Nevertheless, some general trends are demonstrable. The majority of invasive tumor cells appear to be characterized by prominent surface protrusions, decreased junctional contacts and, in the case of epithelium-derived tumor cells, an incomplete basement membrane. The fact that some tumors can invade foreign tissues without loosing their basement membrane is emphasized. Invasive cells frequently form organized associations with preexistent non-neoplastic cells without damaging them. Apparently, the eventual disappearance of the preexistent cells in most invaded tissues is not necessarily due to a direct action on the part of the tumor cells. It rather seems a secondary phenomenon caused by, e.g., the insertion of invasive tumor cells between the preexistent cells and their original stroma. Very often, this seems to be due to the affinity of malignant cells for basement membranes. In addition, the adhesion of tumor cells to basement membranes frequently seems to determine their pattern of spread through a tissue. A process which may turn out to be a key factor in tumor invasion is desmoplasia, the series of host reactions which creates a new environment for the tumor cells which may favor their survival, proliferation, and locomotion. With the rapid development of new techniques, electron microscopy will probably contribute to the elucidation of the exact nature, the degree of similarity to granulation tissue, and the influence on invasion of desmoplastic tumor stroma.

A quantitative ultrastructural study of alterations in the area of the basal cell-stromal interface during experimental oral carcinogenesis

Because of its topographical location, the basal cell in carcinomas must play a significant role in the invasion of adjacent tissues. We have analysed the proportion of the basal cell plasma membrane in direct contact with the adjacent lamina propria during in vivo oral carcinogenesis. Samples of hamster cheek-pouch mucosa treated with DMBA were assigned to hyperplasia, dysplasia and carcinoma groups using strictly defined histopathological criteria. Electron micrographs of basal cells were subjected to stereological intersection counting to provide estimates of the proportion of the total basal cell membrane in contact with the connective tissue (SSBM,PM). In untreated controls, a mean value of 9% was obtained, whereas, for DMBA-induced hyperplasias, dysplasias and carcinomas, values were 8%, 12% and 16% respectively. Statistically, SSBM,PM values were significantly elevated in dysplasias and carcinomas. The changes in this parameter may reflect an increased motility in the transforming basal cell prior to and concomitant with cellular invasion, and may prove to be of value as a structural indicator of malignant transformation.

Ultrastructural morphometry of collagen from lamina propria during experimental oral carcinogenesis and chronic inflammation

Stereological point-counting methods were used to determine the volumetric alterations in collagen from the lamina propria immediately beneath the epithelial-connective tissue junction in hamster check-pouch mucosa treated with the chemical carcinogen DMBA. In addition, a non-neoplastic inflammatory control was evaluated in which a delayed hypersensitivity reaction was induced by the contact-sensitising agent DNCB. DMBA-treated tissues were assigned to histopathologically defined hyperplasia, dysplasia and carcinoma stages. The volume densities of collagen present in unit volume of extracellular lamina propria were found to decrease progressively and significantly in DMBA-treated tissues when compared with values obtained from normal untreated mucosa. Values from the inflammatory control were comparable with those from the dysplasia stage of carcinogenesis. The mechanisms responsible for these decreases in collagen volume density are unknown, but contributory factors might include collagen destruction by enzymes originating in either the epithelium or the cells of the inflammatory infiltrate, dilution of collagen produced by inflammatory oedema or alterations in the synthetic capabilities of fibroblasts.