Basal cell carcinomas grown in nude mice produce and deposit fibronectin in the extracellular matrix

Human prostate side population cells demonstrate stem cell properties in recombination with urogenital sinus mesenchyme

Stem cell enrichment provides a tool to examine prostate stem cells obtained from benign and malignant tissue. Functional assays can enrich stem cells based on common stem cell phenotypes, such as high ATP binding cassette (ABC) transporter mediated efflux of Hoechst substrates (side population assay). This functional assay is based upon mechanisms that protect cells from environmental insult thus contributing to the survival and protection of the stem cell population. We have isolated and analyzed cells digested from twelve clinical prostate specimens based on the side population assay. Prostate stem cell properties of the isolated cells were tested by serial recombination with rat urogenital mesenchyme. Recombinants with side population cells demonstrate an increase in the frequency of human ductal growth and the number of glands per recombinant when compared to recombinants with non-side population cells. Isolated cells were capable of prostatic growth for up to three generations in the recombination assay with as little as 125 sorted prostate cells. The ability to reproducibly use cells isolated by fluorescence activated cell sorting from human prostate tissue is an essential step to a better understanding of human prostate stem cell biology. ABC transporter G2 (ABCG2) was expressed in recombinants from side population cells indicating the side population cells have self-renewal properties. Epithelial cell differentiation of recombinants was determined by immunohistochemical analysis for expression of the basal, luminal, and neuroendocrine markers, p63, androgen receptor, prostate specific antigen, and chromogranin A, respectively. Thus, the ABCG2 expressing side population demonstrates multipotency and self-renewal properties indicating stem cells are within this population.

Establishment of murine basal cell carcinoma allografts: a potential model for preclinical drug testing and for molecular analysis

Dysregulated hedgehog (HH) signaling has been found in numerous cancers, suggesting that therapeutic targeting of this pathway may be useful vs. a wide range of cancers. Basal cell carcinoma (BCC) is an excellent model system for studying the influence of the HH pathway on carcinogenesis because aberrant activation of HH signaling not only is crucial for the development but also for the maintenance of BCC. Genetically engineered BCC mouse models provide one important tool for the study of the biology of human BCCs and for evaluating therapeutic interventions since these mice produce multiple genetically defined tumors within a relatively short period of time. However, these models remain expensive and cumbersome to use for large-scale pre-clinical drug testing. Here we report a method for growing allografts from murine BCC tumors in NOD/SCID mice. These allografts develop faster and reproduce the histology, immunophenotypes and response to at least one anti-BCC drug of the parental autochthonous tumors from which they arise. Therefore, the allograft model provides a practical model for (i) studying BCC carcinogenesis and (ii) initial pre-clinical screening for anti-HH pathway and other anti-BCC drugs.

Genetic mosaicism in basal cell carcinoma

Human basal cell cancer (BCC) shows unique growth characteristics, including a virtual inability to metastasize, absence of a precursor stage and lack of tumour progression. The clonal nature of BCC has long been a subject for debate because of the tumour growth pattern. Despite a morphologically multifocal appearance, genetic analysis and three-dimensional reconstructions of tumours have favoured a unicellular origin. We have utilized the X-chromosome inactivation assay in order to examine clonality in 13 cases of BCC. Four parts of each individual tumour plus isolated samples of stroma were analysed following laser-assisted microdissection. In 12/13 tumours, the epithelial component of the tumour showed a monoclonal pattern suggesting a unicellular origin. Surprisingly, one tumour showed evidence of being composed of at least two non-related monoclonal clones. This finding was supported by the analysis of the ptch and p53 gene. Clonality analysis of tumour stroma showed both mono- and polyclonal patterns. A prerequisite for this assay is that the extent of skewing is determined and compensated for in each case. Owing to the mosaic pattern of normal human epidermis, accurate coefficients are difficult to obtain; we, therefore, performed all analyses both with and without considering skewing. This study concludes that BCC are monoclonal neoplastic growths of epithelial cells, embedded in a connective tissue stroma at least in part of polyclonal origin. The study results show that what appears to be one tumour may occasionally constitute two or more independent tumours intermingled or adjacent to each other, possibly reflecting a local predisposition to malignant transformation.

Neuroendocrine cell differentiation in the CWR22 human prostate cancer xenograft: association with tumor cell proliferation prior to recurrence

BACKGROUND

Neuroendocrine (NE) cell differentiation is proposed to facilitate prostate cancer (CaP) recurrence following androgen deprivation through secretion by NE cells of growth factors and neuropeptides that support survival and proliferation of CaP cells and vasculature.

METHODS

The effect of androgen deprivation on NE differentiation and tumor cell proliferation in the CWR22 model of human CaP was determined by immunohistochemical analysis of the NE cell marker synaptophysin and the cell proliferation marker Ki67.

RESULTS

A significant increase in the number of NE cells was observed in CWR22 tumors between 28 and 66 days after castration compared to intact mice, that preceded the increase in tumor cell proliferation that began 70 days after androgen deprivation heralding recurrence. There was a significant positive correlation between the number of tumor-associated NE cells and proliferating CaP cells in tumors from mice after 28-34 days of androgen withdrawal.

CONCLUSION

In the CWR22 model, androgen deprivation induces an increase in tumor-associated NE cells prior to increased tumor cell proliferation, with NE cells possibly promoting tumor survival and recurrent disease.

Anaplastic neoplasms arising from basal cellcarcinoma xenotransplants into SCID-beige mice

BACKGROUND

An animal model for the study of basal cell carcinoma (BCC) is required to better understand its biology. Several attempts to grow BCC in immuno-incompetent animals have been only modestly successful.

METHODS

To test the ability of BCC to grow in a mouse with complete and severe immuno-incompetence, 14 individual BCC were transplanted into the subcutaneous tissue of 18 SCID-beige mice (T, B and natural killer cell deficient). Light microscopy and immunophenotypic analyses were performed on primary BCC and first and seventh passage tumors.

RESULTS

Transplantation of three BCC yielded rapidly growing anaplastic tumors for a tumor take of 18% (3/18). SCID-beige mice without tumor growth had mostly scars or epidermoid cysts at the transplant sites. The three patients whose BCC gave rise to the anaplastic tumors were significantly older than those without tumor growth (87 vs. 64, p = 0.001), but they did not differ with respect to BCC type or general health. These three anaplastic tumors were histologically and immunophenotypically similar, being composed of dyscohesive, pleomorphic cells that expressed vimentin and smooth muscle actin. In the first passage mice these tumors were locally invasive, tumor-forming nodules associated with an expansion of donor inflammatory cells (T and B lymphocytes and plasma cells), rare remnants of BCC epithelium and epidermoid cysts. By the seventh passage, the tumors were homogenous and metastasized widely throughout the mice. Changing transplantation location to the dermis to wound environment or supplementing the tumor with BCC-derived fibroblasts did not alter the phenotype or growth rate in SCID-beige mice. Anaplastic tumors also grew easily in SCID mice (T and B cell deficient). However, transplantation of the anaplastic tumors into normal mice (CB-17) or less severely immunodeficient mice (NCr and Balb/c: T and natural killer cell deficient) did not allow for growth. Furthermore, tumor growth could not be maintained in vitro.

CONCLUSION

Empirically, these data suggest that BCC has the potential to become an aggressive metastatic neoplasm, given the right immune and stromal environment. Moreover, a functional B lymphocyte system appears to prevent this growth. As human lymphocytes also engraft in SCID-beige mice, the original host immune response could be responsible for the lack of tumor growth in the majority of xenografts. Furthermore, the anaplastic and metastatic phenotype of these BCC derived neoplasms may be the experimental equivalent of metastatic BCC and BCC associated with carcinosarcoma.

Nonrandom numerical chromosome abnormalities in basal cell carcinomas

Clonal chromosome abnormalities were found in 22 of 23 short-term cultured basal cell carcinomas (BCC) of the skin. The karyotypic abnormalities were nonrandom and in several cases included evidence of clonal evolution. Especially in cultures showing an epithelial growth pattern, simple numerical changes, most commonly +18, +9, +20, +7, and +5, predominated and presumably constitute pathogenetically important aberrations present in the neoplastic parenchyma. Also, several structural rearrangements of chromosome arm 9q were seen, which may be of particular interest against the background that a gene for familial BCC (Gorlin syndrome), the PTCH gene, maps to this region. Finally, most of the clonal aberrations detected in predominantly fibroblast-like cultures are likely to reflect changes acquired by cells of the tumor stroma, which raises the question whether mutations also of this tumor component may play a pathogenetic role in BCC development.

Integrin alpha 5 beta 1 expression is required for inhibition of keratinocyte migration by ganglioside GT1b

Polysialoganglioside GT1b, a keratinocyte membrane glycosphingolipid, inhibits normal keratinocyte adhesion and migration on a fibronectin matrix. The specificity of the inhibition for cells plated on a fibronectin matrix and competition of GT1b inhibition with peptide RGDS suggest that GT1b abrogates the alpha 5 beta 1/fibronectin interaction. We examined the effects of GT1b on the adhesion and migration of keratinocyte-derived cell lines and correlated GT1b responsiveness and alpha 5 beta 1 integrin expression. GT1b (5 nM) significantly inhibited migration of normal human keratinocytes, immortalized keratinocytes, and squamous cell carcinoma SCC12F2 cells on fibronectin, but not on collagen I. Concentrations as high as 5 microM had no effect on SCC13 or HaCaT cells. Likewise, GT1b inhibited fibronectin-dependent cell adhesion of normal human keratinocytes, immortalized keratinocytes, and SCC12F2 cells, but had no effect on SCC13 or HaCaT cells. Flow cytometric and Western immunoblot analysis of integrin expression showed significantly decreased alpha 5 and beta 1 integrin expression in SCC13 and HaCaT cells compared to normal keratinocytes, immortalized keratinocytes, and SCC12F2 cells. Incubation with TGF-beta 1 increased alpha 5 beta 1 integrin expression and induced responsiveness to GT1b in HaCaT cells. These data imply that GT1b "response" requires sufficient expression of alpha 5 beta 1 and further suggest that the mechanism of the inhibitory effect of GT1b involves GT1b/alpha 5 beta 1 interaction.

Use of CD34 in assessing the relationship between stroma and tumor in desmoplastic keratinocytic neoplasms

It has been hypothesized that the ability for neoplastic growth of epithelial-derived neoplasms depends upon the stroma. There are currently some studies which show that the stroma surrounding basal cell carcinomas (BCC) is derived from the tumor. In contrast, other studies provide evidence that the stroma is a host-derived response to the tumor. In order to further examine the nature of stroma enveloping cutaneous epithelial neoplasms, we examined a series of tumors which contain abundant stroma, including morpheic type BCC (MBCC), desmoplastic trichoepitheliomas (DTE), and microcystic adnexal carcinomas (MAC). The spindle-shaped cells surrounding the epithelial islands of the two malignant tumors, MBCCs and MACs, were negative in 70% and 100% of cases, respectively, for CD34. In contrast, the spindle-shaped cells surrounding the islands of the benign DTEs were positive for CD34 in 80% of cases. The results suggest that whereas stromal cells surrounding DTEs resemble the CD34-positive perifollicular cells, the spindle-shaped stromal cells surrounding MBCC and MAC are CD34 negative, and may be derived from sources other than the normal mesenchymal tissue surrounding cutaneous appendages.

Ganglioside GT1b inhibits keratinocyte adhesion and migration on a fibronectin matrix

Highly sialylated gangliosides have been shown to alter cellular adhesion to a fibronectin matrix. The effect of these gangliosides on the adhesion, spreading, and migration of cultured keratinocytes on a fibronectin matrix has not been explored. Ganglioside GT1b significantly prevented attachment of keratinocytes to fibronectin and also detached previously adherent keratinocytes in a concentration-dependent manner without cell toxicity. GT1b did not affect adhesion of keratinocytes to wells coated with laminin, type I or type IV collagen, 804G extracellular matrix, or albumin. GT1b also inhibited keratinocyte migration on fibronectin in a concentration-dependent manner at concentrations as low as 5 nM GT1b, but had no effect on migration of keratinocytes plated on other matrices. GT1b binds to intact fibronectin and to the 120-kD RGDS-containing cell-binding fibronectin fragment, but not to the heparin- or gelatin-binding fragments of fibronectin. Although RGDS competes with GT1b in inhibiting adhesion, GT1b does not diminish binding of keratinocytes to a derivatized RGDS substratum, suggesting that the GT1b effect involves a non-RGDS site in the cell-binding region that modulates RGDS/alpha 5 beta 1 integrin receptor interaction. Through a specific effect on keratinocyte interaction with fibronectin, GT1b may participate in the regulation of cell adhesion and migration on a fibronectin substratum, which are important events during wound healing and the spreading of cutaneous neoplasia.

Epithelial-stromal interactions in basal cell cancer: the PDGF system

A proposed progenitor cell for basal cell carcinoma is a stem cell located in the bulge of the hair follicle. Previous investigations have shown that basal cell carcinoma has a specific stroma requirement for its growth. Likewise the development of a normal hair follicle requires the inductive force of a specialized structure with condensed mesenchyme that eventually forms the dermal hair papilla. Investigations in mouse embryos also strongly indicate that induction/growth of skin structures is dependent on platelet-derived growth factor (PDGF) alpha-receptor expression in the mesenchyme. We therefore investigated the expression of PDGF A and B chain and PDGF alpha and beta receptors in basal cell carcinoma and in normal skin by immunohistochemistry and in situ hybridization. alpha and beta receptors were found in the specific stroma components of basal cell carcinoma, dermal hair papilla, and sweat glands, but not in the epithelial structures. The A and B chains, on the other hand, were mainly found in basal cell carcinoma cells, in hair matrix, and in sweat gland epithelium. This "appositional" expression of PDGF/PDGF receptor closely resembles that found in epithelial/mesenchymal structures during normal development. The findings also suggest that PDGF receptor expression is one of the characteristics of the specific stroma that is necessary for basal cell carcinoma growth.

Cellular and molecular composition of human skin in long-term xenografts on SCID mice

We report on the immunophenotypical characterization of adult human skin transplanted onto severe combined immunodeficient (SCID) mice. Thirty animals were followed for up to 12 months after receiving split-thickness xenografts, of which 28 were tolerated for the whole test period. Antigen mapping revealed an almost complete preservation of human cellular and extracellular tissue components in long-term transplants including skin immune cells (Langerhans-cells, macrophages, lymphocytes) and also parts of the engrafted endothelium. Hence, xenografts on SCID mice offer a versatile experimental tool for the in vivo study of both human skin immune cell function and endothelial cell-mediated interactions in an environment completely devoid of interferences by adoptive host immune response.

Human cell adhesion molecule uvomorulin is differentially expressed in various skin tumors

The cell adhesion molecule uvomorulin is important in cell recognition processes, both during tissue formation in embryonic development and in the maintenance of adult epithelia. In addition, uvomorulin appears to play a crucial role in carcinogenesis. Therefore, in the present study, the expression of uvomorulin in normal human skin and several benign and malignant proliferative skin lesions was evaluated by immunofluorescence microscopy using affinity purified antibodies. In normal human epidermis, basal and suprabasal keratinocytes showed a strong and homogeneous staining of the cell membrane. In contrast, uvomorulin expression was decreased in squamous cell, as well as in solid basal cell, carcinoma. Interestingly, solid basal cell carcinoma showed a dimorphic staining pattern with a reduced fluorescence of the inner cell layers and normal staining of the peripheral basal cells. In contrast, no such dimorphic staining pattern could be observed in squamous cell carcinoma, in which uvomorulin expression was homogeneously reduced. Decreased expression of uvomorulin was not specific for malignant skin lesions, since it could also be observed in condylomata acuminata. These studies demonstrate that human uvomorulin is differentially expressed in proliferative skin disorders, which may account at least in part for the differences observed in the clinical course between squamous cell and basal cell carcinoma.

Differential expression of laminin isoforms and beta 4 integrin epitopes in the basement membrane zone of normal human skin and basal cell carcinomas

The basement membrane zone biology of normal human skin and basal cell carcinomas was explored by indirect immunofluorescence with monoclonal antibodies recognizing five subunit polypeptides of three different laminin isoforms as well as the beta 4 integrin epitopes. The laminin antibodies were specific for A, B1, and B2 chains of classic laminin, for the M chain of merosin, or for the S chain in S-laminin. Immunostaining of normal human skin revealed a strong signal with antibodies for A, B1, and B2 chain epitopes. A weak immunosignal was detected with an anti-M chain antibody, whereas the S-chain epitopes were undetectable, even following pretreatment of sections with hyaluronidase. Thus, the laminin at the epidermal-dermal junction of normal human skin is primarily of the classic type, with some merosin molecules being present. The staining of six nodular basal cell carcinomas revealed the presence of A, B1, and B2 chain epitopes in a linear pattern, but, in contrast to normal skin, the antibody recognizing M-chain epitopes yielded a strong immunosignal, and S-chain epitopes could also be readily detected. Staining for beta 4 integrins, potential receptors for laminin, revealed a strong staining reaction in normal skin as well as in the superficial portions of the basal cell carcinoma. However, the immunofluorescence pattern in the deeper portions of the lesions was scattered and interrupted. Thus, altered composition of the basement membrane of nodular basal cell carcinomas with respect to laminin isoforms and their interactions with putative cell-surface receptors, the beta 4 integrins, may change the containment of the tumor islands, contributing to the local aggressive behavior of basal cell carcinomas.

Growth of human basal cell carcinomas transplanted to C57/Balb/C bgJ/bgJ nu/nu (beige-nude) mice

The purpose of this study was to measure growth parameters of transplanted basal cell carcinoma (BCC) to beige-nude mice during a 4-month observation time. Forty male beige-nude mice were transplanted with human BCC with our reported subcutaneous implantation technique. Initial volume and wet weight were determined for each tumor. The tumors were measured every 2 weeks by calipers with a final volume determined at 120 days, at which time the tumors were harvested, weighed, and processed for routine histology. Thirty-two tumor sites were positive for persistent tumor at harvest. Tumor volumes declined by an average of 51% and average tumor weight by 33%. There were increased numbers of mast cells surrounding the BCC tumor lobules. These results indicate that BCC can survive for 120 days in the beige-nude mouse.

Biology of basal cell carcinoma (Part I)

Basal cell carcinoma is the most common malignancy in humans. Although rarely metastatic, it is capable of significant local destruction and disfigurement. This two-part article reviews the current understanding of basal cell carcinoma biology. Part I examines significant clinical, histologic, and ultrastructural features that relate to invasive potential. Genetic characteristics, including tumor growth rate, chromosomal abnormalities, and oncogene presence, are discussed, and expression of important cell and matrix proteins, including keratin, fibronectin, and HLA antigens, are reviewed. Further topics to be explored in Part II include host immunologic responses, theories of pathogenesis, and valuable second-line therapeutic regimens for treatment of multiple cancers.

IgG subclasses in the serum and skin in subacute cutaneous lupus erythematosus and neonatal lupus erythematosus

IgG subclasses differ in their biologic and chemical properties, such as complement fixation, protein and cellular binding, and placental transfer. In this study, IgG subclasses of anti-Ro/SSA antibodies in subacute cutaneous lupus (SCLE) and neonatal lupus (NLE) are examined in the serum and in the skin. IgG subclasses in NLE beginning in utero (NLE-heart disease) are compared to subclasses in NLE beginning after birth (NLE-skin disease). Human skin was grafted onto athymic mice, mice were injected with one of eight anti-Ro/SSA maternal NLE sera (four heart block, four skin disease) or seven anti-Ro/SSA SCLE sera, and grafts were examined for IgG subclasses using monoclonal anti-human IgG subclass reagents in an immunofluorescent technique. Lesional skin was examined from four SCLE patients. IgG1 was the only IgG subclass detected in the grafts and skin lesions. IgG1 was the predominant anti-Ro/SSA IgG subclass detected in SCLE and NLE sera in an ELISA using a synthetic Ro/SSA polypeptide. These studies show that the maternal anti-Ro/SSA autoantibodies in NLE-heart disease sera are predominantly IgG1 and are therefore likely to be present in the fetus at the time of gestation, when heart block usually develops. Second, differences in the clinical presentations of NLE (in utero vs. postnatal disease) cannot be attributed to differences in anti-Ro/SSA IgG subclasses. Finally, the subclass bound in the skin in SCLE is IgG1, a subclass capable of mediating tissue injury via complement or cellular effectors.

Localization of integrin receptors for fibronectin, collagen, and laminin in human skin. Variable expression in basal and squamous cell carcinomas

VLA integrins in human skin were examined by indirect immunofluorescence utilizing antibodies recognizing the beta 1, alpha 2, alpha 3, or alpha 5 subunits. Staining of fetal, newborn, or adult skin with antibodies to beta 1, alpha 2, or alpha 3 subunits gave essentially similar staining patterns: intense staining was associated with the basal layer of the epidermis, hair follicles, and blood vessel walls. The alpha 5 subunit could be detected only in epidermis and the inner root sheath of hair follicles in fetal skin. In epidermis, the staining reaction for the beta 1 subunit was not only found in sites interfacing with the basement membrane zone, but also around the entire periphery of these cells. We speculate that these receptors might have previously unrecognized functions in cell-cell interactions or that these findings may suggest the presence of previously unrecognized ligands in the intercellular spaces of keratinocytes. Examination of nine nodular basal cell carcinomas revealed a prominent staining reaction with anti-beta 1 and anti-alpha 3 antibodies at the periphery of the tumor islands. In contrast, staining of five squamous cell carcinomas revealed either the absence of integrins or altered and variable expression. Thus, matrix components and their receptors may participate in modulation of growth, development, and organization of human skin.

Use of nude (athymic) mice for the study of hypertrophic scars and keloids: vascular continuity between mouse and implants

Hypertrophic scars and keloids appear to be unique to humans since animals are not known to form these lesions. Therefore, in an effort to develop an experimental model for their study, implants of these human lesions were made in nude (athymic) mice (nu/nu) in suprascapular subcutaneous pockets. The implants were recovered from 2 to 246 days. By histological and fine structural parameters all implants remained viable and their morphological character was maintained. Selected mice were injected with barium to confirm by microangiography vascular flow between mouse and implant. Hoechst stain for DNA, used to distinguish mouse cells from human cells, confirmed vascular anastamosis between host and implant: barium-filled vessels in the interior of the implant demonstrated human endothelial cells. Peripheral vascularization of the implant with minimal ingrowth of mouse vessels occurs during the first 8 days. Anastamosis probably occurs sometime before 16 days postimplantation, or earlier, depending upon the availability of patent microvessels in the implanted tissue. The presence of the implant does not appear to prompt a continuing vascular growth into or throughout the implant. The time frame of 16 days postimplantation should be taken into account when developing schemata of experimental or therapeutic modalities.

Basal cell carcinoma xenografts in nude mice: studies on epithelial differentiation and stromal relationships

Thirty-three basal cell carcinomas (BCC) were transplanted into athymic mice, and foci of tumour were identified in 17 grafts recovered after intervals of 2-5 months. Fifteen of these xenografts contained apparently normal differentiated epithelia, considered to derive from elements within the original tumours. The level of differentiation was very close in original and corresponding xenograft BCC. Morphologically recognizable 'specialized' stroma was present in some but not all xenografted BCC, and was also present in some grafts containing only differentiated elements. A monoclonal antibody specific to human type IV collagen showed intact epithelial and also vascular basement membranes within the graft. Surprisingly, mouse cells were found to line these vessels, and the stroma around normal and neoplastic epithelial islands was a mixture of mouse and human cells, with no consistent composition. These observations question the proposed dependence of BCC on its 'specialized' stroma.

Fibronectin gene expression by epithelial tumor cells in basal cell carcinoma: an immunocytochemical and in situ hybridization study

Previous observations have demonstrated that fibronectin is deposited in high abundance in basal cell carcinoma stroma. In this study, the nature of fibronectin and the site of its synthesis were explored in 10 basal cell carcinomas of the nodulo-ulcerative type by immunocytochemistry and in situ hybridization. First, simultaneous localization of epithelial tumor cell islands and fibronectin epitopes was carried out by double immunofluorescence staining with monoclonal anti-cytokeratin antibodies and polyclonal fibronectin antibodies, the latter recognizing both the cellular and plasma types of the protein. Large amounts of fibronectin were deposited in the basal cell carcinoma stroma, with the highest concentration present in the immediate proximity of the epithelial cell islands. Immunofluorescence with a monoclonal anti-fibronectin antibody, which is directed against the ED-domain of cellular fibronectin and does not recognize the plasma type of fibronectin, revealed essentially the same staining pattern as that obtained with the polyclonal anti-fibronectin antibody. This observation suggested that fibronectin in BCC was predominantly of the cellular type. Second, in situ hybridizations, utilizing a human fibronectin specific cDNA, demonstrated that the highest concentration of fibronectin mRNA was found in the most peripheral cell layer of the epithelial tumor islands. The presence of fibronectin mRNAs in the tumor cells of the central regions of the islands, as well as within occasional stromal cells, was also noted. Thus, two lines of evidence suggest that the epithelial tumor cells are predominantly responsible for the synthesis and deposition of fibronectin in basal cell carcinoma. The presence of fibronectin may explain the characteristic biologic behavior of basal cell carcinomas, including low degree of metastatic potential and local destructive nature of the tumors.

Fibronectin extracellular matrix assembly by human epidermal cells implanted into athymic mice

Human epidermal keratinocytes reorganize into epidermal inclusion cysts when implanted subcutaneously into athymic mice. During the organization and maturation of these cysts, fibronectin accumulates in the surrounding extracellular matrix and the basement membrane proteins bullous pemphigoid antigen and laminin appear at the epithelial-stromal interface. The sequence in which these proteins appear parallels that seen during reepithelialization of a skin wound in vivo. Fibronectin appears during aggregation of the epidermal cells and persists in the area surrounding the cysts for at least 7 days. Bullous pemphigoid antigen and laminin appear later (by 4 and 7 days, respectively) and ultimately become organized into a continuous band at the periphery of the cyst. This distribution of bullous pemphigoid antigen and laminin at the stromal-epithelial interface persists at least 5 weeks, suggesting that the implanted epidermal cells are capable of developing and maintaining a stable basement membrane zone. Fibronectin, which is abundant in the matrix adjacent to the epidermal cysts and in the surrounding stroma during cyst organization and maturation, diminishes to undetectable levels by 5 weeks. While much of the fibronectin derives from the host tissues, species-specific antibodies to human fibronectin reveal that at least a portion of this protein is synthesized and deposited by the implanted epidermal cells.

Transplantation of human basal cell carcinoma to C57/BALB/C bgJ/bgJ-nu/nu (beige-nude) mouse

The purpose of this study was to evaluate the transplantation of BCC to the C57/BALB/C bgJ/bgJ-nu/nu (beige-nude) mouse. This animal has two gene defects which are expressed as impairment of natural killer cells (NK cells) as well as the absence of a thymus. The results demonstrate that human BCC can be successfully transplanted to the C57 beige-nude mouse without the need for supplemental immunosuppression. It may be that the impairment of NK cell activity in the beige-nude mouse model plays a significant role in tumor transplantation.

Production of fibronectin by epithelium in a skin equivalent

Although human keratinocytes in vitro have been shown to produce fibronectin, whether keratinocytes can contribute fibronectin to the dermal-epidermal junction or wound matrix is unknown. In order to approach this problem experimentally, we used the "skin equivalent" model composed of a native collagen gel populated with cultured fibroblasts and covered by cultured keratinocytes. By using bovine fibroblasts to populate the gel, fetal bovine serum in the culture medium, and human keratinocytes to form the epithelium, we were able to be certain that any human fibronectin produced in the culture was synthesized by the keratinocytes. A monoclonal antibody to fibronectin was found to recognize human but not bovine fibronectin. When the skin equivalent was stained by indirect immunofluorescence with antifibronectin, fibronectin was visible as an intensely staining band at the dermal-epidermal junction. In sections in which the dermis and epidermis had separated, the staining was usually limited to the dermal aspect of the skin equivalent. The results indicate that epithelium can contribute fibronectin to the dermal-epidermal junction and suggest that dermal staining in skin sections may originate from the epidermis. Since the developing skin equivalent has a rapidly growing epithelium and simulates a healing wound, contribution of fibronectin by the epithelium, in addition to that possibly contributed by serum and fibroblasts, may be of importance in wound healing.