Alterations of class I HLA genes in human colon cancers

Increased tumorigenicity after differentiation of colon cancer cell line: absence of association with mucin synthesis

BACKGROUND/AIMS

Postconfluence differentiation followed by a decrease in mucin synthesis has been described for the colonic adenocarcinoma cell line Caco-2. Because the onset of differentiation usually heralds the end of proliferation, we expected Caco-2 would be more tumorigenic in the exponential phase. Thus, we compared tumorigenicity, clonigenicity, and mucin synthesis in the exponential and stationary growth phases.

METHODS

We estimated mucin synthesis in Caco-2 cells by measuring the amount of high-molecular-weight [3H]glucosamine-labeled glycoprotein released into the culture medium and in the cytosolic fraction. Colony forming efficiency in soft agar and tumorigenicity in nude mice were assessed.

RESULTS

Cells in the exponential phase synthesized significantly more mucin compared with stationary phase cells. Pretreatment with benzyl-GalNAc reduced production in both phases but did not change clonigenicity. Colonies did not grow from cells seeded in the exponential phase. The average weight of xenografts raised from postconfluence cells was twice that of xenografts raised from cells in the exponential phase.

CONCLUSIONS

Neither exponential cell growth nor increased mucin production predicts clonigenicity and tumorigenicity. It is speculated that a stable process takes place in Caco-2 cells after confluence which makes them more clonigenic in vitro and enhances tumor growth in vivo.

MHC antigen expression in human oral squamous carcinoma cell lines

This study quantified the constitutive and interferon-gamma (IFN-gamma) stimulated expression of MHC class I (HLA-ABC and beta 2 microglobulin) and class II antigens (HLA-DR, -DP, -DQ) on normal and malignant oral keratinocytes using radioimmunoassay and immunocytochemical techniques. Normal keratinocytes and three of four malignant cell lines (H103, H157, H314) expressed MHC class I antigens constitutively; IFN-gamma increased MHC class I expression with significant changes in normals, H157 and H314. Normal keratinocytes expressed significantly more constitutive MHC class I antigens than H103 and H157 and significantly more IFN-gamma stimulated MHC class I antigens than H103, H157 and H314. MHC class II antigens predominantly were not expressed constitutively on normals, H103 and H157 but, in H314, HLA-DR, -DP and -DQ antigens were demonstrated on 35, 11 and 5 per cent of cells, respectively, and resulted in a non-coordinated pattern of expression (HLA-DR greater than -DP = -DQ). IFN-gamma induced HLA-DR on normals, H103 and H157, whilst HLA-DP and -DQ remained undetectable. In H314, IFN-gamma enhanced HLA-DR, -DP and -DQ (significant increase of HLA-DQ) but the interrelationship between these antigens was maintained (HLA-DR greater than -DP = -DQ). Normal keratinocytes expressed significantly more IFN-gamma stimulated HLA-DR than H103 and H157 but significantly less HLA-DR than H314 under similar experimental conditions. One oral malignant cell line (H191) did not express MHC class I and MHC class II antigens either constitutively or in response to IFN-gamma. The results demonstrate aberrant patterns of MHC expression (absence, enhanced, diminished) in the different malignant oral keratinocyte cell lines.

MHC antigens on human tumors

MHC class I antigens on tumor cells are expected to play an important role because they regulate the sensitivity to antitumoral immunological mechanisms. Overall or selective qualitative or quantitative changes in MHC molecules may modify the recognition of tumor cells by components of the immune system. It seems clear that MHC antigen expression on tumor cells is important in triggering the immune response by autologous lymphocytes. A deficiency in or lack of MHC class I antigens may have profound effects on T and NK cell activity. In experimental models, variation in the expression of MHC class I antigens has been shown to exert a decisive influence on local tumor growth and metastasis. However, there is little information about the influence of selective loss of individual locus products on the behavior of human tumor cells. Total and selective HLA losses have been found in a large variety of tumors, and different mechanisms have been shown to be responsible for these changes. In some examples, HLA losses are associated with a poor degree of tissue differentiation and poor prognosis. In other tumors, however, no such association has been found. We do not know whether HLA class II expression in neoplastic cells plays an immunological role, although, with the exception of melanoma, HLA class II expression is more frequently observed in tumors with a more favorable prognosis. Finally, there is no doubt that we need to learn more about how to manipulate the expression of MHC class I and II antigens in human tumors, in order to stimulate immune response.(ABSTRACT TRUNCATED AT 250 WORDS)

Double minute chromosomes and a homogeneously staining chromosome region in C3H10T1/2 murine cells transformed "in vitro" by proton radiation

Four foci (type II or type III) of transformed cells, isolated from the murine line C3H10T1/2 after exposure to proton radiations, were expanded and cytogenetically examined. While the overall numerical chromosome distributions were similar, there were some differences between the various cell lines with regard to the presence and frequency of specific-marker chromosomes and to the colony-forming efficiency in soft-agarose medium. No association between any of these markers and the transformed phenotype could be established. However, in the line F4, derived from a type II focus, numerous double-minute chromosomes (DM) were observed after passage 22, and the phenomenon became more pronounced in the subclone C2. The finding of DMs in radiation-transformed cells is unusual. The DMs were observed in long-term subcultures, and in one of them they were partially replaced by a homogeneously staining chromosome region (HSR). DNAs from transformed cells of the line F4 and subclone C2 was digested with restriction enzymes and analyzed by Southern blotting with probes for seven oncogenes commonly amplified in cancer cells (c-myc, N-myc, N-ras, Ki-ras, Ha-ras, c-myb, c-abl) and with probes for the mouse MHC class I region. None of the regions tested was structurally altered or amplified in these transformed cells. The origin of the genetic material carried by DMs or homogeneously staining intrachromosomal regions (HSR) in cells of the line F4 and subclone C2, where it is believed to provide a selective advantage for in vitro growth, remains unknown.

HLA class I gene expression on human primary tumours and autologous metastases: demonstration of selective losses of HLA antigens on colorectal, gastric and laryngeal carcinomas

The expression of HLA class I antigens was studied in 99 primary tumour (colorectal, gastric and laryngeal carcinomas) and 57 autologous metastases using immunohistological techniques and monoclonal antibodies against class I monomorphic determinants, HLA-B isotypic determinants and HLA polymorphic determinants. Fourteen per cent of colorectal, 9.6% of gastric and 20% of laryngeal carcinomas completely lacked class I molecules. Selective losses of HLA-B antigens were also detected in 8.8, 3.4 and 5.8% of these tumours respectively. Taking into account complete and selective loss of HLA-B the average alteration in the class I molecules expression totalled 21%. The comparison of class I expression between primary tumours and autologous metastases showed differences in 24% of the patients. These differences consisted mainly in a decrease of class I expression by metastases. Nevertheless, four types of divergence were detected in laryngeal carcinomas, namely: +/-, +/+, -/+, -/-. In addition, a clear correlation between degree of differentiation and class I expression was observed in laryngeal tumours. Finally, when class I gene RFLPs were compared with DNA from 15 tumours and autologous normal mucosa or peripheral lymphocytes, no differences were detected between these samples.

The relationship between MHC antigen expression and metastasis

From the studies summarized here a complex picture of the role played by MHC products in determining tumorigenicity and metastasis is emerging. In order to be able to understand this relationship better, it is necessary to consider several factors. 1. Each tumor system or neoplastic tissue is unique, and its behavior reflects the influence of cell-specific characteristics, as well as its ability to modulate other cells and tissues--including cells belonging to the immune system--and also to be modulated by other cells and soluble factors. 2. Since metastasis formation is a multistep process in which only small subpopulations of tumor cells with complex and defined phenotypes are able to colonize secondary tissues, elimination of even one single phenotypic component of this structured process can easily reverse the metastatic capacity of the cells. Acquisition of metastatic ability, on the other hand, would be a more difficult task, since any new characteristic expressed by the cells or induced experimentally, such as gene transfection or results of IFN treatment, must be expressed in a temporal manner and in concert with other cellular characteristics. Therefore, an experimental protocol measuring a specific element in determining metastasis can easily produce conflicting results, depending on the type of cells and genetic background of the host studied. 3. The level of specific MHC products on tumor cells is one among many other cell characteristics that may determine the metastatic potential of cells. Moreover, each of the class 1 MHC products, and the relationship among them, including other than the classical K, L, or D products (Brickell et al., 1983), should be regarded as independent entities, with possible different regulatory roles in cell-cell recognition, in a general sense, which may be involved in determining invasiveness and homing as well as recognition by the immune system. 4. Both specific T-cell and nonspecific natural mediated immunity (which is much less understood) are involved in the selection of the metastatic cell population. 5. Immunogenicity of tumors is not necessarily determined by high levels of MHC antigen expression; it is also dependent on the level of TSA. Thus, immunoselection mediated by T lymphocytes during metastasis formation could be directed against both MHC and TSA antigens. Therefore, low expression of MHC antigens by metastatic cells as a result of immunoselection is not always observed.(ABSTRACT TRUNCATED AT 400 WORDS)