Defective HLA class II expression in a regulatory mutant is partially complemented by activated ras oncogenes

Induction of intercellular adhesion molecule 1 and class II histocompatibility antigens in colorectal tumour cells expressing activated ras oncogene

Aims-To determine whether there is a correlation between activation of the ras oncogene and the induction of MHC class II antigens and intercellular adhesion molecule 1 (ICAM-1) by interferon-gamma (IFN-gamma).Methods-Expression of class II antigens, ICAM-1 and intracellular ras oncoprotein (p21) in established colorectal cell lines and short term cultures of primary colorectal tumour cells was determined by flow cytometry and mutation in the ras gene by sequencing of amplified segments of the gene.Results-The cell lines showed a variation in their modulation of MHC class II antigens and ICAM-1, ranging from no induction to a 98-fold increase in class II antigen expression in the HT29 cell line. Previous work indicated that most tumours could not be induced to express class II antigens. Four of the five least inducible lines either contained mutant ras or highly expressed the oncoprotein. The four highly inducible cell lines all contained non-mutant ras. Of the 21 tumours studied in primary culture, 10 were inducible, one of which contained mutant ras. Of the remaining non-inducible tumours, four were mutant.Conclusions-Correlations between ras activation and failure to respond to IFN-gamma could not be shown to be significant. Therefore, ras activation, and concomitant subversion of intracellular signalling pathways, is probably not the major determinant in failure to activate class II antigens and ICAM-1.

Activation of MHC class I, II, and CD40 gene expression by histone deacetylase inhibitors

Epigenetic mechanisms are involved in regulating chromatin structure and gene expression through repression. In this study, we show that histone deacetylase inhibitors (DAIs) that alter the acetylation of histones in chromatin enhance the expression of several genes on tumor cells including: MHC class I, II, and the costimulatory molecule CD40. Enhanced transcription results in a significant increase in protein expression on the tumor cell surface, and expression can be elicited on some tumors that are unresponsive to IFN-gamma. The magnitude of induction of these genes cannot be explained by the effect of DAIs on the cell cycle or enhanced apoptosis. Induction of class II genes by DAIs was accompanied by activation of a repressed class II transactivator gene in a plasma cell tumor but, in several other tumor cell lines, class II was induced in the apparent absence of class II transactivator transcripts. These findings also suggest that the abnormalities observed in some tumors in the expression of genes critical to tumor immunity may result from epigenetic alterations in chromatin and gene regulation in addition to well-established mutational mechanisms.

Sequential changes in MHC antigen expression induced by the v-Ki-ras oncogene

A series of early-passage cell lines were transformed with the v-Ki-ras oncogene with the aim of examining the effect of an activated ras gene on the ability of these cells to express major histocompatibility complex (MHC) antigens. These cell lines were found to undergo multiple phenotypic changes upon transformation and subsequent proliferation. At early passage, the predominant effect of ras was an increased ability to express class II antigens when induced with interferon gamma (IFN gamma). For class I antigens, maximum levels of expression induced with IFN gamma were largely unaffected, however, decreased sensitivity to induction with this lymphokine was noted. With subsequent in vitro or in vivo passage, both class I and class II antigen inducibility was attenuated. The latter phenotypic change was found to be transferable by coculture, implicating a soluble IFN gamma antagonist. Conditioned media from ras-transformed cells treated to activate their latent transforming growth factor beta (TGF beta) content mediated similar changes in MHC antigen inducibility, suggesting that TGF beta may be involved in modulating MHC antigen expression in ras-transformed cells.

Molecular genetics of human malignant melanoma

Due to a variety of known and unknown control mechanisms, the human genome is remarkably stable when compared to most other species. The long latency periods of most solid tumors, during which the cell undergoes malignant transformation, are presumably due to this stability. The molecular basis responsible for the induction of genetic instability and the resultant biological characteristics manifest in tumor populations is not well understood. The discovery of both oncogenes and tumor suppressor genes, however, has placed the phenomenon of human genome stability on a more solid conceptual footing. These types of genes clearly place multiple barriers to oncogenic transformation, and traversing these barriers apparently requires both time and the accumulation of genetic defects that cannot be corrected. The evolution of neoplasias can, therefore, be predicted to be due to: (1) consistent and progressive loss of tumor suppressor genes; (2) gene amplification, resulting in the over-expression of proteins that aid in tumor progression; (3) gene mutation, which alters the orderly biochemistry of the normal cell; (4) genes that allow a cell like the melanocyte to escape the confining nature of the epidermis and to invade through the dermis into the circulatory and lymphatic systems in order to disseminate itself to other organs (e.g., proteolytic enzymes, enzyme inhibitors, integrins, metastases genes, chemotactic factors etc.); (5) factors, perhaps such as TGF beta 2, that may impact negatively on MHC antigens and confuse host defense mechanisms; and (6) S.O.S.-type genes, which may be expressed as a direct response to the accumulating damage in an attempt to correct the damage, but that may then become part of the problem instead of the solution. The extraordinary plasticity and instability of the genome of a melanoma cell suggests an inordinate amount of genetic flux. In addition to activating and inactivating various genes, this constant shuffling and rearranging of the genome in neoplasms such as MM may be constantly altering gene dose. Cytogenetic and molecular biological studies have been the Rosetta stone for understanding the etiological relevant genetic events in human cancers. Genetic alterations fundamental to the pathology of MM have begun to be defined. Studies designed to understand these perturbations at the biochemical and organismic level are underway.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of HLA-A,B,C, beta 2-microglobulin (beta 2m), HLA-DR, -DP, -DQ and of HLA-D-associated invariant chain (Ii) in soft-tissue tumors

Non-neoplastic mesenchymal cells, along with 33 benign and 87 malignant soft-tissue tumors (STT) were examined for expression of HLA-A,B,C, beta 2-microglobulin (beta 2m), HLA-DR, -DP, and -DQ molecules and the HLA-D associated invariant chain (Ii). Serial frozen sections were immunostained using monoclonal antibodies (MAbs) to monomorphic framework determinants of HLA sublocus products, beta 2m and Ii, and to CD53, a recently defined broadly distributed pan-leucocyte molecule. Compared with the normal state, an induction/neo-expression of HLA-A,B,C/beta 2m was found in a considerable number of tumors of muscle, peripheral nerve, cartilage-forming, adipose, and vascular tissues. Conversely, some tumors of fibrous origin and of autonomic ganglia showed an abnormal abrogation/loss of HLA-A,B,C/beta 2m with respect to their cells of origin. Small, round tumor cells present in various types of STT exhibited a heterogenous pattern of expression of these molecules with a preponderance of HLA-A, B,C/beta 2m-negativity. HLA-D/Ii determinants were rarely detectable in STT. Besides their expression in some fibrohistiocytic tumors, they were only occasionally found in tumors of smooth-muscle, peripheral-nerve and vascular origin as well as in one clear-cell sarcoma. In all tumors but one, there was no microtopographic association between HLA-D/Ii-positive tumor cells and inflammatory cells. CD53 allowed discrimination between dendritic interstitial cells (DIC) and neoplastic cells and additionally revealed that, in contrast to other solid tumors, STT are generally characterized by an extreme scarcity of lymphohistiocytic infiltrates. Our data indicate that, aside from very rare exceptions, aberrant induction or abrogation of MHC molecules in STT occurs in the absence of lymphohistiocytic stromal infiltrates, suggesting that these alterations might not be a consequence of local cytokine effects.

mXBP/CRE-BP2 and c-Jun form a complex which binds to the cyclic AMP, but not to the 12-O-tetradecanoylphorbol-13-acetate, response element

Proto-oncogene products c-Fos and c-Jun form a complex which binds with high affinity to the 12-O-tetradecanoylphorbol-13-acetate (TPA) response DNA element and which stimulates transcription of phorbol ester- inducible genes. We have previously identified, by screening a lambda gt11 expression library, murine protein mXBP, which binds to a sequence which overlaps the 3' end of the murine class II major histocompatibility complex A alpha gene X box, a conserved transcription element found upstream of all class II genes. Here, we demonstrate that the target sequence for mXBP is a consensus cyclic AMP response element (CRE). mXBP is a member of the leucine zipper family of DNA-binding proteins and has significant homology to oncoproteins c-Fos and c-Jun. The inferred amino acid sequence of mXBP shows near identity to human CRE-BP1, except it does not contain an internal proline-rich domain. Immunoprecipitation and glutaraldehyde cross-linking studies show that mXBP/CRE-BP2 can form a complex with c-Jun. Complex formation is dependent on intact leucine zipper domains in both proteins. mXBP-c-Jun complexes can coexist with c-Fos-c-Jun complexes and can bind with high affinity to CRE, but not to TPA response DNA element, sequences. These results suggest that changes in the expression of mXBP/CRE-BP2, c-Fos, and c-Jun, which alter the ratio of mXBP-c-Jun to c-Fos-c-Jun complexes, would affect the relative expression of cyclic AMP and phorbol ester-responsive genes. This provides support for a combinatorial model of gene regulation, whereby protein-protein interactions which alter the DNA binding specificity of protein complexes can expand the flexibility of cellular transcriptional responses.

mXBP/CRE-BP2 and c-Jun form a complex which binds to the cyclic AMP, but not to the 12-O-tetradecanoylphorbol-13-acetate, response element

Proto-oncogene products c-Fos and c-Jun form a complex which binds with high affinity to the 12-O-tetradecanoylphorbol-13-acetate (TPA) response DNA element and which stimulates transcription of phorbol ester- inducible genes. We have previously identified, by screening a lambda gt11 expression library, murine protein mXBP, which binds to a sequence which overlaps the 3' end of the murine class II major histocompatibility complex A alpha gene X box, a conserved transcription element found upstream of all class II genes. Here, we demonstrate that the target sequence for mXBP is a consensus cyclic AMP response element (CRE). mXBP is a member of the leucine zipper family of DNA-binding proteins and has significant homology to oncoproteins c-Fos and c-Jun. The inferred amino acid sequence of mXBP shows near identity to human CRE-BP1, except it does not contain an internal proline-rich domain. Immunoprecipitation and glutaraldehyde cross-linking studies show that mXBP/CRE-BP2 can form a complex with c-Jun. Complex formation is dependent on intact leucine zipper domains in both proteins. mXBP-c-Jun complexes can coexist with c-Fos-c-Jun complexes and can bind with high affinity to CRE, but not to TPA response DNA element, sequences. These results suggest that changes in the expression of mXBP/CRE-BP2, c-Fos, and c-Jun, which alter the ratio of mXBP-c-Jun to c-Fos-c-Jun complexes, would affect the relative expression of cyclic AMP and phorbol ester-responsive genes. This provides support for a combinatorial model of gene regulation, whereby protein-protein interactions which alter the DNA binding specificity of protein complexes can expand the flexibility of cellular transcriptional responses.

Recurrent mutation of immunoglobulin and c-myc genes and differential expression of cell surface antigens occur in variant cell lines derived from a Burkitt lymphoma

The phenotypic and molecular genetic characteristics of 4 variant sublines of the Burkitt lymphoma cell line Namalwa have been examined. The sublines are DNA-fingerprint-identical and derived from a monoclonal tumour, as shown by a rearrangement of the T-cell-receptor beta-chain gene common to the 4 sublines. There is non-co-ordinate expression of MHC class-I MHC class-II, surface immunoglobulin and a number of antigens recognized by CD MAbs on the different sublines. These different phenotypes of the cells are reminiscent of B cells arrested in varying states of cellular maturity. On Southern blots there are different patterns of restriction fragments hybridizing with Ig heavy- and light-chain gene probes among the sublines, indicating that multiple rearrangements or mutations of Ig genes have occurred in the cells. Different patterns of hybridizing fragments among the sublines were also found by using c-myc probes, implying the existence of different mutations of the c-myc locus. The c-myc mutation found in one of the sublines mapped to the 5' flanking sequence and in another 3' to the c-myc locus. Using the J17BS8 probe, which detects a restriction fragment length polymorphism in the 3' flanking region of the c-myc gene, a 4-fold variation in the gene copy number among the subline was found and one of the sublines was shown to be hemizygous for c-myc. Examination of DNA from early cultures of Namalwa cells showed that the alternations in Ig and c-myc structure had occurred on prolonged culture of the cells.

Transcriptional enhancement of the human gene encoding for a melanoma-associated antigen (ME491) in association with malignant transformation

A cloned DNA fragment (lambda R31) containing the human gene for melanoma-associated ME491 antigen was transfected into mouse fibroblast cell lines and the antigen expression was studied. Our preliminary observation of higher expression of the antigen in more malignant Ltk- cells and weaker expression in less malignant NIH3T3 cells tempted us to investigate the antigen expression in Harvey(H)-ras-transformed NIH3T3 cells. It was observed that malignant transformation of the lambda R31-transfected NIH3T3 cells by H-ras oncogene enhanced the antigen expression to some extent. Northern blot analysis suggested that the enhancement occurred at the transcriptional level. Nucleotide sequence analysis of the 5'-regulatory region of the ME491 antigen gene in lambda R31 identified a number of consensus sequence motifs for binding of transcription factors such as Sp1, AP-2 and polyomavirus enhancer binding proteins 2 and 3. A consensus sequence motif for binding of AP-1, known as a ras-responsive element, was not found in that region. The significance and possible involvement of the transcription factors in the enhancement of ME491 antigen expression are discussed.

ras mutations in human leukemia and related disorders

The clinical association of an increased incidence of acute myelogenous leukemia (AML) with previous chemoradiotherapy, the detection of specific karyotypic changes in these secondary (therapy-induced) cases of AML and the discovery of increasing levels of oncogene-specific RNA in leukemia cells suggest that one potential site of action of environmental agents might be the proto-oncogenes in human hematopoietic stem cells. The location of human proto-oncogenes at the sites of chromosome breaks and/or translocations in cells from some patients with leukemia or lymphoma is a striking observation. These data stimulated research into the mechanism of activation of specific oncogenes that change the biology of human hematopoietic cells. Recent investigations have focused upon several areas that might alter cell biology including: 1) translocation and/or inversion of chromosome fragments containing a proto-oncogene to a location where other gene sequences can stimulate oncogene activation, 2) replication of copy number of proto-oncogenes or increased transcriptional activity and 3) point mutation in proto-oncogenes leading to a structurally altered protein. The third area of research has recently received significant attention with respect to the potential role of three ras genes (c-Harvey-ras, c-Kirsten-ras and N-ras) in human leukemias and myelodysplastic syndromes. Recent studies have proposed a model for leukemogenic transformation of human hematopoietic cells by the product of a mutated ras oncogene. Mutations at codons 12, 13 or 61 of the first exon of its 4.7 Kb of DNA (for c-Ha-ras) have been described. Other data revealing an absence of such mutations in the ras genes of many human leukemias and the absence of detectable transcription of ras genes in many alkylating agent-associated cases of AML, suggest that while ras mutations may be involved in some settings, there are probably multiple genetic pathways to leukemogenic transformation of human hematopoietic cells.

HLA class II mRNA accumulation by activated human T cells following growth in conditioned medium

The expression of HLA Class II beta genes by seven CD4- or CD8-positive T cell clones grown in conditioned medium was examined on the mRNA and cell surface levels. Monoclonal antibodies directed against Class II glycoproteins demonstrated the presence of these molecules on the cell surface. In addition, Northern blot analysis demonstrated that cDNA probes for the DR, DP, and DQ beta genes hybridized to mRNA isolated from each clone. Because we were interested in differences in expression of relative levels of DR, DQ and DP, mRNA isolated from the clones was quantified by means of densitometry. Our results demonstrated that different ratios of DR, DQ and DP beta chain messages were expressed by the clones. Subsequent studies established the kinetics of the accumulation of DR beta mRNA messages by T cells during culture and showed that it could be regulated by factors contained within conditioned medium. Our results confirm that the accumulation of Class II mRNA following growth of T cells in conditioned medium appears to be a general feature.

Alternative splicing of HLA-DQB transcripts and secretion of HLA-DQ beta-chain proteins: allelic polymorphism in splicing and polyadenylylation sites

HLA class II antigens are highly polymorphic cell-surface proteins involved in initiation and regulation of the immune response. Allelic sequence variation primarily affects the structure of the first external domains of alpha and beta component chains. Here we provide evidence for other types of allelic polymorphism for the genes encoding these chains. Sequences of two cDNA clones corresponding to HLA-DQB mRNAs from an HLA-homozygous cell line exhibit both alternative splicing and read-through of polyadenylylation. Furthermore, alternative splicing that deletes the transmembrane exon is associated with only a subset of HLA-DQB alleles, while the polyadenylylation-site read-through is found in a larger subset. This suggest that polymorphic cis-acting elements within the HLA-DQB gene control both processing steps. Proteins, presumably encoded by alternatively spliced mRNAs lacking transmembrane exons, are immunoprecipitated with a monomorphic monoclonal antibody directed against HLA-DQ. These proteins are found in supernatants of cultured cell lines for which secretion is predicted, but not in those of cell lines that do not contain alternatively spliced mRNAs.

Conserved upstream sequences of human class II major histocompatibility genes enhance expression of class II genes in wild-type but not mutant B-cell lines

Class II major histocompatibility genes contain a conserved upstream sequence (CUS) that is important in the expression of these genes. This region has been divided into two major elements, the X box and the Y box. The ability of these elements to mediate transcription of a heterologous promoter was assayed upon transfection into a B-cell line (Raji), a class II-specific trans-acting factor-deficient B-cell line (RJ2.2.5 cells), and a T-cell line (Jurkat). The results showed that the X box element was responsible for directing tissue-specific expression when Raji cells were compared to Jurkat cells. The X box could not direct expression of the heterologous promoter in the trans-acting factor-deficient cell line, indicating that the X box is an ultimate target of the missing or defective factor in the RJ2.2.5 cell line. The Y box directed an equal but extremely low level of transcription in this system in both the mutant and wild-type B-cell lines, suggesting that this element is not involved in B-cell expression or as a target of the mutant factor.

An enhancer factor defect in a mutant Burkitt lymphoma cell line

RJ 2.2.5 is an immunoselected mutant of the Burkitt lymphoma line Raji. It fails to display MHC class II antigens at the cell surface due to a transcriptional defect. We have identified the function of a regulatory factor that is defective in RJ 2.2.5 cells; this factor is absolutely required for the activity of an MHC class II gene enhancer.