Rearranged immunoglobulin light chain genes as minimal residual disease markers in intermediate- and high-grade malignant B cell non-Hodgkin's lymphoma

Minimal residual disease (MRD) detection in B cell non-Hodgkin's lymphoma (NHL) patients has been shown to be possible using the rearranged heavy (IgH) chain gene as a tumor marker. To explore a second independent tumor marker, we used specific PCR primer sets to identify tumor-specific rearranged Ig light chain (IgL) genes. Rearranged IgL genes were amplified from lymphoma DNA by multiplex PCR using separate primer sets for the Igkappa and the Iglambda genes. They were considered to be of tumor origin if they were monoclonal, and if the same rearrangement was isolated from at least two independent PCR products. From 12 out of 13 intermediate- and high-grade malignant NHL, PCR products could be obtained with IgL specific primers. PCR products from five NHL were studied in detail by cloning and sequencing. The rearranged IgL genes showed 85-100% homology with their closest germ line counterparts. Intraclonal IgL sequence heterogeneity was studied in five lymphomas and detected in only one. Minimal disease was studied in three patients by PCR, followed by Southern hybridization of the PCR product with a lymphoma-specific oligonucleotide probe, which allowed for detection of lymphoma DNA following 1000-fold dilution. Blood samples from one patient, who is in long-term clinical remission, were negative for the lymphoma-specific rearranged Igkappa gene. In the second patient the rearranged Iglambda gene was detected during the first clinical remission, that was followed by a nodal relapse, but not during the second remission, that has been stable for almost 3 years now. The third patient was negative for the rearranged Iglambda gene in blood samples up to 102 months after diagnosis. Circulating lymphoma cells were detected in blood and bone marrow samples which were negative by morphological and immunological criteria. Our studies show that the rearranged IgL gene can be used as a second independent tumor marker in intermediate- and high-grade malignant NHL.

Expression of differentiation-related genes in colorectal cancer: possible implications for prognosis

Although differentiation grade is an important prognostic factor for colorectal tumors, its usefulness is limited since its predictive value for tumor behavior is not very significant. This might be related to the subjective nature of histological assessment of differentiation grade, which allows the distinction of only three grades, and with limited reproducibility. Characterization of the differentiation process at the biochemical level may improve our understanding of normal and malignant differentiation, and is expected to provide molecular markers with higher discriminative potential than histomorphology. Several studies have compared gene expression in undifferentiated and differentiated colon carcinoma cells, and many differentially expressed genes have been identified. Some of these, including HLA class I, nucleophosmin, adenylosuccinate lyase, alpha-tubulin, and a novel gene designated Drg1, were found to be expressed at different levels in neoplastic as compared to normal tissue. In this review the rationale, implementation, and results of this approach are discussed, as well as the characteristics of two novel differentially expressed genes, ICT1 (previously named DS-1) and Drg1.

Detection of minimal disease using rearranged immunoglobulin heavy chain genes from intermediate- and high-grade malignant B cell non-Hodgkins lymphoma

Rearranged immunoglobulin heavy chain (IgH) genes provide unique clonal markers for B cells. Since amplification of the rearranged gene by polymerase chain reaction (PCR) and demonstrating that the amplified sequence is indeed derived from tumor cells is more problematic in non-Hodgkin's lymphoma (NHL) than in other B cell malignancies, we used a comprehensive PCR primer set and formulated stringent selection criteria to identify tumor-specific rearranged IgH genes. Rearranged IgH genes amplified from lymphoma DNA were considered to be of tumor origin if they were monoclonal, and if the same rearrangement was amplified with at least two independent VH-specific primers. From 11 of 13 (85%) intermediate- and high-grade malignant NHL, IgH rearrangements were isolated. Intraclonal IgH sequence heterogeneity was studied in four lymphomas, and detected in two of them. PCR using a lymphoma-specific primer followed by Southern hybridization of PCR product with a specific probe allowed detection of lymphoma DNA after 10,000-fold dilution. Circulating lymphoma cells were detected in patient blood and bone marrow samples which were negative by morphological and immunological criteria. Thus, also in intermediate- and high-grade malignant lymphoma, sensitive minimal disease detection using the rearranged IgH gene as a marker appears feasible.

A novel gene which is up-regulated during colon epithelial cell differentiation and down-regulated in colorectal neoplasms

To identify new molecular markers for differentiation of normal and neoplastic colon epithelium, we have studied changes in gene expression during the in vitro differentiation of the HT29-D4 colon carcinoma cell line. Using a modified differential display procedure, we cloned a novel cDNA, designated differentiation-related gene 1 (Drg1). Drg1 mRNA has a length of approximately 3 kb and is induced approximately 20-fold during in vitro differentiation of the colon carcinoma cell lines HT29-D4 and Caco-2. The absence of Drg1 induction in growth-inhibited A431 epidermoid carcinoma cells indicates that Drg1 up-regulation in colon carcinoma cells is not a result of decreased proliferation. The Drg1 cDNA contains an open-reading frame of 1182 bp that encodes a protein with a predicted molecular weight of 43 kd. Drg1 mRNA is expressed most prominently in placental membranes and prostate, kidney, small intestine, and ovary tissues. Compared to normal colon mucosa, Drg1 mRNA expression is decreased in colon adenomas and adenocarcinomas. An antiserum raised against recombinant Drg1 protein detected a band of the expected size in Western blots. Immunohistochemistry showed that in normal colon Drg1 protein is expressed in the cytoplasm and basolateral membranes of surface epithelial cells that border the gut lumen, indicating that Drg1 protein is expressed late during differentiation, just before apoptosis and shedding of cells into the colon lumen.

Identification of mRNAs that show modulated expression during colon carcinoma cell differentiation

To investigate the working hypotheses that stem cells or their early descendants are prime targets for neoplastic transformation, and that the degree to which a neoplasm retains the immature phenotype is an important determinant of tumor aggressiveness, we have identified several mRNAs that are downregulated during the in vitro differentiation of HT29-D4 colon carcinoma cells. These genes include heat-shock cognate protein Hsc70, adenylosuccinate lyase, B23/nucleophosmin, alpha-tubulin, and a novel gene designated DS-1. The DS-1 mRNA has a length of approximately 0.9 kb and is downregulated 4.7-fold upon differentiation. From the DS-1 cDNA, a protein of 206 amino acids with a molecular mass of 24 kDa and an isoelectric point of 10.9 can be deduced. An antiserum directed against a synthetic peptide detected a minor band of the expected size in Western blots, as well as a major band of lower size that may represent a processed form of the protein.

Inhibition of EGF-induced signal transduction by microgravity is independent of EGF receptor redistribution in the plasma membrane of human A431 cells

Epidermal growth factor (EGF)-induced c-fos and c-jun expression is strongly suppressed in microgravity. We investigate here whether this is due to inhibition of processes occurring during the initiation of EGF-induced signal transduction. For this purpose, EGF-induced receptor clustering is used as a marker. The lateral distribution of EGF receptors is directly visualized at an ultrastructural level by the label-fracture method. Quantification of the receptor distributions shows that EGF-induced receptor redistribution is similar under normal and microgravity conditions. This suggests that microgravity influences EGF-induced signal transduction downstream of EGF binding and EGF receptor redistribution, but upstream of early gene expression in human A431 cells.

Immunogold labelling in combination with cryoultramicrotomy, freeze-etching, and label-fracture

During the past years, the methods of ultrastructural visualization of intracellular and cell-surface proteins have been improved considerably, mainly as the result of the development of low-temperature preservation in combination with immunocytochemical labelling procedures using poly- or monoclonal antibodies. In this contribution we will discuss the combination of immunogold labelling with cryoultramicrotomy and two replica methods, i.e. freeze-etching and label-fracture. The main advantage of cryoultramicrotomy is that it enables post-sectioning labelling, thus providing complete accessibility of all cellular antigens, located both intracellularly and on the cell surface. Important parameters that influence the labelling (i.e. label-efficiency), including penetration of the label and antibodies in the section, effects of fixatives on antigenicity, and steric hindrance, will be discussed in detail. The replica methods have the advantage of enabling an analysis of the lateral distribution of antigens located at the cell surface. The label efficiency is of particular importance in these studies and in this context several parameters will be discussed, including accessibility and effect of fixatives.

Sulfhydryl reagents alter epidermal growth factor receptor affinity and association with the cytoskeleton

Sulfhydryl (SH) reagents are known to influence the characteristics of many ligand-receptor systems. The SH reagent N-ethylmaleimide has been demonstrated to interact with EGF receptors, and to inhibit EGF receptor kinase activity. The data presented in this paper concern the effect of SH reagents on two intriguing features of the EGF receptor system, namely the presence of low and high affinity EGF binding sites, and the interaction of EGF receptors with the cytoskeleton. SH reagents were observed to induce a disappearance of high, but not low, affinity EGF receptors from the cell surface, and an increase in receptor-cytoskeleton interaction. Comparison of the effects of membrane-permeant and membrane-impermeant SH reagents on wild type and structurally modified EGF receptors suggested that sulfhydryl groups on the cytoplasmic, rather than the extracellular, receptor domain are involved. This indicates that the cytoplasmic domain of the EGF receptor plays a role in the high affinity binding of EGF, and in the interaction of EGF receptors with the cytoskeleton. Experiments with an anti-EGF receptor antibody that specifically blocks the binding of EGF to low affinity receptors indicated that EGF induces a shift in the EGF receptor from low to high affinity. SH reagents probably affect EGF binding by inhibiting this EGF-induced receptor conversion.

Interaction of epidermal growth factor receptors with the cytoskeleton is related to receptor clustering

Recently it has been established that cytoskeleton-associated epidermal growth factor (EGF) receptors are predominantly of the high-affinity class and that EGF induces a recruitment of low-affinity receptors to the cytoskeleton. The nature of this EGF-induced receptor-cytoskeleton interaction, however, is still unknown. Therefore, we have studied the association of mutated EGF receptors with the cytoskeleton. Receptor deletion mutants lacking almost all intracellular amino acid residues displayed no interaction with the cytoskeleton, demonstrating that the cytoplasmic receptor domain is involved in this interaction. Further analysis revealed that receptor-cytoskeleton interaction is independent of receptor kinase activity and the C-terminal 126 amino acid residues, which include the auto-phosphorylation sites. Furthermore, it is shown that the high-affinity receptor subclass is not essential for association of low-affinity receptors to the cytoskeleton. EGF receptor-cytoskeleton interaction was increased, however, by treatment with sphingomyelinase, an enzyme known to induce membrane protein clustering, indicating that EGF receptor clustering may cause the association to the cytoskeleton.

Direct visualization and quantitative analysis of epidermal growth factor-induced receptor clustering

Several observations have indicated that clustering of growth factor receptors plays an important role in the action of growth factors. In this investigation, we have used the label fracture method to study the effects of epidermal growth factor (EGF) on the lateral distribution of its receptors in A431 epidermoid carcinoma cells. This method allows a direct visualization of immunogold-labeled plasma membrane receptors on ultrastructural level and in addition permits an quantitative analysis of their lateral distribution. EGF receptors were immunogold-labeled according to standard procedures with the monoclonal anti-EGF receptor antibody 2E9 (IgG1), which binds to the EGF receptor in a 1:1 ratio. In the absence of EGF, EGF receptors located on the surface of A431 cells were found to be clustered, as deduced from Poisson variance analysis (p less than 0.001). Following treatment of A431 cells with EGF, receptor clustering increased rapidly, reaching the maximum within 10 min. Maximal clustering was maintained for 1 h, after which the lateral distribution of receptors returned to the control situation within another hour.

Immunocytochemical demonstrations of cytoplasmic and cell-surface EGF receptors in A431 cells using cryo-ultramicrotomy, surface replication, freeze-etching and label fracture

In this paper we describe the use of a number of complimentary methods to visualize cytoplasmic and cell-surface located epidermal growth factor (EGF) receptors in cultured A431 cells. Cryo-ultramicrotomy in combination with immuno-gold labelling will be shown to provide an excellent method in visualizing cytoplasmic located EGF receptors in addition to cell-surface located EGF receptors. An important aspect in this method involves the possible effects of the fixatives on antigenicity. Using radioactive labelled anti EGF receptor antibodies, it was shown that formaldehyde as a fixative had no significant effect on label-efficiency. The density and lateral distribution of EGF receptors at the cell surface has been studied by three methods, i.e. surface replication, freeze etching and label fracture, all methods in conjunction with immuno-gold labelling. These methods allow in principle a quantitation of the surface distribution of the EGF receptors. The surface-replication method involves, however, dehydration and critical-point drying steps, and using radioactive labelled anti EGF receptor antibodies it was shown that in particular OsO4 fixation and dehydration caused a significant loss of cell-associated antibodies. This disadvantage is overcome by freeze etching and the label-fracture method, and as such these techniques provide the best methods for quantitative analysis of the planar distribution of cell-surface located EGF-receptors.