Immunoglobulin class-switch recombination occurs in mantle cell lymphomas

Mantle cell lymphoma (MCL) is an IgM-expressing B cell lymphoma that originates from naive B cells and responds poorly to chemotherapy. We show here that several MCLs harbour isotype-switched subclones. Similar to the situation in normal B cells, in vitro stimulation of MCL cell lines with CD40 ligand (CD40L) and interleukin-4 induced expression of activation-induced cytidine deaminase (AID) and germline transcription at the immunoglobulin heavy chain gene locus. Additionally, the occurrence of switch-circle transcripts and mature IgG transcripts after stimulation indicated ongoing class-switch recombination in mantle cell lymphoma cell lines. Furthermore, stimulation of primary MCL cells in vitro induced expression of class-switched IgG mRNA in the tumour cells. Our data indicate that mantle cell lymphomas have retained the ability to undergo class-switch recombination if appropriate stimuli, such as the CD40 ligand, are provided.

Regulation of telomerase activity by alternate splicing of human telomerase reverse transcriptase mRNA in a subset of neuroblastomas

It has been proposed that the regulation of telomerase takes place at the transcriptional level, the expression of the catalytic subunit human telomerase reverse transcriptase (hTERT) being crucial for telomerase activity (TA). Recently, differential splicing of hTERT mRNA has been demonstrated in various tissues during embryonal development, and it has been suggested that only full-length transcripts translate into functionally active telomerase. With this in view, we analyzed the different hTERT transcripts by reverse transcriptase-polymerase chain reaction in neuroblastic tumors and compared the results with the TA, the tumor growth fraction, and the MYCN status. In a series of 38 neuroblastic tumors, high TA and full-length hTERT transcripts were found in nine samples, whereas nine samples showed absence of both enzymatic activity and hTERT transcripts. Interestingly, in another eight samples, low or absent TA coincided with a lack of full-length hTERT transcripts. Eleven samples contained hTERT transcripts with low or undetectable TA and one sample had low TA but no hTERT transcripts. TA correlated with MYCN amplification and was weakly associated with the proliferative activity. Moreover, a significant correlation with tumor progression was observed. Our findings point at a posttranscriptional regulation of TA in a subset of neuroblastic tumors. Because high TA was detected only in tumors with full-length hTERT transcripts, reverse transcriptase-polymerase chain reaction analysis of archival neuroblastic tumor samples might help to appraise the malignant potential in individual cases.

High telomerase activity is associated with cell cycle deregulation and rapid progression in endometrioid adenocarcinoma of the uterus

Telomerase activity, a mechanism granting cellular immortality, has been detected in most cancer entities, but its association with clinical, histopathologic, and prognostic parameters is not fully understood. We investigated whether quantitative telomerase levels are correlated to established prognostic factors, telomere lengths, cell cycle kinetics, and the clinical course in endometrioid adenocarcinoma of the uterus (EC). A modified telomeric repeat amplification protocol (TRAP) was used to quantify the relative telomerase activity in a series of 53 primary tumors. Mean telomere length was determined by Southern blot analysis. Cell cycle kinetics were studied immunohistochemically on paraffin sections using monoclonal antibodies to 2 distinct proliferation-specific proteins: Ki-67, which is expressed throughout the cell cycle, and a novel cell cycle-associated protein, repp86, the expression of which is restricted to the cell cycle phases S, G2, and M. The ratio of the 2 immunolabeling indices defines the rate of transition through the restriction point. Telomerase activity was detected in 50 of 53 ECs (94%). Its levels correlated significantly with FIGO stage (P =.01) and FIGO grade (P =.003) but not with myometrial invasion. They were weakly associated with the overall proliferative activity (Ki-67, r =.48) but significantly with the repp86 index (r =.64) and even more strongly with the repp86:Ki-67 ratio (r =.77). There was no correlation with mean telomere length. In the group of tumors with high telomerase activity, 5 patients had relapses and 2 died of the disease within a median follow-up period of 29 months. Recurrence showed no relation to FIGO grade and stage. No events were observed in the group with low telomerase activity. In a multivariate model including tumor stage, histopathologic grade, depth of myometrial invasion, and Ki-67 indices, telomerase activity emerged as the only independent predictor of disease progression (P =.0002). It is concluded that beyond a link to proliferation, high telomerase activity reflects a deregulation of the cell cycle associated with an increased rate of cells entering S phase and a higher degree of malignancy. Therefore, quantitative analysis of telomerase activity may be useful for identifying EC patients at high risk for recurrence.

Transcriptional repression of the human fibronectin gene in laryngeal squamous cell carcinoma cells

PURPOSE

The aim of the experiments was to analyze the mRNA expression pattern and verify the repression of FN gene expression in laryngeal squamous cell carcinoma (SCC) cells in comparison with benign mucosal keratinocytes.

METHODS

Messenger RNA from SCC cells and benign keratinocytes was reverse transcribed and subjected to PCR following differential display (DD) analysis of the amplicons. Northern hybridization was carried out to confirm the reduction of the FN-mRNA expression in both laryngeal SCC cells and larynx carcinoma biopsies, in contrast to adjacent normal mucosa. Quantitation of protein synthesis was performed with homogenates of fresh tumor biopsies and their normal phenotypes, as well as of benign keratinocytes and laryngeal SCC cell lines, respectively, using ELISA. In the liposome-mediated transient transfection assay, FN promoter activity was analyzed by linking the FN promoter sequence to the chloramphenicol acetyltransferase (CAT) reporter gene. Transfection efficacy was monitored by co-transfection with pGL3 control vector.

RESULTS

A 191 bp mRNA fragment revealing a 99% homology with the human FN-mRNA was detected, the expression of which was repressed 20 times as much in SCC cells as compared to benign phenotypes. Northern hybridization confirmed the distinctly reduced expression of FN-mRNA in both laryngeal SCC cells and larynx carcinoma biopsies, in contrast to adjacent normal mucosa. The quantitation experiments showed a correlation between the range of FN synthesis and the expression of FN-mRNA in cell lines and the biopsies which were used. The 1.28 kb FN gene promoter drove expression of the CAT reporter gene, which was similar to the FN-mRNA expression showed by DD and Northern hybridization.

CONCLUSIONS

The mechanisms leading to the low level of FN in many tumors have not yet been sufficiently investigated. Our findings suggest that the decrease of FN in laryngeal SCC cells is transcriptionally regulated.

p53 analysis of laryngeal cancer in exon 4 to 9

p53 gene mutations are a common genetic alteration in human cancer and codon 72/exon 4 polymorphism of the p53 gene has been implicated in cancer risk. Therefore in this study the p53 gene status of 32 shock-frozen tumor specimens from larynx carcinomas was analyzed by PCR and sequencing of exon 4 through 9. Four mutations (12.5%) in exon 5, 7, 8 and 9 were detected in the carcinoma specimen. Analysis of codon 72 revealed in eight cases a homozygosity for proline (CCC) and in 24 cases heterozygosity or homozygosity for arginine (CGC). The group with the proline/proline genotype had a median age 10.3 years lower than the remaining patients and included the only two non-smokers. Firstly, these results confirm the p53 mutational status of laryngeal cancer without any clinical correlation and secondly may suggest an oncogenic potential for the proline/proline genotype of codon 72 for laryngeal cancer as has already been assumed for lung cancer.

Telomerase activity in melanocytic lesions: A potential marker of tumor biology

Telomerase activation, being a cardinal requirement for immortalization, is a crucial step in the development of malignancy. With a view toward diagnostic and biological aspects in melanocytic neoplasia, we investigated the relative levels of telomerase activity in 72 nevi and 16 malignant melanomas by means of a modified telomeric repeat amplification protocol (TRAP) assay, including an internal amplification standard. We further compared telomerase activity with the expression of two different proliferation-specific proteins, Ki-67 and repp86, a protein expressed exclusively in the cell cycle phases S, G2, and M. Telomerase activity was associated with the overall growth fraction (Ki-67) but showed a closer correlation with the expression of repp86. Both telomerase activity and proliferation indices discriminated clearly between malignant melanomas and nevi, but not between common and dysplastic nevi. Nonetheless, a portion of nevi exhibited markedly elevated telomerase activity levels without proportionally increased proliferation. This was independent of discernible morphological changes. Clinicopathological correlations showed an association between high telomerase activity and early metastatic spread in melanomas, linking telomerase to tumor biology. Our results provide arguments in favor of an occasional progression from nevi to melanomas and imply that proliferation measurements in combination with telomerase assays may help to elicit early malignant transformation that is undetectable by conventional morphology.

Transcriptional repression of the human galactocerebrosidase gene in squamous cell carcinomas of the larynx

Alterations of gene expression in squamous cell carcinoma (SCC) cell lines derived from the larynx and keratinocytes derived from adjacent normal mucosa of the larynx have been studied using the mRNA differential display technique. Lane-to-lane comparison of reverse transcribed mRNA showed a strong repression of a 148 bp fragment in SCC cells. The fragment was reamplified and cloned. Sequencing revealed a 99.3% homology with a region in exon 17 of the human galactocerebrosidase (GALC) gene. Northern blot analysis confirmed the differential expression of this gene in both carcinoma cell lines and laryngeal SCC biopsies in contrast with corresponding normal mucosa. To provide further evidence for the differential expression rate, both types of cells were transiently transfected with a 152 bp (-176 to -24) high regulatory promoter element of the 5' flanking region of the GALC gene. Results of 3 independent transfection experiments indicated a 16-fold repression of the GALC gene expression in SCC cells compared with benign keratinocytes. However, neither mutation nor other alterations of the promoter sequence were detected. Expression of the GALC gene is thus greatly affected in SCCs of the larynx.

Cell lineage specificity in G-CSF receptor gene methylation

In hematopoiesis the evolution of specialized cell lineages from a common stem cell is mediated by lineage-specific growth factors. The role of DNA methylation in the multilevel regulation of the differential gene expression, especially in the case of growth factor receptor genes, has remained elusive. In earlier studies we showed a lineage-specific methylation pattern of the M-CSF receptor gene c-fms in blood monocytes and tissue macrophages. Here, we provide evidence that a lineage-specific hypomethylation exists for the G-CSF receptor gene for myelomonocytic cells but not in lymphocytes without any interindividual differences. Constant differences were found between alveolar and peritoneal macrophages with a lesser degree of methylation in peritoneal macrophages. Acute myelomonocytic leukemias showed an increased methylation as compared with normal granulocytes and monocytes. All permanent cell lines analyzed revealed hypermethylation of the G-CSF receptor gene. Lymphocytes of B-CLL showed a strong hypermethylation of this gene. Increased methylation has been shown to be inversely correlated with transcriptional gene activities. We conclude that the methylation pattern of growth factor receptor genes may be one of the regulatory mechanisms in multi-lineage differentiation.

Analysis of telomerase expression and proliferative activity in the different layers of cyclic endometrium

To gain better insights into cell kinetics under physiological conditions, telomerase activity in the functional and basal layers of cyclic endometrium (n = 33) was compared with the immunostaining of glandular and stromal cells within these layers (n = 25). Two immunohistochemical proliferation markers were used to demarcate cells in the G1 phase of the cell cycle. In contrast to previous expectations, telomerase activity and both glandular and stromal proliferative activities were all significantly higher in the functional than in the basal endometrium (P < 0.002). The course of telomerase activity in the endometrial layers during the ovarian cycle was significantly associated with the proliferative scores for the functional and basal endometrial glands and the functional stroma but not the stromal compartment of the basal layer. Our findings indicate that the telomerase activity in cyclic endometrium is associated with the total number of proliferating glandular and stromal cells in the functional layer. Proliferating daughter cells of telomerase-competent stem cells may account for the lower levels of telomerase detected in normal basal endometrium.

Longevity of lobsters is linked to ubiquitous telomerase expression

Mammals have high growth rates in embryonic and juvenile phases and no growth in adult and senescent phases. We analyzed telomerase activity in a fundamentally different animal which grows indeterminately. Lobsters (Homarus americanus) grow throughout their life and the occurrence of senescence is slow. A modified TRAP assay was developed and the lobster telomeric repeat sequence TTAGG was determined. We detected telomerase activities which were dependent on RNA and protein components, required dGTP, dATP and dTTP, but not dCTP. Telomerase products with a five nucleotide periodicity were generated. High telomerase activities were detected in all lobster organs. We conclude that telomerase activation is a conserved mechanism for maintaining long-term cell proliferation capacity and preventing senescence, not only in cellular models or embryonic life stages but also in adult multicellular organisms.

Regulation of telomerase activity in quiescent immortalized human cells

Telomerase is a key enzyme in carcinogenesis; telomerase activity has been found in more than 90% of human tumors. Understanding the regulation of this enzyme will improve our knowledge of tumor biology and may lead to novel strategies in cancer therapy. We examined effects of growth arrest on telomerase activity in the human immortalized cell lines U 937 (lymphoma) and L 428 (Hodgkin's disease). Cells were starved by serum depletion for 4 days. After readdition of serum, a recovery phase followed. Cell proliferation was monitored with the monoclonal antibody Ki-S5. In the absence of serum, telomerase levels declined fivefold. After serum readdition, recovery to threefold increased level was observed. Furthermore, the prevalence of telomerase-positive cells in normal tissues is an important issue for understanding tumorigenesis. Our TRAP assay is robust against false positives and in mixed cell samples, we found a rather limited sensitivity of the telomere repeat amplification protocol (TRAP) assay. This means that adequate screenings for telomerase-positive somatic cells have to include enrichment steps.

Telomerase activity in 'immortal' fish

Eukaryotic chromosome termini consist of telomeres, short sequence repeats. According to the telomere hypothesis, DNA replication leads to telomere shortening, resulting in a cellular mitotic clock. Telomerase resets it by telomere synthesis. In mammals with a limited growth phase, telomerase activity in somatic tissues is restricted to stem cell derivatives with high proliferation potential. But other animals, like some fish, grow throughout their life with little senescence. All somatic cells require a high proliferation capacity and telomerase should be active in all cells, irrespective of fish age. Indeed, we detected high telomerase activities in all analyzed organs of rainbow trout (Oncorhynchus mykiss).

Telomere shortening in uterine leiomyomas

OBJECTIVE

To gain a better understanding of proliferation control mechanisms in a common benign tumor, we investigated the mean telomere length and the clonality of uterine leiomyomas.

STUDY DESIGN

Deoxyribonucleic acid from uterine leiomyomas and from the adjacent normal myometrium of 51 patients (total number of uterine leiomyomas 107; 28 patients with single leiomyoma, 23 patients with multiple leiomyomas ranging from 2 to 8 myoma nodules per case) was hybridized to a telomeric oligonucleotide probe by Southern blot and chemiluminescent detection. The mean telomere length was evaluated by densitometry. Clonality was assessed with use of the phosphoglycerokinase gene polymorphism.

RESULTS

The mean telomere length was significantly shorter in uterine leiomyomas (median 7950 bp, interquartile range 7261 to 8372 bp) than in normal myometrium (median 9688 bp, interquartile range 8528 to 10535 bp) (P < .001). There was no correlation between tumor size and telomere attrition. Multiple uterine leiomyomas were found to have an independent clonal origin.

CONCLUSIONS

Telomere attrition in uterine leiomyomas reflects enhanced proliferation activity in the course of tumor evolution. The basic telomere lengths differ in the myocytes from which the uterine leiomyomas originate, probably explaining the lack of correlation between telomere attrition and tumor size.

Expression of a novel mRNA in human head and neck squamous cell carcinoma cells

AIMS

The differential display reverse transcription polymerase chain reaction (DDRT-PCR) technique was used to search for differences between the mRNA expression profiles of squamous cell carcinoma (SCC) cell lines established from head and neck tumours and normal keratinocytes from the mucosa of the upper aerodigestive tract.

METHODS

Total RNA prepared from both cell types was reverse transcribed into cDNA then amplified in a PCR mixture. To compare the electrophoretic patterns, mRNAs were amplified by nested PCR using specific oligonucleotides. Additionally, using labelled cDNA probes, northern hybridisation was carried out on three cancer cell lines of different origin, a biopsy from a parotid gland pleomorphic adenoma, healthy mucosa, and keratinocytes.

RESULTS

Comparison of the separated bands revealed a fragment with a differential expression pattern in the SCC cells. This cloned sequence of a 336 base pair mRNA fragment exhibited no significant homology with known transcripts. Additionally, after amplification and sequencing of the 3' end of the fragment no homology with a known human gene sequence was found. However, low homology with a genomic sequence of a nematode was found. Northern hybridisation confirmed the selective expression of this fragment in SCC cells versus the cancer cell lines of different origin, the biopsy of the pleomorphic adenoma, keratinocytes, and healthy mucosa.

CONCLUSIONS

This is the first differentially expressed human genome transcript of squamous cell carcinoma of the head and neck identified by DDRT-PCR. It may prove useful, in the future, to characterise this tumour type.

Molecular basis of artifacts in the detection of telomerase activity and a modified primer for a more robust 'TRAP' assay

Human somatic cells have essentially no telomerase activity. Telomerase is linked to tumor genesis and is a valuable marker for malignant growth. Extreme paucity of the enzyme neccessitated development of a PCR-based assay, 'telomeric repeat amplification protocol' (TRAP). Unfortunately, this method is not without difficulties. Amplification products are not related to the size of the amplified telomerase products. Furthermore, false positive results can occur, and careful control of reaction conditions is crucial. We analyzed in detail the molecular basis of artifacts. Based on these data, reverse PCR primer was changed and both problems in the TRAP assay were eliminated.

DNA ploidy and protein synthesis in squamous cell carcinoma cell lines of the head and neck

Aneuploidy as abnormal nuclear DNA content, is considered almost positive evidence of malignancy. In this study three diploid and three aneuploid squamous cell carcinoma (SCC) cell lines were examined for DNA content by flow cytometry. The DNA indices of the SCC cell lines were found to range from 1.0 to 2.1. The mitotic activity of the diploid cell lines was 1.6 times higher and the cells were smaller than aneuploid cells. To find a molecular basis for these differences, the pattern of the de-novo synthesized proteins was analyzed by means of [35S]methionine incorporation, electrophoresis, and autoradiography. In all aneuploid SCC cell lines tested in this experiment, the increase of nuclear DNA content is associated with the synthesis of a novel protein with a molecular mass of approximate 55 kDa as well as with altered synthesis rates of two preexisting proteins (50 kDa and 100 kDa). For determination of the amino acid uptake in diploid and aneuploid cells, the accumulation of [35S]methionine was measured as a function of time by liquid scintillation counting. No significant difference was found in the uptake rate between diploid and aneuploid cells with the same protein content. However, discrepancies were revealed when equal numbers of cells with different DNA index were used, suggesting, that protein turnover is different in diploid and aneuploid SCC cells.

Amplification of c-myc but not of c-erbB-2 is associated with high proliferative capacity in breast cancer

Proliferative capacity provides an independent prognostic marker of progression in breast cancer. Little is known about the molecular mechanisms influencing the cell division rate in mammary carcinomas. In order to address this issue, the copy numbers of c-erbB-2 (HER/neu) and c-myc protooncogenes that have been shown to be amplified in aggressive types of cancers were determined in 60 mammary carcinomas and related to the proliferation rate. The proliferative activity was determined by labeling of the proliferation-associated nuclear antigen which is defined by the recently described monoclonal antibody Ki-S1. Approximately one-third of samples under investigation displayed a Ki-S1 labeling index exceeding 30%. In this subgroup, amplification of c-myc was found in 52.6%, whereas in the remaining cases, 26.1% exhibited an enhanced copy number of c-myc (P < 0.025). By contrast, c-erbB-2 amplification was not found to be associated with a higher proliferation index. Except for one case of invasive lobular carcinoma, both protooncogenes exhibited regular copy numbers in the low proliferation subgroup (< 20%; P < 0.03). We conclude from our findings that c-myc amplification may be one of the molecular causes underlying the highly proliferating phenotype of mammary carcinoma, known to be associated with an unfavorable clinical course.

DNA analysis to aid in the diagnosis of chronic myeloproliferative disorders

Diagnosing chronic myeloproliferative disorders (CMPD) can be difficult because of overlap and possible transitions between the different conditions and their similarity to reactive myeloproliferations. DNA analysis was applied to improve differentiation of CMPDs. All subtypes of CMPD analyzed, including chronic myeloid leukemia, agnogenic myeloid metaplasia, polycythemia vera, and essential thrombocythemia, had in common that granulocytes and bone marrow cells were clonal in origin, as shown by X chromosome-linked DNA polymorphism in conjunction with methylation patterns (n = 32). Reactive myeloproliferations, by contrast, showed polyclonal inactivation patterns. Clonality could not distinguish CMPD from cases of myelodysplastic syndrome because the latter (n = 7) also exhibited clonal hematopoiesis. Because of their clonal origin, peripheral granulocytes were used in all cases (n = 201) to detect bcr gene rearrangement. Despite possible morphologic overlap between different types of CMPD, bcr gene rearrangement was specific for chronic myeloid leukemia and could be applied to differentiate chronic myeloid leukemia from other CMPDs in cases of equivocal morphologic diagnosis. Chronic myeloproliferative disorders represent clonal hemopoietic diseases that probably have specific underlying genetic defects. Thus DNA analysis can aid substantially in the differential diagnosis of CMPD.

Lineage-specific methylation of the c-fms gene in blood cells and macrophages

DNA methylation belongs to the multilevel genetic control system regulating differentiation processes and gene expression. The extent to which DNA methylation contributes to the differentiation of hematopoietic cells is elusive. In the present study we investigated the methylation state of the c-fms/M-CSF receptor gene in normal human blood cells and tissue macrophages. The methylation pattern of the c-fms gene as detected by isoschizomeric restriction analysis with MspI/HpaII showed only slight interindividual variations in normal donors, whereas constant differences were found between granulocytes and monocytes from the same donor. The second intron of the c-fms gene contains several CpG loci which were found to be hypomethylated on both alleles in monocytes and tissue macrophages. By contrast, these positions were methylated in granulocytes and lymphocytes that did not express the c-fms gene. In comparison to monocytes alveolar and peritoneal macrophages revealed an enhanced demethylation. There were constant differences in c-fms gene methylation between alveolar and peritoneal macrophages with a higher degree of demethylation in alveolar macrophages. We conclude that c-fms gene demethylation is involved in the differentiation of monocytes and macrophages from immature precursors and that the demethylation of lineage-specific growth factor receptor genes might provide an important step in lineage commitment of hematopoietic cells.

Increased expression of growth factor genes for macrophages and fibroblasts in bronchoalveolar lavage cells of a patient with pulmonary histiocytosis X

Pulmonary histiocytosis X is the local manifestation of a systemic disorder of unknown cause characterised by infiltration of Langerhans cell like histiocytes and parenchymal fibrosis. In a male smoker with histologically proved histiocytosis X and functional impairment bronchoalveolar lavage showed an increase in CD-1/OKT-6 antigen positive histiocytes to 8%. Northern blot analysis of RNA from bronchoalveolar lavage cells showed an exaggerated expression of the M-CSF gene and of the c-fms gene encoding for the corresponding receptor. An increased level of c-sis RNA, which encodes the B chain of platelet derived growth factor, was also found. Diffuse reticulonodular infiltrates on the chest radiograph resolved with glucocorticoid treatment and CD-1/OKT-6 antigen positive histiocytes fell to 3%. Macrophage colony stimulating factor, c-fms and c-sis gene expression were reduced almost to normal after treatment. The results suggest that macrophage colony stimulating factor and platelet derived growth factor may have a role in the initiation or maintenance of pathological reactions in pulmonary histiocytosis X.

A frequent EcoRI RFLP demonstrated within the human M-CSF receptor gene (CSFIR)

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Increased methylation of the c-fms protooncogene in acute myelomonocytic leukemias

DNA methylation provides an epigenetic information possibly involved in differentiation processes and gene regulation. In this study we investigated the methylation state of the c-fms/M-CSF receptor gene in normal human blood cells and leukemias. The methylation pattern of the c-fms gene as detected by isoschizomeric restriction analysis with MspI/HpaII showed only slight interindividual variations in normal donors, but there were constant differences between granulocytes and monocytes from the same donor. Of 21 acute myelomonocytic leukemias investigated, 85% revealed a methylation pattern different from that of normal monocytes. One or more restriction sites which were at least partly unmethylated in normal monocytes proved to be methylated in leukemic cells. In contrast, leukemias of lymphocytic origin showed hypomethylation of the c-fms gene. There was no correlation between the methylation state of the c-fms gene and its expression at the RNA level, but an increase in monocyte/macrophage-specific differentiation markers could be observed in those samples which exhibited a methylation pattern similar to that of normal monocytes. The increased DNA methylation within the c-fms gene might reflect the inactivation of differentiation genes in leukemic cell clones, contributing to their maturation arrest. Furthermore, neoplastic hematopoietic cells seem to exhibit lineage-specific differences in c-fms gene methylation.

Proliferation, macrophage colony-stimulating factor, and macrophage colony-stimulating factor-receptor expression of alveolar macrophages in active sarcoidosis

Alveolar macrophages (AM) in sarcoidosis display an enhanced mitotic activity. Immunocytochemical detection of the proliferation-associated Ki-67 antigen revealed significant increase in the number of proliferating AM in active sarcoidosis as compared with inactive stages of disease. Macrophage proliferation may provide an additional marker of disease activity. Since growth of macrophages is regulated by hematopoietic growth factors, we examined the expression of macrophage colony-stimulating factor (M-CSF), granulocyte M-CSF, and interleukin-3 by bronchoalveolar lavage cells in active sarcoidosis. Expression of granulocyte M-CSF or interleukin-3 genes could not be detected. AM in active sarcoidosis displayed M-CSF RNA to a comparable level like normal AM. They differed, however, in about 50% of cases analyzed, from normal AM by an enhanced level of c-fms proto-oncogene (M-CSF-receptor) expression. The enlarged proportion of proliferating AM in active sarcoidosis may be the result of an increased influx of strongly fms expressing macrophage precursors into the alveoli and autostimulation of macrophages by M-CSF.

M-CSF and M-CSF-receptor gene expression in acute myelomonocytic leukemias

The role of hematopoietic growth factors in the pathogenesis of human leukemias is still obscure. In this study, RNA from 24 human acute myelomonocytic leukemias (AML) was used to analyze the expression of the macrophage colony stimulating factor (M-CSF) and its corresponding receptor (c-fms). Fifty percent of AML cells exhibited c-fms transcripts of regular length but at a lower level than in normal monocytes/macrophages. In most cases the reduced c-fms expression of AML cells was not associated with autostimulatory M-CSF expression. Only a few cases of AML showed co-expression of M-CSF and c-fms, which by contrast was regularly observed in cultivated blood monocytes and some tissue macrophage subsets. Higher levels of c-fms expression could be found in AMLs with a more mature monocytic immunophenotype. Permanent myelomonocytic cell lines expressed c-fms only after induction of monocytic differentiation. Neither the M-CSF gene nor the c-fms gene were rearranged in AML cells. In AML cells the homozygote genotype of the c-fms gene predominated. Our results do not provide evidence for the involvement of M-CSF and c-fms genes in human myeloid leukemogenesis. c-fms expression appears to indicate monocytic differentiation within the myelomonocytic lineage. We found autostimulatory M-CSF expression to be a physiologic feature of some tissue macrophages and hence not necessarily associated with neoplastic proliferation.

Modulation of c-fms proto-oncogene expression in human blood monocytes and macrophages

The gene product of the c-fms proto-oncogene is a transmembrane protein with tyrosine-kinase activity that is obviously related to the receptor for the colony-stimulating-factor CSF-1. By Northern blot analysis, we investigated the expression of the cellular counterpart of v-fms in purified normal human blood mononuclear cells and different macrophage populations. The proto-oncogene c-fms expression was demonstrable in blood monocytes but not in blood lymphocytes. Short-term cultivated blood monocytes exhibited an increased expression of c-fms in comparison to freshly isolated blood monocytes, possibly due to a temporary down regulation of c-fms during the separation procedure of blood monocytes. A comparably high rate of fms-RNA expression was found in most of the analyzed samples of resident peritoneal macrophages, while resident alveolar macrophages showed a considerably lower level of c-fms expression. In this, alveolar macrophages resembled long-term cultivated adherent blood monocytes, which showed a down regulation of c-fms expression. By correlating these data obtained by Northern blot analysis with phenotypic properties of the analyzed monocyte/macrophage populations, it is concluded that different levels of c-fms expression in monocytes/macrophages correspond to their stage of differentiation and maturity.

Multinucleated giant cells generated in vitro. Terminally differentiated macrophages with down-regulated c-fms expression

Although multinucleated giant cells (MGCs) are a known feature of granulomatous reactions, little is known about their destination and function. In this study human blood monocyte (BM)-derived giant cells were generated by lymphokine stimulation in vitro. Their immunophenotype and ultrastructural morphology resembled that of MGCs occurring in vivo. Mitotic activity within MGCs could not be established either in vitro or in vivo. Enzyme equipment of MGCs was elevated in comparison with monocyte-macrophages. In comparison with unfused monocyte-macrophages, MGCs did not reveal a higher level of interleukin-1 production or cytostatic activity. They showed, however, a 20-30-fold increase in the production of oxygen-free radicals in response to zymosan. Transcription of the proto-oncogene c-fms was enhanced in short-term cultivated BM and was rapidly down-regulated in MGCs after fusion had occurred. It is concluded that MGCs represent highly stimulated cells of monocyte-macrophage lineage at a terminal stage of maturation.

Human neutrophilic and eosinophilic granulocytes display different levels of c-fos proto-oncogene expression: an in situ hybridization study

The cellular homologue of the retroviral oncogene v-fos has been shown to be involved in cell differentiation of hematopoietic cells. By use of the human promyelocyte cell line HL-60, several in vitro differentiation studies suggested a selective activation of c-fos during monocytic differentiation of myeloid precursor cells. In contrast to these observations, we found high levels of c-fos mRNA in purified normal human granulocytes, whereas c-fos was only faintly expressed in blood monocytes. In situ hybridization revealed that the high level of c-fos expression is restricted to neutrophilic granulocytes, whereas c-fos transcription is not detectable in eosinophilic granulocytes. These results indicate that in vitro differentiation systems can be misleading and may not reflect the in vivo situation. The high level of c-fos expression in neutrophilic granulocytes may be caused by superinduction due to the reduced capacity for protein synthesis in these cells.

The protooncogene c-fos is transcriptionally active in normal human granulocytes

Total cellular RNA of highly purified normal human blood cell populations was analyzed for the expression of the protooncogene c-fos, the cellular counterpart of the transforming FBJ virus. In marked contrast to previous findings based on in vitro studies with permanent leukemic cell lines, c-fos transcription was restricted to granulocytes. Neither blood monocytes nor blood lymphocytes or alveolar macrophages revealed detectable levels of c-fos transcription. Whereas this cellular oncogene is constitutively expressed in granulocytes, the monocytic cell line U-937 showed a transient c-fos transcription only after induction of differentiation. The contradiction between the results found in vivo and in vitro is discussed.

Lineage-specific expression of c-fos and c-fms in human hematopoietic cells: discrepancies with the in vitro differentiation of leukemia cells

In vitro differentiation studies using the bipotential human leukemia cell line, HL60, have indicated that high levels of expression of two proto-oncogenes, c-fos and c-fms, are restricted to the myelomonocytic lineage. No such expression has been detected in induced granulocytic cells. In striking contrast to these observations, we found that c-fos mRNA levels are very high in purified human granulocytes, but barely detectable in blood monocytes and tissue macrophages. Human granulocytes contain, however, relatively low levels of c-fos protein, indicating that c-fos mRNA is inefficiently translated or that the protein is rapidly degraded in these cells. In closer agreement with the in vitro results, the level of the expression of c-fms is high in purified blood monocytes and undetectable in granulocytes. We found, however, that the evolution of monocytes into tissue macrophages is accompanied by a significant decrease in c-fms expression, suggesting that the function of c-fms is restricted to specific stages of monocytic differentiation. Our observations also show that results obtained using in vitro differentiation systems have to be regarded with caution, since they may not reflect the in vivo situation.