Increased serum levels of soluble receptors for tumor necrosis factor in cancer patients.

Soluble forms of the two molecular species of the cell surface receptors for tumor necrosis factor (TNF) have been detected in normal urine. Using enzyme-linked immunosorbent assays for these soluble receptors, we determined their levels in the sera of 40 healthy subjects and 59 patients with solid tumors. The mean +/- SD concentrations of both the soluble type I (p55) and type II (p75) receptors were significantly higher in the cancer patients than in the healthy controls: 1.96 +/- 1.19 versus 0.79 +/- 0.19 ng/ml (P less than 0.001) and 6.43 +/- 4.8 versus 3.2 +/- 0.6 ng/ml (P less than 0.001), respectively. The incidence and the extent of the increase correlated with the staging of disease. Sera of the cancer patients had a marked inhibitory effect on the in vitro cytocidal activity of TNF. This inhibition was proportional to the content of soluble TNF receptors and could be fully abolished by the addition to the sera of specific antibodies against the receptors. Among the cancer patients, the incidence of increase in the concentrations of soluble TNF receptors (about 70%) greatly exceeded that of the serum carcinoembryonic antigen (about 26%), a commonly used cancer marker. The origin of the serum soluble TNF receptors in cancer patients and the physiological implications of their effect on TNF function remain to be elucidated.

The c-fos proto-oncogene in murine 3LL carcinoma clones controls the expression of MHC genes.

The c-fos proto-oncogene and H-2K class I major histocompatibility antigens are differentially expressed in low-metastatic Lewis lung carcinoma clones, but not in high-metastatic clones. Interferons induce mRNA expression of fos and H-2 in non-expressor cells and elevate mRNA steady state levels of expressor cells. Transfection of non-expressor cells by v-fos or c-fos genes induces the transcription of H-2K mRNA and elevates the levels of H-2 proteins, but not of other gene products. These results, correlated with observations in other cell systems, suggest that the c-fos proto-oncogene controls the expression of MHC genes coding for class 1 antigens.

Expression of major histocompatibility class I genes in differentiating leukemic cells is temporally related to activation of c-fos proto-oncogene.

The relationship between the expression of the c-fos proto-oncogene and the expression of the class I major histocompatibility (MHC) antigens during the early stages of induced differentiation in three different leukemic cell lines was examined. In the U937 histiocytic lymphoma line TPA induced an increase in mRNA and cell surface MHC expression which followed induction of c-fos. In contrast, in the murine erythro-leukemia cell line, DMSO induced declining constitutive c-fos levels that were accompanied by declining mRNA and cell surface MHC expression. In the pluripotent HL60 promyelocytic line induction of macrophage differentiation with TPA led to c-fos induction and rising MHC levels, whereas induction of granulocyte differentiation with DMSO did not induce c-fos expression and was followed by declining MHC levels. Taken together, the results suggest that the c-fos proto-oncogene might be involved in the control of class I MHC antigen expression during differentiation.

Nuclear antigen expressed by proliferating cells.

We describe a novel mouse monoclonal antibody (PRA-72) that recognizes a nuclear antigen associated with cell proliferation. The monoclonal antibody stained the nuclei of logarithmically growing cultured stromal cells. The nuclear staining disappeared when these cells entered Gzero phase of the cell cycle. Western blot analysis revealed a nuclear protein which appeared as a doublet at 35-40 KD, which was undetectable in extracts from confluent cells. Immunocytological study of purified cell populations from various cell cycle phases revealed peripheral nuclear staining in all stages except mitosis, when the chromosomes were observed enveloped with the antigen. In co-cultures of quiescent stromal cells and proliferating hemopoietic precursors, only the latter showed nuclear staining by PRA-72 monoclonal antibody. Further indications for selective expression of the antigen by proliferating cells were found by an immunohistochemical study of various tissues including newborn mouse bone marrow and its surrounding connective tissue, mouse tongue epithelium, and human carcinoma of the colon. This antibody may, therefore, prove useful in the evaluation of human tumors.

c-fos transfection of 3LL tumor cells turns on MHC gene expression and consequently reduces their metastatic competence.

Transfection with c-fos genes of cells of a highly metastatic (H-2K- H-2D+) clone, DI22, of the 3LL carcinoma, causes activation of H-2K gene expression. Experiments were carried out to test whether these transfectants exhibit reduced metastatic competence. Studying II mouse c-fos, 6 mouse c-fos and 2 v-fos transfected clones, we observed that clones expressing high steady-state levels of the fos mRNA also expressed elevated levels of H-2K and H-2D mRNA, and high levels of cell-surface H-2K and H-2D glycoproteins. The transfectants were tested for generation of spontaneous metastasis following intra-footpad inoculation of the tumor cells. Clones expressing high levels of fos and of H-2 antigens, particularly those expressing high levels of cell-surface H-2Kb molecules, showed a reduction of their metastatic competence. Statistical analysis revealed that c-fos transfectants are significantly less metastatic than the parental cells. The molecular mechanisms of c-fos activation of H-2 genes is briefly discussed.

The reversal of the metastatic phenotype by gene transfer.

When studying the function of MHC-restricted immune responses in controlling metastatic growth we discovered that highly metastatic clones of mouse tumours express the H-2D but lack expression of the H-2K gene of the MHC system. The de novo expression of the H-2K antigen, after H-2K gene transfection, resulted in the reversal of a metastatic to a non-metastatic phenotype. This reversal was causally related to the acquisition of H-2K-restricted immunogenic properties. Immunization with H-2K-transfected cells, after surgical removal of the local tumour, abolished or significantly reduced the growth of metastases. We subsequently observed that H-2K expression is correlated with expression of the c-fos oncogenes. Transfection of H-2K-negative cells with v-fos or c-fos genes resulted in the expression of H-2K. Our studies suggest that one of the main functions of the c-fos proto-oncogenes is control of the expression of the MHC genes. Searching for additional molecular properties which characterize the metastatic phenotype, we observed that the metastatic clones of each of our lung-metastasizing tumours expresses an fms-related oncogene. This was correlated with a membrane-bound tyrosine kinase, which has the properties of growth factor receptors. We examine the possibility that our fms-like gene codes for this protein kinase, which represents a receptor for a local growth factor that controls metastatic growth in the lung.