Fc Receptor-Like Structures on in Vitro-Cultured Human Ovarian Tumor Cells

FcR may function as a progression factor of nonlymphoid tumors

Tumor progression is a multistep process involving genetic and epigenetic changes in a transformed clone. Some of these changes may be induced by host factors which may also select for transformed cellular variants with a high ability to survive and propagate. In this article we review studies showing that receptors for the Fc portion of IgG may be expressed on cells from human or animal tumors of nonlymphoid origin. We also review data demonstrating that at least with respect to cells transformed in vitro with Polyoma virus, transformation per se is not sufficient for the induction of Fc receptor expression. We also summarize preliminary data showing that Fc receptor expression is causally involved in conferring a high malignancy phenotype upon transformed cells. Possible mechanisms to explain these observations are discussed.

Some cellular and molecular characteristics of high and low tumorigenicity variants of polyoma-virus transformed cells

We analyzed several cellular and molecular properties of BALB/c 3T3 cellular clones transformed in vitro with polyoma virus and exhibiting a high or low tumorigenicity phenotype. We also analyzed the same clones after a single in vivo passage in syngeneic mice. This passage invariably induced and/or selected variants exhibiting a very high tumorigenicity phenotype. BALB/c mice bearing tumors induced by the inoculation of the above cells, regardless of their tumorigenicity phenotype, have a lower number of L3T4 positive splenocytes than appropriate controls. The response to Con-A of spleen cells from such mice was also suppressed. Concomitantly, an increase in Mac-1 positive splenocytes could be measured. In spite of the non-specific suppression of T cells, spleen cells from tumor-bearers showed a specific proliferative response to polyoma antigens. Molecular analysis of polyoma transformed cells showed no differences between the various cells with respect to integration of the polyoma viral genes or with respect to src, myc and fos proto-oncogenes. In vitro maintained cells and in vivo passaged cells seemed to differ, however, in the content of polyoma middle T. Whereas polyoma virus transformed cells maintained only in culture never expressed low affinity receptors for IgG (Fc gamma RII), certain in vivo passaged cells did. This expression could be measured both at the protein and the mRNA level. Those in vivo passaged cells which expressed F alpha RII gave tumors following a long latency period. Ongoing experiments will indicate whether or not Fc gamma RII expression is linked to long latency of tumor development.

Increased expression of Fc gamma receptor in cancer patients and tumor bearing mice

In this study we report on some lines of ongoing research performed in our laboratory, in relation to the increased expression of FcR on tumor cells, as well as on cells present in the tumor-bearing host, and its possible role in tumor progression. In a previous study we have shown that a Polyoma virus (PyV)-induced anaplastic carcinoma (SEYF-a tumor) contained an FcR-expressing subpopulation of tumorigenic cells. We tested the effect of in vivo passaging of FcR-expressing and of non-FcR-expressing sub-populations of SEYF-a tumor cells on the expression of FcR, as revealed by the ability of these cells to bind the 2.4G2 monoclonal antibody, which is directed against mouse Fc gamma 2b/gamma 1R. It was found that upon in vivo passaging these two sub-populations became practically identical in their ability to bind anti-Fc gamma R antibody. On the other hand, in vitro passaging of FcR-expressing SEYF-a cells resulted in a gradual decrease in the expression of Fc gamma R. These results, indicating that the expression of Fc gamma R on tumor cells, per se, is dependent on a factor present in the in vivo environment were confirmed using 3T3 cells transformed in vitro by PyV (C) and forming tumors at first injection to mice (CTC). C cultures of various clones did not express Fc gamma R, while CTC cultures (cultures from tumors) became positive. We also detected an increase in the level of a soluble form of Fc gamma 2b/gamma 1R in the circulation of mice bearing PyV induced tumors. This increase paralleled the appearance of palpable tumors. A similar pattern of increase was observed in mice inoculated with the c-H-ras transformed tumorigenic clone 8/F/5, but not in mice inoculated with non-tumorigenic 3T3 cells. Data published by us show that metastatic breast cancer patients had significantly elevated Fc gamma R levels on their peripheral blood mononuclear cells (PBMC). Experiments presented here indicate a direct correlation between increased Fc gamma R levels on PBMC and tumor mass in colon, ovary and lung metastatic carcinoma patients. The possibility that malignantly transformed cells have the potential to cause proliferation of Fc gamma R expressing T cells was tested. It was found that extract derived from r-H-ras transformed 3T3 cells triggers the proliferation of a T cell hybridoma expressing Fc gamma R.