Constitutive over-expression of transforming growth factor-alpha in rat liver epithelial cells leads to increased cell cycling without transformation.

Over-expression of transforming growth factor-alpha (TGF-alpha) is consistently seen in spontaneous transformants of rat liver derived epithelial cells (RLE phi 13) and has been implicated in the transformation of other cultured cells. We have constitutively over-expressed TGF-alpha in RLE phi 13 cells, which are known to express epidermal growth factor receptors, to determine if TGF-alpha over-expression plays a role in transformation or differentiation, or both, of these cells. Early passage RLE phi 13 cells were infected with a replication-defective murine retrovirus that expresses both the full length coding sequence for human TGF-alpha and the neomycin-resistance gene. Integration of the transcriptionally active provirus and expression of TGF-alpha mRNA were confirmed. Neither morphologic transformation nor molecular evidence for differentiation was noted in TGF-alpha-producing clones. However, these clones did exhibit an accelerated growth rate, increased expression of several cell cycle related genes including mitotic cyclic B1, proliferating cell nuclear antigen, c-myc, and p53 as well as increased expression of the preneoplastic marker enzyme, glutathione-S-transferase. This suggests that over-expression of TGF-alpha results in increased cell cycling, and that subsequent events must be necessary for cellular transformation or differentiation or both.

Brain microvascular smooth muscle expresses class II antigens.

Mouse (BALB/c) splenic lymphocytes co-cultured in vitro with syngeneic brain-derived microvascular smooth muscle (SM) proliferate and become activated. After subsequent transfer of the activated lymphocytes to a syngeneic host, a vasculitis develops in the host. Investigation of the possible antigen-presenting properties of the cultured SM has resulted in the demonstration of class II (Ia) antigens on the SM. Fluorescence-activated cell sorter analysis has shown that an average of 31% of unstimulated SM cells in culture were positive when stained with an anti-IE of the appropriate haplotype (H2d), and an average of 20% were positive with an anti-IA of the H2d haplotype. Controls consisting of irrelevant antibodies of the same isotype, as well as an anti-IA of the H2s haplotype, were negative. In contrast, BALB/c-derived brain microvascular endothelial cells showed considerably less class II antigen expression (7% for both IA and IE).

The physiology of B cells as studied with tumor models.

B-cell tumors have been extraordinary sources of information about antibodies, their genes, and the cells that express them. An important principle that has emerged from the study of lymphoid tumors is that the long-held view that malignant lymphoid cells are "frozen" at a fixed point in differentiation is not generally valid. Presentation of immunoregulatory signals to transformed B cells can profoundly influence their proliferation, morphology, differentiation, gene expression, and immunoglobulin synthesis. In addition to their responsiveness to immunoregulatory signals, some tumors of B lineage elaborate immunoregulatory signals. Until quite recently B-cell tumors were used primarily as monoclonal sources of molecules of immunological interest. While they continue to be important sources of receptors, growth and differentiation factors, differentiation antigens, and immunoregulatory factors, they are being used with increasing frequency to define the molecular events that occur in B cells subsequent to receipt of an immunoregulatory signal. While the use of tumor cells as models of normal cells is often viewed with some skepticism, it is difficult to find examples wherein tumors have been misleading. Quite to the contrary, B-cell tumors have regularly provided powerful tools for dissecting the molecular events that underlie B-cell development, function, and regulation.