Virus-induced transformation without cell division

Rat C6 glioma cell growth is related to glucose transport and metabolism

In order to establish whether growth of glioma cells is associated with glucose transport and metabolism, we investigated expression of the glucose transporter and hexokinase, as well as glucose transport and glucose phosphorylation in rat C6 glioma cells growing at different rates. Rat C6 glioma cells were subcloned to produce four different cell lines (CL1, CL2, CL3 and CL4) differing in growth, differentiation and morphology: CL1 cells were slow-growing with an astrocytic appearance whereas CL4 cells grew rapidly and were small and spindle-shaped. Immunocytochemical analysis using glial fibrillary acidic protein and galactocerebroside antibodies revealed that CL1 and CL4 cells differentiate to astrocytes and oligodendrocytes respectively. Both of these cell lines expressed GLUT1 mRNA predominantly, whereas little GLUT3 mRNA was evident by Northern-blot analysis. The GLUT1 mRNA level was much higher in CL4 than in CL1 cells, and the uptake of 2-deoxy-D-glucose and 3-O-methyl-D-glucose by CL4 cells was markedly higher than that by CL1 cells, indicating a correlation between the growth rate, glucose transporter (GLUT1) level and glucose-transport rate of C6 glioma cells. We then studied glucose metabolism by CL1 and CL4 cells by measuring their hexokinase activities and intracellular concentrations of glucose and ATP. The mitochondrial hexokinase activity of CL4 cells was about three times higher than that of CL1 cells, whereas the cytosolic hexokinase activity of CL4 cells was only about half that of CL1 cells. As the total amount of cellular hexokinase protein in CL4 cells was only slightly higher (about 20%) than that in CL1 cells, the hexokinase protein of CL4 cells was considered to have moved from the cytosol to the mitochondrial membranes. Consistent with the increased mitochondrial hexokinase activity of CL4 cells, the intracellular glucose concentration was undetectable, and the ATP concentration was higher than that of CL1 cells, suggesting that glucose transport is the rate-limiting factor for overall glucose metabolism is rapidly growing C6 cells. Therefore the present data demonstrate that glioma cell growth is related to glucose transport, which is closely associated with glucose metabolism.

Reflections on viruses and cancer

In recent years human and animal cancers have increasingly been shown to have a viral component in their aetiology. Oncogenic viruses will continue to be discovered although with certain cancers there is also an important environmental component, and with others--congenital cancers and cancers of early childhood--an important genetic component. There is thus the probability that 'cancer' may not be an entity. Rather it may be a syndrome, the phenotypic expression of alteration of cellular metabolism, differentiation and cell death. More information is needed on the mathematics of cell division and destruction, in vivo and in vitro, and the involvement of 'biological clocks', i.e. ageing processes. These data, when available, should help us to understand better the nature of cancer and lead us to more effective methods of prevention and cure.

Early molecular replication of human immunodeficiency virus type 1 in cultured-blood-derived T helper dendritic cells

The rate and efficiency of key steps in the life cycle of the human immunodeficiency virus type 1 was examined in three primary cell types, T cells, monocytes, and T helper dendritic cells using the same quantity of virus involved and same cell number. The results show that viral DNA synthesis proceeds much more rapidly and efficiently in primary T helper dendritic cell populations than in primary T cell and monocyte populations. The increased rate of virus DNA synthesis is attributable either to an increase in the efficiency and the rate of uptake of the virus particles by the T helper dendritic cells, as compared with that in other cell types, or to an increased efficiency and rate of viral DNA synthesis in the T helper dendritic cells. In the subsequent phase of viral expression the appearance of spliced viral mRNA products also occur more rapidly in cultures of primary-blood-derived T helper dendritic cells than is the case in primary T cells and monocytes. The increased efficiency of the early steps of HIV-1 replication in primary-blood-derived T helper dendritic cells than in other blood-derived mononuclear cells raises the possibility that these cells play a central role in HIV-1 infection and pathogenesis.

Microsomal aspects of carcinogenesis and neoplasia

Neither immunologic nor genetic concepts of carcinogenesis have yet been decisively confirmed, and epigenetic theories, as formulated so far, are either non-predictive or insufficiently consistent with morphologic and experimental evidence. Computing data, concerned with carcinogenic mechanisms and neoplastic changes at the level of the endoplasmic reticulum, may lead to a new coherent understanding of tumor pathogenesis. Carcinogenic agents initiate biophysical perturbations, chemical alterations and conformational transitions in the membrane lattice of the endoplasmic reticulum. Foremost among the resulting neoplastic changes is an increased, irreversible separation of polyribosomes from membranes of the ergastoplasm. The carcinogenic process, apparently, deletes a protein required for polysome attachment. Since microsomal cytochromes can be synthesized by membrane-bound polysomes only, the translation of genetic information for their biosynthesis is irreversibly restricted. A similar, self-perpetuating deficiency may be postulated for the polysome attachment protein. Activities, depending on cytochromes P-450 and b5, are hampered, e.g. those of the monoxygenase system. Cholesterogenesis is derepressed. Ratios of phospholipids/cholesterol are decreased, and lipid-protein complexes, altered both in structure and function. Another distinct effect of the membrane-polysome separation is the unmasking of thiol-disulfide exchange enzymes which, in turn, stimulate the biosyntehsis of proteins and of deoxyribonucleotides involved in cell replication.