1-Methylnicotinamide and NAD metabolism in normal and transformed normal rat kidney cells

NAD, 1-methylnicotinamide, S-adenosylmethionine, and S-adenosylhomocysteine levels were analyzed in different clones of untransformed normal rat kidney cells and in cells transformed by different viruses. No consistent changes in the levels of these metabolites were apparent as a result of malignant transformation, and also differences in the levels of metabolites did not correlate with growth rate in the various cell lines. 3-Deazaadenosine prevented synthesis of 1-methylnicotinamide but not of NAD. The S-denosylmethionine/S-adenosylhomocysteine ratio did not change in serum-starved, growth-arrested cells although 1-methylnicotinamide synthesis increased about twofold. These results were used to consider possible physiological roles for 1-methylnicotinamide. Its intracellular levels did not correlate with growth rate and were not altered by transformation. No evidence was obtained that its synthesis is involved with maintenance of nicotinamide of S-adenosylmethionine levels. Thus the biological function for 1-methylnicotinamide remains a mystery.     

Pituicytes in normal and Jimpy mice

Summary Neural lobes of control and Jimpy mice were examined electron microscopically. The ultrastructure and incidence of pituicytes was examined following reports of reductions in astrocyte and oligodendrocyte populations in areas of the CNS of Jimpy mice. The failure to demonstrate any modification of structure or numbers of the pituicytes in the affected animals suggests that the pituicytes are not as closely related to the satellite cells of the CNS as has previously been proposed.Grateful thanks to Miss M. Pehrson for supply of animals used in these experiments, and to Mrs. J. Griffin for technical assistance.     

Enucleation of normal and transformed cells

A quantitative analysis based on centrifugal force requirements for enucleation was developed to examine the response of a number of untransformed and transformed cell lines to cytochalasin mediated enucleation. Examination of the extent of cell enucleation as a function of centrifugal force resulted in a series of response curves demonstrating that enucleation g force requirements varied between Balb/c 3T3, Swiss 3T3, and Kirsten sarcoma virus transformed Balb/c 3T3 (3T3-K). A four times greater centrifugal force was required to reach 50% enucleation for transformed Balb/c 3T3-K when compared to Swiss 3T3. A qualitative correlation could be observed between ease of enucleation and the existence of a well-formed stress fiber network. A comparison of cytochalasin B and D suggested that cytochalasin D was far more effective in the enucleation of transformed cells. Experiments with 2-deoxyglucose and monensin provided evidence that decreasing cellular ATP levels, either directly or potentially by uncoupling ion transport from ATP generation, can decrease the efficiency of enucleation. It is suggested that the organization of the cytoskeleton is affected by the altered cellular ATP levels which can affect the centrifugal requirements of enucleation.     

Proteoglycans in normal and neoplastic monocytes

35S proteoglycans produced by normal and neoplastic (U-937) monocytes after a 20-h pulse with [35S]sulfate in vitro have been isolated and compared. Both cell types produce exclusively chondroitin sulfate proteoglycan (CSPG), which are released into the medium and are not contained within the cells. The neoplastic cell-derived molecules were much larger in molecular size, due to the substitution of galactosaminoglycan chains, with an approximate Mr of 60,000. The corresponding chains in monocyte CSPG had an Mr of approx. 20,000. The latter chains were also found to be more sulfated than their neoplastic counterparts.     

Stabilising normal and mis-sense variant alpha-glucosidase

alpha-Glucosidase (EC 3.2.1.3) is a lysosomal enzyme that hydrolyses alpha-1,4- and alpha-1,6-linkages of glycogen to produce free glucose. A deficiency in alpha-glucosidase activity results in glycogen storage disorder type II (GSD II), also called Pompe disease. Here, d-glucose was shown to be a competitive inhibitor of alpha-glucosidase and when added to culture medium at 6.0 g/L increased the production of this protein by CHO-K1 expression cells and stabilised the enzyme activity. D-Glucose also prevented alpha-glucosidase aggregation/precipitation and increased protein yield in a modified purification scheme. In fibroblast cells, from adult-onset GSD II patients, D-glucose increased the residual level of alpha-glucosidase activity, suggesting that a structural analogue of d-glucose may be used for enzyme enhancement therapy.     

Mechanisms of normal and tumor-derived angiogenesis

Often those diseases most evasive totherapeutic intervention usurp the human body's own cellular machineryor deregulate normal physiological processes for propagation.Tumor-induced angiogenesis is a pathological condition that resultsfrom aberrant deployment of normal angiogenesis, an essential processin which the vascular tree is remodeled by the growth of newcapillaries from preexisting vessels. Normal angiogenesis ensures thatdeveloping or healing tissues receive an adequate supply of nutrients.Within the confines of a tumor, the availability of nutrients islimited by competition among actively proliferating cells, anddiffusion of metabolites is impeded by high interstitial pressure (Jain RK. Cancer Res 47: 3039-3051, 1987). As a result, tumorcells induce the formation of a new blood supply from the preexisting vasculature, and this affords tumor cells the ability to survive andpropagate in a hostile environment. Because both normal and tumor-induced neovascularization fulfill the essential role of satisfying the metabolic demands of a tissue, the mechanisms by whichcancer cells stimulate pathological neovascularization mimic thoseutilized by normal cells to foster physiological angiogenesis. Thisreview investigates mechanisms of tumor-induced angiogenesis. Thestrategies used by cancer cells to develop their own blood supply arediscussed in relation to those employed by normal cells duringphysiological angiogenesis. With an understanding of blood vesselgrowth in both normal and abnormal settings, we are better suited todesign effective therapeutics for cancer.