Regulation of purine biosynthesis in cultured Drosophila melanogaster cells: I.--Conditional activity of hypoxanthine-guanine-phosphoribosyltransferase and 5-nucleotidase

Nucleoside and nucleobase transport and metabolism in wild type and nucleoside transport-deficient Aedes albopictus cells

Nucleoside and nucleobase transport and metabolism were measured in ATP-depleted and normal Aedes albopictus mosquito cells (line C-7-10) by rapid kinetic techniques. The cells possess a facilitated diffusion system for nucleosides, which in its broad substrate specificity and kinetic properties resembles that present in many types of mammalian cells. The Michaelis-Menten constant for uridine transport at 28 degrees C is about 180 microM. However, the nucleoside transporter of the mosquito cells is resistant to inhibition by nmolar concentrations of nitrobenzylthioinosine and the cells lack high affinity nitrobenzylthioinosine binding sites. The cells also possess an adenine transporter, which is distinct from the nucleoside transporter. They lack, however, a hypoxanthine transport system and are deficient in hypoxanthine phosphoribosyltransferase activity, which explains their failure to efficiently salvage hypoxanthine from the medium. The cells possess uridine and thymidine phosphorylase activities and, in contrast to cultured mammalian cells, efficiently convert uracil to nucleotides. An adenosine-resistant variant (CAE-3-6) of the C-7-10 cell line is devoid of significant nucleoside transport activity but transports adenine normally. Residual entry of various nucleosides into these cells and of hypoxanthine and cytosine into wild type and mutant cells is strictly non-mediated. The rate of permeation of various nucleosides and of hypoxanthine into the CAE-3-6 cells is related to their hydrophobicity. Uridine permeation into CAE-3-6 cells exhibits an activation energy of about 20 kcal/mol. At high uridine concentrations permeation is sufficiently rapid to partly overcome the limitation in nucleoside salvage imposed by the nucleoside transport defect in these cells.

Dihydrofolate reductase activity and resistance to aminopterin in various species of Drosophila

The aim of our work was to compare the mechanisms of resistance to aminopterin, inhibitor of the dihydrofolate reductase enzyme, between different Drosophila species and those described for cultured cells. Moreover we compared the systematic species divisions based on morphological traits and those based on a molecular approach. For this purpose, the effect of aminopterin on viability and wing phenotype was studied in different Drosophila species. Dihydrofolate reductase was measured in adult flies. We found an important dihydrofolate reductase activity in the melanogaster sub-group compared to the other species studies. Wing effect was observed only in this sub-group. The effects of aminopterin on the wing phenotype were very similar to the phenotype of rudimentary mutants. Both deplete the pyrimidine pool and it has been shown by the studies of the structural genes of the nucleotide pyrimidine pathway that the wing tissue is very sensitive to every pertubation of this metabolism. The D. ananassae species was found to be fully resistant at the concentrations of the inhibitor tested. No or very little dihydrofolate reductase activity was detected. The binding of the enzyme to the inhibitor was comparable to that found in the Oregon strain of D. melanogaster. The purine and pyrimidine salvage pathways were investigated and the D. ananassae species displayed an important thymidine kinase activity. The D. ananassae flies were sensitive on Sang medium compared to the Oregon flies but were able to use exogenous bases or nucleosides more efficiently.(ABSTRACT TRUNCATED AT 250 WORDS)

Subpopulations of fibroblasts from mouse skeletal muscle defined by clonal variation for 5' nucleotidase expression

A primary cloning technique has been employed for the isolation of nine spontaneously transformed cell lines from mouse skeletal muscle. Four of these lines were isolated after selection for partial resistance to the purine (adenine) analog 2'6'diaminopurine and five were isolated from non-selected control dishes. Four of the nonselected lines and three of the selected lines demonstrated a fibroblastoid morphology in vitro. The other two cell lines (one from each group) were epithelioid. Two of the three selected fibroblastoid lines were found to contain significant quantities of the enzyme 5'nucleotidase (EC3.1.3.5), whereas the four nonselected fibroblastlike lines, one selected fibroblastlike line, and the two epithelioid lines did not. In the two cell lines expressing 5'nucleotidase activity, this expression was stable in the absence of selective pressure. Histochemical staining of mouse skeletal muscle for 5'nucleotidase activity demonstrated positive staining in the cells of small blood vessels and in a subset of the connective tissue cells. The bulk of the skeletal muscle tissue, however, had no detectable 5'nucleotidase activity. We propose that the two cultivatable types of fibroblastoid cell lines represent distinct classes of fibroblastlike cells in vivo, reflecting alternative states of stable cellular differentiation involving 5'nucleotidase expression.

Regulation of purine biosynthesis in cultured Drosophila melanogaster cells: II/relationships between hypoxanthine-guanine-phosphoribosyl transferase and 5'-nucleotidase

All in vitro cell lines from Drosophila melanogaster do not possess measurable hypoxanthine - guanine - phosphoribosyltransferase (HGPRT) and 5'-nucleotidase activities. Nevertheless these enzymatic activities could be detected by the modification of culture conditions or treatment of crude extracts from Drosophila cells (1). A Drosophila melanogaster hemocyte line enabled demonstration of a relationship between the activities of HGPRT and 5'-nucleotidase. Only the addition of azaserine to the culture medium allows detection of a measurable amount of HGPRT and 5'-nucleotidase in cells devoid of endogenous synthesis of purine nucleotides. This action of azaserine suggests that the simultaneous expression of both enzymes is first directed by the suppression of the 5'-nucleotidase inhibition by pyrimidine nucleotides, and later on by the 5'-nucleotidase activity hydrolyzing the mononucleotides which inhibited the HGPRT, resulting its expression. This regulation system is confirmed by the simultaneous recovery of HGPRT and 5'-nucleotidase activities after heating cell cultures or cell extracts. Under such experimental conditions, 5'-nucleotidase is desensitized towards its negative effectors, while HGPRT regulation remains unchanged.