No abstract

IL-1 is released by activated monocytes and is thought to be a key mediator of the host immune response. The availability of the purified and, more recently, recombinant IL-1 has allowed the characterization of other biological properties of this molecule. Thus, IL-1 is thought to have the same properties as hemopoietic 1, a growth factor that has been shown to act on primitive murine hemopoietic cells. Here we report that rIL-1 acts synergistically with granulocyte/macrophage CSF (GM-CSF) or granulocyte CSF in the stimulation of clonogenic cells from many patients with acute myeloblastic leukemia (AML). Although IL-1 by itself has no effect on AML blasts, it can support colony formation under conditions where there is detectable production of endogenous GM-CSF. IL-1 also promotes the growth of multipotential progenitors from normal human bone marrow cells in the presence of GM-CSF. These observations support the hypothesis that in the hemopoietic system, IL-1 has a selective effect on primitive precursors.

Mutants induced at the adenine phosphoribosyl transferase (aprt) locus by dTTP or dCTP pool imbalances were examined for alterations in genomic DNA sequences. No observable changes were detected by Southern blot analysis of most mutant DNAs, suggesting induction of base pair alterations or other events below our level of detection (-30 base pairs). However, in a few strains (11 from a total collection of 125 mutant cell strains), we were able to localize these events to restriction endonuclease recognition sequences when the mutations resulted in the loss or gain of a particular site. The distribution of lost or gained sites in aprt-deficient mutants induced by the two types of pool imbalances clearly varied, with those occurring in a mutator strain with increased dCTP clustering at one end of the aprt gene. Mutants induced by dTTP also revealed novel events: multiple restriction site modifications in a small region of the aprt gene in one mutant and a small (-50 base pairs) insertion or duplication of DNA sequences. As in previous studies, very few deletion or insertion mutants were detected at the aprt locus. The significance of these findings in terms of the known biochemical and genetic consequences of these pool imbalances is discussed.Imbalances of the pools of DNA synthetic precursors, the deoxyribonucleoside triphosphates, have profound genetic effects on cells (12,17). Thymidylate starvation induces a recA-dependent, error-prone repair system in Escherichia coli (7) and recombination in yeast cells (13). Excess thymidylate induces mutations in phage (3) and yeast cells (2). In cultured mammalian cells, both thymidylate deprivation and excess produce gross genetic abnormalities-chromosome breaks, deletions, and sister chromatid exchanges (1,12,22,24). Effects of pool imbalances on single-gene loci have also been reported in the form of increased mutational frequencies (5) or rates (16,20,29) and altered sensitivities to DNAdamaging agents (15,23). Despite the wide range of events induced by deoxyribonucleoside triphosphate pool imbalances, the molecular mechanisms by which the events arise are unknown. In vitro DNA-synthesizing systems with either procaryotic or eucaryotic enzymes indicate that pool balance plays an important role in accurate base pairing (11) and, in procaryotes, "editing" activities (9). However, the contribution of these factors to the final effects observed in vivo (mutations and gross chromosomal abnormalities) is not clear.In the experiments reported here, we made use of a cloned probe for a "selectable locus" to determine the molecular basis of mutations induced by imbalances of both dTTP (produced with excess exogenous thymidine) and dCTP (with somatic cell mutations; Table 1). The selectable locus investigated was that coding for adenine phosphoribosyl transferase (aprt). This locus is attractive for these analyses for a number of reasons. The data presented here suggest that most mutarts induced at the aprt locus by both types of pool imbalance are either point mutations or del...

Thy- mutants, in addition to being resistant to arabinosyl cytosine (arcC), show cross-resistance to 5-fluorouracil (5FU). When Chinese hamster ovary (CHO) cells were exposed to a selection system using both araC and 5FU, the resistant clones isolated were identical to thy- mutants by the following criteria: (1) all were auxotrophic for thymidine with a high reversion frequency to thymidine prototrophy; (2) those tested had a high level of dCTP relative to wild-type cells, while dTTP and dATP levels were unaffected, and (3) all tested had a 7- to 50-fold higher rate of spontaneous mutation than the wild-type strain for at least one independent genetic marker. Although spontaneous thy- mutants were rare, the frequencies of thy- mutants in untreated and mutagenized cultures are consistent with the conclusion that the thy- phenotype is the consequence of a single mutation in CHO cells.

The effects of recombinant interleukin-6 (IL-6) on the proliferation of blast precursors present in the peripheral blood of patients with acute myeloblastic leukemia (AML) was investigated. IL-6 had little effect by itself; however, it synergized with granulocyte macrophage colony- stimulating factor (GM-CSF) and interleukin-3 (IL-3) in the stimulation of AML blast colony formation. Responsiveness of blast progenitors to IL-6 was heterogeneous. On normal bone marrow cells the same synergy was observed on granulocyte and monocyte precursors (GM-CFC), while there was no significant effect on erythroid and multipotential precursors.