DNA replication and cell-cycle progression of cultured mouse FM3a cells after treatment with 8-methoxypsoralen plus near UV-radiation

Inducible expression of exogenous genes in Dictyostelium discoideum using the ribonucleotide reductase promoter

We report here the development of a regulated gene expression system for Dictyostelium discoideum based on the DNA-damage inducibility of the rnrB gene. rnrB, which codes for the small subunit of the enzyme ribonucleotide reductase, responds to DNA-damaging agents at all stages of the D.discoideum life cycle. Doses that have little effect on development have previously been shown to increase the level of the rnrB transcript by up to 15-fold. Here we show that all elements necessary for DNA-damage induction are contained in a 450 bp promoter fragment. We used a fusion of the rnrB promoter with the gene encoding GFP to demonstrate an up to 10-fold induction at the RNA level, which appears in all aspects similar to induction of the endogenous rnrB transcript. Using a fusion with the lacZ gene we observed an up to 7-fold induction at the protein level. These results indicate that the rnrB promoter can be used to regulate the expression of specific genes in D.discoideum. This controllable gene expression system provides the following new characteristics: the induction is rapid, taking place in the order of minutes, and the promoter is responsive at all stages of the D.discoideum life cycle.

Molecular analysis of Fanconi anaemia

The autosomal recessive genetic disease, Fanconi anaemia, is perceived as another manifestation of defective cellular DNA repair, just as in the autosomal recessive disease Xeroderma pigmentosum. The biochemistry and cellular biology of Xeroderma pigmentosum have been convincingly elucidated, but the same has not been true for Fanconi anaemia. In this review we consider the pleiotropic nature of Fanconi anaemia, its clinical and cellular variability and its genetic heterogeneity. We take into account the wealth of experimental findings available and offer a novel hypothesis involving feedback control of DNA replication during S phase of the cell cycle to explain the basic defect in the disease.

8-Methoxypsoralen and longwave ultraviolet irradiation are a novel antiproliferative combination for vascular smooth muscle

BACKGROUND

Smooth muscle cell proliferation plays a major role in the genesis of restenosis after angioplasty or vascular injury. Although the effects of arterial exposure to high-energy radiation sources such as laser have been investigated in detail, the effects on vascular cells of low-intensity radiant energy in combination with photoactive agents have not been extensively characterized. Psoralens are photoactive agents that are known to be well tolerated when used in conjunction with local exposure to ultraviolet light in the A band (UVA) for the treatment of various dermatologic proliferative disorders.

METHODS AND RESULTS

We have investigated the effects of psoralen/UVA (PUVA) exposure on the proliferation of bovine aortic smooth muscle cells. Proliferation and viability were assessed over a 14-day period by trypan blue exclusion counts. Cell cycle effects were evaluated by thymidine incorporation and flow cytometry with DNA quantitation after addition of serum or platelet-derived growth factor B-chain (PDGF-BB) to subconfluent cells synchronized by serum withdrawal. No effect was observed after exposure to 8-methoxypsoralen (8-MOP) at concentrations up to 10 microM or UVA irradiation at energies up to 2.5 J/cm2. Longwave ultraviolet light and 8-MOP were found to behave synergistically as potent inhibitors of DNA synthesis in bovine aortic smooth muscle cells with the EC50 in combination ranging from 7 microM at 0.35 J/cm2 to 0.2 microM at 2.1 J/cm2. Similar antiproliferative effects were obtained by an inverse variation of dose and energy delivered. After serum stimulation, inhibition of DNA synthesis was found with either an immediate or delayed (16-hour) application of PUVA. This effect was independent of subsequent 8-MOP washout. Flow cytometry of cells treated with PUVA at several times after serum stimulation demonstrated for each time point a block in further cell cycle progression for cells in all phases of the cell cycle. Evaluation of [125I]-labeled PDGF and epidermal growth factor (EGF) binding revealed no effect of PUVA on the apparent number or affinity of PDGF binding sites present but did reveal a dose-dependent inhibition by PUVA of EGF binding. This inhibition of EGF binding occurred increasingly at higher PUVA doses than the cell cycle inhibition and accordingly did not appear to represent a critical mechanism for the antiproliferative effect. Cell counting after a single exposure to PUVA (1 microM, 1.5 J/cm2) revealed complete stasis of cell proliferation over a 28-day period without recurrent exposure. No increase in trypan-positive cells was noted over this period.

CONCLUSIONS

PUVA treatment represents a novel method for locally inhibiting proliferation of vascular smooth muscle cells without producing cytolysis.

Cytometric analysis of the proliferative capacity of HUT 102 lymphoblasts exposed to long-wave UV light and psoralen

Cultures of HUT 102 lymphoblasts, comprised of near-diploid and hyperdiploid cells (11 and 22 pg of DNA/nucleus), were irradiated for 2 h by long wave ultraviolet light (UV-A) (2.1 mW/cm2), reacted for the same time in the dark with suprapharmacologic concentrations of 8-methoxypsoralen (8-MOP) (15 micrograms/ml) and exposed to 8-MOP and UV-A (PUVA) under identical conditions. Flow cytometric determinations of cellular DNA content and IdUrd incorporation indicated that UV-A irradiated cells incorporated IdUrd at the control levels and that the number of cells in S and G2 + M phases of the cell cycle likewise were identical to controls. The dark reaction of HUT 102 cells with 8-MOP has, however, resulted in a transient increase of IdUrd incorporation, but it has not affected cellular proliferation rates. On the other hand, no IdUrd incorporation was detected after PUVA. The analysis of the DNA content of intact and PUVA-exposed cultures showed that the number of near-diploid S-phase cells was greater 24 h after PUVA, whereas the number of hyperdiploid cells in all phases of the cell cycle had decreased. Under stated conditions the viability of HUT 102 cells and their cell cycle disturbances by PUVA are determined in part by the amount of DNA in target lymphoblasts.

Maturation of nascent DNA fragment is disturbed after treatment of cultured mouse FM3A cells with 8-methoxypsoralen plus near-ultraviolet radiation

By the method of sedimentation in 5-20% alkaline sucrose gradient, the process of maturation of the nascent DNA fragment was studied with cultured mouse FM3A cells treated with 8-methoxypsoralen plus near-ultraviolet radiation. This treatment is known to cause crosslinks of the chromosomal DNA strands. The profile of the newly-replicated DNA, labeled for 10 min with [3H]thymidine immediately after treatment, was the same as that of the untreated cells, where the incorporated radioactivity was present in the intermediate DNA fragment (about 50-80 S). But, when the treated cells were labeled after several hours of incubation, the labeled DNA became much shorter due to inhibition of maturation of the initial DNA fragment (the Okazaki fragment) to the intermediate DNA. With the use of aphidicolin, a specific inhibitor of eukaryotic DNA polymerase alpha, it became apparent that, in addition to formation of the crosslinks, further DNA replication is required to cause this inhibition of DNA maturation. Aphidicolin also suppressed the inhibition of incorporation of [3H]thymidine into cellular DNA after treatment, but inhibition of this incorporation resumed after its removal.

DNA crosslinks and DNA replication in mouse FM3A cells after treatment with 8-methoxypsoralen plus near-ultraviolet radiation

The rate of DNA-chain elongation was studied in mouse FM3A cells after treatment with 8-methoxypsoralen plus near-ultraviolet radiation using the minimal doses (1 microgram/ml 8-methoxypsoralen plus 1-2.5 kJ/m2 of near-ultraviolet radiation) which inhibited cell-cycle progression or DNA replication. A rapid decrease in incorporation of [3H]thymidine and recovery to some extent during incubation after treatment have been reported (Hyodo, M., Fujita, H., Suzuki, K., Yoshino, K., Matsuo, I. and Ohkido, M. (1982) Mutat. Res. 94, 199-211). The results of the present study showed that the rate was not changed suggesting that the decrease in [3H]thymidine incorporation was not due to the rate of DNA-chain elongation, but was due to change in the frequency of initiation of replication. Formation of DNA crosslinks was then studied by the sedimentation of pre-labeled DNA in an alkaline sucrose gradient. The results showed that, at these doses of 8-methoxypsoralen plus near-ultraviolet radiation, approx. 2-7 crosslinks were formed per 10(9) Da. It was also suggested that some of the DNA crosslinks might be repaired during the prolonged incubation, but unrepaired crosslinks were still present after 24 h incubation.