Laurence Hurley

PMID: 20377208;PMCID: PMC2868086;Abstract:

To understand the mechanisms controlling platelet-derived growth factor receptor β (PDGFR-β) expression in malignancies, we have cloned and characterized the first functional promoter of the human PDGFR-β gene, which has been confirmed by luciferase reporter gene assays. The transcription initiation sites were mapped by primer extension. Promoter deletion experiments demonstrate that the proximal, highly GC-rich region (positions -165 to -139) of the human PDGFR-β promoter is crucial for basal promoter activity. This region is sensitive to S1 nuclease and likely to assume a non-B-form DNA secondary structure within the supercoiled plasmid. The G-rich strand in this region contains a series of runs of three or more guanines that can form multiple different G-quadruplex structures, which have been subsequently assessed by circular dichroism. A Taq polymerase stop assay has shown that three different G-quadruplex-interactive drugs can each selectively stabilize different G-quadruplex structures of the human PDGFR-β promoter. However, in transfection experiments, only telomestatin significantly reduced the human PDGFR-β basal promoter activity relative to the control. Furthermore, the PDGFR-β mRNA level in Daoy cells was significantly decreased after treatment with 1 μM telomestatin for 24 h. Therefore, we propose that ligand-mediated stabilization of specific G-quadruplex structures in the human PDGFR-β promoter can modulate its transcription. © 2010 American Chemical Society.

PMID: 9811834;PMCID: PMC24853;Abstract:

Psorospermin is a plant natural product that shows significant in vivo activity against P388 mouse leukemia. The molecular basis for this selectivity is unknown, although psorospermin has been demonstrated to intercalate into DNA and alkylate N7 of guanine. Significantly, the alkylation reactivity of psorospermin at specific sites on DNA increased 25- fold in the presence of topoisomerase II. In addition, psorospermin trapped the topoisomerase II-cleaved complex formation at the same site. These results imply that the efficacy of psorospermin is related to its interaction with the topoisomerase H-DNA complex. Because thermal treatment of (N7 guanine)-DNA adducts leads to DNA strand breakage, we were able to determine the site of alkylation of psorospermin within the topoisomerase II gate site and infer that intercalation takes place at the gate site between base pairs at the +1 and +2 positions. These results provide not only additional mechanistic information on the mode of action of the anticancer agent psorospermin but also structural insights into the design of an additional class of topoisomerase II poisons. Because the alkylation site for psorospermin in the presence of topoisomerase II can be assigned unambiguously and the intercalation site inferred, this drug is a useful probe for other topoisomerase poisons where the sites for interaction are less well defined.

PMID: 1588557;Abstract:

(+)-CC-1065 is a potent antitumor antibiotic produced by Streptomyces zelensis. Previous studies have shown that the potent cytotoxic and antitumor activities of (+)-CC-1065 are due to the ability of this compound to covalently modify DNA. (+)-CC-1065 reacts with duplex DNA to form a (NS-adenine)-DNA adduct which lies in the minor groove of DNA overlapping with a five base-pair region. As a consequence of covalent modification with (+)-CC-1065, the helix bends into the minor groove and also undergoes winding and stiffening. In the studies described here, we have constructed templates for helicase-catalyzed unwinding of DNA that contain site-directed (+)-CC-1065 and analogue DNA adducts. Using these templates we have shown that (+)-CC-1065 and select synthetic analogues, which have different levels of cytotoxicity, all produce a significant inhibition of unwinding of a 3′-tailed oligomer duplex by helicase II when the displaced strand is covalently modified. However, the extent of helicase II inhibition is much more significant for (+)-CC-1065 and an analogue which also produced DNA winding when the winding effects are transmitted in the opposite direction to the helicase unwinding activity. This observed pattern of inhibition of helicase-catalyzed unwinding of drug-modified templates was the same for a 3′-T-tail, for different duplex region sequences, and with the Escherichia coli rep protein. Unexpectedly, the gel mobility of the displaced drug-modified single strand was dependent on the species of drug attached to the DNA. Last, strand displacement by helicase II coupled to primer extension by E. coli DNA polymerase I showed the same pattern of inhibition when the lagging strand was covalently modified. In addition, the presence of helicase II on single-stranded regions of templates caused the premature termination of primer extension by DNA polymerase. These results are discussed from the perspective that (+)-CC-1065 and its analogues have different effects on DNA structure, and these resulting structural changes in DNA molecules are related to the different in vivo biological consequences caused by these drug molecules. © 1992 American Chemical Society.