Aspects of the secondary and tertiary structure of DNA

Modulation of DNA binding of nuclear transcription factors with leucine-zipper motifs by particular endogenous polyamines in murine central and peripheral excitable tissues

Transcriptional regulation is one of the most important functions of polyamines in the nucleus of eukaryotic cells. The addition of the endogenous polyamines spermine and spermidine markedly increased DNA binding activity of the transcription factor activator protein-1 (AP1) in a concentration-dependent manner at a concentration range of 50 to 500 microM in nuclear extracts of murine whole brain when determined in the absence of added MgCl(2) on gel retardation electrophoresis. Similar but less potent potentiation was seen with DNA binding of cAMP responsive element binding protein (CREB), while both polyamines were ineffective in affecting that of c-Myc irrespective of the addition of MgCl(2). Unlabeled AP1 probe was invariably more potent in competing for AP1 binding than unlabeled CREB probe in either the presence or absence of spermine and spermidine. In addition to whole brain, both polyamines significantly increased AP1 binding in retina, adrenal and pituitary, without significantly affecting that in spleen. Moreover, ultraviolet and circular dichroism spectra analyses revealed that these two polyamines induced DNA topological transition of AP1 probe under the conditions favorable for the increase in AP1 binding. These results suggest that both spermine and spermidine may modulate gene transcription through cis- and trans-actions on AP1 binding in the nucleus in murine central and peripheral structures with high excitability.

Interaction of the antitumor agents cis,cis,trans-Pt(IV)(NH3)2Cl2(OH)2 and cis,cis,trans-Pt(IV)[(CH3)2CHNH2]2Cl2(OH)2 and their reduction products with PM2 DNA

The ability of two platinum(IV) antitumor agents, cis,cis,trans-PtIV[(CH3)2CHNH2]2Cl2(OH)2 (2) and cis,cis,trans-PtIV(NH3)2Cl2(OH)2 (4), to interact with PM2 DNA was examined. Analysis using gel electrophoresis showed that neither compound is able to alter the electrophoretic mobilities of the three forms of PM2 DNA in the gel. However, incubation of 2 and 4 with 2 equiv of Fe(ClO4)2 X 6H2O or 1 equiv of ascorbic acid results in reduction to yield the divalent complexes cis-PtII(NH3)2Cl2 (1) and cis-PtII-[(CH3)2CHNH2]2Cl2 (3). The structures of the reduction products were characterized by using elemental analysis as well as infrared and 195Pt NMR spectroscopies. Both 1 and 3 were found to bind to and unwind supercoiled form I PM2 DNA. The aforementioned observations support the suggestion that reduction is a means of activating the antitumor properties of 2 and 4.

Palladium or platinum exacerbates hydroxyl radical mediated DNA damage

Strand breakage of supercoiled pBR322 DNA by a Fenton system is increased in the presence of palladium or platinum (Pt) ions. Neither Pd nor Pt ions can substitute for iron in the Fenton system. We have obtained several lines of evidence that Pd and Pt ions in the presence of a Fenton system can augment the production of OH., as monitored by a spectrophotometric method quantifying hydroxylated salicylate or by a fluorometric method quantifying catechol production. Furthermore, the promoting effect of both metal ions on OH. production was substantiated by the identification of multiple hydroxylated products of salicylate [2,3-dihydroxybenzoate (A), 2,5-dihydroxybenzoate (B), and catechol (C)] using HPLC. The concentrations of A, B, and C produced in the control were 4.5, 8.0, and 2.0 microM, respectively; whereas, their respective concentrations increased to 23.6, 42.0 and 10.0 microM with the addition of Pd ions. The observed phenomenon was further confirmed by the identification of HO-DMPO spin adducts using ESR spectroscopy. Taken together, our data suggest that the mechanism of Pd or Pt ion-mediated exacerbation of DNA damage by a Fenton system is due to the promotion of OH. production by these metal ions.