Heme oxygenase 1 (HO-1) challenges the angiogenic switch in prostate cancer.

Prostate cancer (PCa) is the second leading cause of cancer-associated death in men. Once a tumor is established it may attain further characteristics via mutations or hypoxia, which stimulate new blood vessels. Angiogenesis is a hallmark in the pathogenesis of cancer and inflammatory diseases that may predispose to cancer. Heme oxygenase-1 (HO-1) counteracts oxidative and inflammatory damage and was previously reported to play a key role in prostate carcinogenesis. To gain insight into the anti-tumoral properties of HO-1, we investigated its capability to modulate PCa associated-angiogenesis. In the present study, we identified in PC3 cells a set of inflammatory and pro-angiogenic genes down-regulated in response to HO-1 overexpression, in particular VEGFA, VEGFC, HIF1α and α5ß1 integrin. Our results indicated that HO-1 counteracts oxidative imbalance reducing ROS levels. An in vivo angiogenic assay showed that intradermal inoculation of PC3 cells stable transfected with HO-1 (PC3HO-1) generated tumours less vascularised than controls, with decreased microvessel density and reduced CD34 and MMP9 positive staining. Interestingly, longer term grown PC3HO-1 xenografts displayed reduced neovascularization with the subsequent down-regulation of VEGFR2 expression. Additionally, HO-1 repressed nuclear factor κB (NF-κB)-mediated transcription from an NF-κB responsive luciferase reporter construct, which strongly suggests that HO-1 may regulate angiogenesis through this pathway. Taken together, these data supports a key role of HO-1 as a modulator of the angiogenic switch in prostate carcinogenesis ascertaining it as a logical target for intervention therapy.

Ensemble and single particle photophysical properties (two-photon excitation, anisotropy, FRET, lifetime, spectral conversion) of commercial quantum dots in solution and in live cells.

In this work, we characterized streptavidin-conjugated quantum dots (QDs) manufactured by Quantum Dot Corporation. We present data on: (1) two-photon excitation; (2) fluorescence lifetimes; (3) ensemble and single QD emission anisotropy; (4) QDs as donors for Forster resonance energy transfer (FRET); and (5) spectral conversion of QDs exposed to high-intensity illumination. We also demonstrate the utility of QDs for (1) imaging the binding and uptake of biotinylated transferrin on living cells, and (2) resolving by fluorescence lifetime imaging microscopy (FLIM) signals originating from QDs from those of spatially and spectrally overlapping visible fluorescent proteins (VFPs).

Actinomycin D binding to single-stranded DNA: sequence specificity and hemi-intercalation model from fluorescence and 1H NMR spectroscopy.

We have studied the sequence specificity in the binding of the potent antitumor drug actinomycin D (AMD) to single-stranded DNA (ssDNA) by fluorescence and NMR spectroscopy and by molecular modeling. The significant absorption and emission changes accompanying the interaction of the fluorescent derivative 7-amino-AMD with DNAs varying in length and base composition were used to calculate affinity constants for the drug-DNA complexes. The guanine-containing trinucleotide sequences AGT, AGA, and TGT embedded within 25-base oligonucleotides, constituted favorable binding sites. In contrast, the sequence TGA did not bind the drug appreciably. Among the DNAs studied, the highest affinity was for the tetranucleotide sequence TAGT. The binding was length dependent, an oligonucleotide of at least 14 bases being required for effective complex formation (Ka > 10(4) M1=). AMD also bound to poly(d(AGT)). Gel electrophoresis confirmed that the complex was formed between the drug and individual unstructured DNA strands. The 1H NMR spectra of oligonucleotides containing the TAGT site and their complexes with AMD provided further insight into the mode(s) of interaction. A comparison of the measured chemical shifts with those estimated from ring-current calculations provided strong evidence for a hemi-intercalation of AMD between the A and G purine bases with a preference for one of two possible relative orientations. The latter were modeled as complexes with the sequence T3AGT3 and refined by force field calculations with the AMBER program. The biological implications for this novel form of interaction of AMD with single-stranded DNA are discussed.

Determination of DNA helical handedness by fluorescence resonance energy transfer.

Fluorescence resonance energy transfer (FRET) has been used to determine the helical handedness, twist and rise of different DNA conformations. The approach is based on the construction of a set of molecules consisting of two fused helical segments, one of which is in a known reference helical form. The duplexes are covalently labeled at one end with a donor and at the other with an acceptor. By systematically shifting the position of the junction while maintaining constant the total length in base-pairs, the variation in the efficiency of energy transfer can be shown to depend primarily and sensitively on the differences in helical twist and rise of the two constituent segments. If the latter have the same helical sense, one predicts a FRET signal that is a monotonic function of the junctional position. In contrast, a periodic function arises when two segments are of opposite handedness. The formalism includes explicit consideration of dye orientation (the dipole-dipole orientation factor kappa) and an implementation valid for single helix molecules, and introduces new functions of measured fluorescence signals for establishing the FRET efficiency. The method has been applied to a family of oligonucleotides forming hairpin duplexes containing an antiparallel-stranded (aps) d(m5C.G)m segment labeled at the 5' end with fluorescein (donor) and a second parallel- stranded d(A.T)N-m segment (psAt-DNA) labeled at the hairpin loop with the sulfoindocyanine dye Cy3. The segment lengths were in the range 4 to 12, but the total length N was maintained constant at 16. The d(m5C.G) sequence was chosen due to its capacity for adopting a B or a Z conformation at low and high concentrations of salt, respectively. The parallel-stranded d(A.T) sequence served as the second segment in order to determine the helical rise and twist of psAT-DNA, presumed to be right-handed from molecular modeling and a prior study of topologically constrained DNA. A Z-DNA/ps-DNA junction was created between the two segments by inducing a B-Z transition in d(m5C.G)m with MgCl2. The range of required salt concentration was established by circular dichroism measurements. FRET efficiency values of 0.38 to 0.41 were obtained for the oligonucleotides with the d(m5C.G) segment in the B conformation. In contrast, upon induction of the B-Z transition the FRET efficiency was a decreasing function of the d(m5C.G) content (0.38 to 0.28 for m = 6 to 12). Helical parameters were estimated from functional fits of the data, and were consistent with the known properties of B- and Z-DNAs and with the conclusion that psAT-DNA has a helical rise and twist close to that of B-DNA. The approach outlined here is not restricted to DNA but can be applied to other helical structures, e.g. RNA, proteins, and protein-nucleic acid complexes.

On the structures of crambescins B and C1.

Revised structures have been assigned to the cyclic guanidine-containing crambescins B [3] and C1 [5], from the Mediterranean sponge Crambe crambe. The revisions were based on the fabms/cid/ms spectra of the [M+H]+ ions from crambescins B and C1 and hrfabms measurements on key fragment ions in the ms/ms spectra, which identify losses of C9H19 and C8H18N3O side-chains.