Cranberries (V. macrocarpon) were the best source of ursolic acid and its esters among the fruit and products tested. These compounds may limit prostate carcinogenesis through matrix metalloproteinase inhibition.
We compared the nucleosomal organization, histone H1 subtypes, and histone H1 phosphorylated isoforms of ras-transformed and parental 10T1/2 mouse fibroblasts. In agreement with previous studies, we found that ras-transformed mouse fibroblasts have a less condensed chromatin structure than normal fibroblasts. ras-transformed and parental 10T1/2 cells had similar amounts of H1 subtypes, proteins that have a key role in the compaction of chromatin. However, labeling studies with 32P and Western blot experiments with an antiphosphorylated H1 antibody show that interphase ras-transformed cells have higher levels of phosphorylated H1 isoforms than parental cells. G1/S phase-arrested ras-transformed cells had higher amounts of phosphorylated H1 than G1/S phase-arrested parental cells. Mouse fibroblasts transformed with fes, mos, raf, myc, or constitutively active mitogen-activated protein (MAP) kinase kinase had increased levels of phosphorylated H1. These observations suggest that increased phosphorylation of H1 is one of the consequences of the persistent activation of the mitogen-activated protein kinase signal transduction pathway. Indirect immunofluorescent studies show that phosphorylated H1b is localized in centers of RNA splicing in the nucleus, suggesting that this modified H1 subtype is complexed to transcriptionally active chromatin.
Mammalian ribonucleotide reductase, which occupies a key position in the synthesis of DNA, is a highly controlled enzyme activity, because it is solely responsible for the de novo reduction of ribonucleoside diphosphates to their corresponding deoxyribonucleoside diphosphate forms, required for DNA synthesis. Ribonucleotide reductase consists of two dissimilar protein components often called M1 and M2, which are independently regulated during cell proliferation. The M1 component contains multiple effector binding sites and is responsible for the complex allosteric regulation of the enzyme, whereas the M2 protein contains nonheme iron and a unique tyrosyl-free radical required for ribonucleotide reduction. Since the reaction is rate limiting for DNA synthesis, ribonucleotide reductase plays an important role in regulating cell division, and hence, cell proliferation. There are many inhibitors of ribonucleotide reductase and perhaps the most valuable one from a cell biology, biochemistry, and clinical point of view is the hydroxamic acid, hydroxyurea. This drug has also been very useful as a selective agent for isolating a variety of mammalian mutant cell lines altered in ribonucleotide reductase gene expression. Regulatory, structural, and biological characteristics of ribonucleotide reductase are reviewed, including evidence that ribonucleotide reductase, particularly the M2 protein, has an important early role to play in tumor promotion. In addition, modifications in the expressions of genes altered in hydroxyurea-resistant mutants and cultured in the absence or presence of hydroxyurea are discussed, with emphasis on changes in M2 protein, M1 protein, and the iron-storage protein ferritin.(ABSTRACT TRUNCATED AT 250 WORDS)
Proanthocyanidin-rich extracts were prepared by fractionation of the fruit of the North American cranberry (Vaccinium macrocarpon). In vitro growth inhibition assays in eight tumor cell lines showed that selected fractions inhibited the growth of H460 lung tumors, HT-29 colon and K562 leukemia cells at GI 50 values ranging from 20 to 80 µg ml −1 . Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) of one of these fractions found it to be composed of polyflavan-3-ols, which are primarily tetramers through heptamers of epicatechin containing one or two A-type linkages.Whole cranberry extract and the proanthocyanidin fractions were screened for effect on the expression of matrix metalloproteinases in DU 145 prostate carcinoma cells. The expression of MMP-2 and MMP-9 was inhibited in response to whole cranberry extract and to a lesser degree by the proanthocyanidin fractions.
An expression vector was constructed in which TGF‐beta 1 was placed under the control of the metallothionein promoter. Cys223 and Cys225 in the TGF‐beta 1 propeptide were converted to serines, mutations which result in dissociation of the pro‐peptide and secretion of bioactive TGF‐beta 1 [Brunner, A.M., Marquardt, H., Malacko, A.R., Lioubin, M.N. and Purchio, A.F. (1989) J. Biol. Chem., 264, 13660–13664]. A fibrosarcoma was transfected with this plasmid and a clone (17.18) was selected in which TGF‐beta 1 mRNA was able to be induced six‐fold following zinc sulphate treatment. These cells increased the secretion of bioactive TGF‐beta 1 14‐fold and exhibited a coincidental increase in jun‐B mRNA expression, suggesting that secreted TGF‐beta 1 was acting to induce this early response gene by autocrine activation. Following zinc sulphate induction, the tumor cells became progressively more motile and able to invade collagen gels. In contrast to parental tumor not bearing the TGF‐beta 1 expression vector, zinc sulphate stimulation of clone 17.18 enhanced collagenase IV and procathepsin L mRNA levels and enhanced the secretion of many collagenolytic proteases into the medium. Since the action of TGF‐beta generally decreases proteolysis by suppression of protease transcription, we compared the response of normal parental fibroblasts to ras‐transformed fibrosarcomas and confirmed that TGF‐beta could greatly enhance collagenase IV and procathepsin L mRNA levels while having little effect on non‐transformed fibroblasts. These experiments indicate that induction of TGF‐beta secretion can enhance motility and protease production through autocrine activation, thus increasing the invasion potential of fibrosarcomas.
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