Activation of p53 transcriptional activity by 1,10-phenanthroline, a metal chelator and redox sensitive compound

p53, a tumor suppressor gene, functioning as a transcription factor, has been recently shown in a cell free system to be subject to redox (reduction/oxidation) regulation. Oxidants or metal chelating reagents disrupt wildtype p53 conformation and decrease or abolish its DNA binding activity, while reductants restore wildtype conformation and increase DNA binding. We have extended these observations to intact cell systems by using luciferase transactivation assay in two murine tumor cell lines, both harboring endogenous wildtype p53. The results showed that none of these in vitro active reagents, except 1,10-phenanthroline (OP) has a significant effect on p53 transactivation activity. OP, a metal chelator and p53 inactivator in cell free systems, however, induces p53 transactivation activity as well as sequence-specific DNA binding in a dose dependent manner. OP also differentially induces endogenous expression of several known p53 target genes such as Waf-1 and Mdm-2, but not Bax, Gadd45, and PCNA. Increased p53 activity induced by OP is not due to elevated p53 mRNA nor to protein levels. Furthermore, the OP-induced p53 transcriptional activation is not due to its potential DNA intercalating activity, but mainly due to its metal chelating activity. OP was also found to induce dramatically apoptotic cell death in these tumor cells harboring wildtype p53, to a less extent in MEF cells from p53 knockout mice and not at all in Saos-2 cells without p53 or Rb. We concluded from this study that (a) unlike what has been seen in vitro, OP induces p53 activity in intact cells (b) OP activates p53 transcriptional activity without increasing p53 protein; and (c) activation of p53 may contribute to apoptosis, but is not required.

Characterization of a putative p53 binding site in the promoter of the mouse tissue inhibitor of metalloproteinases-3 (TIMP-3) gene: TIMP-3 is not a p53 target gene

We have recently cloned the promoter of the mouse tissue inhibitor of metalloproteinases-3 (TIMP-3) gene and have identified a putative p53 binding site (5'-GGGCTTGCTT GACGTCCA GAACAGGGTC-3'), which contains two p53 consensus binding motifs (bold) with two nucleotide mismatches (underlined) in the second motif and an 8 bp spacer in between. Since both p53 and TIMP-3 are involved in cell cycle progression, we tested the hypothesis that TIMP-3 is a p53 downstream effector gene, mediating p53 activity. A good correlation between p53 protein levels and TIMP-3 expression was found among mouse liver cell lines. However, when TIMP-3 promoter driven luciferase constructs were tested for p53 responsiveness in these cells, the construct containing the putative p53 binding site did not show significant difference from the one having the p53 site deleted. The gel retardation assay showed that the oligo (T3) made from the putative p53 binding site in the mouse TIMP-3 promoter did not bind to p53 protein, nor did an oligo (T3W) with a correction for the two mismatched nucleotides in the second motif. When the 8 bp spacer was removed, however, the oligo T3WSF (same as the T3W with spacer free) but not T3SF (T3 without spacer) binds to p53, indicating that both the spacer between two motifs and consensus binding sites determined the p53 binding. It is worth noting that under a less stringent assay condition (0.2 microg instead of 1.0 microg of dI/dC), T3SF did weakly bind to p53. Lastly, the compounds that induce p53 transactivation activity did not induce TIMP-3 expression. We concluded from this study that TIMP-3 is not a p53 downstream effector gene.

Suppression of in vivo tumor growth and induction of suspension cell death by tissue inhibitor of metalloproteinases (TIMP)-3

Tissue inhibitor of metalloproteinases-3(TIMP-3), a novel member of TIMP family genes, has been recently cloned and shown to be expressed in preneoplastic but not in neoplastic mouse JB6 epidermal cells (Sun et al. 1994 Cancer Res., 54, 11139). This down regulation of the gene appears to be attributable at least in part to alteration of gene methylation (Sun et al. 1995 J. Biol. Chem., 270, 19312). Little is known, however, about the role of TIMP-3 in human cancers. We screened several human tumor cell lines for TIMP-3 expression and found that a colon carcinoma line, DLD-1, did not express TIMP-3. If down regulation of TIMP-3 is causally related to carcinogenesis, re-expression by transfection may reverse the tumor cell phenotype. We therefore overexpressed human TIMP-3 in DLD-1 cells. TIMP-3 transfectants showed a serum-dependent growth inhibition in monolayer culture and a decreased growth potential in nude mice in a manner dependent on the level of TIMP-3 expression. A transfectant expressing a high level of active hTIMP-3 completely lost the ability to form tumors following s.c. injection into nude mice. We also tested TIMP-3 expressing cells and neocontrol TIMP-3 negative cells for their ability to grow in liquid suspension culture, since both cells grew in semi-solid soft agar. As compared to neocontrol cells, TIMP-3 overexpressors formed large aggregates, followed by cell death. This effect was not mimicked by BB94, a broad MMP inhibitor. We conclude from this study that (i) TIMP-3 overexpression in human colon carcinoma cells induces growth arrest in low serum conditions and inhibits in vivo tumor growth and (ii) the TIMP-3-induced large aggregate formation and subsequent cell death under suspension growth cannot be explained by its MMP inhibitory activity.

[Protective effects of chrominum on myocardial damage in rats]

To prove the protective effects of trivalent chromium (Cr3+) on myocardial damage, its ultrastructure and electro-physiological changes were observed in different groups of rats with intraperitoneal injection of normal saline, Cr3+ and selenium, and injection of adriamycin (ADR) by their tail vein. Results of ultrastructural observations showed nuclear margin of myocardial cells was obscure, cytoplasm became coarse and sparse, mitochondria vacuolar, myocardiofibril loose, broken and lytic in the group treated with ADR, myocardiopathic changes reduced and myocardial filaments arranged in good order in that with Cr3+ and selenium. QRS complex, Q-T interval, APD50 and APD90 in electrocardiograph (ECG) prolonged in the group with ADR and selenium, and no changes were observed in that with Cr3+. It suggests Cr3+ and selenium have apparently protective effects on rat's myocardium, and Cr3+ also can reverse the changes in ECG caused by ADR, which is of importance in prevention and treatment of cardiovascular diseases.

[Acute toxicity and anti-inflammatory effect of processed products of gamboge]

The acute toxicity and anti-inflammatory effect of processed and raw Gamboge were compared. The results showed that the acute toxicity of processed Gamboge was less than that of the raw one, while both had significant anti-inflammatory effect alike. Among the differently processed products, those boiled with lotus leaf juice and steamed by high pressure were better.

[Substance P in synovial fluid in patients with temporomandibular joint dysfunction syndrome]

Radioimmunoassay technique was used to measure substance P levels in synovial fluid samples from thirty patients with temporomandibular joint dysfunction syndrome (TMJDS). Twenty-four samples (80%) were found to have substance P. Concentrations of substance P in the synovial fluid from patients with painful TMJDS were higher than those patients without pain (P < 0.05). The study supported the evidence for the secondary synovitis in painful TMJDS, and suggested that the nervous system play a role in the pathophysiology of TMJDS.

Sphingosine 1-phosphate generated in the endoplasmic reticulum membrane activates release of stored calcium

Sphingosine and sphingosine derivatives induce Ca2+ release from inositol 1,4,5-trisphosphate (InsP3)-sensitive Ca2+ pools in permeabilized cells (Ghosh, T. K., Bian, J., and Gill, D. L. (1990) Science 248, 1653-1656). To further assess the mechanism of sphingoid base-mediated Ca2+ release, the effects of sphingosine and sphingosine derivatives on Ca2+ fluxes were characterized using a microsomal membrane vesicle fraction (B3) enriched in rough endoplasmic reticulum (ER) prepared from cells of the DDT1MF-2 cell smooth muscle line (Ghosh, T. K., Mullaney, J. M., Tarazi, F. I., and Gill, D. L. (1989) Nature 340, 236-239). Addition of 15 microM sphingosine to Ca2+ pump-loaded B3 vesicles induced a delayed but thereafter rapid Ca2+ release from vesicles which was dependent on the presence of ATP and was blocked by ADP. Sphingosylphosphorylcholine (SPC) released Ca2+ to the same extent (more than 80% of pumped Ca2+), but in contrast to sphingosine, there was no lag and the effect was independent of ATP or ADP. The EC50 for sphingosine and SPC in activating Ca2+ release was 1 and 3 microM, respectively. Such observations are consistent with the view that sphingosine, unlike SPC, must be modified by an ATP-requiring kinase activity located within the ER membrane. Sphingoid bases do not appear to release Ca2+ through InsP3 receptors since heparin had no effect on sphingoid base-mediated Ca2+ release. Sphingosine 1-phosphate (sph-1-P), the likely active Ca(2+)-releasing derivative of sphingosine, was synthesized by phospholipase D-catalyzed cleavage of SPC, purified, and tested for Ca(2+)-releasing activity. sph-1-P at 10 microM induced Ca2+ release from both B3 vesicles and permeabilized DDT1MF-2 cells to exactly the same extent as sphingosine. Unlike sphingosine, the effect of sph-1-P was immediate and not blocked by ADP. Using B3 membrane vesicles incubated with [gamma-32P]ATP and sphingosine under the same conditions as Ca2+ flux studies, a labeled band was detected on TLC which ran identically with authentic sph-1-P. Formation of this labeled product was prevented by removal of exogenous sphingosine and blocked by ADP. Sphingosine- but not SPC-mediated Ca2+ release was blocked by 10 mM oxalate. 10 mM oxalate also blocked the formation of 32P-labeled sph-1-P indicating that it is an inhibitor of sph-1-P formation. The studies establish that the ER membrane contains the necessary kinase to convert sphingosine to sph-1-P which functions as a powerful mediator of Ca2+ release through a non-InsP3 receptor-mediated mechanism in the same ER membrane, perhaps reflecting a novel Ca2+ signaling pathway.

Polymerizable phosphatidylcholines: importance of phospholipid motions for optimum phospholipase A2 and C activity

Cross-linkable short-chain phosphatidylcholines with thiols at the chain terminus have been synthesized and characterized. These micelle-forming species were used to investigate two water-soluble phospholipases. When reduced, the thiol lipids were excellent substrates for phospholipase A2. Once cross-linked, they became extremely poor substrates. This is consistent with a mechanism in which a key step is the partial extraction of the substrate phosphatidylcholine from an aggregate. In contrast, phospholipase C activity was slightly enhanced if the product diglyceride was tethered to the aggregate through disulfide formation. For this enzyme such a kinetic effect is consistent with the hydrophobic diglyceride biasing the enzyme to the interface.

Intracellular Ca2+ pool content is linked to control of cell growth

A close correlation was observed between intracellular Ca2+ pool depletion and refilling and the onset of DNA synthesis and proliferation of DDT1MF-2 smooth muscle cells. The intracellular Ca2+ pump inhibitors 2,5-di-tert-butyl-hydroquinone (DBHQ) and thapsigargin (TG) specifically emptied identical inositol 1,4,5-trisphosphate (InsP3)-sensitive Ca2+ pools and both arrested cell growth at concentrations corresponding to Ca2+ pump blockade. However, an important distinction was observed between the two inhibitors with respect to their reversibility of action. Upon removal of DBHQ from DBHQ-arrested cells, Ca2+ pools immediately refilled, and 14 hr later cells entered S phase followed by normal cell proliferation; the time for entry into S phase was identical to that for cells released from confluence arrest. Although TG irreversibly blocked Ca2+ pumping and emptied Ca2+ pools, high serum treatment of TG-arrested cells induced recovery of functional Ca2+ pools in 6 hr (via probable synthesis of new pump); thereafter cells proceeded to S phase and normal cell proliferation within the same time period (14 hr) as that following release of DBHQ-arrested cells. The precise relationship between Ca2+ pump blockade and growth arrest indicates that Ca2+ pool emptying maintains cells in a G0-like quiescent state; upon refilling of pools, normal progression into the cell cycle is resumed. It is possible that a specific cell cycle event necessary for G0 to G1 transition depends upon signals generated from the InsP3-sensitive Ca2+ pool.

Depolarization-induced calcium release from isolated triads measured with impermeant fura-2

Depolarization-induced Ca2+ release was studied in a mixture of triads and terminal cisternae isolated from rabbit skeletal muscle. The vesicles were actively loaded with known amounts of Ca2+ in the absence of precipitating anions in a solution containing 100 mM K propionate buffer. Changes in extravesicular Ca2+ were monitored with 10 microM Fura-2 (membrane impermeant form). Ca2+ release was initiated by diluting an aliquot of the loaded vesicles into a TEACl release solution designed to maintain a constant [K+].[Cl-] product. Fast release, defined as the percentage of total Ca2+ loaded which released in less than 10 sec, occurred when extravesicular free Ca2+ was in the submicromolar range and was unaffected by 5 mM caffeine under depolarizing conditions, change in external pH to 6.5, and an increase in external Mg2+ concentration from 0.1 to 0.2 mM. Thus, the Ca2+ release measured in these studies is distinct from Ca(2+)-induced Ca2+ release. The fast release more than doubled when a greater dilution (1:20 versus 1:10) of the loaded vesicles into the release solution, which would produce a larger depolarization, was used. The percentage of loaded Ca2+ which released rapidly in a particular triad preparation was similar to the percentage of vesicles structurally coupled as visualized by electron microscopy.

Intracellular calcium release mediated by sphingosine derivatives generated in cells

Soluble and hydrophobic lipid breakdown products have a variety of important signaling roles in cells. Here sphingoid bases derived in cells from sphingolipid breakdown are shown to have a potent and direct effect in mediating calcium release from intracellular stores. Sphingosine must be enzymically converted within the cell to a product believed to be sphingosine-1-phosphate, which thereafter effects calcium release from a pool including the inositol 1,4,5-trisphosphate-sensitive calcium pool. The sensitivity, molecular specificity, and reversibility of the effect on calcium movements closely parallel sphingoid base-mediated inhibition of protein kinase C. Generation of sphingoid bases in cells may activate a dual signaling pathway involving regulation of calcium and protein kinase C, comparable perhaps to the phosphatidylinositol and calcium signaling pathway.