Characterization and detection of cellular and proteomic alterations in stable stathmin-overexpressing, taxol-resistant BT549 breast cancer cells using offgel IEF/PAGE difference gel electrophoresis.

Stathmin/oncoprotein 18, a protein that regulates microtubule dynamics, is highly expressed in a number of tumors including leukemia, lymphoma, neuroblastoma, breast, ovarian, and prostate cancers. High stathmin levels have been associated with the development of resistance to the widely used anti-cancer drug taxol ((®)Taxol, paclitaxel). The mechanisms of stathmin-mediated taxol resistance are not well-understood at the molecular level. To better understand the role of stathmin in taxol resistance, we stably overexpressed stathmin twofold in BT549 human breast cancer cells and characterized several cell processes involved in the mechanism of action of taxol. After stable overexpression of stathmin, neither the cell doubling time nor the mitotic index was altered and the microtubule polymer mass was reduced only modestly (by 18%). Unexpectedly, microtubule dynamicity was reduced by 29% after stathmin overexpression, resulting primarily from reduction in the catastrophe frequency. Sensitivity to taxol was reduced significantly (by 44%) in a clonogenic assay, and stathmin appeared to protect the cells from the spindle-damaging effects of taxol. The results suggest that in the stably stathmin-overexpressing clones, compensatory gene expression occurred that resulted in normal rates of cell proliferation and prevented the increase in catastrophe frequency expected in response to stathmin. Stathmin overexpression protected the cells from taxol-induced abnormal mitoses, and thus induced taxol resistance. Using offgel IEF/PAGE difference gel electrophoresis, we identified a number of proteins whose expression is reduced in the taxol-resistant stathmin-overexpressing cell lines, including proteins involved in the cytoskeleton and cell structure, the stress response, protein folding, glycolysis, and catalysis.

Heat shock protein 60 response to exercise in diabetes: effects of alpha-lipoic acid supplementation.

The pathophysiology of diabetes includes oxidative stress and impaired heat shock protein (HSP) expression. We studied the effects of alpha-lipoic acid (LA) supplementation for 8 weeks and acute exercise on HSP60 expression and the oxidative stress marker 4-hydroxynonenal adducts (4-HNE) in streptozotocin-induced diabetic (SID) and nondiabetic control rats. Diabetes was associated with decreased HSP60 in the heart and increased levels of HSP60 and 4-HNE in the liver. LA increased HSP60 in the liver of control and diabetic rats and decreased 4-HNE in the liver and heart. Acute exercise increased liver 4-HNE, which was offset by LA. In conclusion, diabetes induced oxidative stress and impaired myocardial HSP60 expression, while LA partially offsets these alterations in a tissue-specific manner.

The effects of some Mannich bases on heat shock proteins HSC70 and GRP75, and thioredoxin and glutaredoxin levels in Jurkat cells.

Mannich bases interact with cellular thiols and inactivate thioredoxin reductase. In this study, the effects of cytotoxic mono-Mannich bases 2, 3 and cyclic Mannich base C1 on the expression of cytoprotective heat shock proteins (HSC70 and GRP75) and on levels of thioredoxin (TRX) and glutaredoxin (GRX) were investigated in Jurkat cells. Cells were exposed to the compounds for 24 h in cell culture medium with 1% FBS. C1 and 2 increased the levels of HSC70 (200% of control) in all the concentrations tested, but 3 did not affect HSC70 levels. Whereas 3 increased GRP75 expression (123-154%), 2 and C1 either did not affect (95-87% for 2, and 88% for C1) or slightly decreased GRP75 expression (82% for 2 and 67% for C1). Mannich bases generally decreased GRX levels (68%, 63-77% and 33-71% for 2, 3 and C1, respectively), but 3 increased GRX levels at 1 microg/ml (142%). Whereas 2 and 3 decreased TRX levels (30-79% and 37-44% of control, respectively), C1 increased the expression of TRX (156-201%). Our results suggest that decreases in GRX and TRX due to the alkylating effects of Mannich bases might have prevented cell division and decreased survival in Jurkat cells, which could not be prevented by increased heat shock protein expression.

Exercise training modulates heat shock protein response in diabetic rats.

Strenuous exercise induces oxidative stress and modification of intracellular proteins. Exercise training, however, upregulates endogenous antioxidant defenses and heat shock protein (HSP) expression. In diabetes, perturbations in the endogenous antioxidant and HSP protection have been reported. The aim of this study was to examine the effect of 8 wk of endurance training on HSP expression and oxidative stress markers in the skeletal muscle, heart, and liver of streptozotocin-induced diabetic (SID) and nondiabetic control rats. Induction of diabetes decreased HSP72 expression in heart, liver, and vastus lateralis muscles. SID increased heme oxygenase-1, an oxidative stress-inducible HSP, in liver, red gastrocnemius muscle, and vastus lateralis muscle and glucose-regulated protein 75 in liver. SID increased HSP90 levels in the heart, but levels decreased in the liver. Diabetes induced oxidative stress marker protein carbonyl levels and tissue inflammation. Although endurance training increased the expression of HSP72 in all of the tissues examined, this induction was less pronounced in diabetic rats than in nondiabetic controls. Furthermore, endurance training induced the activation and expression of transcriptional regulator heat shock factor-1 only in nondiabetic control animals. In summary, diabetes may increase susceptibility to oxidative damage and impair HSP protection, but endurance training may offset some of the adverse effects of diabetes by upregulating tissue HSP expression. Our results suggest that diabetes impairs HSP protection, possibly via transcriptionally mediated mechanisms.

An inter-subunit disulfide bond affects affinity of human lung extracellular superoxide dismutase to heparin.

Human extracellular superoxide dismutase (EC-SOD) was purified to homogeneity from lung tissue and the nature of the binding of heparin to EC-SOD was investigated. The enzyme was purified using three column chromatographic steps, and 127 microg of purified EC-SOD was obtained. A specific anti-human EC-SOD antibody was obtained by immunization with the purified enzyme. Western blot analysis of the heparin affinity chromatography product indicated that the presence of the inter-subunit disulfide bond affects the affinity of EC-SOD for heparin. The affinity of EC-SOD for heparin is a very important feature of the enzyme because it controls the distribution of the enzyme in tissues. The present study suggests that, not only the processing of the C-terminal region but inter-subunit disulfide bonds also play a role in determining the tissue distribution of EC-SOD. Moreover, the results obtained here also suggest that the redox state of the tissues might regulate the function of the EC-SOD.

Exercise-induced oxidative stress and muscle stress protein responses in trotters.

Acute exercise induces oxidative stress and heat shock protein (HSP) expression. Information on the protection of stress proteins against oxidant insult and muscle damage during moderate exercise is scanty. We aimed to show how a single bout of moderate exercise affects the markers of oxidative stress and heat shock factor-1 (HSF1; the transcriptional regulator of HSP synthesis), and HSP70, HSP90 and glucose-regulated protein (GRP75) expression in horses. Eight clinically normal and regularly trained standardbred trotters were treadmill-exercised for 45 min at moderate intensity. Blood samples were collected prior to and immediately after exercise and at 4 and 24 h of recovery. Muscle biopsy samples from the middle gluteal muscle were taken before exercise and after 4 h of recovery. Acute exercise did not activate HSF1 or induce expression of HSP70, HSP90 or GRP75 in skeletal muscle. One bout of acute exercise increased protein oxidation, which was measured by protein carbonyls in plasma and muscle, but it did not effect 4-hydroxynonenal protein adducts, which are markers of lipid peroxidation. Furthermore, mild muscle damage was observed 4 h after exercise. Our results showed that horses are susceptible to oxidative stress. One bout of exercise at moderate intensity and duration did not induce HSP responses despite the increased protein oxidation and tissue inflammation in equine muscle.

Modulation of the stathmin-like microtubule destabilizing activity of RB3, a neuron-specific member of the SCG10 family, by its N-terminal domain.

RB3 is a neuron-specific homologue of the SCG10/stathmin family proteins, possessing a unique N-terminal membrane-associated domain and the stathmin-like domain at the C terminus, which promotes microtubule (MT) catastrophe and/or tubulin sequestering. We examined herein the contribution of the N-terminal subdomain of RB3 to the regulation of MT dynamics. To begin with, we determined the effects of full-length (RB3-f) and short truncated (RB3-s) forms of RB3 on the polymerization of MT in vitro. RB3-s had a deletion of amino acids 1-75 from the N terminus, leaving the so-called stathmin-like domain, consisting of residues 76-217. Although both RB3-f and RB3-s exhibited MT-depolymerizing activity, RB3-f was less effective. The binding affinity for tubulin was also lower in RB3-f. Direct observation of the dynamics of individual MTs using dark field microscopy revealed that RB3-s slowed MT elongation velocity, increased catastrophes, and reduced rescues. This effect is almost identical to that by stathmin/oncoprotein 18. On the other hand, the MT elongation rate increased at lower concentrations of RB3-f. In addition, RB3-f, indicated higher rescue frequency than control as well as the catastrophe in a dose-dependent manner. The functionality of RB3-f indicated that full-length RB3 has not only stathmin-like MT destabilizing activity but also MT-associated protein-like MT stabilizing activity. Possibly, the balance of these activities is altered in a concentration-dependent manner in vitro. This interesting regulatory role of the unique N-terminal domain of RB3 in MT dynamics would contribute to the physiological regulation of neuronal morphogenesis.