The two actin-binding regions on the myosin heads of cardiac muscle.

In the presence of myosin S1 or myosin heads, actin filaments tend to form bundles. The biological meaning of the bundling of actin filaments has been unclear. In this study, we found that the cardiac myosin heads can form the bundles of actin filaments more rapidly than can skeletal S1, as monitored by light scattering and electron microscopy. Moreover, the actin bundles formed by cardiac S1 were found to be more stable against mechanical agitation. The distance between actin filaments in the bundles was approximately 20 nm, which is comparable to the length of a myosin head and two actin molecules. This suggests the direct binding of S1 tails to the adjacent actin filament. The "essential" light chain of cardiac myosin could be cross-linked to the actin molecule in the bundle. When monomeric actin molecules were added to the bundle, the bundles could be dispersed into individual filaments. The three-dimensional structure of the dispersed actin filaments was reconstructed from electron cryo-microscopic images of the single actin filaments dispersed by monomer actin. We were able to demonstrate that cardiac myosin heads bind to two actin molecules: one actin molecule at the conventional actin-binding region and the other at the essential light-chain-binding region. This capability of cardiac myosin heads to bind two actin molecules is discussed in view of lower ATPase activity and slower shortening velocity than those of skeletal ones.

Matrix metalloproteinase-9 and vascular endothelial growth factor: a possible link in adult T-cell leukaemia cell invasion.

Plasma from a total of 57 patients with adult T-cell leukaemia (ATL) (acute ATL, 39 patients; lymphoma ATL, one patient; chronic ATL, 15 patients; smouldering ATL, two patients) and 20 healthy controls was analysed for the presence of type IV gelatinase activity with clinical features. A significant elevation of plasma matrix metalloproteinase-9 (MMP-9) was observed in some ATL patients, particularly in the patients with malignant cell infiltration. MMP-9 was found to be secreted into the conditioned medium from all ATL cell lines examined. Moreover, the corresponding mRNA was detectable both in all ATL cell lines examined and in the majority of primary acute ATL cells, indicating that ATL cells are capable of synthesizing and secreting MMP-9. We previously demonstrated that a high incidence of ATL cell infiltration was closely related to a high plasma level of vascular endothelial growth factor (VEGF) produced by ATL cells themselves. This present study showed that the presence of increased plasma MMP-9 was closely associated with elevated plasma VEGF in ATL patients. Furthermore, we showed that both increased plasma MMP-9 and VEGF were significantly related to high ATL cell infiltration. All these findings strongly suggest that MMP-9 and VEGF act co-operatively in the process of ATL cell invasion.

Resveratrol induces downregulation in survivin expression and apoptosis in HTLV-1-infected cell lines: a prospective agent for adult T cell leukemia chemotherapy.

Resveratrol, a phytoalexin found in grapes and wine, has been shown to exhibit a wide range of pharmacological properties and is believed to play a role in the chemoprevention of human cancer. Resveratrol has also been shown to induce antiproliferation and apoptosis of several leukemia cell lines. In the present study, we investigated the effect of resveratrol in adult T cell leukemia. Our present observations showed that resveratrol induced growth inhibition in all five human T cell lymphotrophic virus-1-infected cell lines examined, with 50% effective dose of 10.4-85.6 mM. In the resveratrol-treated cells, induction of apoptosis was confirmed by annexin V-based analyses and morphological changes. The most surprising observation was that resveratrol treatment resulted in a gradual decrease in the expression of survivin, an antiapoptotic protein, during cell apoptosis. These findings indicate that resveratrol inhibits the growth of human T cell lymphotrophic virus-1-infected cell lines, at least in part, by inducing apoptosis mediated by downregulation in survivin expression. In view of the accumulating evidence that survivin may be an important determinant of a clinical response in adult T cell leukemia, our present findings have led to the suggestion that resveratrol, a common constituent of the human diet, merits further investigation as a potential therapeutic agent for this incurable disease.