ИСТИНА

Our scanning electron microscopy study revealed that neutrophils can develop dynamic thread-like membrane tubulovesicular extensions (cytonemes) upon adhesion to fibronectin-coated substrata in the presence of: (i) agents disrupting actin cytoskeleton; (ii) inhibitor of GTPase dynamin; (iii) nitric oxide (NO) donor; (iiii) inhibitors of vacuolar-type ATPase or glucose metabolism. Cytonemes have a uniform diameter along their entire length (150 – 250 nm depending on conditions) and consist of membrane vesicles and tubules that are aligned in a row. Cytonemes can reach 100 µm in length during 20 minutes. Proteome analysis has revealed that: (i) the cytonemes contain bactericide agents of neutrophils, cytoplasmic proteins such as actin cytoskeleton and S100 proteins, energy-metabolizing (presumably glycolytic) enzymes; (ii) the content of cytonemes does not depend on agent inducing their formation. Neither fMLP nor LPS, stimuli for regulated secretion of neutrophils, induced the formation of cytonemes. Cytonemes may represent a constitutive neutrophil exocytotic trafficking that occurs as the membrane vesicle budding. Active GTPase dynamin and integrity of the cytoskeleton are required for cleavage of the vesicles from the plasma membrane during endocytosis. In our experiments an inhibitor of dynamin dynasore initiated the formation of cytonemes, which were similar in size and composition to the cytochalasin D-induced extensions. Drawing an analogy with endocytosis, we assume that the inhibition of dynamin or actin depolymerization blocks separation of secretory vesicles from the plasma membrane. As a result the secretory process extends from the cells as cytonemes. Highly dynamic and flexible cytonemes change the adhesive interaction of neutrophils with the environment due to the possibility to establish direct contact with the cells, bacteria or substrates at a distance.