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The role of protein kinase C (PKC) isoforms in the regulation of cell shape [switch between fibroblast-like and crescent shape (CS)] and of locomotion of human fibrosarcoma HT1080 cells has been investigated. The PKC activator phorbol myristate acetate (PMA) induced the transition of elongated fibroblast-like cells into CS cells and stimulated locomotion. Both responses to PMA were inhibited by the PKC inhibitor Ro 31-8220. Analysis of the time course showed that stimulation of shape changes (formation of CS cells) and locomotor activity (increase in the proportion and speed of locomoting cells) was maximal in the early phase of the response (up to 2.5 hr) and significantly decreased later (15 to 21 hr). CS formation and stimulated locomotion correlated closely with a marked redistribution from the cytosol to the membrane of PKC isoforms α, β1 and γ in the early phase (0.5 to 2 hr) following activation with PMA. The subsequent reduction of the proportion of CS cells and of cell locomotion correlated with down-regulation of these isoforms in the second phase (16 to 21 hr). In contrast, the total amount and distribution of PKC β2 remained almost unchanged with 10^–8 M PMA up to 21 hr. Furthermore, changes in shape and locomotion did not correlate with the responses of PKC δ to PMA. Inhibition of PMA-stimulated locomotion by the more specific inhibitor Gö 6976 is consistent with a role of PKC α and β1 in this response. Ro 31-8220 alone induced a moderate down-regulation of PKC isoforms α and δ, but it also inhibited the more pronounced down-regulation of these isoforms by PMA. Our results indicate that activation of PKC isoforms α, γ and β1, but not β2 or δ, stimulates locomotion and formation of CS cells in human fibrosarcoma HT1080 cells. Int. J. Cancer 88:195–203, 2000. © 2000 Wiley-Liss, Inc.

In the near future, several space missions are scheduled, which will closely investigate short-period comets. Some of these (e.g., ROSETTA) will also deliver landing probes for in situinvestigations of the nucleus' surface. Therefore there is now renewed interest in the structure and behavior of cometary surface layers.

Models describing the buildup of mantles on cometary nuclei are reviewed and their predictions are compared with observations. Mantles restrained by gravity forces only are unstable under almost all conditions. A new model that emphasizes the importance of cohesive forces within the refractory material of cometary nuclei is introduced to explain the prevailing inactivity of nuclear surfaces. Numerical calculations describe the growth of depleted layers of refractory matrix material (crusts), their activity levels, and the vapor pressure under such crusts. It is found that over a wide range of parameters cohesion of the matrix material is stronger than the vapor pressure building up underneath the crust. These conditions lead to stable crusts but per sedo not explain the activity of cometary nuclei. Structural inhomogeneities of cometary nuclei with varying dust-to-ice ratios and physical parameters are inferred to explain the restricted and in many cases persistent activity of comets.

Comet P/Faye 1991 XXI (1991 n) was observed with the planetary camera (PC) of the Hubble Space Telescope (HST) between October 29 and November 21, 1991, when its geocentric distance was in the range 0.62–0.67 AU. The resulting high resolution—a single PC pixel projected to a distance of ∼20 km at the comet—made it possible to clearly discriminate the nucleus and to study the dust coma within ∼100 km from the nucleus. The spherical aberration which affected the early operation of the HST has severely complicated the analysis and image restoration using the Richardson–Lucy method has failed to give satisfactory results. The coma is dominated by the point spread function (PSF) of the nucleus up to a radial distance of ∼100 km and cannot be recovered. Beyond, it is affected by the spherical aberration up to approximately 750 km and was analyzed by comparison with a grid of models convolved with appropriate PSFs. Beyond 750 km, it remains unaffected and can be studied directly. From the outer to the innermost regions, the coma presents an elongated shape which may be explained either by an active source on the nucleus or, more likely, by a projection effect of the dust tail. If this second interpretation is correct, then the temporal evolution of the comet is very slow and smooth, suggesting an extended source of dust on the nucleus. The dust production rate, corrected for the projection effect of the tail, amounts to 125 kg sec−1.

Using two different cytometers, an Epics Profile II and a FACScan, we determined the extent to which changes in forward and right angle scatter are a reliable measure for changes in polymorphonuclear leukocyte (PMN) shape, volume, and actin polymerization and whether distinct types of shape changes in PMNs can be recognized. PMN stimulation can substantially change the positions of PMNs in the scatter diagram of the FACScan but not of the Epics Profile II. Within the limits of the experiments, it has been possible to determine whether or not a shape change has taken place using the FACScan but not using the Epics Profile II. However, using either cytometer, it has not been possible to determine which type of shape change (e.g., spherical vs. polarized vs. nonpolar cells) has taken place. Furthermore, forward or right angle scatter changes are not a reliable measure for changes in cell volume or actin polymerization of human PMNs.

The PKC-inhibitor Ro 31-8220 inhibits stimulated fluid pinocytosis of human PMNs induced by the PKC-activators phorbol myristate acetate (PMA, IC₅₀ = 1.35×10−6M) or diacylglycerols (OAG, diC8) by 95%, whereas Ro 31-8220 has no effect on D₂O- or fNLPNTL-induced pinocytosis and enhances cytochalasin D-induced pinocytosis. Also formation of F-actin induced by PMA or diacylglycerols is selectively inhibited. The results indicate that a Ro 31-8220-sensitive PKC is involved in signal transduction for enhanced pinocytosis and F-actin formation in response to one class of stimuli (classical activators of PKC) but not to others.Copyright 1993, 1999 Academic Press

Various authors have associated increased susceptibility to infectious diseases in certain patients to inhibitors of neutrophil chemotaxis demonstrable in serum or diluted plasma of these patients. The present experiments showed, however, that serum and diluted plasma but not undiluted plasma from normal human donors consistently inhibited chemotactic migration of autologous human neutrophil granulocytes. Therefore, the presence of such inhibitors in the circulating blood can only be assessed by the evaluation of undiluted plasma. The findings suggest that the experimental conditions which have been used in the past to demonstrate such inhibitors in the circulating blood of patients with increased susceptibility to infections are inadequate, and results need reexamination. The inhibitors affect random locomotion and chemotaxis of neutrophil granulocytes but not phagocytosis or the metabolic burst resulting in nitroblue-tetrazolium reduction. On the other hand, phagocytosis of Staphylococcus albusrendered neutrophils chemotactically unresponsive. The significance of so-called cellular defects of neutrophil chemotaxis in such patients is also considered.

The present study demonstrates new properties of H-7. The protein kinase inhibitor H-7 is a potent activator of several neutrophil functions. Stimulation of initially spherical nonmotile neutrophils elicits vigorous shape changes within a few seconds, increases in cytoskeletal actin, altered F-actin distribution, increased adhesiveness and a relatively small increase in pinocytic activity. H-7 has also chemokinetic activities. Depending on the experimental condition, H-7 may elicit or inhibit neutrophil locomotion. It failed to induce chemotaxis. Thus, the response pattern elicited by H-7 is different from that of other leukocyte activators such as chemotactic peptides, PMA or diacylglycerols. The finding that H-7 can elicit shape changes, actin polymerization and pinocytosis suggests that these events can occur without activation of protein kinase C (PKC). PMA-induced shape changes and stimulation of pinocytosis were not inhibited by H-7.