ALBERT

Description: While studies concerning mitogenic factors have been an important area of research for many years, much less is understood about the mechanisms of action of cell surface growth inhibitors. We have purified an 18 kDa cell surface sialoglycopeptide growth inhibitor (CeReS-18) which can reversibly inhibit the proliferation of diverse cell types. The studies discussed in this article show that three mouse keratinocyte cell lines exhibit sixty-fold greater sensitivity than other fibroblasts and epithelial-like cells to CeReS-18-induced growth inhibition. Growth inhibition induced by CeReS-18 treatment is a reversible process, and the three mouse keratinocyte cell lines exhibited either single or multiple cell cycle arrest points, although a predominantly G0/G1 cell cycle arrest point was exhibited in Swiss 3T3 fibroblasts. The sensitivity of the mouse keratinocyte cell lines to CeReS-18-induced growth inhibition was not affected by the degree of tumorigenic progression in the cell lines and was not due to differences in CeReS-18 binding affinity or number of cell surface receptors per cell. However, the sensitivity of both murine fibroblasts and keratinocytes could be altered by changing the extracellular calcium concentration, such that increased extracellular calcium concentrations resulted in decreased sensitivity to CeReS-18-induced proliferation inhibition. Thus the increased sensitivity of the murine keratinocyte cell lines to CeReS-18 could be ascribed to the low calcium concentration used in their propagation. Studies are currently under way investigating the role of calcium in CeReS-18-induced growth arrest. The CeReS-18 may serve as a very useful tool to study negative growth control and the signal transduction events associated with cell cycling.

Description: A 66-kDa sialoglycoprotein has been identified as the parental membrane molecule of an earlier described sialoglycopeptide (SGP), an 18-kDa molecule released by protease treatment of intact bovine cerebral cortex cells that was shown to be a potent inhibitor of cellular proliferation. The 66-kDa parental sialoglycoprotein (p-SGP) was purified approximately 2,400-fold, to apparent homogeneity, from bovine cerebral cortex cell membranes by its release during incubation with 3 M NaCl, preparative isoelectric focusing and lectin affinity chromatography. Although a membrane-associated molecule, the p-SGP appeared to be tightly bound to the cell membrane, since it was not released during incubations in the absence of 3 M NaCl. Incubation of the membrane preparations with 3 M urea proved to be too harsh, and the antigenicity required to follow the purification of the p-SGP was abolished. Analyses by SDS-PAGE, under reducing and nonreducing conditions, suggested that the p-SGP membrane component was a single polypeptide without subunit structure. The p-SGP was shown to be structurally related to the SGP fragment by immunoblots with IgG raised to the SGP inhibitor, and functionally related to the SGP by its ability to inhibit Swiss 3T3 proliferation at concentrations strikingly similar to that previous measured with the SGP fragment.

Description: A photometrically and geometrically reduced data base is being produced for the Galilean Satellites using Voyager Imaging data. The basic data set used is essentially all the useful satellite images returned by Voyager. Each frame was radiometrically calibrated and many are projected into cartographic formats. Mosaics of low, medium and high resolution frames being made for each satellite consist of registered digital images with intensity values scaled through a traceable calibration procedure to normal albedo values. Many of the mosaics are being made in two versions. One version is an albedo version and the second is a maximum discrimination version in which large variations in brightness across the picture are suppressed.

Description: Infrared observations were made of the outer planet satellites. These data provide vital information about the thermophysical properties of satellite surfaces, including internal heat sources for Io. Observations include both broad and narrow band measurements in the 2 to 20 micrometer spectral range. Types of observation and target priority were determined to make maximum use of existing data from Voyager and other missions, on-going and planned missions such as Galileo, were supported and techniques and data for planning new missions and instrumentation were developed.

Description: Cell proliferation is governed by the influence of both mitogens and inhibitors. Although cell contact has long been thought to play a fundamental role in cell cycling regulation, and negative regulators have long been suspected to exist, their isolation and purification has been complicated by a variety of technical difficulties. Nevertheless, over recent years an ever-expanding list of putative negative regulators have emerged. In many cases, their biological inhibitory activities are consistent with density-dependent growth inhibition. Most likely their interactions with mitogenic agents, at an intracellular level, are responsible for either mitotic arrest or continued cell cycling. A review of naturally occurring cell growth inhibitors is presented with an emphasis on those factors shown to be residents of the cell surface membrane. Particular attention is focused on a cell surface sialoglycopeptide, isolated from intact bovine cerebral cortex cells, which has been shown to inhibit the proliferation of an unusually wide range of target cells. The glycopeptide arrest cells obtained from diverse species, both fibroblasts and epithelial cells, and a broad variety of transformed cells. Signal transduction events and a limited spectrum of cells that are refractory to the sialoglycopeptide have provided insight into the molecular events mediated by this cell surface inhibitor.

Description: The tumor necrosis factor-alpha (TNF)-resistant, SV40-transformed, murine fibroblast cell lines, F5b and F5m, became sensitive to TNF-mediated cytolysis after treatment with a biologically active 18 kDa peptide fragment (SGP) derived from a 66-kDa parental cell surface sialoglycoprotein. Neither TNF nor the SGP alone exhibited cytotoxicity to the two SV40-transformed cell lines. However, Balb/c 3T3 cells, incubated with SGP alone or with SGP and TNF, were not killed. Therefore, SGP can selectively sensitize cells for TNF alpha-mediated cytotoxicity. This selective sensitization may be due to the previously documented ability of the SGP to selectively mediate cell cycle arrest.

Description: Our laboratory has purified an 18 kDa cell surface sialoglycopeptide growth inhibitor (CeReS-18) from intact bovine cerebral cortex cells. Evidence presented here demonstrates that sensitivity to CeReS-18-induced growth inhibition in BALB-c 3T3 cells is influenced by calcium, such that a decrease in the calcium concentration in the growth medium results in an increase in sensitivity to CeReS-18. Calcium did not alter CeReS-18 binding to its cell surface receptor and CeReS-18 does not bind calcium directly. Addition of calcium, but not magnesium, to CeReS-18-inhibited 3T3 cells results in reentry into the cell cycle. A greater than 3-hour exposure to increased calcium is required for escape from CeReS-18-induced growth inhibition. The calcium ionophore ionomycin could partially mimic the effect of increasing extracellular calcium, but thapsigargin was ineffective in inducing escape from growth inhibition. Increasing extracellular calcium 10-fold resulted in an approximately 7-fold increase in total cell-associated 45Ca+2, while free intracellular calcium only increased approximately 30%. However, addition of CeReS-18 did not affect total cell-associated calcium or the increase in total cell-associated calcium observed with an increase in extracellular calcium. Serum addition induced mobilization of intracellular calcium and influx across the plasma membrane in 3T3 cells, and pretreatment of 3T3 cells with CeReS-18 appeared to inhibit these calcium mobilization events. These results suggest that a calcium-sensitive step exists in the recovery from CeReS-18-induced growth inhibition. CeReS-18 may inhibit cell proliferation through a novel mechanism involving altering the intracellular calcium mobilization/regulation necessary for cell cycle progression.

Description: Internal heat flow from radioactive decay in Triton's interior along with absorbed thermal energy from Neptune total 5 to 20 percent of the isolation absorbed by Triton, thus comprising a significant fraction of Triton's surface energy balance. These additional energy inputs can raise Triton's surface temperature between about 0.5 and 1.5 K above that possible with absorbed sunlight alone, resulting in an increase of about a factor of about 1.5 to 2.5 in Triton's basal atmospheric pressure. If Triton's internal heat flow is concentrated in some areas, as is likely, local effects such as enhanced sublimation with subsequent modification of albedo could be quite large. Furthermore, indications of recent global albedo change on Triton suggest that Triton's surface temperature and pressure may not now be in steady state, further suggesting that atmospheric pressure on Triton was as much as ten times higher in the recent past.

Description: Four geyser-like plumes were discovered near Triton's south pole in areas now in permanent sunlight. Because Triton's southern hemisphere is nearing a maximum summer solstice, insolation as a driver or a trigger for Triton's geyser-like plumes is an attractive hypothesis. Trapping of solar radiation in a translucent, low-conductivity surface layer (in a solid-state greenhouse), which is subsequently released in the form of latent heat of sublimation, could provide the required energy. Both the classical solid-state greenhouse consisting of exponentially absorbed insolation in a gray, translucent layer of solid nitrogen, and the 'super' greenhouse consisting of a relatively transparent solid-nitrogen layer over an opaque, absorbing layer are plausible candidates. Geothermal heat may also play a part if assisted by the added energy input of seasonal cycles of insolation.

Description: One model for the mechanism driving the plumes of the four active geyser-like eruptions observed by Voyager 2 on Triton is a heating up of nitrogen ice in a subsurface greenhouse environment, where nitrogen gas pressurized by solar heating explosively vents to the surface carrying clouds of ice and dark particles into the atmosphere. A temperature increase of less than 4 K above the ambient surface value of 38 + or - 3 K suffices to drive the plumes to 8-km altitude. Each eruption may last a year or more, over the course of which 0.1 cu km of ice is sublimed.