Expression, synthesis, and phosphorylation of HSP28 family during development and decay of thermotolerance in CHO plateau-phase cells.

We investigated a correlation between development of thermotolerance and expression, synthesis, or phosphorylation of HSP28 family in CHO plateau phase cells. After heating at 45.5 degrees C for 10 min, thermotolerance developed rapidly and reached its maximum 12-18 hr after heat shock. This acquired thermal resistance was maintained for 72 hr and then gradually decayed. In parallel, the levels of three 28 kDa heat shock proteins, HSP28a along with its two phosphorylated isoforms (HSP28b,c), increased and reached their maximum 24-48 hr after heat shock. The levels of these polypeptides, except HSP28c, remained elevated for 72 hr and then decreased. The level of HSP28 mRNA increased rapidly and reached its maximum 12 hr after heat shock. However, unlike thermotolerance and the levels of HSP28 family proteins, the level of HSP28 mRNA decreased rapidly within 72 hr. These results demonstrate a correlation between the amount of intracellular HSP28 family proteins and development and decay of thermotolerance.     

Specific protein phosphorylation in interferon-treated uninfected and virus-infected mouse L929 cells: enhancement by double-stranded RNA.

The enhanced phosphorylation of specific protein(s) observed in extracts from interferon-treated cells (in the presence of ATP and double-stranded [ds] RNA) was also seen in intact mouse L929 cells upon treatment with dsRNA, polyriboinosinic.polyribocytidylic acid [poly(rI.rC)] or reovirus dsRNA, using 32Pi as radiolabel. Labeling of a 65,000-dalton protein(s) with 32P was greatly increased in interferon-treated cells in the presence of added dsRNA, suggesting that the expression in vivo of the kinase activity involved is regulated by dsRNA. This was used as a test system to investigate whether the activity of interferon-induced enzyme(s) is stimulated following virus infection, possibly owing to the accumulation of dsRNA. No obvious increase in 32P-labeling of 65,000-dalton protein(s) was observed upon infection of interferon-treated cells with mengovirus or vesicular stomatitis virus. A basal level of 32P-labeling of the 65,000-dalton protein(s) was detected in interferon-treated cells in the absence of added dsRNA, indicating a basal level of expression of the kinase activity involved. The possible implications of these results are discussed.     

Dexamethasone induces gelsolin synthesis and altered morphology in L929 cells

When L929 cells are exposed to 5 μg/ml dexamethasone, synthesis of a 90,000 M(r) polypeptide is induced within 12 h. Flattening of the cells begins at about this time and progresses to become quite prominent after 48 h of exposure. Two-dimensional PAGE and partial proteolytic fingerprints identify the 90,000 M(r) polypeptide as gelsolin, a Ca(++)-dependent inhibitor of actin polymerization. Thus, this system provides evidence that gelsolin may have a role in regulating cell shape in response to physiological agents such as glucocorticoids.     

Cellular RNA synthesis in normal and mengovirus-infected L-929 cells.

Cellular RNA synthesis was studied in mouse L-929 cells and in these cells infected with mengovirus. RNA polymerases I, II, and III were partially purified and their chromatographic properties were analyzed by DEAE-Sephadex A-25 chromatography. RNA polymerase II was purified from mouse liver and its subunit structure was compared to that of normal and virus-infected L-929 cells by two-dimensional gel electrophoresis. By these criteria, the enzymes from all three sources were identical. The RNA synthetic activities and capacities of chromatins from normal and virus-infected cells were compared under a variety of conditions. The endogenous activity in chromatin from infected cells was inhibited relative to controls but the residual activity responded normally to stimulation by ammonium sulfate, heparin, and Sarkosyl. The template capacity of the chromatins was compared with added RNA polymerase II and by a rifampicin challenge assay utilizing Escherichia coli RNA polymerase. Identical results were obtained in each case. The number of growing RNA chains and the rates of their elongations were determined. The results showed that nuclei and chromatin from infected cells have a smaller number of RNA polymerase II molecules engaged in RNA synthesis than normal cells do but that the active molecules elongate RNA chains at the same rate.     

Heat-induced preferential synthesis and redistribution of HSP 70 and 28 families in Chinese hamster ovary cells

We observed that members of two HSP families (70 and 28 kDa) preferentially redistributed into the nucleus after heating at 45.5 degrees C for 10 min. The rates of synthesis and redistribution of these proteins were different for each member of HSP families during incubation period at 37 degrees C after heat shock. The maximum rates of synthesis of HSP 70 and HSP 28 families, except HSP 28c, were 6-9 hr after heat shock, whereas the maximum rates of redistribution were 3-6 hr after heat shock. These results suggest that the rates of redistribution of these proteins may be dependent on the amount of intracellular proteins as well as the alteration of binding affinity of nucleoproteins following heat shock.     

Phosphorylation of HSP27 during development and decay of thermotolerance in Chinese hamster cells

The small molecular weight heat shock protein HSP27 was recently shown to confer a stable thermoresistant phenotype when expressed constitutively in mammalian cells after structural gene transfection. These results suggested that HSP27 may also play an important role in the development of thermotolerance, the transient ability to survive otherwise lethal heat exposure after a mild heat shock. In Chinese hamster O23 cells increased thermoresistance is first detected at 2 h after a triggering treatment of 20 min at 44 degrees C, attains a maximum at 5 hours, and decays thereafter with a half-life of 10 h. We found that the development and decay of transient thermotolerance cannot be solely explained on the basis of changes in the cellular concentration of HSP27. The cellular HSP27 concentration is not increased appreciably at 2 h after heat shock and attains a maximum at 14 h. Similar results were obtained in the case of another heat shock protein, HSP70. HSP70 follows slightly faster kinetics of accumulation (peaks at 10 h) and decays much more rapidly (ti/2 = 4h) than HSP27 (t1/2 = 13h). HSP27 has 3 isoelectric variants A, B, and C of which B and C are phosphorylated. In cells maintained at normal temperature, HSP27A represents more than 90% of all HSP27. Shifting the cell culture temperature from 37 to 44 degrees C induces the incorporation of 32P into the more acidic B and C forms, a process that occurs very rapidly since the reduction in the concentration of the A form and a corresponding increase in the level of B and C is detectable by immunoblot analysis within 2.5 min at 44 degrees C. Analyses performed at various times during development and decay of transient thermotolerance revealed a close relationship between the effect of heat shock on HSP27 phosphorylation and cell ability to survive. For example, fully thermotolerant cells (5 h post-induction) are refractory to induction of HSP27 phosphorylation by a 20-min heat shock. The induction of HSP27 phosphorylation was also studied in a family of clonal cell lines of O23 cells that are thermoresistant as a result of the constitutive expression of a transfected human HSP27 gene. In these thermoresistant cells, phosphorylation of the endogenous hamster HSP27 is induced to a level comparable to that found in the thermosensitive parental cells. However, phosphorylation of the exogenous human protein, which represents more than 80% of total HSP27 in these cells, was much less induced.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differences in preferential synthesis and redistribution of HSP70 and HSP28 families by heat or sodium arsenite in Chinese hamster ovary cells

Since both heat and sodium arsenite induce thermotolerance, we investigated the differences in synthesis and redistribution of stress proteins induced by these agents in Chinese hamster ovary cells. Five major heat shock proteins (HSPs; Mr 110, 87, 70, 28, and 8.5 kDa) were preferentially synthesized after heat for 10 min at 45.5 degrees C, whereas four major HSPs (Mr 110, 87, 70, and 28 kDa) and one stress protein (33.3 kDa) were preferentially synthesized after treatment with 100 microM sodium arsenite (ARS) for 1 hr. Two HSP families (HSP70a,b,c, and HSP28a,b,c) preferentially relocalized in the nucleus after heat shock. In contrast, only HSP70b redistributed into the nucleus after ARS treatment. Furthermore, the kinetics of synthesis of each member of HSP70 and HSP28 families and their redistribution were different after these treatments. The maximum rates of synthesis of HSP70 and HSP28 families, except HSP28c, were 6-9 hr after heat shock, whereas those of HSP70b and HSP28b,c were 0-2 hr after ARS treatment. In addition, the maximum rates of redistribution of HSP70 and HSP28 families occurred 3-6 hr after heat shock, whereas that of HSP70b occurred immediately after ARS treatment. The degree of redistribution of HSP70b after ARS treatment was significantly less than that after heat treatment. These results suggest that heat treatment but not sodium arsenite treatment stimulates the entry of HSP70 and HSP28 families into the nucleus.     

Downregulation of ERK2 is essential for the inhibition of radiation-induced cell death in HSP25 overexpressed L929 cells

We previously reported that overexpression of HSP25 delayed cell growth, increased the level of p21(waf), reduced the levels of cyclin D1, cyclin A and cdc2, and induced radioresistance in L929 cells. In this study, we demonstrated that HSP25 induced-radioresistance was abolished by transfection with plasmids containing antisense hsp25 cDNA. Extracellular regulated kinase (ERK) and MAP kinase/ERK kinase (MEK) expressions as well as their activation (phospho-forms) were inhibited by hsp25 overexpression. Furthermore, when control vector transfected cells were treated with PD98059, MEK inhibitor, they became resistant to radiation, suggesting that inhibition of ERK1/2 activities was essential for radioresistance in L929 cells. To confirm the relationship between ERK1/2 and hsp25-mediated radioresistance, ERK1 or ERK2 cDNA was transiently transfected into the hsp25 overexpressed cells and their radioresistance was examined. HSP25-mediated radioresistance was abolished by overexpression of ERK2, but not by overexpression of ERK1. Alteration of cell cycle distribution and cell cycle related protein expressions (cyclin D, cyclin A and cdc2) by hsp25 overexpression were also recovered by ERK2 cDNA transfection. Increase in Bcl-2 protein by hsp25 gene transfection was also reduced by subsequent ERK2 cDNA-transfection. Taken together, these results suggest that downregulation of ERK2 is essential for the inhibition of radiation-induced cell death in HSP25 overexpressed cells.     

Persistence of mumps virus in mouse L929 cells

The characteristics of a persistent infection of L929 cells with mumps virus (MuV) is presented. The persistent infection (L-MuV cells) was regulated by interferon (IFN) produced endogenously and almost all the properties showed that the carrier culture was maintained by horizontal transmission of the virus. Small-plaque mutants, but not temperature-sensitive variants, were selected during the persistent infection. MuV released from L-MuV cells (MuV-pi) replicated efficiently in L929 cells, while infection of L929 cells with the original MuV-o resulted in an abortive infection. The efficient replication of MuV-pi in L929 cells can be explained by the findings that MuV-pi induced IFN more slowly and had lower susceptibility to IFN in L929 cells than MuV-o did. M protein was synthesized to a considerable degree in MuV-pi-infected cells, while it could not be detected in MuV-o-infected cells. By contrast, MuV-pi formed small plaques in Vero cell monolayers and the yield of MuV-pi in Vero cells was lower than that of MuV-o. M protein induced by MuV-pi decayed easily in Vero cells. M protein was considered to be a limiting factor for MuV replication in both cell lines.     

Impairment of reovirus mRNA 'cap' methylation in interferon-treated mouse L929 cells.

Reovirus mRNAs synthesized in vitro by the virionassociated enzyme have a 5' 'cap 1' structure (m7G(5')ppp(5')GmpCp...). However, about one third to one half of the reovirus mRNAs formed in mouse L929 cells have a 5' 'cap 2' structure (m7G(5')ppp(5')GmpCmp...) and the rest have a 5' 'cap 1' structure. The finding that virus mRNA 'cap' methylation is impaired in extracts of interferon-treated cells prompted us to study the effect of interferon on virus mRNA 'cap' methylation in vivo. Using labeling with [3H]-guanosine and dual labeling with [3H]methionine and [14C]uridine we compared the 5' structures of reovirus mRNAs accumulating between 5 and 11 h after infection in: L929 cells treated with 390 to 2600 U/ml of a partially purified mouse interferon preparation and untreated L929 cells. The treatment resulted in a 70 to 98% decrease in the 24 h virus yield and in a 50 to 55% decrease in the label accumulated in virus mRNAs. The 'capping' of virus mRNAs and the methylation of their 5' terminal and adjacent G residues were not diminished in interferon-treated cells. However, the percent of 'cap 2' termini was 36 to 47% lower in virus mRNAs from interferon-treated cells than in virus mRNAs from control cells. The interferon treatment did not result in the appearance of additional methylated nucleotides in the virus mRNAs.     

Regulation of macromolecular synthesis in reovirus-infected L-929 cells I. Effect of L-histidinol.

The histidine analogue L-histidinol, reported by Vaughan and Hansen (1973) to establish a potent, readily reversible inhibition of eukaryotic protein synthesis in vivo, was used to investigate the regulation of macromolecular synthesis in reovirus-infected L-929 cells. The addition of L-histidinol to normal L cells led to a total inhibition of protein synthesis. The inhibition appeared to be a consequence neither of isotope dilution resulting from elevated endogenous amino acids nor of an inability of treated cells to accumulate exogenous amino acids. Addition of L-histidine to histidinol-arrested cells resulted in a complete recovery of protein synthesis. Similarly, protein synthesis in reovirus-infected L cells examined 17 h postinfection (31 C) was totally inhibited by histidinol treatment and was readily reversed by the addition of histidine. Reovirus-infected cells treated with histidinol had an essentially unaltered capacity to synthesize reovirus single-stranded RNA relative to unperturbed cultures but a diminishing ability to maintain genome RNA synthesis. Addition of L-histidine to arrested cultures led to a complete recovery of genome RNA synthesis. The L-histidinol-mediated arrest of protein synthesis was both very effective and easily reversed, suggesting the general applicability of this novel inhibitor to investigations of regulation of macromolecular synthesis in both normal and virus-infected eukaryotic cells.     

Detailed characterization of heat shock protein synthesis and induced thermotolerance in seedlings of Sorghum bicolor L.

Tolerance of both protein synthesis and seedling growth to apreviously lethal high temperature can be induced by prior exposureto a sub-lethal temperature during which the synthesis of heatshock proteins (HSPs) occurs. In this study, a thermal gradientbar was used to measure the physiological effects of temperatureon seedlings of sorghum (Sorghum bicolor L.) in conjunctionwith studies of gene expression. The duration of HSP synthesis,both during continued high temperature treatment or on returnto normal temperatures, was found to be very finely modulatedand was dependent on the severity of the initial heat shock.The synthesis of heat shock proteins and the induction of thermotolerancewere rapid, reversible and reinducible phenomena. Maximal thermotolerancewas obtained after treatments that induced the full complementof HSPs. Subsequent treatments that repressed HSP synthesis,also abolished thermotolerance. The presence of HSPs, however,was not sufficient for the tissue to be in a thermotolerantstate and the results suggest that either their de novo synthesis,or some other factor, is required for the induction of thermotolerance.Pre-existing HSPs did not inhibit the synthesis of new HSPs.Although the kinetics of the synthesis of HSPs and the developmentof thermotolerance show a tight correlation, the kinetics ofthe decay of thermotolerance and the degradation of HSPs werenot linked. The functional state or distribution of HSPs maywell change during the recovery process. Key words: Heat shock, thermotolerance, Sorghum bicolor, growth, protein synthesis     

Achievement of thermotolerance trough hsps phosphorylation in sea urchin embryos.

TPA treatment of sea urchin embryos is able to induce thermotolerance. Evidence is provided that TPA treatment induces phosphorylation of a constitutive stress protein of 38 KDa.     

Mechanism of interferon action. Increased phosphorylation of protein synthesis initiation factor eIF-2 alpha in interferon-treated, reovirus-infected mouse L929 fibroblasts in vitro and in vivo

The effect of interferon (IFN) treatment and virus infection on the phosphorylation both in vitro and in vivo of the alpha subunit of protein synthesis initiation factor eIF-2 (eIF-2 alpha) was examined in mouse fibroblast L929 cells. The [gamma-32P]ATP-mediated in vitro phosphorylation of eIF-2 alpha catalyzed by cell-free extracts prepared from IFN-treated, uninfected cells was dependent upon exogenously added double-stranded RNA (dsRNA). However, the dsRNA requirement for eIF-2 alpha phosphorylation in vitro was eliminated by prior infection of cells with reovirus Dearing strain virions but not with defective top component particles. The enhanced phosphorylation in vitro of eIF-2 alpha and ribosome-associated protein P1 depended in a similar manner upon the multiplicity of virus infection. The extent of phosphorylation in vivo of eIF-2 alpha prepared from L929 cells was also examined by utilizing two-dimensional isoelectric focusing/sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting techniques. About 5-10% of the eIF-2 alpha was typically phosphorylated in vivo in untreated, mock-infected cells, whereas 25-30% was phosphorylated in IFN-treated, reovirus-infected cells. An intermediate extent of eIF-2 alpha phosphorylation, routinely between 15 and 20%, was observed with either IFN treatment or reovirus infection alone. The integrity of eIF-4A and eIF-4B was also examined by two-dimensional electrophoresis and immunoblotting, and no significant alterations in molecular size or charge heterogeneity were detected when these factors were prepared from IFN-treated, reovirus-infected cells as compared to untreated, uninfected cells.