Heat shock, also synthesis

Exposure of neutrophils to heat shock also results in the synthesis of HSPs and a decrease in their ability to generate reactive oxidants. This is not due to cell death, because the response is reversible and other cellular functions are unaffected. For example, after 20 min exposure at 45 °C, the NADPH oxidase is non-functional, but arachidonic acid release is 73% of control values and PGE2 formation is unaffected. Oxidase activity returns to normal levels 150 min later. Several HSPs are synthesised (e.g. hsp70 and hsp85 at 41 °C, hsp48 and hsp60-65 at 43 °C). (The hsp numbers refer to the relative molecular masses of the proteins.)... 

In this section we shall look for evidence that imperfections in the synchrony, first of division then of DNA replication, reflect the fact that, in this system, cells can engage in DNA replication beyond a critical time limit antecedent to the time when most cells show synchronous division. In a preceding section it was reported that asynchronous entry of the cells into DNA replication continued for 40 or so minutes after the end of heat shocks. Also, evidence was presented that there is a time point 35 or so minutes before the shocks are ended, after which no cell that takes part in synchronous division at its peak can have entered into DNA synthesis. What is then the contribution to synchronous division of the fraction of cells that in fact enter DNA synthesis in the critical 1.25-hour interval between the two indicated times These cells will not have had time to finish S and normal G2 before they are supposed to participate in the first synchronous division. We shall see that in fact they contribute negatively to the synchrony, either by dividing later than at the time when synchronous division is at its peak or by not dividing at all. 

Figure 36-4. Illustration of the tight correlation between the presence of RNA polymerase II and RNA synthesis. A number of genes are activated when Chirono-mus tentans larvae are subjected to heat shock (39 °C for 30 minutes). A Distribution of RNA polymerase II (also called type B) in isolated chromosome IV from the salivary gland (at arrows). The enzyme was detected by immunofluorescence using an antibody directed against the polymerase. The 5C and BR3 are specific bands of chromosome IV, and the arrows indicate puffs. B Autoradiogram of a chromosome IV that was incubated in H-uridine to label the RNA. Note the correspondence of the immunofluorescence and presence of the radioactive RNA (black dots). Bar = 7 pm. (Reproduced, with permission, from Sass H RNA polymerase B in polytene chromosomes. Cell 1982 28 274. Copyright 1982 by the Massachusetts Institute of Technology.)...

Stop protein translation sites. Furthermore, protein synthesis and stability may also be regulated by constantly changing cellular processes and extracellular signals such as heat shock proteins, growth factors, and toxins. The end result of these processes could lead to changes in protein localization and interactions, generation of protein fragments, and alteration in protein function and turnover rates. 

Some of the monoclonal antibodies mentioned below recognize different p53 molecule conformations. Also, detection of p53 with different antibodies depends on the time of its synthesis. It has been suggested that the p53 epitope for antibody 1620 remains cryptic immediately after synthesis in human keratinocytes and may not be exposed until late in the life of the protein (Spandau, 1994). Furthermore, different conformations of p53 may predominate in different differentiation stages of the cell or tissue. In addition, differentiation-specific cellular proteins and other proteins that may bind to p53 may mask epitopes on p53 at various stages of differentiation. For example, heat shock protein 70 is known to associate with p53 (Hainaut and Milner, 1992). 

Cold stress may induce synthesis of heat-shock (stress) proteins. Exposure of cells to cold shock may lead to the induction of one or more of the classes of molecular chaperones that also are induced by heat shock. This is strong evidence that low temperature, like high temperature, can lead to non-native protein structures in vivo and, therefore, to the requirement for enhanced chaperoning activity. Induction of cold-induced protein chaperones has been seen in bacteria (Salotra et al., 1995), in whole organism studies of ectothermic animals (Petersen et al., 1990 Yocum et ah, 1991),... 

The universality of the heat shock response has been proved by comparative studies not only within the domains of bacteria and eucarya but also, more recently, within the domain of archaea. Thus the phenomenon of acquired thermotolerance associated with the synthesis of specific proteins could also be found in mesophilic and thermophilic archaea [49-52]. 

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