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Using both electron microscopy and immunological methods, we have characterized a number of changes occurring in rat fibroblasts after heat-shock treatment. Incubation of the cells for 3 h at 42°-43°C resulted in a number of changes within the cytoplasm including: a disruption and fragmentation of the Golgi complex; a modest swelling of the mitochondria and subtle alterations in the packing of the cristae; and alterations in cytoskeletal elements, specifically a collapse and aggregation of the vimentin-containing intermediate filaments around the nucleus. A number of striking changes were also found within the nuclei of the heat-treated cells: (a) We observed the appearance of rod-shaped bodies consisting of densely packed filaments. Using biochemical and immunological methods, these nuclear inclusion bodies were shown to be comprised of actin filaments. (b) Considerable alterations in the integrity of the nucleoli were observed after the heat-shock treatment. Specifically, there appeared to be a general relaxation in the condensation state of the nucleoli, changes in both the number and size of the granular ribonucleoprotein components, and finally a reorganization of the nucleolar fibrillar reticulum. These morphological changes in the integrity of the nucleoli are of significant interest since previous work as well as studies presented here show that two of the mammalian stress proteins, the major stress-induced 72-kD protein and the 110-kD protein, localize within the nucleoli of the cells after heat-shock treatment. We discuss these morphological changes with regards to the known biological and biochemical events that occur in cells after induction of the stress response.In an effort to understand the many changes occurring in mammalian cells after physiological stress, we have been examining the stress response at both the cellular and biochemical levels. Previous studies from numerous laboratories have defined many of the basic parameters governing the stress response in a variety of different organisms (for reviews see references 3, 34, and 43). Briefly, in almost all organisms studied to date, physiological stress is characterized by the rapid and preferential transcription of genes encoding the stress proteins and a concomitant decrease in the transcription and/or processing of those genes that were active before the environmental insult. These changes at the transcriptional level are accompanied by alterations in translational events occurring in the stressed cell. Specifically, two classes of polysomes are observed: a very active class in which high levels of the stress-induced mRNAs are being translated, and a somewhat inactive class containing mRNAs that were translationally active before the insult. The mechanisms by which these transcriptional and translational changes occur in the stressed cell remain unknown. The net result of these new events is the increased synthesis and accumulation of a small number of proteins referred to as the stress proteins and a decreased production of most ...

Abstract. We have examined and compared a number of cellular and biochemical events associated with the recovery process of rat fibroblasts placed under stress by different agents. Metabolic pulse-labeling studies of cells recovering from either heat-shock treatment, exposure to sodium arsenite, or exposure to an amino acid analogue of proline, L-azetidine 2-carboxylic acid, revealed interesting differences with respect to the individual stress proteins produced, their kinetics of induction, as well as the decay in their synthesis during the recovery period. In the initial periods of recovery, the major stress-induced 72-kD protein accumulates within the altered nucleoli in close association with the pre-ribosomal-containing granular region. During the later times of recovery from stress, the nucleoli begin to regain a normal morphology, show a corresponding loss of the 72-kD protein, and the majority of the protein now begins to accumulate within the cytoplasm in three distinct locales: the perinuclear region, along the perimeter of the cells, and finally in association with large phase-dense structures. These latter structures appear to consist of large aggregates of phase-dense material with no obvious encapsulating membrane. More interestingly we show, using doublelabel indirect immunofluorescence analysis, that much of the perinuclear and cell perimeter-distributed 72-kD protein coincides with the distribution of the cytoplasmic ribosomes. We discuss the possible implications of the presence of the 72-kD stress proteins within the pre-ribosomal-containing granular region of the nucleolus as well as its subsequent colocalization with cytoplasmic ribosomes in terms of the translational changes which occur in cells both during and after recovery from physiological stress.A organisms from the simplest prokaryotes, yeast, plants, on up to higher eukaryotes respond in a remarkably similar manner to abrupt changes in their environmental circumstance. This apparent defensive mechanism, classically termed the heat-shock response, is now more commonly referred to as the stress response owing to the wide variety of different agents that elicit basically the same cellular changes as those observed after hyperthermic treatment (for reviews see references 3, 8, and 25). Interestingly, the most obvious commonality amongst the various agents that induce the stress response is their ability to promote the accumulation in the cell of abnormal or denatured proteins. The general theme of the stress response in all organisms is the rapid and almost exclusive synthesis of a small number of proteins, the so-called heat-shock or stress proteins, and a corresponding decreased production of most other cellular polypeptides. While considerable work has resulted in identifying the stress proteins in terms of their apparent molecular size, little has been established regarding their mode of action in the cell. However, a recent burst of activity from many laboratories working at the molecular, cellular, and biochemical levels has recen...

Mammalian cells grown at 37C contain a single low-molecular-weight heat shock (or stress) protein with an apparent mass of 28 kilodaltons (kDa) whose synthesis increases in cells after exposure (6,23,24,26,27,37). The only obvious common property of these proteins from different organisms is their homology to the a-crystallin proteins present ill the lens (24,25,43). Because both the a-crystallins and the low-MW HSPs are isolated as rather large aggregates (i.e., 200 to 800 kDa from normal, nonheated cells) (1-3, 4, 6, 7, 14, 15, 46), we suspect that their observed homology resides in those domains responsible for the self-assembling properties of the proteins.We recently described the characterization and purification of the low-MW HSP from HeLa cells (6). The

This study reports the detection of single mammalian cells, specifically T cells (T lymphocytes) labeled with dextran-coated superparamagnetic iron oxide particles, using magnetic resonance microscopy. Size amplification due to sequestration of the superparamagnetic particles in vacuoles enhances contrast in localized areas in high-resolution magnetic resonance imaging. Magnetic resonance images of samples containing differing concentrations of T cells embedded in 3% gelatin show a number of dark regions due to the superparamagnetic iron oxide particles, consistent with the number predicted by transmission electron microscopy. Colabeling of T cell samples with a fluorescent dye leads to strong correlations between magnetic resonance and fluorescence microscopic images, showing the presence of the superparamagnetic iron oxide particles at the cell site. This result lays the foundation for our approach to tracking the movement of a specific cell type in live animals and humans.