Cellular and biochemical events in mammalian cells during and after recovery from physiological stress.

TLDR

The study examines how the 72‑kD stress protein’s presence in nucleolar pre‑ribosomal regions and its later colocalization with cytoplasmic ribosomes may alter translational activity during and after stress recovery. Researchers compared rat fibroblast recovery after heat‑shock, sodium arsenite, or L‑azetidine 2‑carboxylic acid exposure, using metabolic pulse‑labeling to track stress‑protein kinetics and double‑label immunofluorescence to map protein–ribosome colocalization. During recovery, the 72‑kD stress protein first accumulates in nucleoli, then redistributes to perinuclear, peripheral, and cytoplasmic aggregates, and largely colocalizes with ribosomes, suggesting a role in translational regulation.

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 double-label 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.