Alteration of cellular adhesion by heat shock

Cellular mechanisms underlying temperature-induced bleaching in the tropical sea anemone Aiptasia pulchella

Temperature-induced bleaching in symbiotic cnidarians is a result of the detachment and loss of host cells containing symbiotic algae. We tested the hypothesis that host cell detachment is evoked through a membrane thermotropic event causing an increase in intracellular calcium concentration, [Ca2+]i, which could then cause collapse of the cytoskeleton and perturb cell adhesion. Electron paramagnetic resonance measurements of plasma membranes from the tropical sea anemone Aiptasia pulchella and the Hawaiian coral Pocillopora damicornis labeled with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) revealed no membrane thermotropic event. In addition, intracellular imaging using Fura-2AM as well as labeling anemones with 45Ca revealed no significant change in [Ca2+]i. However, bleaching could be evoked at ambient temperature with 25 mmol l–1 caffeine without affecting [Ca2+]i. [Ca2+]i could be altered with ionomycin in isolated host cells, but ionomycin could not induce bleaching in A. pulchella. As caffeine can affect levels of intracellular protein phosphorylation, the ability of other agents that alter intracellular levels of protein phosphorylation to evoke bleaching was investigated. The protein phosphatase inhibitor vanadate could induce bleaching in A. pulchella. Two-dimensional gels of 32P-labeled proteins from cold-shocked, caffeine-treated and control anemones show that both temperature shock and caffeine alter the array of phosphorylated host soluble proteins. We conclude that cnidarian bleaching is linked to a temperature-induced alteration in protein phosphorylation.

Heat stress lipids and schizophrenia

The neurodevelopmental hypothesis of schizophrenia implicates abnormal or disrupted neural growth during embryogenesis. It is postulated here that stress-inducing agents acting upon a compromised cellular system resulting from abnormal plasma membrane lipids could effect the neuronal abnormalities observed in schizophrenia. The heat stress response is induced by exposure to hyperthermia as well as a variety of other agents. The response to these agents includes the cessation of most transcriptional and translational activities, accompanied by the induction of a highly specific set of proteins. A concomitant reduction in metabolic activity including cell cycle delays is also observed. Much of the enormous literature on the heat stress response concentrates on protein and DNA interactions, especially with regard to transcriptional control. However, a variety of lipids are intrinsically involved in the heat stress response. This paper will provide a brief introduction to the heat shock proteins and will explore the roles that lipids play in the heat shock response.

Thermal response of synchronous CHO cells with different shapes

This study examines the differential heat sensitivity of rounded suspension cells versus flattened monolayer cells. G1 populations of two different Chinese hamster ovary lines were used to eliminate possible cell cycle artifacts. The cell populations were heated at 43 and 45 degrees C. In all cases, cells treated in suspension were less sensitive to heat killing than cells treated as monolayers.

Stress causes alteration in attachment of rat hepatocytes to matrix protein substratum

The effect of different types of stress on the attachment of rat hepatocytes to various matrix protein substrata, such as collagen IV, fibronectin and laminin, was investigated. Study of the kinetics of attachment of adult hepatocytes subjected to heat-shock at 45 degrees C for 30 min showed significantly lower attachment to collagen IV, fibronectin and laminin substrata when compared to untreated controls. The alteration in attachment was observed after heat-treatment for 10 min and the extent of alteration appeared to increase with duration of the heat-treatment, as well as with increase in temperature. Foetal rat hepatocytes, which appeared to attach much more readily than adult rat hepatocytes to these substrata, particularly to laminin, also showed significantly lower attachment to all three substrata after heat-treatment at 45 degrees C for 30 min. This alteration in attachment appeared to be specific for matrix proteins as there was no significant effect on interaction of cells with non-matrix proteins, such as Con A and asialoglycoproteins. While the attachment of adult hepatocytes appeared to attain near control levels in about 4 h, the foetal cells recovered in about 2 h after heat-shock, indicating that the heat-shock effect is reversible and the recovery is faster in foetal hepatocytes. Other stress-causing agents, such as heavy metals, also caused an alteration in attachment of hepatocytes to these matrix proteins. Attachment of adult and foetal hepatocytes to collagen substratum was reduced by 100-microM concentrations of heavy metals in the order Zn > Cd > La > As > Cu for adult cells and La > Zn > As/Cu > Cd for foetal cells. These heavy metals also caused significant reduction in attachment of adult hepatocytes to fibronectin and laminin, although the extent of inhibition was less than that for collagen substrata. However, these heavy metals did not significantly affect the attachment of foetal hepatocytes to laminin substratum indicating that the effect of heavy metals appeared to vary with the nature of the matrix protein substratum. On heat-shock, incorporation of [3H]leucine into cytoskeletal proteins such as cytokeratins CK8 and CK18 was reduced and significant amounts of two new proteins having an average molecular mass of 80 kDa and 90 kDa were found to be tightly associated with cytoskeletal proteins.