Induction of the Stress Response by Isolation of Rabbit Type II Pneumocytes

Abstract

Protein synthesis by isolated rabbit type II pneumocytes was evaluated by incorporation of labeled amino acids, gel electrophoresis, and fluorography. Type II alveolar epithelial cells preferentially synthesize a small number of proteins immediately following isolation and simultaneously exhibit a depression of all other protein synthesis. Examination of the time course of the appearance and decline of these proteins showed them to be actively synthesized during the first 14 h after isolation. Decline in their production was accompanied by a gradual enhancement in the synthesis of other proteins. Actin synthesis was not measurable 1 h after isolation, but increased to 9% of total label incorporated by 14 h. This recovery was independent of attachment to an extracellular matrix. Treatment with actinomycin D immediately following cell isolation abolished the synthesis of these proteins, suggesting a requirement for active mRNA production. A subset of these proteins are induced by heat treatment of cultured type II cells. The half-life, intracellular localization, isoelectric points, apparent molecular weights, and heat inducibility of this group of proteins are similar to stress proteins found in other mammalian systems. These stress proteins are unique in that their synthesis is induced by the cell isolation process. Possible mechanisms by which cell isolation may induce the stress response are discussed.