Effects of hyper- and hypoosmotic stress on protein synthesis in cultured epidermal cells of common carp

Abstract

SUMMARY: Effects of osmotic stress on protein synthesis in a carp epidermal cell line, EPC, were investigated by means of two-dimensional polyacrylamide gel electrophoresis. Hypoosmotic stress (150 mOsm/kg H2O) induced the increased synthesis of six proteins, P1 (124 kDa, isoelectric point (pI) 6.1), P2 (69 kDa, pI 5.4), P3 (68 kDa, pI 5.5), P4 (61 kDa, pI 6.3), P5 (58 kDa, pI 5.4), and P6 (49 kDa, pI 6.2). The increase of the synthesis of P1, P2, P4, P5, and P6 occurred within the initial 3 h of hypoosmotic stress and continued thereafter, while that of P3 was transient. Hypoosmotic stress also induced the decreased synthesis of a protein P7 (60 kDa, pI 6.5–6.8). The decrease of the synthesis of P7 occurred from 12 h of hypoosmotic stress and continued thereafter. Hyperosmotic stress (450 mOsm/kg H2O) transiently induced the increased synthesis of three proteins, P1, P3, and P8 (60 kDa, pI 5.8–6.1). Subcellular distribution analysis revealed that P2 and P6 were recovered in both the cytosolic and the membranous fractions, while P1, P3, P4, P5, P7, and P8 were recovered only in the cytosolic fraction. These changes of protein synthesis are discussed in view of physiological response of cells to osmotic stress.