PROTEIN-SYNTHESIS INHIBITION INDUCES CYTORESISTANCE IN CULTURED HUMANPROXIMAL TUBULAR (HK-2) CELLS

After sublethal injury, proximal tubular cells acquire resistance to f urther attack. This study evaluated whether this could be a possible c onsequence of decreased protein synthesis, a potential correlate of ce ll damage. To this end, cultured human proximal tubular cells (HK-2) w ere subjected to 0-24 h of protein synthesis inhibition (>98%), either by adding protein synthesis inhibitors [cycloheximide (CH) or verruca rin A] or by inducing sublethal ATP depletion (antimycin A + 2-deoxygl ucose). After 24 h of these treatments, significant resistance to Ca2 ionophore/ATP depletion-induced attack was noted (assessed by vital d ye exclusion, compared with normal cells). That less than or equal to 6 h of protein synthesis inhibition caused no cytoresistance implied t he importance of evolving protein depletion rather than nonspecific dr ug effects or protein synthesis inhibition per se. CH plus ATP depleti on did not induce additive benefits, suggesting a common mechanism. Cy toresistance was dissociated from the extent of free Ca2+ loading and ATP depletion but was associated with a decrease in membrane deacylati on. CH removal promptly restored protein synthesis and cytoresistance was lost; conversely, ATP recovery did not restore protein synthesis a nd cytoresistance persisted. The emergence of cytoresistance correlate d with the disappearance/dephosphorylation of an unidentified 130-kDa tyrosine-phosphorylated protein/protein complex (denoted pp-130). The functional significance of this change was suggested by the fact that tyrosine phosphatase inhibition with orthovanadate maintained pp-130 e xpression and prevented the cytoresistant state. We conclude that prot ein synthesis inhibition in HK-2 cells can induce a cytoresistant stat e. Suppression in phospholipase activity and altered tyrosine phosphor ylation events may have functional significance in this regard.