CALRETICULIN - A STRESS PROTEIN-INDUCED IN THE RENAL EPITHELIAL-CELL LINE NBL-1 BY AMINO-ACID DEPRIVATION

Confluent monolayer cultures of the bovine kidney cell line NBL-1 were starved of amino acids in the presence of tracer concentrations of [S -35]-methionine. Fluorographs of SDS-polyacrylamide gel separated memb rane proteins revealed increased labelling of at least two proteins in starved cells relative to those in cells grown in complete medium. Th e patterns of Coomassie blue stained proteins from Concanavalin A-puri fied fractions of cells grown under fed and amino acid-starved conditi ons were similar but fluorography indicated the presence of one major labelled glycoprotein with a molecular weight of 62 kD in starved cell s which was not present in fed cells. N-terminal amino acid analysis o f the first 15 amino acids of the 62 kD protein and a protein of 60 kD found in control cells identified both proteins as calreticulin. N-te rminal amino acid sequence analysis of a second amino acid starvation- up-regulated protein identified it as glucose-regulated protein GRP78. The amino acid sequences of calreticulin, GRP78 and two transport pro teins known to be induced in amino acid starvation, have a common moti f near the C-terminal end of the molecule. It is suggested that calret iculin is a member of a novel class of stress proteins induced by amin o acid starvation.