EXPRESSION AND PHOSPHORYLATION OF BIP GRP78, A MOLECULAR CHAPERONE INTHE ENDOPLASMIC-RETICULUM, DURING THE DIFFERENTIATION OF A MOUSE MYELOBLASTIC CELL-LINE/

To determine the functional significance of endoplasmic reticulum chap erones in hematopoietic cells, we analyzed the expression and post-tra nslational modification of BiP/GRP78 and GRP94 as well as the cytoplas mic chaperones HSP70 and HSC70 during the differentiation of a mouse m yeloid leukemia cell line, M1. The amounts of BiP/GRP78 and GRP94 incr eased several-fold when M1 cells were induced to differentiate into ma crophage-like cells by treatment with interleukin-6 (IL-6). Synthesis began to increase at 4 hr after IL-6 treatment. The phosphorylated for m of BiP/GRP78 increased during the later stages of differentiation. T hese data suggested that the chaperone activity of BiP/GRP78 and GRP94 may be needed for differentiated macrophage-like cells or for the dif ferentiation event itself, and that functionally different BiP/GRP78 a ccumulate during the differentiation of M1 cells.