Protein disulphide isomerase from human peripheral blood neutrophils

Protein disulphide isomerase (PDI) is a 56 kDa resident polypeptide of the endoplasmic reticulum of many cell types. We evaluated the ability of human peripheral blood polymorphonuclear neutrophils (PMN) to synthesize both mRNA and proteins. Using in vitro [35S]-methionine labeling of purified PMN, followed by immunoprecipitation of cell lysates with immobilized polyclonal and monoclonal antibodies and analysis by gel electrophoresis, PMN were shown to synthesize many proteins, including actin. In contrast, incorporation of [35S]-methionine into PDI was not detected. Purification of total RNA from PMN and analysis by Northern blots demonstrated the presence in PMN of PDI-RNA. Western immunoblot evaluations of total PMN protein display an immunoreactive-PDI of 56 kDa. Indirect immunofluorescence studies suggest an abundance of immunoreactive-PDI throughout PMN. We therefore conclude that PDI is synthesized in precursor cells of the bone marrow. Phorbol 12-myristate 13-acetate, a reagent known to affect the degranulation of specific granules, causes the release of immunoreactive-PDI into a post-centrifugation supernatant. PDI, a ubiquitous endoplasmic reticulum resident protein, is shown here to be associated with specific granules in a cell type which has lost its intracellular membrane network during terminal differentiation.