De novo synthesis and secretion of a 36-kD protein by cells that form lupus inclusions in response to alpha-interferon.

In response to the pure recombinant human alpha-IFN, IFLrA, Raji and Daudi were the only two cell lines among 19 human lymphoblastoid cell lines tested that formed the human lupus inclusions (LI) to a high frequency. Raji, Daudi, and five other cell lines were examined for protein changes that might accompany LI formation. Their selection was based upon T or B origin, association with Epstein-Barr virus, and ability to form LI. A trace protein of an estimated molecular mass of 36 kD (p36) and an isoelectric point of 5.6 was detected on two-dimensional gels only of alpha-IFN-treated Raji and Daudi cells. Gamma-IFN did not induce p36 or LI in any of these seven cell lines. In Daudi cells p36 and LI formed simultaneously in response to IFLrA, and persisted until the alpha-IFN-induced death of the culture. In Raji cells, p36 and LI appearance and disappearance coincided with the addition and removal of alpha-IFN. Fractionation of Raji cells with nonionic-detergent buffer placed p36 with the inclusions in the cytoplasmic supernatant. With detergent-free buffer p36 and LI were distributed evenly between the nuclear and cytoplasmic fractions. Pulse-chase experiments revealed that p36 was secreted. The de novo synthesis of p36 with alpha-IFN treatment was shown by labeling the cell proteins with 35S methionine before and after the addition of alpha-IFN. These results along with previous results on the de novo synthesis of LI in the endoplasmic reticulum (which is involved in the processing and secretion of proteins) suggest a role for LI in the synthesis and secretion of p36.