Upregulation of a Myristylated 74-kDa Protein by Interferon Treatment of Daudi Cells

Labeling of unstimulated human Daudi B lymphoblastoid cells with exogenously added [³H]myristate resulted in acylation of a broad spectrum of different proteins, most of which are currently unknown. Among this array of labeled proteins, a unique 74-kDa acylated protein was induced in interferon (IFN)-treated cells. In the present study, we defined the myristylation kinetics of this protein and examined the subcellular distribution before and after activation with IFN-α/β. This acylated protein was detected only at a very low level in the membrane fraction of untreated cells, and its level increased 3—4-fold by treatment with IFN. This induction occurred over a short period of time and was IFN-α/β dose-dependent. No significant induction was observed with IFN-γ. Incorporation of [³H]myristate was completely abolished by cycloheximide. The fatty acid associated with this protein was probably linked to a nascent chain through an amide linkage, as it was not released by alkaline hydroxylamine treatment and was identified as myristic acid by HPLC after its release from the polypeptide chain by acid methanolysis. In contrast to other IFN-induced proteins, whose synthesis started at 10 h and was maintained for 20 h, this protein was present in the plasma membrane for a short period of time, between 4 and 6 h after IFN-α/β treatment, and was no longer present in this cellular compartment. This event appears to be transient and suggests that a degradation or a negative regulation of transcription starts from 6—7 h after continuous IFN treatment. As many other myristylated proteins are implicated in cellular regulation, it is possible that this 74-kDa protein may have a regulatory role in cell proliferation and the inhibition of viral replication.