Biochemical characterization of the membrane-associated phosphorylating proteins involved in the anti-proliferative effect of human recombinant interferon-alpha 2a (rIFN-alpha 2a) in Daudi cells.

The anti-proliferative effect of interferons (IFNs) was investigated, focusing on the physiological activities of membrane-associated proteins involved in the progress of cell proliferation. In preliminary screening of the inhibitory effect of IFNs against the cell growth of various human hematopoietic tumor cells, Daudi cell was the most sensitive to rIFN-alpha 2a. SDS-PAGE followed by autoradiography detected that treatment of Daudi cells with rIFN-alpha 2a significantly reduced phosphorylation of the membrane-associated Mr 98,000 and 70,000 polypeptides. To determine the physiological significance of these phosphorylating polypeptides in mediation of the IFN effects, they were purified from Daudi cells. It was found that the molecular weight of the purified polypeptides was approximately 330,000 and it (designated 330-kDa protein) was consist of two distinct subunits [alpha-subunit (Mr 98,000) and beta-subunit (Mr 70,000)]. The biochemical properties, such as subunit structure, subunit phosphorylation, requirements for phosphorylating activity and protease sensitivity of the 330-kDa protein were similar to those reported for Na+, K(+)-ATPase. Evidence provided here suggests that the anti-proliferative action of IFNs may, at least in part, be implicated in the IFN-induced physiological impairment of the membrane-associated 330-kDa protein.