Human IFN Alpha Alters Phosphorylation of Ribosomal Proteins

Incubation of HeLa cells with human alpha interferon (HuIFN-α) resulted in increased phosphorylation of total ribosomal proteins (ribosome-associated and ribosome structural proteins) above that found for cells incubated in medium alone. Maximum phosphorylation of these proteins occurred with 4000 units/ml of HuIFN-α, 1–2 h of incubation of cells with HuIFN-α and a ³²P pulse period of 1 h. Fractionation of total ribosomal proteins into ribosome-associated and 80S ribosomal structural proteins showed that the interferon-induced increase in phosphorylation was associated only with a 36K ribosome-associated polypeptide and phosphorylation of 80S ribosomal structural proteins was inhibited in interferon-treated cells. The level of inhibition of phosphorylation of ribosomal structural proteins in large and small subunits in interferon-treated cells was 14–19% and 76–81%, respectively. The inhibition of phosphorylation of ribosomal structural proteins persisted for 24 h following an initial 2 h of incubation of cells with interferon. Interferon treatment inhibited phosphorylation of several proteins associated with purified 80S ribosomes. Interferon treatment considerably reduced yields of coxsackievirus B3 in HeLa cells, but had little to no effect on rates of protein synthesis during 10 h of incubation of cells with interferon. The results show that interferon induces rapid (within 1 h) phosphorylation-dephosphorylation reactions involving ribosome-associated and ribosomal structural proteins of HeLa cells.