Interferon-induces expression of cyclin-dependent kinase-inhibitors p21(WAF1) and p27(Kip1) that prevent activation of cyclin-dependent kinase by CDK-activating kinase (CAK)

Abstract

To understand the mechanism of interferon (IFN)-mediated suppression of cell cycle progression, we have earlier shown that IFN-α enhances the expression of underphosphorylated retinoblastoma protein by inhibiting the cyclin-dependent kinase-2. In the studies presented here, we investigated the mechanism of inhibition of CDKs in IFN-treated cells by delineating the potential role(s) of CDK-inhibitors (CKIs) and CDK-activating kinase (CAK). We report that IFN-α inhibits the H-1 kinase activity associated with CDK-4 or CDK-2 due to induction of expression of CDK-inhibitor p21(WAF1) (but not p27(Kip1)) as its immunodepletion from IFN-treated extracts restored the CDK-associated H-1 kinase activity. In addition, we also show that IFN-α induces expression of CDK-inhibitors p21(WAF1) and p27(Kip1) and inhibited the H-1 kinase activity associated with CDK-2 or CDK-4. The observed IFN-γ-mediated inhibition of CDK-2 and CDK-4 kinase activity was due to enhanced interactions with p21(WAF1) and p27(Kip1), respectively. We also demonstrated that IFN-induced CKIs prevent CAK from activating the CDK-2 as immunodepletion of induced CKIs from the inhibitory extracts resulted in the restoration of CAK-mediated activation of CDK-2.