Unconventional Role of the Inwardly Rectifying Potassium Channel Kir2.2 As a Constitutive Activator of RelA in Cancer

The constitutive activation of NF-κB is a major event leading to the initiation, development, and progression of cancer. Recently, we showed that the size of preestablished tumors was reduced after the depletion of Kir2.2, an inwardly rectifying potassium channel. To determine the precise mechanism of action of Kir2.2 in the control of tumor growth, we searched for interacting proteins. Notably, NF-κB p65/RelA was identified as a binding partner of Kir2.2 in a yeast two-hybrid analysis. Further analyses revealed that Kir2.2 directly interacted with RelA in vitro and coimmunoprecipitated with RelA from cell lysates. Kir2.2 increased RelA phosphorylation at S536 and facilitated its translocation from the cytoplasm to the nucleus, thereby activating the transcription factor and increasing the expression level of NF-κB targets, including cyclin D1, matrix metalloproteinase (MMP)9, and VEGF. Kir2.2 was overexpressed in human cancer and the expression level was correlated with increased colony formation and tumor growth in mouse tumor models. On the basis of these findings, we propose an unconventional role for Kir2.2 as a constitutive RelA-activating protein, which is likely to contribute to tumor progression in vivo.