TBK1 and cancer: However, a substantial amount of surface-expressed NaK in certain types of cells has been suggested to function as non-canonical cardiotonic steroid-binding receptors [7] that form complexes with caveolin-1, Src kinase and epidermal growth factor receptor (EGFR) to activate multiple signaling cascades [8-11] that are markedly different between normal and cancer cells [2-4].