Updated project metadata. CK2 is an hetero-tetrameric protein made of two CK2α catalytic subunits and two regulatory CK2β subunits. The free CK2α subunit and the tetrameric holoenzyme have distinct substrate specificity profiles suggesting that the spatiotemporal organization of the individual CK2 subunits observed in living cells is crucial in the control of the many cellular processes that are governed by this pleiotropic kinase. Indeed, sub-stoichiometric expression of CK2β compared to CK2α in a subset of breast cancer tumors was correlated with the induction of EMT markers and increased epithelial cell plasticity in breast carcinoma progression. Using phosphotyrosine profiling with affinity capture and LC/MS-MS, we show that decreased expression of CK2β in MCF10A mammary epithelial cells triggers the phosphorylation of a number of tyrosine phosphorylated proteins and promotes the striking activation of the FAK1-Src-PAX1 signaling pathway. Moreover, morphometric analyses also revealed that CK2β loss increases the number and the spatial distribution of focal adhesion signaling complexes. Together, our finding allows positioning CK2β as a gatekeeper for cell spreading by restraining the focal adhesion maturation and invasion of mammary epithelial cells.