Phosphorylation of plectin by Akt3 promotes triple-negative breast cancer cell invasive migration.

Triple-negative breast cancer (TNBC) lacks targeted therapeutics and is aggressive with a poor prognosis. The phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway, frequently deregulated in cancers, plays crucial roles in tumorigenesis and cancer progression. However, the distinct functions of the three Akt isoforms (Akt1, Akt2, Akt3) in these processes are not well understood. Here, we focus on Akt3, the least-studied Akt isoform, which is overexpressed in 28% of TNBC cases and significantly promotes TNBC growth, stemness, and epithelial-mesenchymal transition. Through a genome-wide proteomic screen, we identified plectin, a member of the plakin family, as an Akt3 substrate in TNBC cells. The depletion of plectin potently inhibits TNBC cell migration and invadopodia formation, albeit with mild effects on cell growth. The phosphorylation of plectin at Ser4268 by Akt promotes its colocalization with vimentin and TNBC cell migration. Our findings underscore the importance of Akt3-plectin signaling as a potential TNBC therapeutic target.