Targeting of MARK2, but not other MARKs, suppresses TNBC progression by inhibition of the mutant p53-driven signaling pathway

Triple-negative breast cancer (TNBC) is the most challenging subtype of breast cancer to treat due to the lack of effective targeted therapies. Here we show that increased expression of microtubule affinity-regulating kinase 2 (MARK2), but not other MARKs (MARK1, MARK3, and MARK4), is associated with poor prognosis in TNBC patients. Silencing MARK2 expression leads to impaired TNBC progression via inhibition of mutant p53 (mutp53) signaling. In contrast, silencing any of the other three MARKs enhances or fails to affect TNBC cell growth or migration without impacting mutp53 expression. Importantly, direct silencing of mutp53 expression phenocopies the effect of MARK2 abrogation in TNBC cells, further supporting a functional link. Moreover, ectopic expression of MARK2 or its kinase-dead mutant enhances mutp53 signaling, thereby promoting TNBC progression; however, MARK2 overexpression fails to affect wild-type p53 (wtp53) expression or cell growth in luminal breast cancer cells. Significant inverse associations are further identified between MARK2, THBS1, or HBEGF (two direct target genes of mutp53) levels and overall survival as well as disease-free survival in TNBC patients harboring mutTP53, whereas the relationship between MARK2 and survival is absent in all subtypes expressing wtTP53. MARK2 is predominantly expressed in the nucleus of TNBC cells, where it interacts with and stabilizes mutp53 through the UBA and Spacer domains. Consistent with this, MARK2-ΔUBA or MARK2-ΔSpacer mutant proteins fail to bind mutp53 and suppress its signaling, thereby impairing TNBC progression as dominant-negative inhibitors of MARK2. Our results suggest that inhibition of MARK2 expression—rather than its kinase activity—may serve as an effective therapeutic strategy for TNBC with mutTP53.