Systematic microRNA screening identifies miR-19b as regulator of temozolomide response through targeting PP2A serine-threonine phosphatase in glioblastoma

Despite standard of care, glioblastoma IDH wt (GBM) inevitably recur accentuating the need to elucidate mechanisms of therapy resistance. The DNA alkylating agent temozolomide (TMZ) triggers futile DNA mismatch repair cycles and persistent DNA double strand breaks, but tumors counteract this genotoxic stress by inducing DNA damage repair and survival pathways. GBM cells overexpressing miR-19b-3p were reproducibly selected by TMZ treatment in systematic lentiviral microRNA screens, a finding that was investigated mechanistically. Attenuation of miR-19b in glioblastoma cell lines and primary glioblastoma stem cells (GSCs) induced DNA damage as indicated by enhanced CHK1 and CHK2 phosphorylation, gH2AX foci formation, and senescence. These phenotypes were further enhanced by TMZ treatment. Enhanced expression of miR-19b in GBM tissues was associated with downregulation of regulatory subunit PPP2R5E of Ser/Thr phosphatase PP2A in the mesenchymal subtype of GBM in agreement with miR-19b targeting PPP2R5E. Knocking down PPP2R5E antagonized the phenotypes elicited by miR-19b attenuation, and these effects were reversed in miR-19b attenuated/PPP2R5E knockdown cells suggesting a role of the miR-19b/PPP2R5E axis in TMZ-induced DNA damage response. In agreement with PP2A reactivation by miR-19b attenuation, PP2A activating drug, FTY720, or knocking down endogenous PP2A inhibiting proteins (PAIP), acted synergistically with TMZ to induce cell death. Enhanced TMZ resistance elicited by knocking down PPP2R5E was confirmed in orthotopic mouse GSC xenografts. These results provide insights in TMZ resistance mechanisms of GBM elicited by PPP2R5E targeting of miR-19b. Attenuation of miR-19b or PPP2R5E expression could potentially be exploited in adjuvant therapy of GBM. ### Competing Interest Statement The authors have declared no competing interest.