Targeting mitophagy through PINK1 splicing sensitizes myeloid malignancies to venetoclax

Abstract Venetoclax, a BH3 mimetic that impairs mitochondrial function by inhibiting BCL2, has shown remarkable efficacy in the treatment of acute myeloid leukemia (AML). However, intrinsic and acquired resistance inevitably limit the clinical response. Venetoclax resistance is associated with augmented mitophagy, which acts as a pro-survival mechanism to eliminate damaged mitochondria. We have identified a new mechanism of mitochondrial surveillance that supports mitophagy through enhanced splicing of PTEN induced kinase-1 (PINK1), which plays an essential role in mitophagy initiation. We find that mitochondrial dysfunction modifies splicing of PINK1 to remove a poison intron, increasing the stability and abundance of PINK1 mRNA and protein. Thus, venetoclax also increases PINK1 splicing and stability. Inhibiting the PINK1 splicing regulator glycogen synthase kinase-3 (GSK3) enhances venetoclax sensitivity in myeloid malignancies by reducing PINK1 expression through splicing perturbation and inhibiting mitophagy activation. GSK-3 regulates PINK1 splicing by interacting with the U2 small nuclear ribonucleoprotein (U2 snRNP) splicing complex. Genetic or pharmaceutical inhibition of U2 snRNP proteins SF3B1 or PRPF8 recapitulates the disruption of PINK1 splicing and enhances sensitivity to venetoclax. Splice-switching oligonucleotides (SSOs) that promote retention of the poison intron in PINK1 dramatically reduce abundance of PINK1 mRNA and enhance sensitivity of myeloid malignancies to venetoclax. In summary, we have identified a new mechanism of mitochondria quality control mediated by enhanced PINK1 splicing. Targeting the splicing machinery to inhibit PINK1-dependent mitophagy represents a viable approach to enhance venetoclax sensitivity.