LAUSR

The role of major intron splicing in PCa is well established and highly investigated. However, the equally important and impactful minor spliceosome (MiS) and minor intron splicing have remained underexplored in PCa. Here for the first time, we show that minor intron containing genes (MIGs) are enriched as direct interactors of PCa-causing genes and that their expression levels correspond to different stages of PCa progression. Accordingly, we show that U6atac expression and MiS activity reinforces cell growth and correlates with PCa progression. Consequently, highly proliferative PCa cells are strongly susceptible to siU6atac-mediated MiS inhibition. In this sense, siU6atac is significantly more efficient in lowering the tumor burden of castration resistant prostate cancer (CRPC) cells and organoids than the current state-of-the-art combination therapy. Mechanistically, we show that inhibition of the MiS through siU6atac causes minor and major intron mis-splicing and aberrant expression of MIG and non-MIG transcripts and encoded proteins, which enriches for MAPK activity, DNA repair, and cell cycle. Single cell-RNAseq confirms cell cycle defects and lineage dependency on the MiS from primary to CRPC and neuroendocrine PCa. Finally, our data provides strong evidence that Androgen receptor signaling functions as a regulator of MiS activity throughout PCa disease progression to CRPC while p38MAPK influences MiS activity in neuroendocrine PCa. Furthermore, we discovered that MiS inhibition in neuroendocrine PCa shifts alternative splicing in favor of canonical REST1 isoform thereby blocking lineage plasticity and progression to lethal therapy resistant PCa. This finding positions the MiS as yet another disruptor of a crucial molecular pathway underpinning the emergence of CRPC and neuroendocrine PCa. Based on these findings we posit that the MiS may be a common denominator of prominent PCa driver genes and a driving factor of advanced lethal PCa. We hypothesize that the MiS represents a point of vulnerability in therapy-resistant PCa. Citation Format: Anke Augspach, Mark Andrew Rubin, Rahul Kanadia. Minor intron splicing is critical for survival of lethal prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr A013.