Zhaojian Liu

Splicing Factor PQBP1 Curtails BAX Expression to Promote Ovarian Cancer Progression

Abstract Splicing factor polyglutamine binding protein‐1 (PQBP1) is abundantly expressed in the central nervous system during development, and mutations in the gene cause intellectual disability. However, the roles of PQBP1 in cancer progression remain largely unknown. Here, it is shown that PQBP1 overexpression promotes tumor progression and indicates worse prognosis in ovarian cancer. Integrative analysis of spyCLIP‐seq and RNA‐seq data reveals that PQBP1 preferentially binds to exon regions and modulates exon skipping. Mechanistically, it is shown that PQBP1 regulates the splicing of genes related to the apoptotic signaling pathway, including BAX. PQBP1 promotes BAX exon 2 skipping to generate a truncated isoform that undergoes degradation by nonsense‐mediated mRNA decay, thus making cancer cells resistant to apoptosis. In contrast, PQBP1 depletion or splice‐switching antisense oligonucleotides promote exon 2 inclusion and thus increase BAX expression, leading to inhibition of tumor growth. Together, the results demonstrate an oncogenic role of PQBP1 in ovarian cancer and suggest that targeting the aberrant splicing mediated by PQBP1 has therapeutic potential in cancer treatment.

Rad50 promotes ovarian cancer progression through NF‐κB activation

AbstractRad50 is a component of MRN (Mre11‐Rad50‐Nbs1), which participates in DNA double‐strand break repair and DNA‐damage checkpoint activation. Here, we sought to investigate the clinical and functional significance of Rad50 in high‐grade serous ovarian cancer (HGSOC). We found that Rad50 was frequently upregulated in HGSOCs and enhanced Rad50 expression inversely correlated with patient survival. In addition, ectopic expression of Rad50 promoted proliferation/invasion and induced EMT of ovarian cancer cells, whereas knockdown of Rad50 led to decreased aggressive behaviors. Mechanistic investigations revealed that Rad50 induced aggressiveness in HGSOC via activation of NF‐κB signaling pathway. Moreover, we identified CARD9 as an interacting protein of Rad50 in ovarian cancer cells and the activation of NF‐κB pathway by Rad50 is CARD9 dependent. Our findings provide evidence that Rad50 exhibits oncogenic property via NF‐κB activation in HGSOC.

Splice-switching of the oncogenic BCS1L isoform suppresses ovarian cancer progression by disrupting mitochondrial function

Abstract Increasing evidences demonstrate that mitochondrial function is essential for cancer cell survival and metastasis. However, the role of mitochondrial metabolic reprogramming in ovarian cancer progression remains largely unknown. Here, we report that mitochondrial chaperone BCS1L generates two major alternative-spliced isoforms, a full-length isoform ( BCS1L-L ) and a short isoform lacking exon 2 ( BCS1L-S ). Interestingly, BCS1L-L is elevated in several human cancers, and it significantly increased oxidative phosphorylation and ATP production in the present work, which is required for the survival of cancer cells. In contrast, BCS1L-S was unable to localize to the mitochondria as BCS1L-L did, and this led to impaired metabolic function. Mechanistically, splicing factor USP39 promoted exon 2 inclusion, thus facilitating the generation of oncogenic BCS1L-L and, thereby, maintaining mitochondrial homeostasis and survival of ovarian cancer cells. Importantly, we developed splice-switch antisense oligonucleotides (ASOs) that successfully induced exon 2 skipping and decreased BCS1L-L abundance, resulting in impaired tumor growth. These findings suggest that targeting oncogenic BCS1L-L by ASOs is a novel approach for ovarian cancer treatment.