Depletion of Paraspeckle Protein 1 Enhances Methyl Methanesulfonate-Induced Apoptosis through Mitotic Catastrophe

PSPC1 Inhibition Synergizes with Poly(ADP-ribose) Polymerase Inhibitors in a Preclinical Model of BRCA-Mutated Breast/Ovarian Cancer

Poly (ADP-ribose) polymerase (PARP) inhibitors are effective against BRCA1/2-mutated cancers through synthetic lethality. Unfortunately, most cases ultimately develop acquired resistance. Therefore, enhancing PARP inhibitor sensitivity and preventing resistance in those cells are an unmet clinical need. Here, we investigated the ability of paraspeckle component 1 (PSPC1), as an additional synthetic lethal partner with BRCA1/2, to enhance olaparib sensitivity in preclinical models of BRCA1/2-mutated breast and ovarian cancers. In vitro, the combined olaparib and PSPC1 small interfering RNA (siRNA) exhibited synergistic anti-proliferative activity in BRCA1/2-mutated breast and ovarian cancer cells. The combination therapy also demonstrated synergistic tumor inhibition in a xenograft mouse model. Mechanistically, olaparib monotherapy increased the expressions of p-ATM and DNA-PKcs, suggesting the activation of a DNA repair pathway, whereas combining PSPC1 siRNA with olaparib decreased the expressions of p-ATM and DNA-PKcs again. As such, the combination increased the formation of γH2AX foci, indicating stronger DNA double-strand breaks. Subsequently, these DNA-damaged cells escaped G2/M checkpoint activation, as indicated by the suppression of p-cdc25C (Ser216) and p-cdc2 (Tyr15) after combination treatment. Finally, these cells entered mitosis, which induced increased apoptosis. Thus, this proves that PSPC1 inhibition enhances olaparib sensitivity by targeting DNA damage response in our preclinical model. The combination of olaparib and PSPC1 inhibition merits further clinical investigation to enhance PARP inhibitor efficacy.

PSPC1 is a potential prognostic marker for hormone-dependent breast cancer patients and modulates RNA processing of ESR1 and SCFD2

Breast cancer is the most common cancer type among women worldwide. The majority of breast cancer expresses estrogen receptor (ER) and endocrine therapy is a standard treatment of ER-positive breast cancer. However, development of the therapy resistance is still a major challenge and thus new therapeutic approaches are needed. Here we show that an RNA-binding protein, PSPC1, play a crucial role in ER-positive breast cancer growth through post-transcriptional gene regulation. We showed that siRNA-mediated PSPC1 silencing suppressed the proliferation of ER-positive breast cancer cells. Strong immunoreactivity (IR) of PSPC1 was correlated with poor prognosis for ER-positive breast cancer patients. Using immunoprecipitation, RNA-immunoprecipitation (RIP) and quantitative PCR (qPCR) experiments, we showed that PSPC1 interacted with PSF and was involved in post-transcriptional regulation of PSF target genes, ESR1 and SCFD2. Strong SCFD2 IR was correlated with poor prognosis for ER-positive breast cancer patients and combinations of PSPC1, PSF, and SCFD2 IRs were potent prognostic factors. Moreover, we identified DDIAS and MYBL1 as SCFD2 downstream target genes using microarray analysis, and finally showed that SCFD2 silencing suppressed tamoxifen-resistant breast tumor growth in vivo. These results indicated that PSPC1 and SCFD2 axis could be a promising target in the clinical management of the disease.

The Prognosis Value of PSPC1 Expression in Nasopharyngeal Cancer

Background

Paraspeckle component 1 (PSPC1) is overexpressed in various cancer and correlated with poor survival in the patients. However, little is known about its expression and role in the progression of nasopharyngeal carcinomas (NPC). The purpose of this study is to examine PSPC1 expression in NPC and explore its role in clinical prognosis of radiation therapy.

Methods

The association of PSPC1 expression with clinicopathological features of 109 NPC patients was examined using partial correlation analysis. Cancer tissues were obtained prior to clinical treatment. All cases were diagnosed and pathologically confirmed to be poorly differentiated or undifferentiated NPC without distant metastasis. The patients were then treated with radiation and followed-up. Survival analysis was performed.

Results

Partial correlation analysis revealed that the PSPC1 expression in NPC was correlated with N classification, recurrence, prognosis and radiosensitivity in NPC patients, but not with the gender, age, pathohistological pattern, clinical stage, and T classification. The overexpression of PSPC1 was detected in 64 samples (58.72%). Kaplan–Meier survival analysis revealed that the overall survival (OS) was longer in NPC patients with PSPC1 low expression than that in those with PSPC1 high expression. Moreover, patients with the overexpression of PSPC1 had a low progression-free survival and distant metastasis-free survival rate, compared to those who had a low expression of PSPC1. Although not statistically significant, patients with high expression of PSPC1 had a lower locoregional recurrence-free survival rate than those with low expression, and the curves between the two groups was well separated.

Conclusion

PSPC1 overexpression was associated with poor prognosis for NPC, which might be a novel useful biomarker to predict the response of NPC to radiation therapy and its clinical outcome.

Influence of Kv11.1 (hERG1) K+ channel expression on DNA damage induced by the genotoxic agent methyl methanesulfonate

Besides their crucial role in cell electrogenesis and maintenance of basal membrane potential, the voltage-dependent K⁺ channel Kv11.1/hERG1 shows an essential impact in cell proliferation and other processes linked to the maintenance of tumour phenotype. To check the possible influence of channel expression on DNA damage responses, HEK293 cells, treated with the genotoxic agent methyl methanesulfonate (MMS), were compared with those of a HEK-derived cell line (H36), permanently transfected with the Kv11.1-encoding gene, and with a third cell line (T2) obtained under identical conditions as H36, by permanent transfection of another unrelated plasma membrane protein encoding gene. In addition, to gain some insights about the canonical/conduction-dependent channel mechanisms that might be involved, the specific erg channel inhibitor E4031 was used as a tool. Our results indicate that the expression of Kv11.1 does not influence MMS-induced changes in cell cycle progression, because no differences were found between H36 and T2 cells. However, the canonical ion conduction function of the channel appeared to be associated with decreased cell viability at low/medium MMS concentrations. Moreover, direct DNA damage measurements, using the comet assay, demonstrated for the first time that Kv11.1 conduction activity was able to modify MMS-induced DNA damage, decreasing it particularly at high MMS concentration, in a way related to PARP1 gene expression. Finally, our data suggest that the canonical Kv11.1 effects may be relevant for tumour cell responses to anti-tumour therapies.

PSPC1 Potentiates IGF1R Expression to Augment Cell Adhesion and Motility

Paraspeckle protein 1 (PSPC1) overexpression in cancers is known to be the pro-metastatic switch of tumor progression associated with poor prognosis of cancer patients. However, the detail molecular mechanisms to facilitate cancer cell migration remain elusive. Here, we conducted integrated analysis of human phospho-kinase antibody array, transcriptome analysis with RNA-seq, and proteomic analysis of protein pulldown to study the molecular detail of PSPC1-potentiated phenotypical transformation, adhesion, and motility in human hepatocellular carcinoma (HCC) cells. We found that PSPC1 overexpression re-assembles and augments stress fiber formations to promote recruitment of focal adhesion contacts at the protruding edge to facilitate cell migration. PSPC1 activated focal adhesion-associated kinases especially FAK/Src signaling to enhance cell adhesion and motility toward extracellular matrix (ECM). Integrated transcriptome and gene set enrichment analysis indicated that PSPC1 modulated receptor tyrosine kinase IGF1R involved in the focal adhesion pathway and induction of diverse integrins expression. Knockdown IGF1R expression and treatment of IGF1R inhibitor suppressed PSPC1-induced cell motility. Interestingly, knockdown PSPC1-interacted paraspeckle components including NONO, FUS, and the lncRNA Neat1 abolished PSPC1-activated IGF1R expression. Together, PSPC1 overexpression induced focal adhesion formation and facilitated cell motility via activation of IGF1R signaling. PSPC1 overexpression in tumors could be a potential biomarker of target therapy with IGF1R inhibitor for improvement of HCC therapy.