American Association for Cancer Research
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FIGURE 4 from Targeting MALAT1 Augments Sensitivity to PARP Inhibition by Impairing Homologous Recombination in Prostate Cancer

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posted on 2023-10-09, 14:20 authored by Anjali Yadav, Tanay Biswas, Ayush Praveen, Promit Ganguly, Ankita Bhattacharyya, Ayushi Verma, Dipak Datta, Bushra Ateeq

MALAT1 knockdown restrains cell-cycle progression and instigates apoptosis in prostate cancer cells. A, Flow cytometry analysis for accessing the cell-cycle distribution by propidium iodide (PI) DNA staining assay in MALAT1-silenced prostate cancer cells. The percentage of cells in each phase was calculated using FlowJo software. B, Representative images depicting EdU incorporation in the same cells as in A. Nuclei were stained with Hoechst 33342. Scale bar, 20 µm. Right, bar graph showing quantification of EdU uptake in the indicated cells. C, qRT-PCR analysis showing expression of genes associated with G1 and S-phase of the cell cycle in MALAT1-silenced 22RV1 cells. The expression level for each gene was normalized to GAPDH. D, Immunoblot showing the change in expression of E2F1 in the same cells as in A. β-Actin was used as an internal control. E, Line graph showing cell proliferation assay using the same cells as in A, at the indicated time points. F, Flow cytometry–based apoptosis assay using Annexin V-PE and 7-AAD staining in the same cells as in A. The percentage of apoptotic cells was calculated using FlowJo software. G, Immunoblots showing a change in the expression of apoptosis markers in the same cells as in A. β-Actin was used as an internal control. H, Schematic depicting that MALAT1 is a novel regulator of HR and plays an important role in the maintenance of genome stability in prostate cancer. MALAT1 depletion induces HR deficiency by decreasing the expression of several DDR genes and results in DSB accumulation which in turn induces cell-cycle arrest and instigates apoptosis. Experiments were performed with n = 3 biologically independent samples; the data represents mean ± SEM. For B and C, one-way ANOVA with Dunnett multiple comparisons posthoc test was applied, while for E, two-way ANOVA with Tukey multiple comparisons test was applied.


The Wellcome Trust DBT India Alliance (India Alliance)

DST | Science and Engineering Research Board (SERB)

Department of Biotechnology, Ministry of Science and Technology, India (DBT)



PARP inhibitors (PARPi) have emerged as a promising targeted therapeutic intervention for metastatic castrate-resistant prostate cancer (mCRPC). However, the clinical utility of PARPi is limited to a subset of patients who harbor aberrations in the genes associated with the homologous recombination (HR) pathway. Here, we report that targeting metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), an oncogenic long noncoding RNA (lncRNA), contrives a BRCAness-like phenotype, and augments sensitivity to PARPi. Mechanistically, we show that MALAT1 silencing reprograms the homologous recombination (HR) transcriptome and makes prostate cancer cells more vulnerable to PARPi. Particularly, coinhibition of MALAT1 and PARP1 exhibits a decline in clonogenic survival, delays resolution of γH2AX foci, and reduces tumor burden in mice xenograft model. Moreover, we show that miR-421, a tumor suppressor miRNA, negatively regulates the expression of HR genes, while in aggressive prostate cancer cases, miR-421 is sequestered by MALAT1, leading to increased expression of HR genes. Conclusively, our findings suggest that MALAT1 ablation confers sensitivity to PARPi, thus highlighting an alternative therapeutic strategy for patients with castration-resistant prostate cancer (CRPC), irrespective of the alterations in HR genes. PARPi are clinically approved for patients with metastatic CRPC carrying mutations in HR genes, but are ineffective for HR-proficient prostate cancer. Herein, we show that oncogenic lncRNA, MALAT1 is frequently overexpressed in advanced stage prostate cancer and plays a crucial role in maintaining genomic integrity. Importantly, we propose a novel therapeutic strategy that emphasizes MALAT1 inhibition, leading to HR dysfunction in both HR-deficient and -proficient prostate cancer, consequently augmenting their susceptibility to PARPi.