Tulip Nandu

RACK1 MARylation regulates translation and stress granules in ovarian cancer cells

Mono(ADP-ribosyl)ation (MARylation) is emerging as a critical regulator of ribosome function and translation. Herein, we demonstrate that RACK1, an integral component of the ribosome, is MARylated by the mono(ADP-ribosyl) transferase (MART) PARP14 in ovarian cancer cells. MARylation of RACK1 is required for stress granule formation and promotes the colocalization of RACK1 in stress granules with G3BP1, eIF3η, and 40S ribosomal proteins. In parallel, we observed reduced translation of a subset of mRNAs, including those encoding key cancer regulators (e.g., AKT). Treatment with a PARP14 inhibitor or mutation of the sites of MARylation on RACK1 blocks these outcomes, as well as the growth of ovarian cancer cells in culture and in vivo. To reset the system after prolonged stress and recovery, the ADP-ribosyl hydrolase TARG1 deMARylates RACK1, leading to the dissociation of the stress granules and the restoration of translation. Collectively, our results demonstrate a therapeutically targetable pathway that controls polysome assembly, translation, and stress granule dynamics in ovarian cancer cells.

ADP-Ribosylation Levels and Patterns Correlate with Gene Expression and Clinical Outcomes in Ovarian Cancers

Abstract Inhibitors of nuclear PARP enzymes (e.g., PARP-1) have improved clinical outcomes in ovarian cancer, especially in patients with BRCA1/2 gene mutations or additional homologous recombination (HR) DNA repair pathway deficiencies. These defects serve as biomarkers for response to PARP inhibitors (PARPi). We sought to identify an additional biomarker that could predict responses to both conventional chemotherapy and PARPi in ovarian cancers. We focused on cellular ADP-ribosylation (ADPRylation), which is catalyzed by PARP enzymes and detected by detection reagents we developed previously. We determined molecular phenotypes of 34 high-grade serous ovarian cancers and associated them with clinical outcomes. We used the levels and patterns of ADPRylation and PARP-1 to distribute ovarian cancers into distinct molecular phenotypes, which exhibit dramatically different gene expression profiles. In addition, the levels and patterns of ADPRylation, PARP-1 protein, and gene expression correlated with clinical outcomes in response to platinum-based chemotherapy, with cancers exhibiting the highest levels of ADPRylation having the best outcomes independent of BRCA1/2 status. Finally, in cell culture-based assays using patient-derived ovarian cancer cell lines, ADPRylation levels correlated with sensitivity to the PARPi, Olaparib, with cell lines exhibiting high levels of ADPRylation having greater sensitivity to Olaparib. Collectively, our study demonstrates that ovarian cancers exhibit a wide range of ADPRylation levels, which correlate with therapeutic responses and clinical outcomes. These results suggest ADPRylation may be a useful biomarker for PARPi sensitivity in ovarian cancers, independent of BRCA1/2 or homologous recombination deficiency status.

Combinatorial Treatment with PARP-1 Inhibitors and Cisplatin Attenuates Cervical Cancer Growth through Fos-Driven Changes in Gene Expression

Abstract Cervical cancer continues to be a significant cause of cancer-related deaths in women. The most common treatment for cervical cancer involves the use of the drug cisplatin in conjunction with other therapeutics. However, the development of cisplatin resistance in patients can hinder the efficacy of these treatments, so alternatives are needed. In this study, we found that PARP inhibitors (PARPi) could attenuate the growth of cells representing cervical adenocarcinoma and cervical squamous cell carcinoma. Moreover, a combination of PARPi with cisplatin increased cisplatin-mediated cytotoxicity in cervical cancer cells. This was accompanied by a dramatic alteration of the transcriptome. The FOS gene, which encodes the transcription factor Fos, was one of the most highly upregulated genes in the dual treatment condition, leading to increased Fos protein levels, greater Fos binding to chromatin, and the subsequent induction of Fos target genes. Increased expression of Fos was sufficient to hinder cervical cancer growth, as shown by ectopic expression of Fos in cervical cancer cells. Conversely, Fos knockdown enhanced cell growth. Collectively, these results indicate that by inducing FOS expression, PARPi treatment in combination with cisplatin leads to inhibition of cervical cancer proliferation, likely through a Fos-specific gene expression program. Implications: Our observations, which link the gene regulatory effects of PARPi + cisplatin to the growth inhibitory effects of FOS expression in cervical cancer cells, strengthen the rationale for using PARPi with cisplatin as a therapy for cervical cancer.