Yemin Wang

MicroRNAs and DNA damage response: Implications for cancer therapy

The DNA damage response (DDR) pathways play critical roles in protecting the genome from DNA damage. Abrogation of DDR often results in elevated genomic instability and cellular sensitivity to DNA damaging agents. Many proteins involved in DDR are subjected to precise regulation at multiple levels, such as transcriptional control and posttranslational modifications, in response to DNA damage. MicroRNAs (miRNAs) are a class of small non-coding RNAs that negatively regulate gene expression at the post-transcriptional level. The expression levels of some miRNAs change in response to DNA damage. Some miRNAs, such as miR-24, 138, 96 and 182, have been implicated in DDR and/or DNA repair and affect cellular sensitivity to DNA damaging agents. In this review, we summarize recent findings related to the emerging roles of miRNAs in regulating DDR and DNA repair and discuss their potential in cancer therapy.

MicroRNA-138 modulates DNA damage response by repressing histone H2AX expression

Precise regulation of DNA damage response is crucial for cellular survival after DNA damage, and its abrogation often results in genomic instability in cancer. Phosphorylated histone H2AX (γH2AX) forms nuclear foci at sites of DNA damage and facilitates DNA damage response and repair. MicroRNAs (miRNA) are short, nonprotein-encoding RNA molecules, which posttranscriptionally regulate gene expression by repressing translation of and/or degrading mRNA. How miRNAs modulate DNA damage response is largely unknown. In this study, we developed a cell-based screening assay using ionizing radiation (IR)-induced γH2AX foci formation in a human osteosarcoma cell line, U2OS, as the readout. By screening a library of human miRNA mimics, we identified several miRNAs that inhibited γH2AX foci formation. Among them, miR-138 directly targeted the histone H2AX 3′-untranslated region, reduced histone H2AX expression, and induced chromosomal instability after DNA damage. Overexpression of miR-138 inhibited homologous recombination and enhanced cellular sensitivity to multiple DNA-damaging agents (cisplatin, camptothecin, and IR). Reintroduction of histone H2AX in miR-138 overexpressing cells attenuated miR-138–mediated sensitization to cisplatin and camptothecin. Our study suggests that miR-138 is an important regulator of genomic stability and a potential therapeutic agent to improve the efficacy of radiotherapy and chemotherapy with DNA-damaging agents. Mol Cancer Res; 9(8); 1100–11. ©2011 AACR.

Systematic Screen Identifies miRNAs that Target RAD51 and RAD51D to Enhance Chemosensitivity

Homologous recombination mediates error-free repair of DNA double-strand breaks (DSB). RAD51 is an essential protein for catalyzing homologous recombination and its recruitment to DSBs is mediated by many factors including RAD51, its paralogs, and breast/ovarian cancer susceptibility gene products BRCA1/2. Deregulation of these factors leads to impaired DNA repair, genomic instability, and cellular sensitivity to chemotherapeutics such as cisplatin and PARP inhibitors. microRNAs (miRNA) are short, noncoding RNAs that posttranscriptionally regulate gene expression; however, the contribution of miRNAs in the regulation of homologous recombination is not well understood. To address this, a library of human miRNA mimics was systematically screened to pinpoint several miRNAs that significantly reduce RAD51 foci formation in response to ionizing radiation in human osteosarcoma cells. Subsequent study focused on two of the strongest candidates, miR-103 and miR-107, as they are frequently deregulated in cancer. Consistent with the inhibition of RAD51 foci formation, miR-103 and miR-107 reduced homology-directed repair and sensitized cells to various DNA-damaging agents, including cisplatin and a PARP inhibitor. Mechanistic analyses revealed that both miR-103 and miR-107 directly target and regulate RAD51 and RAD51D, which is critical for miR-103/107–mediated chemosensitization. Furthermore, endogenous regulation of RAD51D by miR-103/107 was observed in several tumor subtypes. Taken together, these data show that miR-103 and miR-107 overexpression promotes genomic instability and may be used therapeutically to chemosensitize tumors. Implications: These findings demonstrate a role for miR-103 and -107 in regulating DNA damage repair, thereby identifying new players in the progression of cancer and response to chemotherapy. Mol Cancer Res; 11(12); 1564–73. ©2013 AACR.

Abstract 1238: Targeting the platelet derived growth factor receptor (PDGFR) with the receptor tyrosine kinase inhibitor ponatinib in small cell carcinoma of the ovary, hypercalcemic type

Subunits of the SWI/SNF chromatin-remodeling complex are tumor suppressors that are inactivated in ~20% of all cancers, yet few targeted treatments have shown selective activity in SWI/SNF-mutant cancers. Small cell carcinoma of the ovary, hypercalcemic type (SCCOHT) is a rare, aggressive ovarian cancer in young women that is universally driven by SWI/SNF dysregulation. Given that two-year survival following standard high-dose chemotherapy and radiation in SCCOHT is less than 35%, a great need exists for effective targeted therapies to improve outcomes for these women. We previously demonstrated that SCCOHT tumors are driven by inactivating mutations in SMARCA4, one of two mutually exclusive SWI/SNF ATPases. In addition, we have shown that SCCOHT lacks expression of the alternative SWI/SNF ATPase, SMARCA2. We have now found through integrated genomic and functional analyses in SCCOHT tumors and cell lines that SMARCA4 loss correlates with increased expression of receptor tyrosine kinases (RTKs) including the platelet derived growth factor receptors (PDGFRs). Through integration of high-throughput RNA interference and drug screens in SCCOHT cells we have identified sensitivity to RTK knockdown and RTK inhibitors including the FDA-approved oncology drug, ponatinib. These data corroborate prior studies showing RTK dependence in rhabdoid tumors, rare cancers that are also driven by mutations in the SWI/SNF complex. Of the known ponatinib targets, PDGFR-alpha and FGFR1 were highly expressed in SCCOHT tumors, as confirmed in RNA-Seq data (four tumors) and a SCCOHT tissue microarray (TMA; ten tumors). Furthermore, PDGFR-alpha and -beta phosphorylation and downstream signaling are inhibited by ponatinib in SCCOHT cells, suggesting that these tumors are sensitive to ponatinib due to dependence on signaling through these RTKs. Finally, given ponatinib’s potency in vitro and the proposed mechanism of action, we tested this agent in xenograft models of SCCOHT. In addition to confirming efficacy in a SCCOHT cell line xenograft model, superior efficacy was demonstrated in two patient-derived xenograft (PDX) models of SCCOHT with ponatinib. Thus, ponatinib effectively targets SWI/SNF-mutant SCCOHT tumors through inhibition of PDGFR signaling and may have clinical utility for the treatment of these cancers. Citation Format: Jessica Diane Lang, William Hendricks, Pilar Ramos, Holly Yin, Chris Sereduk, Jeffrey Kiefer, Yemin Wang, Anthony N. Karnezis, Bernard Weissman, David Huntsman, Jeffrey Trent. Targeting the platelet derived growth factor receptor (PDGFR) with the receptor tyrosine kinase inhibitor ponatinib in small cell carcinoma of the ovary, hypercalcemic type [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1238. doi:10.1158/1538-7445.AM2017-1238

Abstract AP25: INHIBITION OF HDAC ACTIVITY SELECTIVELY INHIBITS ARID1A–MUTATED OVARIAN CLEAR CELL CARCINOMA THROUGH A NOVEL P53 REGULATORY MECHANISM

PURPOSE OF THE STUDY: ARID1A is mutated ~50% and 30% of clear cell (OCCC) and endometrioid (OEC) ovarian cancers, respectively. Over 90% of the ARID1A mutations observed in ovarian cancer are frame-shift or nonsense mutations that result in loss of ARID1A protein expression. In several cancers including OCCC, ARID1A and p53 mutations are often mutually exclusive. OCCC carries a worse prognosis compared to the other histosubtypes of ovarian cancer. Thus, there is an urgent clinical need for improved therapeutic strategies. EXPERIMENTAL PROCEDURE: To investigate the role of specific HDACs in the context of ARID1A expression, we examined the effect of knocking down HDACs in an isogenic OCCC cell line with and without ARID1A expression. Utilizing a panel of ARID1A-mutated and wildtype OCCC cell lines, we evaluated the effect of HDAC knockdown and inhibition through a variety of 2D and 3D assays. We also examined the consequence of HDAC inhibition on tumor growth, survival, and dissemination in an in vivo mouse model of ovarian cancer. SUMMARY OF THE DATA: We have discovered that ARID1A is involved in the repression of HDACs, and ARID1A-inactivation promotes aberrant transcriptional regulation of HDACs. Importantly, we uncovered a novel HDAC-dependent regulatory mechanism of p53. Several HDAC inhibitors are currently in clinical trials. We found HDAC inhibitors were more selective in ARID1A-mutated OCCC cell lines compared to ARID1A-wildtype cells. We observed that HDAC inhibition led to a significant increase in apoptosis in ARID1A-mutated cells. In an orthotopic intra-bursal xenograft model using ARID1A wildtype and deficient cells, the HDAC inhibitor suppressed primary tumor growth and inhibited tumor cell dissemination only in the ARID1A-mutated tumors. Significantly, HDAC inhibition significantly improved the survival of mice bearing ARID1A-mutated tumors. CONCLUSIONS: These findings imply that HDAC inhibition represents a novel therapeutic strategy for ARID1A-deficient cancers. This study further elucidates the observed mutual exclusivity of ARID1A and p53. Importantly, we have uncovered a novel regulatory mechanism of p53 mediated through ARID1A and HDACs. Clinically, this study describes a precision medicine approach to the treatment of ARID1A-mutated OCCC. Citation Format: Benjamin G. Bitler, Pyoung Hwa Park, Yang Hai, Katherine M. Aird, Yemin Wang, David G. Huntsman, Kathleen R. Cho, David W. Christianson, Rugang Zhang. INHIBITION OF HDAC ACTIVITY SELECTIVELY INHIBITS ARID1A–MUTATED OVARIAN CLEAR CELL CARCINOMA THROUGH A NOVEL P53 REGULATORY MECHANISM [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr AP25.

Abstract 1947: Identification of microRNAs that regulate DNA damage response

Mammalian cells have developed an elaborate DNA damage response system and DNA repair machinery, which play a critical role in the prevention of cancer and development of resistance to anti-cancer DNA damaging agents. Many proteins involved in DNA damage response, such as phosphorylated histone H2AX (γH2AX) and 53BP1, form nuclear foci at sites of DNA damage and facilitate DNA damage response and repair. The precise regulation of DNA damage response is crucial for cellular survival after DNA damage and its abrogation often results in genomic instability. MicroRNAs (miRNAs) are short, non-coding RNA molecules, which post-transcriptionally regulate gene expression by repressing translation and/or degrading mRNA. Some miRNAs function as oncogenes or tumor suppressors. However, the role of miRNAs in DNA damage response remains largely unknown. Here, we identified miRNAs that regulate DNA damage response, especially γH2AX/53BP1 foci formation, and modulate chemo-/radio-sensitivity of tumor cells. We developed a cell-based screening assay utilizing ionizing radiation (IR)-induced γH2AX/53BP1 foci formation in a human osteosarcoma cell line, U2OS, as a readout. The human miRNA Mimics and Inhibitors Libraries (Dharmacon), consisting of 810 miRNA mimics or inhibitors, were transfected in U2OS cells and screened with an automated high-throughput fluorescence microscope and an automatic foci counter. We found that two and five miRNA mimics reproducibly inhibited IR-induced γH2AX and 53BP1 foci formation, respectively, while none of the miRNA inhibitors inhibited their foci formation. Among these hits, we focused on miR-138, because miR-138 is reported to be deregulated in a subset of cancer and may be involved in tumorigenesis and chemosensitivity of cancer. We found that miR-138 decreased the expression of H2AX and reduced H2AX phosphorylation upon DNA damage. Consistent with a defect in DNA damage response, miR-138 sensitized U2OS cells to DNA damaging agents, such as IR and cisplatin. Importantly, the 3′UTR of H2AX contains a putative miR-138 binding site, suggesting that H2AX may be a direct target of miR-138. Taken together, we have identified some miRNAs which inhibit IR-induced foci formation of γH2AX/53BP1. In particular, miR-138 strongly reduced H2AX-mediated DNA damage response and enhanced the chemo-/radio-sensitivity of cancer cells, suggesting that miR-138 might serve as an important regulator of genome instability and a possible therapeutic target for cancer treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1947.