MND1 and PSMC3IP control PARP inhibitor sensitivity in mitotic cells.

The PSMC3IP-MND1 heterodimer promotes meiotic D loop formation before DNA strand exchange. In genome-scale CRISPR-Cas9 mutagenesis and interference screens in mitotic cells, depletion of PSMC3IP or MND1 causes sensitivity to poly (ADP-Ribose) polymerase inhibitors (PARPi) used in cancer treatment. PSMC3IP or MND1 depletion also causes ionizing radiation sensitivity. These effects are independent of PSMC3IP/MND1's role in mitotic alternative lengthening of telomeres. PSMC3IP- or MND1-depleted cells accumulate toxic RAD51 foci in response to DNA damage, show impaired homology-directed DNA repair, and become PARPi sensitive, even in cells lacking both BRCA1 and TP53BP1. Epistasis between PSMC3IP-MND1 and BRCA1/BRCA2 defects suggest that abrogated D loop formation is the cause of PARPi sensitivity. Wild-type PSMC3IP reverses PARPi sensitivity, whereas a PSMC3IP p.Glu201del mutant associated with D loop defects and ovarian dysgenesis does not. These observations suggest that meiotic proteins such as MND1 and PSMC3IP have a greater role in mitotic DNA repair.

Endoscopic Anatomy and a Safe Surgical Corridor to the Anterior Skull Base.

OBJECTIVE: We describe the possibility to create precise preoperative planning for endonasal endoscopic approaches to the anterior skull base by overlapping endoscopic and radiologic anatomy. The important anatomic structures were marked. Morphometric measurements between these anatomic landmarks were performed endoscopically and compared with radiologic measurements of the same areas to ensure result compatibility. METHODS: Seven cadaver heads injected intravascularly with colored silicone were used for this study. Thin-section brain and paranasal sinus computed tomography scans were obtained on all cadavers. Using 0-degree rigid endoscopes and endonasal endoscopic surgical instruments, the anterior skull base was examined binostrally in all cadavers. Bilateral middle turbinates were identified and preserved. Next, an inferior uncinectomy and middle meatal antrostomy were performed. After performing a frontal antrostomy, bilateral anterior and posterior ethmoidal cells were opened and the skull base was identified and followed to the posterior wall of the frontal sinus. A transnasal transethmoidal sphenoidotomy was done with full exposure to the entire anterior skull base. RESULTS: The anatomic landmarks for endonasal endoscopic skull base approaches were distinguished and measurements were made. The anterior skull base was divided into 3 compartments: anterior (area between the posterior inferior border of the frontal sinus and the course of anterior ethmoidal artery), middle (area between the course of the anterior ethmoidal artery and that of the posterior ethmoidal artery [PEA]), and posterior (area between the course of the PEA and the attachment point of the anterior border of the sphenoid sinus to the skull base) compartments. The distances between important anatomic markers and endoscopic depth measurements of this area were measured. CONCLUSION: During endonasal endoscopic anterior skull base surgery, the area between the anterior border of the sphenoid sinus and PEA artery was safe as the first dissection zone. Preoperative radiologic width and depth measurements facilitate orientation to the endoscopic anatomy during surgery and help predict the endonasal surgical corridor anatomy preoperatively.

Functional Radiogenetic Profiling Implicates ERCC6L2 in Non-homologous End Joining.

Using genome-wide radiogenetic profiling, we functionally dissect vulnerabilities of cancer cells to ionizing radiation (IR). We identify ERCC6L2 as a major determinant of IR response, together with classical DNA damage response genes and members of the recently identified shieldin and CTC1-STN1-TEN1 (CST) complexes. We show that ERCC6L2 contributes to non-homologous end joining (NHEJ), and it may exert this function through interactions with SFPQ. In addition to causing radiosensitivity, ERCC6L2 loss restores DNA end resection and partially rescues homologous recombination (HR) in BRCA1-deficient cells. As a consequence, ERCC6L2 deficiency confers resistance to poly (ADP-ribose) polymerase (PARP) inhibition in tumors deficient for both BRCA1 and p53. Moreover, we show that ERCC6L2 mutations are found in human tumors and correlate with a better overall survival in patients treated with radiotherapy (RT); this finding suggests that ERCC6L2 is a predictive biomarker of RT response.

Haploid genetic screens identify genetic vulnerabilities to microtubule-targeting agents.

The absence of biomarkers to accurately predict anticancer therapy response remains a major obstacle in clinical oncology. We applied a genome-wide loss-of-function screening approach in human haploid cells to characterize genetic vulnerabilities to classical microtubule-targeting agents. Using docetaxel and vinorelbine, two well-established chemotherapeutic agents, we sought to identify genetic alterations sensitizing human HAP1 cells to these drugs. Despite the fact that both drugs act on microtubules, a set of distinct genes were identified whose disruption affects drug sensitivity. For docetaxel, this included a number of genes with a function in mitosis, while for vinorelbine we identified inactivation of FBXW7, RB1, and NF2, three frequently mutated tumor suppressor genes, as sensitizing factors. We validated these genes using independent knockout clones and confirmed FBXW7 as an important regulator of the mitotic spindle assembly. Upon FBXW7 depletion, vinorelbine treatment led to decreased survival of cells due to defective mitotic progression and subsequent mitotic catastrophe. We show that haploid insertional mutagenesis screens are a useful tool to study genetic vulnerabilities to classical chemotherapeutic drugs by identifying thus far unknown sensitivity factors. These results provide a rationale for investigating patient response to vinca alkaloid-based anticancer treatment in relation to the mutational status of these three tumor suppressor genes, and could in the future lead to the establishment of novel predictive biomarkers or suggest new drug combinations based on molecular mechanisms of drug sensitivity.

miR-564 acts as a dual inhibitor of PI3K and MAPK signaling networks and inhibits proliferation and invasion in breast cancer.

Dysregulation of PI3K and MAPK pathways promotes uncontrolled cell proliferation, apoptotic inhibition and metastasis. Individual targeting of these pathways using kinase inhibitors has largely been insufficient due to the existence of cross-talks between these parallel cascades. MicroRNAs are small non-coding RNAs targeting several genes simultaneously and controlling cancer-related processes. To identify miRNAs repressing both PI3K and MAPK pathways in breast cancer, we re-analyzed our previous miRNA mimic screen data with reverse phase protein array (RPPA) output, and identified miR-564 inhibiting both PI3K and MAPK pathways causing markedly decreased cell proliferation through G1 arrest. Moreover, ectopic expression of miR-564 blocks epithelial-mesenchymal transition (EMT) and reduces migration and invasion of aggressive breast cancer cells. Mechanistically, miR-564 directly targets a network of genes comprising AKT2, GNA12, GYS1 and SRF, thereby facilitating simultaneous repression of PI3K and MAPK pathways. Notably, combinatorial knockdown of these target genes using a cocktail of siRNAs mimics the phenotypes exerted upon miR-564 expression. Importantly, high miR-564 expression or low expression of target genes in combination is significantly correlated with better distant relapse-free survival of patients. Overall, miR-564 is a potential dual inhibitor of PI3K and MAPK pathways, and may be an attractive target and prognostic marker for breast cancer.

The miR-644a/CTBP1/p53 axis suppresses drug resistance by simultaneous inhibition of cell survival and epithelial-mesenchymal transition in breast cancer.

Tumor cells develop drug resistance which leads to recurrence and distant metastasis. MicroRNAs are key regulators of tumor pathogenesis; however, little is known whether they can sensitize cells and block metastasis simultaneously. Here, we report miR-644a as a novel inhibitor of both cell survival and EMT whereby acting as pleiotropic therapy-sensitizer in breast cancer. We showed that both miR-644a expression and its gene signature are associated with tumor progression and distant metastasis-free survival. Mechanistically, miR-644a directly targets the transcriptional co-repressor C-Terminal Binding Protein 1 (CTBP1) whose knock-outs by the CRISPR-Cas9 system inhibit tumor growth, metastasis, and drug resistance, mimicking the phenotypes induced by miR-644a. Furthermore, downregulation of CTBP1 by miR-644a upregulates wild type- or mutant-p53 which acts as a 'molecular switch' between G1-arrest and apoptosis by inducing cyclin-dependent kinase inhibitor 1 (p21, CDKN1A, CIP1) or pro-apoptotic phorbol-12-myristate-13-acetate-induced protein 1 (Noxa, PMAIP1), respectively. Interestingly, an increase in mutant-p53 by either overexpression of miR-644a or downregulation of CTBP1 was enough to shift this balance in favor of apoptosis through upregulation of Noxa. Notably, p53-mutant patients, but not p53-wild type ones, with high CTBP1 have a shorter survival suggesting that CTBP1 could be a potential prognostic factor for breast cancer patients with p53 mutations. Overall, re-activation of the miR-644a/CTBP1/p53 axis may represent a new strategy for overcoming both therapy resistance and metastasis.

miR-200c: a versatile watchdog in cancer progression, EMT, and drug resistance.

MicroRNAs (miRNAs) are 20-22-nucleotide small endogenous non-coding RNAs which regulate gene expression at post-transcriptional level. In the last two decades, identification of almost 2600 miRNAs in human and their potential to be modulated opened a new avenue to target almost all hallmarks of cancer. miRNAs have been classified as tumor suppressors or oncogenes depending on the phenotype they induce, the targets they modulate, and the tissue where they function. miR-200c, an illustrious tumor suppressor, is one of the highly studied miRNAs in terms of development, stemness, proliferation, epithelial-mesenchymal transition (EMT), therapy resistance, and metastasis. In this review, we first focus on the regulation of miR-200c expression and its role in regulating EMT in a ZEB1/E-cadherin axis-dependent and ZEB1/E-cadherin axis-independent manner. We then describe the role of miR-200c in therapy resistance in terms of multidrug resistance, chemoresistance, targeted therapy resistance, and radiotherapy resistance in various cancer types. We highlight the importance of miR-200c at the intersection of EMT and chemoresistance. Furthermore, we show how miR-200c coordinates several important signaling cascades such as TGF-ß signaling, PI3K/Akt signaling, Notch signaling, VEGF signaling, and NF-κB signaling. Finally, we discuss miR-200c as a potential prognostic/diagnostic biomarker in several diseases, but mainly focusing on cancer and its potential application in future therapeutics.

Heterozygous deep-intronic variants and deletions in ABCA4 in persons with retinal dystrophies and one exonic ABCA4 variant.

Variants in ABCA4 are responsible for autosomal-recessive Stargardt disease and cone-rod dystrophy. Sequence analysis of ABCA4 exons previously revealed one causative variant in each of 45 probands. To identify the "missing" variants in these cases, we performed multiplex ligation-dependent probe amplification-based deletion scanning of ABCA4. In addition, we sequenced the promoter region, fragments containing five deep-intronic splice variants, and 15 deep-intronic regions containing weak splice sites. Heterozygous deletions spanning ABCA4 exon 5 or exons 20-22 were found in two probands, heterozygous deep-intronic variants were identified in six probands, and a deep-intronic variant was found together with an exon 20-22 deletion in one proband. Based on ophthalmologic findings and characteristics of the identified exonic variants present in trans, the deep-intronic variants V1 and V4 were predicted to be relatively mild and severe, respectively. These findings are important for proper genetic counseling and for the development of variant-specific therapies.