p31comet and TRIP13 recycle Rev7 to regulate DNA repair

Discovery of novel antimyeloma agents targeting TRIP13 by molecular modeling and bioassay

Thyroid hormone receptor-interacting protein-13 (TRIP13) is an AAA+ ATPase that regulates protein complex assembly and disassembly and is known to be a chromosomal instability gene with the ability to repair DNA double-strand breaks. TRIP13 overexpression has been linked to the proliferation and development of many human malignancies, including multiple myeloma (MM). Accordingly, TRIP13 is recognized as a potential drug target for anticancer drug development. Although some TRIP13 inhibitors have been reported, none are under clinical trial or approved for clinical use. This study aimed to identify novel small molecules as potential TRIP13 inhibitors structurally different from previously reported compounds through molecular modeling and bioassays. As a result, five compounds were successfully identified as novel TRIP13 inhibitors. F368-0183 showed the best antiproliferative activity with IC50 = 5.25 μM (NCI-H929 cell line), comparable with the positive control DCZ0415 (IC50 = 9.64 μM). Also, the cellular thermal shift assay confirmed that this compound could interact with the TRIP13 protein in MM cells. In addition, the AAA+ ATPase inhibitory bioassay demonstrated that the five compounds had better inhibitory activity than DCZ0415, having strong correlations with the calculated free energy perturbation (FEP). Further molecular dynamics simulation studies revealed that the novel compounds could significantly interact with 12 residues of TRIP13, especially R386, L139, R389, L135, S138, Y141, and G385. We also assessed the F368-0183 inhibition on a kinase panel, no other targets were found, but the potential binding to other target proteins of these compounds cannot be totally excluded. Therefore, the new molecular scaffolds of these compounds, their efficacy in suppressing MM cell line proliferation, and the displayed TRIP13 AAA+ ATPase inhibitory properties provide important clues for developing novel TRIP13-based multi-target anti-MM drugs.

Germline specific genes increase DNA double-strand break repair and radioresistance in lung adenocarcinoma cells

In principle, germline cells possess the capability to transmit a nearly unaltered set of genetic material to infinite future generations, whereas somatic cells are limited by strict growth constraints necessary to assure an organism's physical structure and eventual mortality. As the potential to replicate indefinitely is a key feature of cancer, we hypothesized that the activation of a "germline program" in somatic cells can contribute to oncogenesis. Our group recently described over one thousand germline specific genes that can be ectopically expressed in cancer, yet how germline specific processes contribute to the malignant properties of cancer is poorly understood. We here show that the expression of germ cell/cancer (GC) genes correlates with malignancy in lung adenocarcinoma (LUAD). We found that LUAD cells expressing more GC genes can repair DNA double strand breaks more rapidly, show higher rates of proliferation and are more resistant to ionizing radiation, compared to LUAD cells that express fewer GC genes. In particular, we identified the HORMA domain protein regulator TRIP13 to be predominantly responsible for this malignant phenotype, and that TRIP13 inhibition or expression levels affect the response to ionizing radiation and subsequent DNA repair. Our results demonstrate that GC genes are viable targets in oncology, as they induce increased radiation resistance and increased propagation in cancer cells. Because their expression is normally restricted to germline cells, we anticipate that GC gene directed therapeutic options will effectively target cancer, with limited side effects besides (temporary) infertility.

Targeting TRIP13 for overcoming anticancer drug resistance (Review)

Cancer is one of the greatest dangers to human wellbeing and survival. A key barrier to effective cancer therapy is development of resistance to anti‑cancer medications. In cancer cells, the AAA+ ATPase family member thyroid hormone receptor interactor 13 (TRIP13) is key in promoting treatment resistance. Nonetheless, knowledge of the molecular processes underlying TRIP13‑based resistance to anticancer therapies is lacking. The present study evaluated the function of TRIP13 expression in anticancer drug resistance and potential methods to overcome this resistance. Additionally, the underlying mechanisms by which TRIP13 promotes resistance to anticancer drugs were explored, including induction of mitotic checkpoint complex surveillance system malfunction, promotion of DNA repair, the enhancement of autophagy and the prevention of immunological clearance. The effects of combination treatment, which include a TRIP13 inhibitor in addition to other inhibitors, were discussed. The present study evaluated the literature on TRIP13 as a possible target and its association with anticancer drug resistance, which may facilitate improvements in current anticancer therapeutic options.

Evolution of Rev7 interactions in eukaryotic TLS DNA polymerase Polζ

Translesion synthesis (TLS) DNA polymerase Polζ is crucial for the bypass replication over sites of DNA damage. The Rev7 subunit of Polζ is a HORMA (Hop1, Rev7, Mad2) protein that facilitates recruitment of Polζ to the replication fork via interactions with the catalytic subunit Rev3 and the translesion synthesis scaffold protein Rev1. Human Rev7 (hRev7) interacts with two Rev7-binding motifs (RBMs) of hRev3 by a mechanism conserved among HORMA proteins whereby the safety-belt loop of hRev7 closes on the top of the ligand. The two copies of hRev7 tethered by the two hRev3-RBMs form a symmetric head-to-head dimer through the canonical HORMA dimerization interface. Recent cryo-EM structures reveal that Saccharomyces cerevisiae Polζ (scPolζ) also includes two copies of scRev7 bound to distinct regions of scRev3. Surprisingly, the HORMA dimerization interface is not conserved in scRev7, with the two scRev7 protomers forming an asymmetric head-to-tail dimer with a much smaller interface than the hRev7 dimer. Here, we validated the two adjacent RBM motifs in scRev3, which bind scRev7 with affinities that differ by two orders of magnitude and confirmed the 2:1 stoichiometry of the scRev7:Rev3 complex in solution. However, our biophysical studies reveal that scRev7 does not form dimers in solution either on its own accord or when tethered by the two RBMs in scRev3. These findings imply that the scRev7 dimer observed in the cryo-EM structures is induced by scRev7 interactions with other Polζ subunits and that Rev7 homodimerization via the HORMA interface is a mechanism that emerged later in evolution.