Ryan M. Naylor

Senescent cells: a novel therapeutic target for aging and age-related diseases

Aging is the main risk factor for most chronic diseases, disabilities, and declining health. It has been proposed that senescent cells—damaged cells that have lost the ability to divide—drive the deterioration that underlies aging and age‐related diseases. However, definitive evidence for this relationship has been lacking. The use of a progeroid mouse model (which expresses low amounts of the mitotic checkpoint protein BubR1) has been instrumental in demonstrating that p16Ink4a‐positive senescent cells drive age‐related pathologies and that selective elimination of these cells can prevent or delay age‐related deterioration. These studies identify senescent cells as potential therapeutic targets in the treatment of aging and age‐related diseases. Here, we describe how senescent cells develop, the experimental evidence that causally implicates senescent cells in age‐related dysfunction, the chronic diseases and disorders that are characterized by the accumulation of senescent cells at sites of pathology, and the therapeutic approaches that could specifically target senescent cells.

CHK1 and WEE1 inhibition combine synergistically to enhance therapeutic efficacy in acute myeloid leukemia ex vivo.

Novel combinations targeting new molecular vulnerabilities are needed to improve the outcome of patients with acute myeloid leukemia. We recently identified WEE1 kinase as a novel target in leukemias. To identify genes that are synthetically lethal with WEE1 inhibition, we performed a short interfering RNA screen directed against cell cycle and DNA repair genes during concurrent treatment with the WEE1 inhibitor MK1775. CHK1 and ATR, genes encoding two replication checkpoint kinases, were among the genes whose silencing enhanced the effects of WEE1 inhibition most, whereas CDK2 short interfering RNA antagonized MK1775 effects. Building on this observation, we examined the impact of combining MK1775 with selective small molecule inhibitors of CHK1, ATR and cyclin-dependent kinases. The CHK1 inhibitor MK8776 sensitized acute myeloid leukemia cell lines and primary leukemia specimens to MK1775 ex vivo, whereas smaller effects were observed with the MK1775/MK8776 combination in normal myeloid progenitors. The ATR inhibitor VE-821 likewise enhanced the antiproliferative effects of MK1775, whereas the cyclin-dependent kinase inhibitor roscovitine antagonized MK1775. Further studies showed that MK8776 enhanced MK1775-mediated activation of the ATR/CHK1 pathway in acute leukemia cell lines and ex vivo. These results indicate that combined cell cycle checkpoint interference with MK1775/MK8776 warrants further investigation as a potential treatment for acute myeloid leukemia.

Centrosome dynamics as a source of chromosomal instability

Accurate segregation of duplicated chromosomes between two daughter cells depends on bipolar spindle formation, a metaphase state in which sister kinetochores are attached to microtubules emanating from opposite spindle poles. To ensure bi-orientation, cells possess surveillance systems that safeguard against microtubule-kinetochore attachment defects, including the spindle assembly checkpoint and the error correction machinery. However, recent developments have identified centrosome dynamics--that is, centrosome disjunction and poleward movement of duplicated centrosomes--as a central target for deregulation of bi-orientation in cancer cells. In this review, we discuss novel insights into the mechanisms that underlie centrosome dynamics and discuss how these mechanisms are perturbed in cancer cells to drive chromosome mis-segregation and advance neoplastic transformation.

Nuclear pore protein NUP88 activates anaphase-promoting complex to promote aneuploidy

The nuclear pore complex protein NUP88 is frequently elevated in aggressive human cancers and correlates with reduced patient survival; however, it is unclear whether and how NUP88 overexpression drives tumorigenesis. Here, we show that mice overexpressing NUP88 are cancer prone and form intestinal tumors. To determine whether overexpression of NUP88 drives tumorigenesis, we engineered transgenic mice with doxycycline-inducible expression of Nup88. Surprisingly, NUP88 overexpression did not alter global nuclear transport, but was a potent inducer of aneuploidy and chromosomal instability. We determined that NUP88 and the nuclear transport factors NUP98 and RAE1 comprise a regulatory network that inhibits premitotic activity of the anaphase-promoting complex/cyclosome (APC/C). When overexpressed, NUP88 sequesters NUP98-RAE1 away from APC/CCDH1, triggering proteolysis of polo-like kinase 1 (PLK1), a tumor suppressor and multitasking mitotic kinase. Premitotic destruction of PLK1 disrupts centrosome separation, causing mitotic spindle asymmetry, merotelic microtubule-kinetochore attachments, lagging chromosomes, and aneuploidy. These effects were replicated by PLK1 insufficiency, indicating that PLK1 is responsible for the mitotic defects associated with NUP88 overexpression. These findings demonstrate that the NUP88-NUP98-RAE1-APC/CCDH1 axis contributes to aneuploidy and suggest that it may be deregulated in the initiating stages of a broad spectrum of human cancers.

Cyclin A2 is an RNA binding protein that controls Mre11 mRNA translation

Cyclin A2 activates the cyclin-dependent kinases Cdk1 and Cdk2 and is expressed at elevated levels from S phase until early mitosis. We found that mutant mice that cannot elevate cyclin A2 are chromosomally unstable and tumor-prone. Underlying the chromosomal instability is a failure to up-regulate the meiotic recombination 11 (Mre11) nuclease in S phase, which leads to impaired resolution of stalled replication forks, insufficient repair of double-stranded DNA breaks, and improper segregation of sister chromosomes. Unexpectedly, cyclin A2 controlled Mre11 abundance through a C-terminal RNA binding domain that selectively and directly binds Mre11 transcripts to mediate polysome loading and translation. These data reveal cyclin A2 as a mechanistically diverse regulator of DNA replication combining multifaceted kinase-dependent functions with a kinase-independent, RNA binding–dependent role that ensures adequate repair of common replication errors.

Krüppel-like Transcription Factor KLF10 Suppresses TGFβ-Induced Epithelial-to-Mesenchymal Transition via a Negative Feedback Mechanism

TGFβ-SMAD signaling exerts a contextual effect that suppresses malignant growth early in epithelial tumorigenesis but promotes metastasis at later stages. Longstanding challenges in resolving this functional dichotomy may uncover new strategies to treat advanced carcinomas. The Krüppel-like transcription factor, KLF10, is a pivotal effector of TGFβ/SMAD signaling that mediates antiproliferative effects of TGFβ. In this study, we show how KLF10 opposes the prometastatic effects of TGFβ by limiting its ability to induce epithelial-to-mesenchymal transition (EMT). KLF10 depletion accentuated induction of EMT as assessed by multiple metrics. KLF10 occupied GC-rich sequences in the promoter region of the EMT-promoting transcription factor SLUG/SNAI2, repressing its transcription by recruiting HDAC1 and licensing the removal of activating histone acetylation marks. In clinical specimens of lung adenocarcinoma, low KLF10 expression associated with decreased patient survival, consistent with a pivotal role for KLF10 in distinguishing the antiproliferative versus prometastatic functions of TGFβ. Our results establish that KLF10 functions to suppress TGFβ-induced EMT, establishing a molecular basis for the dichotomy of TGFβ function during tumor progression. Cancer Res; 77(9); 2387-400. ©2017 AACR.

BubR1 alterations that reinforce mitotic surveillance act against aneuploidy and cancer

BubR1 is a key component of the spindle assembly checkpoint (SAC). Mutations that reduce BubR1 abundance cause aneuploidization and tumorigenesis in humans and mice, whereas BubR1 overexpression protects against these. However, how supranormal BubR1 expression exerts these beneficial physiological impacts is poorly understood. Here, we used Bub1b mutant transgenic mice to explore the role of the amino-terminal (BubR1N) and internal (BubR1I) Cdc20-binding domains of BubR1 in preventing aneuploidy and safeguarding against cancer. BubR1N was necessary, but not sufficient to protect against aneuploidy and cancer. In contrast, BubR1 lacking the internal Cdc20-binding domain provided protection against both, which coincided with improved microtubule-kinetochore attachment error correction and SAC activity. Maximal SAC reinforcement occurred when both the Phe- and D-box of BubR1I were disrupted. Thus, while under- or overexpression of most mitotic regulators impairs chromosome segregation fidelity, certain manipulations of BubR1 can positively impact this process and therefore be therapeutically exploited. DOI: http://dx.doi.org/10.7554/eLife.16620.001

Novel suprasellar location of desmoplastic infantile astrocytoma and ganglioglioma: a single institution’s experience

OBJECTIVE The aim of this study was to describe the clinical presentation, imaging appearance, and differential outcomes based on tumor location in 7 patients with desmoplastic infantile astrocytoma and desmoplastic infantile gangliogliomas (DIA/DIG). METHODS Data of 7 patients with histopathology-proven DIA/DIGs and preoperative imaging were retrospectively reviewed, and age, sex, clinical presentation, imaging characteristics, tumor location, surgical procedure, postoperative morbidity, and overall mortality were recorded. RESULTS Two subgroups of patients with DIA/DIGs were found to exist based on whether their tumor was located in the cerebral hemispheres or suprasellar region. Nearly all patients presented with rapidly enlarging head circumference regardless of tumor location. However, ocular abnormalities, including nystagmus and preference for downward gaze, were specific for patients with suprasellar disease. These patients experienced significant postoperative complications and had poor long-term outcomes. In contrast, patients with hemispheric tumors underwent more extensive resection than patients with suprasellar tumors, had uneventful postoperative courses, and had no documented long-term comorbidities. CONCLUSIONS Postoperative course and long-term outcome for patients with DIA/DIGs were correlated to the anatomical location and radiographic appearance of their tumor at presentation, despite having histologically and molecularly indistinguishable, WHO grade I tumors.

Management of major vascular injury during pedicle screw instrumentation of thoracolumbar spine

OBJECTIVES Vascular injury is a rare complication of spinal instrumentation. Presentation can vary from immediate hemorrhage to pseudoaneurysm formation. In the literature, surgical approach to repair has varied based on anatomy, acuity of diagnosis, infection, and available technology. In this manuscript, we aim to describe our institutional experience with vascular injuries in thoraco-lumbar spine surgery. PATIENTS AND METHODS We report our institutional experience of three cases of vascular injury secondary to pedicle screw misplacement and their management, as well as a review of the literature. RESULTS The first case had a history of previous instrumentation and presented with back pain and fever. The patient was taken for instrumentation exploration via a posterior approach. Aortic violation was discovered at T6 intraoperatively during instrumentation removal and the patient underwent emergent endovascular repair. The second case presented with chronic back pain after multiple prior posterior fusions and CT angiogram showing screw perforation on the aorta at T10. The patient underwent elective endovascular repair with synchronous removal of the instrumentation. The third case presented with radicular leg pain 6 months after L4-S1 posterior lumbar interbody fusion, with CT scan demonstrating the left S1 screw abutting the L5 nerve root and common iliac vein. The patient underwent elective instrumentation revision with intraoperative venography. CONCLUSION Major vascular injury is a known complication of spinal surgery, especially if it involves instrumentation with pedicle screws. Treatment approach has evolved with the advancement of endovascular technology; however, open surgery remains an option when anatomy or infection is prohibitive. In the elective setting, preoperative planning with attention to surgical approach, positioning, and contingencies, should occur in a multidisciplinary fashion. Repair with an aortic stent-graft cuff may minimize unnecessary coverage of the descending thoracic aorta and intercostal arteries.