DAB2IP regulates autophagy in prostate cancer in response to combined treatment of radiation and a DNA-PKcs inhibitor

The scaffold protein disabled 2 (DAB2) and its role in tumor development and progression

BACKGROUND

Disabled 2 (DAB2) is a multifunctional protein that has emerged as a critical component in the regulation of tumor growth. Its dysregulation is implicated in various types of cancer, underscoring its importance in understanding the molecular mechanisms underlying tumor development and progression. This review aims to unravel the intricate molecular mechanisms by which DAB2 exerts its tumor-suppressive functions within cancer signaling pathways.

METHODS AND RESULTS

We conducted a comprehensive review of the literature focusing on the structure, expression, physiological functions, and tumor-suppressive roles of DAB2. We provide an overview of the structure, expression, and physiological functions of DAB2. Evidence supporting DAB2's role as a tumor suppressor is explored, highlighting its ability to inhibit cell proliferation, induce apoptosis, and modulate key signaling pathways involved in tumor suppression. The interaction between DAB2 and key oncogenes is examined, elucidating the interplay between DAB2 and oncogenic signaling pathways. We discuss the molecular mechanisms underlying DAB2-mediated tumor suppression, including its involvement in DNA damage response and repair, regulation of cell cycle progression and senescence, and modulation of epithelial-mesenchymal transition (EMT). The review explores the regulatory networks involving DAB2, covering post-translational modifications, interactions with other tumor suppressors, and integration within complex signaling networks. We also highlight the prognostic significance of DAB2 and its role in pre-clinical studies of tumor suppression.

CONCLUSION

This review provides a comprehensive understanding of the molecular mechanisms by which DAB2 exerts its tumor-suppressive functions. It emphasizes the significance of DAB2 in cancer signaling pathways and its potential as a target for future therapeutic interventions.

Disable 2, A Versatile Tissue Matrix Multifunctional Scaffold Protein with Multifaceted Signaling: Unveiling Role in Breast Cancer for Therapeutic Revolution

The Disabled-2 (DAB2) protein, found in 80-90% of various tumors, including breast cancer, has been identified as a potential tumor suppressor protein. On the contrary, some hypothesis suggests that DAB2 is associated with the modulation of the Ras/MAPK pathway by endocytosing the Grb/Sos1 signaling complex, which produces oncogenes and chemoresistance to anticancer drugs, leading to increased tumor growth and metastasis. DAB2 has multiple functions in several disorders and is typically under-regulated in several cancers, making it a potential target for treatment of cancer therapy. The primary function of DAB2 is the modulation of transforming growth factor- β (TGF-β) mediated endocytosis, which is involved in several mechanisms of cancer development, including tumor suppression through promoting apoptosis and suppressing cell proliferation. In this review, we will discuss in detail the mechanisms through which DAB2 leads to breast cancer and various advancements in employing DAB2 in the treatment of breast cancer. Additionally, we outlined its role in other diseases. We propose that upregulating DAB2 could be a novel approach to the therapeutics of breast cancer.

Disabled-2, a versatile tissue matrix multifunctional scaffold protein with multifaceted signaling: Unveiling its potential in the cancer battle

A multifunctional scaffold protein termed Disabled-2 (Dab2) has recently gained attention in the scientific community and has emerged as a promising candidate in the realm of cancer research. Dab2 protein is involved in a variety of signaling pathways, due to which its significance in the pathogenesis of several carcinomas has drawn considerable attention. Dab2 is essential for controlling the advancement of cancer because it engages in essential signaling pathways such as the Wnt/β-catenin, epidermal growth factor receptor (EGFR), and transforming growth factor-beta (TGF-β) pathways. Dab2 can also repress epithelial-mesenchymal transition (EMT) which is involved in tumor progression with metastatic expansion and adds another layer of significance to its possible impact on cancer spread. Furthermore, the role of Dab2 in processes such as cell growth, differentiation, apoptosis, invasion, and metastasis has been explored in certain investigative studies suggesting its significance. The present review examines the role of Dab2 in the pathogenesis of various cancer subtypes including breast cancer, ovarian cancer, gastric cancer, prostate cancer, and bladder urothelial carcinoma and also sheds some light on its potential to act as a therapeutic target and a prognostic marker in the treatment of various carcinomas. By deciphering this protein's diverse signaling, we hope to provide useful insights that may pave the way for novel therapeutic techniques and tailored treatment approaches in cancer management. Preclinical and clinical trial data on the impact of Dab2 regulation in cancer have also been included, allowing us to delineate role of Dab2 in tumor suppressor function, as well as its correlation with disease stage classification and potential therapy options. However, we observed that there is very scarce data in the form of studies on the evaluation of Dab2 role and treatment function in carcinomas, and further research into this matter could prove beneficial in the generation of novel therapeutic agents for patient-centric and tailored therapy, as well as early prognosis of carcinomas.

Radiotherapy Side Effects: Comprehensive Proteomic Study Unraveled Neural Stem Cell Degenerative Differentiation upon Ionizing Radiation

Cranial radiation therapy is one of the most effective treatments for childhood brain cancers. Despite the ameliorated survival rate of juvenile patients, radiation exposure-induced brain neurogenic region injury could markedly impair patients' cognitive functions and even their quality of life. Determining the mechanism underlying neural stem cells (NSCs) response to irradiation stress is a crucial therapeutic strategy for cognitive impairment. The present study demonstrated that X-ray irradiation arrested NSCs' cell cycle and impacted cell differentiation. To further characterize irradiation-induced molecular alterations in NSCs, two-dimensional high-resolution mass spectrometry-based quantitative proteomics analyses were conducted to explore the mechanism underlying ionizing radiation's influence on stem cell differentiation. We observed that ionizing radiation suppressed intracellular protein transport, neuron projection development, etc., particularly in differentiated cells. Redox proteomics was performed for the quantification of cysteine thiol modifications in order to profile the oxidation-reduction status of proteins in stem cells that underwent ionizing radiation treatment. Via conjoint screening of protein expression abundance and redox status datasets, several significantly expressed and oxidized proteins were identified in differentiating NSCs subjected to X-ray irradiation. Among these proteins, succinate dehydrogenase [ubiquinone] flavoprotein subunit, mitochondrial (sdha) and the acyl carrier protein, mitochondrial (Ndufab1) were highly related to neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and Huntington's disease, illustrating the dual-character of NSCs in cell differentiation: following exposure to ionizing radiation, the normal differentiation of NSCs was compromised, and the upregulated oxidized proteins implied a degenerative differentiation trajectory. These findings could be integrated into research on neurodegenerative diseases and future preventive strategies.

Effect of Autophagy Inhibitors on Radiosensitivity in DNA Repair-Proficient and -Deficient Glioma Cells

Background and Objectives: The development of radioresistance is a fundamental barrier to successful glioblastoma therapy. Autophagy is thought to play a role in facilitating the DNA repair of DNA damage foci in radiation-exposed tumor cells, thus, potentially contributing to their restoration of proliferative capacity and development of resistance in vitro. However, the effect of autophagy inhibitors on DNA damage repair is not fully clear and requires further investigation. Materials and Methods: In this work, we utilized M059K (DNA-PKcs proficient) and M059J (DNA-PKcs deficient) glioma cell lines to investigate the role of autophagy inhibitors in the DNA repair of radiation-induced DNA damage. Cell viability following radiation was determined by trypan blue exclusion in both cell lines. Cell death and autophagy assays were performed to evaluate radiation-induced cell stress responses. DNA damage was measured as based on the intensity of phosphorylated γ-H2AX, a DNA double-stranded breaks (DSBs) marker, in the presence or absence of autophagy inhibitors. Results: The cell viability assay showed that M059J cells were more sensitive to the same dose of radiation (4 Gy) than M059K cells. This observation was accompanied by an elevation in γ-H2AX formation in M059J but not in M059K cells. In addition, the DAPI/TUNEL and Senescence-associated β-galactosidase (SA-β-gal) staining assays did not reveal significant differences in apoptosis and/or senescence induction in response to radiation, respectively, in either cell line. However, acridine orange staining demonstrated clear promotion of acidic vesicular organelles (AVOs) in both cell lines in response to 4 Gy radiation. Moreover, DNA damage marker levels were found to be elevated 72 h post-radiation when autophagy was inhibited by the lysosomotropic agent bafilomycin A1 (BafA1) or the PI3K inhibitor 3-methyl adenine (3-MA) in M059K cells. Conclusions: The extent of the DNA damage response remained high in the DNA-PKcs deficient cells following exposure to radiation, indicating their inability to repair the newly formed DNA-DSBs. On the other hand, radioresistant M059K cells showed more DNA damage response only when autophagy inhibitors were used with radiation, suggesting that the combination of autophagy inhibitors with radiation may interfere with DNA repair efficiency.

DAB2IP predicts treatment response and prognosis of ESCC patients and modulates its radiosensitivity through enhancing IR-induced activation of the ASK1-JNK pathway

Background

Disabled homolog 2 interacting protein (DAB2IP) plays a tumor-suppressive role in several types of human cancers. However, the molecular status and function of the DAB2IP gene in esophageal squamous cell carcinoma (ESCC) patients who received definitive chemoradiotherapy is rarely reported.

Methods

We examined the expression dynamics of DAB2IP by immunohistochemistry (IHC) in 140 ESCC patients treated with definitive chemoradiotherapy. A series of in vivo and in vitro experiments were performed to elucidate the effect of DAB2IP on the chemoradiotherapy (CRT) response and its underlying mechanisms in ESCC.

Results

Decreased expression of DAB2IP in ESCCs correlated positively with ESCC resistance to CRT and was a strong and independent predictor for short disease-specific survival (DSS) of ESCC patients. Furthermore, the therapeutic sensitivity of CRT was substantially increased by ectopic overexpression of DAB2IP in ESCC cells. In addition, knockdown of DAB2IP dramatically enhanced resistance to CRT in ESCC. Finally, we demonstrated that DAB2IP regulates ESCC cell radiosensitivity through enhancing ionizing radiation (IR)-induced activation of the ASK1-JNK signaling pathway.

Conclusions

Our data highlight the molecular etiology and clinical significance of DAB2IP in ESCC, which may represent a new therapeutic strategy to improve therapy and survival for ESCC patients.

Mitotic phosphorylation of tumor suppressor DAB2IP maintains spindle assembly checkpoint and chromosomal stability through activating PLK1-Mps1 signal pathway and stabilizing mitotic checkpoint complex

Chromosomal instability (CIN) is a driving force for cancer development. The most common causes of CIN include the dysregulation of the spindle assembly checkpoint (SAC), which is a surveillance mechanism that prevents premature chromosome separation during mitosis by targeting anaphase-promoting complex/cyclosome (APC/C). DAB2IP is frequently silenced in advanced prostate cancer (PCa) and is associated with aggressive phenotypes of PCa. Our previous study showed that DAB2IP activates PLK1 and functions in mitotic regulation. Here, we report the novel mitotic phosphorylation of DAB2IP by Cdks, which mediates DAB2IP's interaction with PLK1 and the activation of the PLK1-Mps1 pathway. DAB2IP interacts with Cdc20 in a phosphorylation-independent manner. However, the phosphorylation of DAB2IP inhibits the ubiquitylation of Cdc20 in response to SAC, and blocks the premature release of the APC/C-MCC. The PLK1-Mps1 pathway plays an important role in mitotic checkpoint complex (MCC) assembly. It is likely that DAB2IP acts as a scaffold to aid PLK1-Mps1 in targeting Cdc20. Depletion or loss of the Cdks-mediated phosphorylation of DAB2IP destabilizes the MCC, impairs the SAC, and increases chromosome missegregation and subsequent CIN, thus contributing to tumorigenesis. Collectively, these results demonstrate the mechanism of DAB2IP in SAC regulation and provide a rationale for targeting the SAC to cause lethal CIN against DAB2IP-deficient aggressive PCa, which exhibits a weak SAC.

Inhibition of CDK1 attenuates neuronal apoptosis and autophagy and confers neuroprotection after chronic spinal cord injury in vivo

Chronic spinal cord injury (CSCI) results from progressive compression of the spinal cord over time. A variety of factors cause CSCI, and its exact pathogenesis is unknown. Cyclin-dependent kinase 1 (CDK1) is closely related to the apoptosis pathway, but no CSCI-related studies on CDK1 have been conducted. In this study, the role of CDK1 in CSCI was explored in a rat model. The CSCI model was established by screw compression using the cervical anterior approach for twelve weeks. The neurological function of the rats was evaluated using the neurological severity scores (NSS) and motor evoked potentials (MEPs). Pathological changes in spinal cord tissue were observed by hematoxylin-eosin (HE) staining, and Nissl staining was performed to assess the survival of motor neurons in the anterior horn of the spinal cord. Changes in autophagy and apoptosis in anterior horn of spinal cord tissue were detected using transmission electron microscopy and the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, respectively. The expression levels of glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor (IBA) and choline acetyltransferase (CHAT) in the anterior horn were determined using immunohistochemistry assays to investigate astrocytes, microglia and motor neurons, respectively, in the anterior horn. Western blot assays were used to detect the expression levels of CDK1, Bcl-2, Bax, Caspase 3, LC3 and Beclin1. Changes in the expression of CDK1, LC3 and Beclin1 were also observed using immunohistochemistry. The results indicated that CSCI resulted in neuronal injury and a decrease in the NSS. In the CSCI model group, anterior horn astrocytes and microglia were activated, and motor neurons were decreased. Neuronal apoptosis was promoted, and the number of autophagic vacuoles was elevated. Rats treated with the CDK1 shRNA lentivirus exhibited better NSS, more surviving motor neurons, and fewer apoptotic neurons than the model rats. The occurrence of autophagy and the expression of proapoptotic and autophagy-related proteins were lower in the CDK1 shRNA group than the model group. In conclusion, CDK1 downregulation suppressed the activation of anterior horn astrocytes and microglia, promoted motor neuron repair, and inhibited neurons apoptosis and autophagy to promote the recovery of motor function after spinal cord injury.

Synergistic radiosensitizing effect of BR101801, a specific DNA-dependent protein kinase inhibitor, in various human solid cancer cells and xenografts

DNA-dependent protein kinase (DNA-PK), an essential component of the non-homologous end-joining (NHEJ) repair pathway, plays an important role in DNA damage repair (DDR). Therefore, DNA-PK inhibition is a promising approach for overcoming radiotherapy or chemotherapy resistance in cancers. In this study, we demonstrated that BR101801, a potent DNA-PK inhibitor, acted as an effective radiosensitizer in various human solid cancer cells and an in vivo xenograft model. Overall, BR101801 strongly elevated ionizing radiation (IR)-induced genomic instability via induction of cell cycle G₂/M arrest, autophagic cell death, and impairment of DDR pathway in human solid cancer cells. Interestingly, BR101801 inhibited not only phosphorylation of DNA-PK catalytic subunit in NHEJ factors but also BRCA2 protein level in homologous recombination (HR) factors. In addition, combination BR101801 and IR suppressed tumor growth compared with IR alone by reducing phosphorylation of DNA-PK in human solid cancer xenografts. Our findings suggested that BR101801 is a selective DNA-PK inhibitor with a synergistic radiosensitizing effect in human solid cancers, providing evidence for clinical applications.

The roles of GTPase-activating proteins in regulated cell death and tumor immunity

GTPase-activating protein (GAP) is a negative regulator of GTPase protein that is thought to promote the conversion of the active GTPase-GTP form to the GTPase-GDP form. Based on its ability to regulate GTPase proteins and other domains, GAPs are directly or indirectly involved in various cell requirement processes. We reviewed the existing evidence of GAPs regulating regulated cell death (RCD), mainly apoptosis and autophagy, as well as some novel RCDs, with particular attention to their association in diseases, especially cancer. We also considered that GAPs could affect tumor immunity and attempted to link GAPs, RCD and tumor immunity. A deeper understanding of the GAPs for regulating these processes could lead to the discovery of new therapeutic targets to avoid pathologic cell loss or to mediate cancer cell death.

DAB2IP decreases cell growth and migration and increases sensitivity to chemotherapeutic drugs in colorectal cancer

Background

Colorectal cancer (CRC) is one of the most common cancers worldwide with high rates of invasiveness and mortality. DAB2IP (DOC2/DAB2 interactive protein) is a member of the RAS-GTPase-activating protein (RAS-GAP) family that shows a suppressive effect on cancer progression, is downregulated in several cancers. However, the role of DAB2IP in CRC remains elusive.

Methods

Expression of DAB2IP was evaluated in human CRC tissues using immunohistochemistry (IHC), quantitative real-time reverse transcription PCR (qRT-PCR) and immunoblotting. Knockdown and overexpression of DAB2IP in CRC cells were achieved by transfecting siRNAs and DAB2IP expression vectors and assessed by qRT-PCR and immunoblotting. CCK-8, colony formation, wound-healing, and transwell assays were used to evaluate CRC cell growth, migration, and sensitivity to chemotherapeutic drugs. The cell cycle was analyzed by propidium iodide (PI) staining and flow cytometry. Cell apoptosis was evaluated by Annexin V-DAPI double staining and flow cytometry. The effect of DAB2IP overexpression on tumor formation was explored by an in vivo tumorigenesis assay. Finally, immunoblotting was performed to examine the molecules related to the action of DAB2IP in CRC.

Results

Compared with para-cancer tissues, there was a marked decrease of DAB2IP expression in surgically excised CRCs. In cultured CRC cells, enforced expression of DAB2IP inhibited cell growth and migration and sensitized the cells to DNA-acting cisplatin, oxaliplatin, and doxorubicin but not 5-fluorouracil (5-FU). In contrast, knockdown of DAB2IP produced the opposite effect. Moreover, DAB2IP overexpression hindered tumor growth in vivo. We further found that DAB2IP regulated the expression of cell growth, epithelial-mesenchymal transition (EMT), and apoptosis-related proteins in CRC cells and inhibited the phosphorylation of protein kinase B (AKT) and extracellular signal-regulated kinase (ERK).

Conclusions

Expression of DAB2IP inhibited CRC cell growth and migration and sensitized CRC cells to chemotherapeutic drugs. Inhibition of the phosphorylation of AKT and ERK is associated with the effects of DAB2IP expression. Restoration of DAB2IP expression may be a novel target for treating CRC.

Crucial Roles of microRNA-Mediated Autophagy in Urologic Malignancies

Urologic oncologies are major public health problems worldwide. Both microRNA and autophagy, separately or concurrently, are involved in a variety of the cellular and molecular processes of multiple cancers, including urologic malignancies. In this review, we have summarized the related studies and found that microRNA-mediated autophagy acted as carcinogenic factors or suppressors in prostate cancer, kidney cancer, and bladder cancer. MiRNAs, targeted genes, and the different signaling pathways constitute a complex network that orchestrates autophagy regulation, militating the oncogenic and tumor-suppressive effects in urologic malignancies. Aberrant expression of miRNAs may induce the dysregulation of the autophagy process, resulting in tumorigenesis, progression, and resistance to anticancer therapies. Targeting specific miRNAs for autophagy modulation may present as reliable diagnostic and prognostic biomarkers or promising therapeutic strategies for urologic oncologies.

PRKAA/AMPKα phosphorylation switches the role of RASAL2 from a suppressor to an activator of autophagy

RASAL2 (RAS protein activator like 2), a RASGTPase activating protein, can catalyze the hydrolysis of RAS-GTP into RAS-GDP to inactivate the RAS pathway in various types of cancer cells. However, the cellular function of RASAL2 remains elusive. Here we showed that RASAL2 can attenuate PRKAA/AMPKα phosphorylation by recruiting phosphatase PPM1B/pp2cβ, thus inhibiting the initiation of basal autophagy under normal conditions. In addition, we found that glucose starvation could induce dissociation of PPM1B from RASAL2 and then RASAL2 at S351 be phosphorylated by PRKAA, followed by the binding of phosphorylated-RASAL2 with to PIK3C3/VPS34-ATG14-BECN1/Beclin1 complex to increase PIK3C3 activity and autophagy. Furthermore, RASAL2 S351 phosphorylation facilitated breast tumor growth and correlated to poor clinical outcomes in breast cancer patients. Our study demonstrated that the phosphorylation status of RASAL2 S351 can function as a molecular switch to either suppress or promote AMPK-mediated autophagy. Inhibition of RASAL2 S351 phosphorylation might be a potential therapeutic strategy to overcome the resistance of AMPK-activation agents.

Down-regulation of autophagy-associated protein increased acquired radio-resistance bladder cancer cells sensitivity to taxol

BACKGROUND

As a bladder-preserving therapy, radiation therapy (RT) has been widely used in the treatment of bladder cancer (BCa) and made great progress in the past few decades. However, some BCa patients have low RT responsiveness and local recurrence rate after RT could reach 50%. Acquired radio-resistance (ARR) is one of the important reasons for the failure of RT. Unfortunately, these ARR cells also lack sensitivity to chemotherapy and cause tumor recurrence and metastasis.

PURPOSE

To build ARR-phenotype BCa cell model, discuss the possible molecular mechanism of ARR and find effective target molecules to overcome ARR.

MATERIALS AND METHODS

Five thousand six hundred and thirty-seven cells were subjected 30 times to 2 Gy of γ-rays and the surviving cells were called 5637R. Colony formation and MTT assay were applied to evaluate cells sensitivity to ionizing radiation (IR) and anti-neoplastic agents, respectively. Cells abilities of migration and invasion were determined using transwell method. Quantitative real-time polymerase chain reaction (RT-qPCR) and western blot (WB) were respectively utilized to compare the difference of gene and protein expression between 5637 and 5637R cells. Molecule inhibitors and small interfering RNA (siRNA) systems were employed to decrease the expression of target proteins, respectively.

RESULTS

BCa cells survived from fractionated irradiation (FI) exhibited tolerance to both IR and chemotherapy drugs. These ARR cells (5637R) had elevated migration and invasion abilities, accompanied by increased expression of epithelial mesenchymal transition (EMT)-related transcription factors (ZEB1/Snail/Twist). Moreover, 5637R cells showed enhanced cancer stem cell (CSC)-like characteristics with activated KMT1A-GATA3-STAT3 circuit, a newly reported self-renewal pathway of human bladder cancer stem cell (BCSC). Combined with Kaplan-Meier's analysis, we speculated that GATA3/MMP9/STAT3 could be an effective molecular panel predicting poor prognosis of BCa. In order to enhance the sensitivity of resistant cells to radiation, we introduced ERK inhibitor (FR 180204) and STAT3 inhibitor (S3I-201). However, both of them could not enhance ARR cells response to IR. On the other hand, siRNAs were respectively implemented to inhibit the expression of endogenous Beclin1 and Atg5, two important autophagy-related genes, in BCa cells, which significantly increased 5637R cells death upon taxol exposing. Similarly, chloroquine (CQ), a classic autophagy inhibitor, enhanced the cytotoxicity of taxol only on 5637R cells.

CONCLUSIONS

Long-term FI treatment is an effective method to establish the ARR-phenotype BCa cell model, by enriching BCSCs and enhancing cells migration and invasion. Both inhibiting the expression of autophagy-related proteins and using autophagy inhibitor can increase the sensitivity of ARR cells to taxol, suggesting that autophagy may play an important role in ARR cells chemical tolerance.

Beyond DNA Repair: DNA-PKcs in Tumor Metastasis, Metabolism and Immunity

The DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is a key component of the DNA-PK complex that has a well-characterized function in the non-homologous end-joining repair of DNA double-strand breaks. Since its identification, a large body of evidence has demonstrated that DNA-PKcs is frequently overexpressed in cancer, plays a critical role in tumor development and progression, and is associated with poor prognosis of cancer patients. Intriguingly, recent studies have suggested novel functions beyond the canonical role of DNA-PKcs, which has transformed the paradigm of DNA-PKcs in tumorigenesis and has reinvigorated the interest to target DNA-PKcs for cancer treatment. In this review, we update recent advances in DNA-PKcs, in particular the emerging roles in tumor metastasis, metabolic dysregulation, and immune escape. We further discuss the possible molecular basis that underpins the pleiotropism of DNA-PKcs in cancer. Finally, we outline the biomarkers that may predict the therapeutic response to DNA-PKcs inhibitor therapy. Understanding the functional repertoire of DNA-PKcs will provide mechanistic insights of DNA-PKcs in malignancy and, more importantly, may revolutionize the design and utility of DNA-PKcs-based precision cancer therapy.

Wnt/β-catenin signaling pathway induces autophagy-mediated temozolomide-resistance in human glioblastoma

Temozolomide (TMZ) is widely used for treating glioblastoma multiforme (GBM), however, the treatment of such brain tumors remains a challenge due to the development of resistance. Increasing studies have found that TMZ treatment could induce autophagy that may link to therapeutic resistance in GBM, but, the precise mechanisms are not fully understood. Understanding the molecular mechanisms underlying the response of GBM to chemotherapy is paramount for developing improved cancer therapeutics. In this study, we demonstrated that the loss of DOC-2/DAB2 interacting protein (DAB2IP) is responsible for TMZ-resistance in GBM through ATG9B. DAB2IP sensitized GBM to TMZ and suppressed TMZ-induced autophagy by negatively regulating ATG9B expression. A higher level of ATG9B expression was associated with GBM compared to low-grade glioma. The knockdown of ATG9B expression in GBM cells suppressed TMZ-induced autophagy as well as TMZ-resistance. Furthermore, we showed that DAB2IP negatively regulated ATG9B expression by blocking the Wnt/β-catenin pathway. To enhance the benefit of TMZ and avoid therapeutic resistance, effective combination strategies were tested using a small molecule inhibitor blocking the Wnt/β-catenin pathway in addition to TMZ. The combination treatment synergistically enhanced the efficacy of TMZ in GBM cells. In conclusion, the present study identified the mechanisms of TMZ-resistance of GBM mediated by DAB2IP and ATG9B which provides insight into a potential strategy to overcome TMZ chemo-resistance.

Bone marrow stromal cells-derived exosomes target DAB2IP to induce microglial cell autophagy, a new strategy for neural stem cell transplantation in brain injury

Bone marrow stromal cells (MSCs) are a useful source of stem cells for the treatment of various brain injury diseases due to their abundant supply and fewer ethical problems compared with transplant treatment. However, the clinical application of MSCs is limited due to allograft rejection and immunosuppression in the process of MSCs transplantation. According to previous studies, microglial cell autophagy occurs following co-culture with MSCs. In the present study, exosomes were obtained from MSCs and subsequently characterized using transmission electron microscopy, atomic force microscopy and dynamic light scattering particle size analysis. The type of microRNAs (miRs) found in the exosomes was then analyzed via gene chip. The results demonstrated that microglial cell autophagy could be induced by exosomes. This mechanism was therefore investigated further via reverse transcription-quantitative PCR, western blotting and luciferase assays. These results demonstrated that exosomes from MSCs could induce microglial cell autophagy through the miR-32-mediated regulation of disabled homolog 2-interacting protein, thus providing a theoretical basis for the clinical application of miRs in MSCs.

BECN1 promotes radiation-induced G2/M arrest through regulation CDK1 activity: a potential role for autophagy in G2/M checkpoint

Authophagy and G2/M arrest are two important mechanistic responses of cells to ionizing radiation (IR), in particular the IR-induced fibrosis. However, what interplayer and how it links the autophagy and the G2/M arrest remains elusive. Here, we demonstrate that the autophagy-related protein BECN1 plays a critical role in ionizing radiation-induced G2/M arrest. The treatment of cells with autophagy inhibitor 3-methyladenine (3-MA) at 0-12 h but not 12 h postirradiation significantly sensitized them to IR, indicating a radio-protective role of autophagy in the early response of cells to radiation. 3-MA and BECN1 disruption inactivated the G2/M checkpoint following IR by abrogating the IR-induced phosphorylation of phosphatase CDC25C and its target CDK1, a key mediator of the G2/M transition in coordination with CCNB1. Irradiation increased the nuclear translocation of BECN1, and this process was inhibited by 3-MA. We confirmed that BECN1 interacts with CDC25C and CHK2, and which is mediated the amino acids 89-155 and 151-224 of BECN1, respectively. Importantly, BECN1 deficiency disrupted the interaction of CHK2 with CDC25C and the dissociation of CDC25C from CDK1 in response to irradiation, resulting in the dephosphorylation of CDK1 and overexpression of CDK1. In summary, IR induces the translocation of BECN1 to the nucleus, where it mediates the interaction between CDC25C and CHK2, resulting in the phosphorylation of CDC25C and its dissociation from CDK1. Consequently, the mitosis-promoting complex CDK1/CCNB1 is inactivated, resulting in the arrest of cells at the G2/M transition. Our findings demonstrated that BECN1 plays a role in promotion of radiation-induced G2/M arrest through regulation of CDK1 activity. Whether such functions of BECN1 in G2/M arrest is dependent or independent on its autophagy-related roles is necessary to further identify.

Autophagy and Tumour Radiotherapy

Radiotherapy is an important component of cancer treatment modalities. With the rapid development of three-dimensional conformal, intensity-modulated, image-guided radiotherapy and the efficacy of radiotherapy continues to improve. Autophagy, as a catabolic process, is characterized by the formation of a double-membrane vesicle. Radiotherapy is known to induce autophagy in both cancer and normal cells. Here, we reviewed the interaction of radiotherapy and autophagy in the process of cancer treatment. The potential role of autophagy modification in enhancing radiotherapy treatment will also be reviewed.

DAB2IP with tumor-inhibiting activities exhibits frameshift mutations in gastrointestinal cancers

A scaffold protein DAB2 and its interaction partner DAB2IP have putative tumor suppressor gene (TSG) functions. Previous studies identified that both DAB2 and DAB2IP genes were inactivated by promoter hypermethylation in human cancers, but their mutational alterations in cancers remain largely unknown. The aim of our study was to find whether DAB2 and DAB2IP were mutated in gastric (GCs) and colorectal cancers (CRCs) by DNA sequencing. Both DAB2 and DAB2IP have mononucleotide repeats in their coding sequence that could be mutation targets in high microsatellite instability (MSI-H) cancers. We analyzed GC and CRC tissues and found that 8 of 34 GCs (23.5%) and 15 of 79 CRCs (20.0%) with MSI-H harbored DAB2IP frameshift mutations. DAB2 frameshift mutations were found in 2 of 79 CRCs (2.5%) with MSI-H. These mutations were not detected in microsatellite stable (MSS) cancers. We also found intratumoral heterogeneity (ITH) of DAB2IP frameshift mutations in 7 of 16 CRCs (43.8%). Loss of DAB2IP protein expression was found in approximately 20% of GCs and CRCs irrespective of MSI and DAB2IP frameshift mutation status. Our study shows that the TSG DAB2IP harbored frameshift mutations and ITH as well as expression loss. Together these tumor alterations might play a role in tumorigenesis of GC and CRC with MSI-H by down-regulating the tumor-inhibiting activities of DAB2IP.

GSK-3β inhibits autophagy and enhances radiosensitivity in non-small cell lung cancer

Background

Radiotherapy is one of the most common and effective treatment methods for cancer, and improving the radiosensitivity of tumor tissues during the treatment process is vital. We report the mechanisms of glycogen synthase kinase 3 (GSK-3) β-regulated autophagy and the effects of autophagy on radiosensitivity in non-small cell lung cancer (NSCLC).

Method

Immunohistochemical staining was performed to determine GSK-3β tissue expression in 89 NSCLC patients with follow-up data and the expression status of GSK-3β and autophagy in NSCLC tissues after X-ray radiotherapy. Western blots were used to quantitate changes in autophagy-related protein expression after A549 cells were treated with GSK-3β inhibitors and after H460 cells were transfected with GSK-3β mutants with different activities and X-ray irradiated. Clonogenic assays were used to measure the effect of autophagy on cellular proliferation.

Results

GSK-3β expression positively correlated with NSCLC differentiation (P < 0.05), and GSK-3β negativity was associated with a better prognosis in 89 NSCLC patients. After X-ray irradiation, the expression levels of GSK-3β and p62 were decreased in NSCLC tissues, and the expression levels of the autophagy-related protein LC3 were increased. A549 and H460 cells were selected as representative GSK-3β-high and GSK-3β-low expression cell lines. After transfecting H460 cells with different GSK-3β mutants [wild type GSK-3β (GSK-3β-WT), constitutively active GSK-3β (GSK-3β-S9A), and catalytically inactive GSK-3β (GSK-3β-K85R)] and subjecting these cells to X-ray irradiation, AMPK and LC3 expression levels decreased, and p62 expression levels increased. These effects were particularly significant for the GSK-3β-S9A mutant. In A549 cells, after GSK-3β inhibition and X-ray irradiation, AMPK and LC3 protein expression levels increased. Moreover, when autophagy was inhibited, cell proliferation decreased.

Conclusion

Our studies revealed that GSK-3β expression is associated with NSCLC differentiation, and patients with GSK-3β-negative tumors had a better prognosis. X-ray irradiation inhibited GSK-3β expression and promoted autophagy. Therefore, GSK-3β inhibits autophagy and enhances the radiosensitivity of NSCLC cells.

Inactivation of DNA-PK by knockdown DNA-PKcs or NU7441 impairs non-homologous end-joining of radiation-induced double strand break repair

The DNA-dependent protein kinase (DNA-PK) complex plays a pivotal role in non-homologous end-joining (NHEJ) repair. We investigated the mechanism of NU7441, a highly selective DNA-PK inhibitor, in NHEJ-competent mouse embryonic fibroblast (MEF) cells and NHEJ-deficient cells and explored the feasibility of its application in radiosensitizing nasopharyngeal carcinoma (NPC) cells. We generated wild-type and DNA-PKcs^−/− MEF cells. Clonogenic survival assays, flow cytometry, and immunoblotting were performed to study the effect of NU7441 on survival, cell cycle, and DNA repair. NU7441 profoundly radiosensitized wild-type MEF cells and SUNE-1 cells, but not DNA-PKcs^−/− MEF cells. NU7441 significantly suppressed radiation-induced DSB repair post-irradiation through unrepaired and lethal DNA damage, the cell cycle arrest. The effect was associated with the activation of cell cycle checkpoints. The present study revealed a mechanism by which inhibition of DNA-PK sensitizes cells to irradiation suggesting that radiotherapy in combination with DNA-PK inhibitor is a promising paradigm for the management of NPC which merits further investigation.

Inhibiting DNA-PKcs in a non-homologous end-joining pathway in response to DNA double-strand breaks

DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is a distinct factor in the non-homologous end-joining (NHEJ) pathway involved in DNA double-strand break (DSB) repair. We examined the crosstalk between key proteins in the DSB NHEJ repair pathway and cell cycle regulation and found that mouse embryonic fibroblast (MEF) cells deficient in DNA-PKcs or Ku70 were more vulnerable to ionizing radiation (IR) compared with wild-type cells and that DSB repair was delayed. γH2AX was associated with phospho-Ataxia-telangiectasia mutated kinase (Ser1987) and phospho-checkpoint effector kinase 1 (Ser345) foci for the arrest of cell cycle through the G2/M phase. Inhibition of DNA-PKcs prolonged IR-induced G2/M phase arrest because of sequential activation of cell cycle checkpoints. DSBs were introduced, and cell cycle checkpoints were recruited after exposure to IR in nasopharyngeal carcinoma SUNE-1 cells. NU7441 radiosensitized MEF cells and SUNE-1 cells by interfering with DSB repair. Together, these results reveal a mechanism in which coupling of DSB repair with the cell cycle radiosensitizes NHEJ repair-deficient cells, justifying further development of DNA-PK inhibitors in cancer therapy.

Cytolethal Distending Toxin Enhances Radiosensitivity in Prostate Cancer Cells by Regulating Autophagy

Cytolethal distending toxin (CDT) produced by Campylobacter jejuni contains three subunits: CdtA, CdtB, and CdtC. Among these three toxin subunits, CdtB is the toxic moiety of CDT with DNase I activity, resulting in DNA double-strand breaks (DSB) and, consequently, cell cycle arrest at the G2/M stage and apoptosis. Radiation therapy is an effective modality for the treatment of localized prostate cancer (PCa). However, patients often develop radioresistance. Owing to its particular biochemical properties, we previously employed CdtB as a therapeutic agent for sensitizing radioresistant PCa cells to ionizing radiation (IR). In this study, we further demonstrated that CDT suppresses the IR-induced autophagy pathway in PCa cells by attenuating c-Myc expression and therefore sensitizes PCa cells to radiation. We further showed that CDT prevents the formation of autophagosomes via decreased high-mobility group box 1 (HMGB1) expression and the inhibition of acidic vesicular organelle (AVO) formation, which are associated with enhanced radiosensitivity in PCa cells. The results of this study reveal the detailed mechanism of CDT for the treatment of radioresistant PCa.

Block one, unleash a hundred. Mechanisms of DAB2IP inactivation in cancer

One of the most defining features of cancer is aberrant cell communication; therefore, a molecular understanding of the intricate network established among tumor cells and their microenvironment could significantly improve comprehension and clinical management of cancer. The tumor suppressor DAB2IP (Disabled homolog 2 interacting protein), also known as AIP1 (ASK1 interacting protein), has an important role in this context, as it modulates signal transduction by multiple inflammatory cytokines and growth factors. DAB2IP is a Ras-GAP, and negatively controls Ras-dependent mitogenic signals. In addition, acting as a signaling adaptor, DAB2IP modulates other key oncogenic pathways, including TNFα/NF-κB, WNT/β-catenin, PI3K/AKT, and androgen receptors. Therefore, DAB2IP inactivation can provide a selective advantage to tumors initiated by a variety of driver mutations. In line with this role, DAB2IP expression is frequently impaired by methylation in cancer. Interestingly, recent studies reveal that tumor cells can employ other sophisticated mechanisms to disable DAB2IP at the post-transcriptional level. We review the mechanisms and consequences of DAB2IP inactivation in cancer, with the purpose to support and improve research aimed to counteract such mechanisms. We suggest that DAB2IP reactivation in cancer cells could be a strategy to coordinately dampen multiple oncogenic pathways, potentially limiting progression of a wide spectrum of tumors.

DAB2IP in cancer

DOC-2/DAB2 is a member of the disable gene family that features tumor-inhibiting activity. The DOC-2/DAB2 interactive protein, DAB2IP, is a new member of the Ras GTPase-activating protein family. It interacts directly with DAB2 and has distinct cellular functions such as modulating different signal cascades associated with cell proliferation, survival, apoptosis and metastasis. Recently, DAB2IP has been found significantly down regulated in multiple types of cancer. The aberrant alteration of DAB2IP in cancer is caused by a variety of mechanisms, including the aberrant promoter methylation, histone deacetylation, and others. Reduced expression of DAB2IP in neoplasm may indicate a poor prognosis of many malignant cancers. Moreover, DAB2IP stands for a promising direction for developing targeted therapies due to its capacity to inhibit tumor cell growth in vitro and in vivo. Here, we summarize the present understanding of the tumor suppressive role of DAB2IP in cancer progression; the mechanisms underlying the dysregulation of DAB2IP; the gene functional mechanism and the prospects of DAB2IP in the future cancer research.

Resveratrol Ameliorates Alcoholic Fatty Liver by Inducing Autophagy

Alcoholic fatty liver (AFL) is early stage of alcoholic liver disease, which can progress to steatohepatitis, fibrosis, and cirrhosis if alcohol consumption is continued. The pathogenesis of AFL is associated with excessive lipid accumulation in hepatocytes. Resveratrol (RES), a dietary polyphenol found in red wines and grapes, has been shown to have a hepatoprotective effect. Autophagy is a crucial physiological process in cellular catabolism that involves the regulation of lipid droplets. Autophagy maintains a balance between protein synthesis, degradation and self-recycling. In the present study, we evaluated the protective effects of RES (10[Formula: see text]mg/kg, 30[Formula: see text]mg/kg, 100[Formula: see text]mg/kg) on AFL mice fed with an ethanol Lieber-DeCarli liquid diet, and HepG2 cells in the presence of oleic acid and alcohol to investigate whether resveratrol could induce autophagy to attenuate lipid accumulation. The results showed that RES (30[Formula: see text]mg/kg and 100[Formula: see text]mg/kg) treatment significantly attenuated hepatic steatosis and lowered the activities of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), triglyceride (TG), low density lipoprotein cholesterol (LDL-C). H&E staining showed that RES reduced hepatic lipid accumulation. Transmission electron microscopy (TEM) images showed that RES treatment increased the number of autophagosomes and promoted the formation of autophagy. Western blot analysis showed that RES treatment increased the levels of microtubule-associated protein light chain3- II (LC3-II) and Beclin1, decreased expression of p62 protein. In addition, in vitro studies also demonstrated that RES led to the formation of acidic vesicular organelles (AVOs), however, 3-Methyladenine (3-MA), a specific inhibitor of autophagy, obviously inhibited the above effects of RES. In conclusion, RES has protective effects on alcoholic hepatic steatosis, and the potential mechanism might be involved in inducing autophagy.

Tumor suppressor protein DAB2IP participates in chromosomal stability maintenance through activating spindle assembly checkpoint and stabilizing kinetochore-microtubule attachments

Defects in kinetochore-microtubule (KT-MT) attachment and the spindle assembly checkpoint (SAC) during cell division are strongly associated with chromosomal instability (CIN). CIN has been linked to carcinogenesis, metastasis, poor prognosis and resistance to cancer therapy. We previously reported that the DAB2IP is a tumor suppressor, and that loss of DAB2IP is often detected in advanced prostate cancer (PCa) and is indicative of poor prognosis. Here, we report that the loss of DAB2IP results in impaired KT-MT attachment, compromised SAC and aberrant chromosomal segregation. We discovered that DAB2IP directly interacts with Plk1 and its loss inhibits Plk1 kinase activity, thereby impairing Plk1-mediated BubR1 phosphorylation. Loss of DAB2IP decreases the localization of BubR1 at the kinetochore during mitosis progression. In addition, the reconstitution of DAB2IP enhances the sensitivity of PCa cells to microtubule stabilizing drugs (paclitaxel, docetaxel) and Plk1 inhibitor (BI2536). Our findings demonstrate a novel function of DAB2IP in the maintenance of KT-MT structure and SAC regulation during mitosis which is essential for chromosomal stability.

miR-92b targets DAB2IP to promote EMT in bladder cancer migration and invasion

Muscle-invasive or metastatic bladder cancer (BCa) has a very poor prognosis; however, its mechanisms remain largely unknown. Previous studies have discovered multiple microRNAs (miRs) that are involved in BCa progression and regarded as potential biomarkers or therapeutic targets. In this study, we demonstrated that miR-92b could uniquely promote cell migration and invasion of BCa cells, but had no effect on cell proliferation. Mechanistically, our data provided evidence to verify that miR-92b was able to directly target DAB2IP, a well-known tumor suppressor, and inhibit epithelial‑mesenchymal transition of BCa cells. Moreover, the increased expression levels of miR-92b were negatively correlated with DAB2IP, and predicted poor prognosis of patients with BCa. Overall, this study reveals a new promising biomarker and its mechanisms contributing to BCa invasion or metastasis.

Resveratrol Attenuates Aβ25-35 Caused Neurotoxicity by Inducing Autophagy Through the TyrRS-PARP1-SIRT1 Signaling Pathway

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of β-amyloid peptide (Aβ) and loss of neurons. Resveratrol (RSV) is a natural polyphenol that has been found to be beneficial for AD through attenuation of Aβ-induced toxicity in neurons both in vivo and in vitro. However, the specific underlying mechanisms remain unknown. Recently, autophagy was found to protect neurons from toxicity injuries via degradation of impaired proteins and organelles. Therefore, the aim of this study was to determine the role of autophagy in the anti-neurotoxicity effect of RSV in PC12 cells. We found that RSV pretreatment suppressed β-amyloid protein fragment 25-35 (Aβ25-35)-induced decrease in cell viability. Expression of light chain 3-II, degradation of sequestosome 1, and formation of autophagosomes were also upregulated by RSV. Suppression of autophagy by 3-methyladenine abolished the favorable effects of RSV on Aβ25-35-induced neurotoxicity. Furthermore, RSV promoted the expression of sirtuin 1 (SIRT1), auto-poly-ADP-ribosylation of poly (ADP-ribose) polymerase 1 (PARP1), as well as tyrosyl transfer-RNA (tRNA) synthetase (TyrRS). Nevertheless, RSV-mediated autophagy was markedly abolished with the addition of inhibitors of SIRT1 (EX527), nicotinamide phosphoribosyltransferase (STF-118804), PARP1 (AG-14361), as well as SIRT1 and TyrRS small interfering RNA transfection, indicating that the action of RSV on autophagy induction was dependent on TyrRS, PARP1 and SIRT1. In conclusion, RSV attenuated neurotoxicity caused by Aβ25-35 through inducing autophagy in PC12 cells, and the autophagy was partially mediated via activation of the TyrRS-PARP1-SIRT1 signaling pathway.

Radiosensitization by PARP Inhibition in DNA Repair Proficient and Deficient Tumor Cells: Proliferative Recovery in Senescent Cells

Radiotherapy continues to be a primary modality in the treatment of cancer. In addition to promoting apoptosis, radiation-induced DNA damage can promote autophagy and senescence, both of which can theoretically function to prolong tumor survival. In this work, we tested the hypothesis that autophagy and/or senescence could be permissive for DNA repair, thereby facilitating tumor cell recovery from radiation-induced growth arrest and/or cell death. In addition, studies were designed to elucidate the involvement of autophagy and senescence in radiosensitization by PARP inhibitors and the re-emergence of a proliferating tumor cell population. In the context of this work, the relationship between radiation-induced autophagy and senescence was also determined. Studies were performed using DNA repair-proficient HCT116 colon carcinoma cells and a repair-deficient ligase IV(-/-) isogenic cell line. Exposure to radiation promoted a parallel induction of autophagy and senescence that was strongly correlated with the extent of persistent H2AX phosphorylation in both cell lines, however, inhibition of autophagy failed to suppress senescence, indicating that the two responses were dissociable. Exposure to radiation resulted in a transient arrest in the HCT116 cells while arrest was prolonged in the ligase IV(-/-) cells, however, both cell lines ultimately recovered proliferative function, which may reflect maintenance of DNA repair capacity. The PARP inhibitors, olaparib and niraparib, increased the extent of persistent DNA damage induced by radiation exposure as well as the extent of both autophagy and senescence. Neither cell line underwent significant apoptosis by radiation exposure alone or in the presence of the PARP inhibitors. Inhibition of autophagy failed to attenuate radiosensitization, indicating that autophagy was not involved in the action of the PARP inhibitors. As with radiation alone, despite sensitization by PARP inhibition, proliferative recovery was evident within a period of 10-20 days. While inhibition of DNA repair via PARP inhibition may initially sensitize tumor cells to radiation via the promotion of senescence, this strategy does not appear to interfere with proliferative recovery, which could ultimately contribute to disease recurrence.

TNKS1BP1 functions in DNA double-strand break repair though facilitating DNA-PKcs autophosphorylation dependent on PARP-1

TNKS1BP1 was originally identified as an interaction protein of tankyrase 1, which belongs to the poly(ADP-ribose) polymerase (PARP) superfamily. PARP members play important roles for example in DNA repair, telomere stability and mitosis regulation. Although the TNKS1BP1 protein was considered to be a poly(ADP-ribosyl)ation acceptor of tankyrase 1, its function is still unknown. Here we firstly identified that TNKS1BP1 was up-regulated by ionizing radiation (IR) and the depletion of TNKS1BP1 significantly sensitized cancer cells to IR. Neutral comet assay, pulsed-field gel electrophoresis, and γH2AX foci analysis indicated that TNKS1BP1 is required for the efficient repair of DNA double-strand breaks (DSB). The TNKS1BP1 protein was demonstrated to interact with DNA-dependent protein kinase (DNA-PKcs) and poly(ADP-ribose) polymerase 1 (PARP-1), by co-immunoprecipitation analysis. Moreover, TNKS1BP1 was shown to promote the association of PARP-1 and DNA-PKcs. Overexpression of TNKS1BP1 induced the autophosphorylation of DNA-PKcs/Ser2056 in a PARP-1 dependent manner, which contributed to an increased capability of DNA DSB repair. Inhibition of PARP-1 blocked the TNKS1BP1-mediated DNA-PKcs autophosphorylation and attenuated the PARylation of DNA-PKcs. TNKS1BP1 is a newly described component of the DNA DSB repair machinery, which provides much more mechanistic evidence for the rationale of developing effective anticancer measures by targeting PARP-1 and DNA-PKcs.

Cellular Pathways in Response to Ionizing Radiation and Their Targetability for Tumor Radiosensitization

During the last few decades, improvements in the planning and application of radiotherapy in combination with surgery and chemotherapy resulted in increased survival rates of tumor patients. However, the success of radiotherapy is impaired by two reasons: firstly, the radioresistance of tumor cells and, secondly, the radiation-induced damage of normal tissue cells located in the field of ionizing radiation. These limitations demand the development of drugs for either radiosensitization of tumor cells or radioprotection of normal tissue cells. In order to identify potential targets, a detailed understanding of the cellular pathways involved in radiation response is an absolute requirement. This review describes the most important pathways of radioresponse and several key target proteins for radiosensitization.

NSCLC cells demonstrate differential mode of cell death in response to the combined treatment of radiation and a DNA-PKcs inhibitor

The current standard of care for lung cancer consists of concurrent chemotherapy and radiation. Several studies have shown that the DNA-PKcs inhibitor NU7441 is a highly potent radiosensitizer, however, the mechanism of NU7441's anti-proliferation effect has not been fully elucidated. In this study, the combined effect of NU7441 and ionizing radiation (IR) in a panel of non-small cell lung cancer cell lines (A549, H460 and H1299) has been investigated. We found that NU7441 significantly enhances the effect of IR in all cell lines. The notable findings in response to this combined treatment are (i) prolonged delay in IR-induced DNA DSB repair, (ii) induced robust G2/M checkpoint, (iii) increased aberrant mitosis followed by mitotic catastrophe specifically in H1299, (iv) dramatically induced autophagy in A549 and (v) IR-induced senescence specifically in H460. H1299 cells show greater G2 checkpoint adaptation after combined treatment, which can be attributed to higher expression level of Plk1 compared to A549 and H460. The enhanced autophagy after NU7441 treatment in A549 is possibly due to the higher endogenous expression of pS6K compared to H1299 and H460 cells. In conclusion, choice of cell death pathway is dependent on the mutation status and other genetic factors of the cells treated.

Combining carbon ion irradiation and non-homologous end-joining repair inhibitor NU7026 efficiently kills cancer cells

Background

Our previous data demonstrated that targeting non-homologous end-joining repair (NHEJR) yields a higher radiosensitivity than targeting homologous recombination repair (HRR) to heavy ions using DNA repair gene knockouts (KO) in mouse embryonic fibroblast (MEF). In this study, we determined if combining the use of an NHEJR inhibitor with carbon (C) ion irradiation was more efficient in killing human cancer cells compared with only targeting a HRR inhibitor.

Methods

The TP53-null human non-small cell lung cancer cell line H1299 was used for testing the radiosensitizing effect of NHEJR-related DNA-dependent protein kinase (DNA-PK) inhibitor NU7026, HRR-related Rad51 inhibitor B02, or both to C ion irradiation using colony forming assays. The mechanism underlying the inhibitor radiosensitization was determined by flow cytometry after H2AX phosphorylation staining. HRR-related Rad54-KO, NHEJR-related Lig4-KO, and wild-type TP53-KO MEF were also included to confirm the suppressing effect specificity of these inhibitors.

Results

NU7026 showed significant sensitizing effect to C ion irradiation in a concentration-dependent manner. In contrast, B02 showed a slight sensitizing effect to C ion irradiation. The addition of NU7026 significantly increased H2AX phosphorylation after C ion and x-ray irradiations in H1299 cells, but not B02. NU7026 had no effect on radiosensitivity to Lig4-KO MEF and B02 had no effect on radiosensitivity to Rad54-KO MEF in both irradiations.

Conclusion

These results suggest that inhibitors targeting the NHEJR pathway could significantly enhance radiosensitivity of human cancer cells to C ion irradiation, rather than targeting the HRR pathway.

Electronic supplementary material

The online version of this article (doi:10.1186/s13014-015-0536-z) contains supplementary material, which is available to authorized users.

Pretreatment biopsy analysis of DAB2IP identifies subpopulation of high-risk prostate cancer patients with worse survival following radiation therapy

Decreased expression of tumor suppressor DAB2IP is linked to aggressive cancer and radiation resistance in several malignancies, but clinical survival data is largely unknown. We hypothesized that pretreatment DAB2IP reduction would predict worse prostate cancer‐specific survival (PCSS). Immunohistochemistry of pretreatment biopsies was scored by an expert genitourinary pathologist. Other endpoints analyzed include freedom from biochemical failure (FFBF), castration resistance‐free survival (CRFS), and distant metastasis‐free survival (DMFS). Seventy‐nine patients with NCCN‐defined high‐risk prostate cancer treated with radiotherapy from 2005 to 2012 at our institution were evaluated. Twenty‐eight percent (22/79) of pretreatment biopsies revealed DAB2IP‐reduction. The median follow up times were 4.8 years and 5.3 years for patients in the DAB2IP‐reduced group and DAB2IP‐retained group, respectively. Patients with reduced DAB2IP demonstrated worse outcome compared to patients retaining DAB2IP, including FFBF (4‐year: 34 vs. 92%; P < 0.0001), CRFS (4‐year: 58 vs. 96%; P = 0.0039), DMFS (4‐year: 58 vs. 100%; P = 0.0006), and PCSS (5‐year: 83 vs. 100%; P = 0.0102). Univariate analysis showed T stage, N stage, and Gleason score were statistically significant variables. Pretreatment tumor DAB2IP status remained significant in multivariable analyses. This study suggests that about one‐fourth of men with high‐risk prostate cancer have decreased tumor expression of DAB2IP. This subpopulation with reduced DAB2IP has a suboptimal response and worse malignancy‐specific survival following radiation therapy and androgen deprivation. DAB2IP loss may be a genetic explanation for the observed differences in aggressive tumor characteristics and radiation resistance. Further study into improving treatment response and survival in this subpopulation is warranted.

Next generation sequencing profiling identifies miR-574-3p and miR-660-5p as potential novel prognostic markers for breast cancer

Background

Prognostication of Breast Cancer (BC) relies largely on traditional clinical factors and biomarkers such as hormone or growth factor receptors. Due to their suboptimal specificities, it is challenging to accurately identify the subset of patients who are likely to undergo recurrence and there remains a major need for markers of higher utility to guide therapeutic decisions. MicroRNAs (miRNAs) are small non-coding RNAs that function as post-transcriptional regulators of gene expression and have shown promise as potential prognostic markers in several cancer types including BC.

Results

In our study, we sequenced miRNAs from 104 BC samples and 11 apparently healthy normal (reduction mammoplasty) breast tissues. We used Case–control (CC) and Case-only (CO) statistical paradigm to identify prognostic markers. Cox-proportional hazards regression model was employed and risk score analysis was performed to identify miRNA signature independent of potential confounders. Representative miRNAs were validated using qRT-PCR. Gene targets for prognostic miRNAs were identified using in silico predictions and in-house BC transcriptome dataset. Gene ontology terms were identified using DAVID bioinformatics v6.7. A total of 1,423 miRNAs were captured. In the CC approach, 126 miRNAs were retained with predetermined criteria for good read counts, from which 80 miRNAs were differentially expressed. Of these, four and two miRNAs were significant for Overall Survival (OS) and Recurrence Free Survival (RFS), respectively. In the CO approach, from 147 miRNAs retained after filtering, 11 and 4 miRNAs were significant for OS and RFS, respectively. In both the approaches, the risk scores were significant after adjusting for potential confounders. The miRNAs associated with OS identified in our cohort were validated using an external dataset from The Cancer Genome Atlas (TCGA) project. Targets for the identified miRNAs were enriched for cell proliferation, invasion and migration.

Conclusions

The study identified twelve non-redundant miRNAs associated with OS and/or RFS. These signatures include those that were reported by others in BC or other cancers. Importantly we report for the first time two new candidate miRNAs (miR-574-3p and miR-660-5p) as promising prognostic markers. Independent validation of signatures (for OS) using an external dataset from TCGA further strengthened the study findings.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1899-0) contains supplementary material, which is available to authorized users.

DAB2IP regulates the chemoresistance to pirarubicin and tumor recurrence of non-muscle invasive bladder cancer through STAT3/Twist1/P-glycoprotein signaling

There is a high frequency of tumor recurrence in non-muscle invasive bladder cancer (NMIBC) after transurethral resection and postoperative intravesical chemotherapy, however, the molecular mechanisms leading to the chemoresistance and tumor re-growth remain largely unknown. In this study, we observed a significant decrease of DAB2IP expression in high-grade and recurrent NMIBC specimens, which was negatively correlated with Twist1 expression and predicted a lower recurrence-free survival of patients. Mechanistically, DAB2IP could inhibit the phosphorylation and transactivation of STAT3, and then subsequently suppress the expression of Twist1 and its target gene P-glycoprotein, both of which were crucial for the pirarubicin chemoresistance and tumor re-growth of bladder cancer cells. Overall, this study reveals a new promising biomarker modulating the chemoresistance and tumor recurrence of NMIBC after bladder preservation surgery.

microRNA-32 induces radioresistance by targeting DAB2IP and regulating autophagy in prostate cancer cells

The aberrant expression of microRNAs (miRNAs/miRs) has been found in numerous cancer types. miR-32 is an oncomiR in prostate cancer (PCa), however, the mechanisms by which miR-32 functions as a regulator of radiotherapy response and resistance in PCa are largely unknown. In the present study, it was found that DAB2 interacting protein (DAB2IP), the miR-32-dependent tumor-suppressor gene, was downregulated and induced autophagy and inhibited radiotherapy-induced apoptosis in PCa cells. miR-32 expression was upregulated or overexpressed in PCa, and miR-32 inhibited DAB2IP expression through a direct binding site within the DAB2IP 3′ untranslated region. miR-32 mimics enhanced tumor cell survival and decreased radiosensitivity in the PCa cells, which were reversed by miR-32 inhibitor. Flow cytometric analysis revealed that overexpressed miR-32, consistent with the DAB2IP-knockdown results, reduced ionizing radiation (IR)-induced cell apoptosis, which was restored by 4 nM brefeldin A treatment. More significantly, the overexpression of miR-32 and the knockdown of DAB2IP enhanced autophagy in the IR-treated PCa cells. miR-32 regulated the expression of autophagy-related proteins, such as DAB2IP, Beclin 1 and Light chain 3β I/II, as well as phosphorylation of S6 kinase and mammalian target of rapamycin. In conclusion, these data provide novel insights into the mechanisms governing the regulation of DAB2IP expression by miR-32 and their possible contribution to autophagy and radioresistance in PCa.

Sensitization of radio-resistant prostate cancer cells with a unique cytolethal distending toxin

Cytolethal distending toxin (CDT) produced by Campylobacter jejuni is a genotoxin that induces cell-cycle arrest and apoptosis in mammalian cells. Recent studies have demonstrated that prostate cancer (PCa) cells can acquire radio-resistance when DOC-2/DAB2 interactive protein (DAB2IP) is downregulated. In this study, we showed that CDT could induce cell death in DAB2IP-deficient PCa cells. A combination of CDT and radiotherapy significantly elicited cell death in DAB2IP-deficient PCa cells by inhibiting the repair of ionizing radiation (IR)-induced DNA double-strand break (DSB) during G2/M arrest, which is triggered by ataxia telangiectasia mutated (ATM)-dependent DNA damage checkpoint responses. We also found that CDT administration significantly increased the efficacy of radiotherapy in a xenograft mouse model. These results indicate that CDT can be a potent therapeutic agent for radio-resistant PCa.

Reciprocal regulation of hypoxia-inducible factor 2α and GLI1 expression associated with the radioresistance of renal cell carcinoma

PURPOSE

Renal cell carcinoma (RCC) is often considered a radioresistant tumor, but the molecular mechanism underlying its radioresistance is poorly understood. This study explored the roles of hypoxia-inducible factor 2α (HIF2α) and sonic hedgehog (SHH)-GLI1 signaling in mediating the radioresistance of RCC cells and to unveil the interaction between these 2 signaling pathways.

METHODS AND MATERIALS

The activities of SHH-GLI1 signaling pathway under normoxia and hypoxia in RCC cells were examined by real-time polymerase chain reaction, Western blot, and luciferase reporter assay. The expression of HIF2α and GLI1 in RCC patients was examined by immunohistochemistry, and their correlation was analyzed. Furthermore, RCC cells were treated with HIF2α-specific shRNA (sh-HIF2α), GLI1 inhibitor GANT61, or a combination to determine the effect of ionizing radiation (IR) on RCC cells based on clonogenic assay and double-strand break repair assay.

RESULTS

RCC cells exhibited elevated SHH-GLI1 activities under hypoxia, which was mediated by HIF2α. Hypoxia induced GLI1 activation through SMO-independent pathways that could be ablated by PI3K inhibitor or MEK inhibitor. Remarkably, the SHH-GLI1 pathway also upregulated HIF2α expression in normoxia. Apparently, there was a positive correlation between HIF2α and GLI1 expression in RCC patients. The combination of sh-HIF2α and GLI1 inhibitor significantly sensitized RCC cells to IR.

CONCLUSIONS

Cross-talk between the HIF2α and SHH-GLI1 pathways was demonstrated in RCC. Cotargeting these 2 pathways, significantly sensitizing RCC cells to IR, provides a novel strategy for RCC treatment.

VAMP8 facilitates cellular proliferation and temozolomide resistance in human glioma cells

BACKGROUND

Malignant glioma is a common and lethal primary brain tumor in adults. Here we identified a novel oncoprotein, vesicle-associated membrane protein 8 (VAMP8), and investigated its roles in tumorigenisis and chemoresistance in glioma.

METHODS

The expression of gene and protein were determined by quantitative PCR and Western blot, respectively. Histological analysis of 282 glioma samples and 12 normal controls was performed by Pearson's chi-squared test. Survival analysis was performed using the log-rank test and Cox proportional hazards regression. Cell proliferation and cytotoxicity assay were conducted using Cell Counting Kit-8. Autophagy was detected by confocal microscopy and Western blot.

RESULTS

VAMP8 was significantly overexpressed in human glioma specimens and could become a potential novel prognostic and treatment-predictive marker for glioma patients. Overexpression of VAMP8 promoted cell proliferation in vitro and in vivo, whereas knockdown of VAMP8 attenuated glioma growth by arresting cell cycle in the G0/G1 phase. Moreover, VAMP8 contributed to temozolomide (TMZ) resistance by elevating the expression levels of autophagy proteins and the number of autophagosomes. Further inhibition of autophagy via siRNA-mediated knockdown of autophagy-related gene 5 (ATG5) or syntaxin 17 (STX17) reversed TMZ resistance in VAMP8-overexpressing cells, while silencing of VAMP8 impaired the autophagic flux and alleviated TMZ resistance in glioma cells.

CONCLUSION

Our findings identified VAMP8 as a novel oncogene by promoting cell proliferation and therapeutic resistance in glioma. Targeting VAMP8 may serve as a potential therapeutic regimen for the treatment of glioma.

Cancer subclonal genetic architecture as a key to personalized medicine

The future of personalized oncological therapy will likely rely on evidence-based medicine to integrate all of the available evidence to delineate the most efficacious treatment option for the patient. To undertake evidence-based medicine through use of targeted therapy regimens, identification of the specific underlying causative mutation(s) driving growth and progression of a patient's tumor is imperative. Although molecular subtyping is important for planning and treatment, intraclonal genetic diversity has been recently highlighted as having significant implications for biopsy-based prognosis. Overall, delineation of the clonal architecture of a patient's cancer and how this will impact on the selection of the most efficacious therapy remain a topic of intense interest.

DOC-2/DAB2 interacting protein status in high-risk prostate cancer correlates with outcome for patients treated with radiation therapy

PURPOSE

This pilot study investigates the role of DOC-2/DAB2 Interacting Protein (DAB2IP) and enhancer of zeste homolog 2 (EZH2) as prognostic biomarkers in high-risk prostate cancer patients receiving definitive radiation therapy.

METHODS AND MATERIALS

Immunohistochemistry was performed and scored by an expert genitourinary pathologist. Clinical endpoints evaluated were freedom from biochemical failure (FFBF), castration resistance-free survival (CRFS), and distant metastasis-free survival (DMFS). Log-rank test and Cox regression were used to determine significance of biomarker levels with clinical outcome.

RESULTS

Fifty-four patients with high-risk prostate cancer (stage ≥ T3a, or Gleason score ≥ 8, or prostate-specific antigen level ≥ 20 ng/mL) treated with radiation therapy from 2005 to 2012 at our institution were evaluated. Nearly all patients expressed EZH2 (98%), whereas 28% of patients revealed DAB2IP reduction and 72% retained DAB2IP. Median follow-up was 34.0 months for DAB2IP-reduced patients, 29.9 months for DAB2IP-retained patients, and 32.6 months in the EZH2 study. Reduction in DAB2IP portended worse outcome compared with DAB2IP-retained patients, including FFBF (4-year: 37% vs 89%, P=.04), CRFS (4-year: 50% vs 90%, P=.02), and DMFS (4-year: 36% vs 97%, P=.05). Stratified EZH2 expression trended toward significance for worse FFBF and CRFS (P=.07). Patients with reduced DAB2IP or highest-intensity EZH2 expression exhibited worse FFBF (4-year: 32% vs 95%, P=.02), CRFS (4-year: 28% vs 100%, P<.01), and DMFS (4-year: 39% vs 100%, P=.04) compared with the control group.

CONCLUSION

Loss of DAB2IP is a potent biomarker that portends worse outcome despite definitive radiation therapy for patients with high-risk prostate cancer. Enhancer of zeste homolog 2 is expressed in most high-risk tumors and is a less potent discriminator of outcome in this study. The DAB2IP status in combination with degree of EZH2 expression may be useful for determining patients with worse outcome within the high-risk prostate cancer population.

Mechanisms of radiation toxicity in transformed and non-transformed cells

Radiation damage to biological systems is determined by the type of radiation, the total dosage of exposure, the dose rate, and the region of the body exposed. Three modes of cell death—necrosis, apoptosis, and autophagy—as well as accelerated senescence have been demonstrated to occur in vitro and in vivo in response to radiation in cancer cells as well as in normal cells. The basis for cellular selection for each mode depends on various factors including the specific cell type involved, the dose of radiation absorbed by the cell, and whether it is proliferating and/or transformed. Here we review the signaling mechanisms activated by radiation for the induction of toxicity in transformed and normal cells. Understanding the molecular mechanisms of radiation toxicity is critical for the development of radiation countermeasures as well as for the improvement of clinical radiation in cancer treatment.

Overcoming intratumor heterogeneity of polygenic cancer drug resistance with improved biomarker integration

Improvements in technology and resources are helping to advance our understanding of cancer-initiating events as well as factors involved with tumor progression, adaptation, and evasion of therapy. Tumors are well known to contain diverse cell populations and intratumor heterogeneity affords neoplasms with a diverse set of biologic characteristics that can be used to evolve and adapt. Intratumor heterogeneity has emerged as a major hindrance to improving cancer patient care. Polygenic cancer drug resistance necessitates reconsidering drug designs to include polypharmacology in pursuit of novel combinatorial agents having multitarget activity to overcome the diverse and compensatory signaling pathways in which cancer cells use to survive and evade therapy. Advances will require integration of different biomarkers such as genomics and imaging to provide for more adequate elucidation of the spatially varying location, type, and extent of diverse intratumor signaling molecules to provide for a rationale-based personalized cancer medicine strategy.