DNA Polymerase θ: a Multifunctional and Error-prone DNA End Repair Enzyme / 生物化学与生物物理进展

DNA polymerase theta (Polθ), also known as DNA polymerase θ, is the member of the DNA polymerase A family and plays a crucial role in the repair of DNA double-strand breaks (DSB). Polθ has 3 distinct structural domains: the N-terminal helicase-like domain with a conserved sequence, the C-terminal polymerase domain, and the central domain, which is a disordered sequence connecting these two regions. Notably, Polθ is the only known polymerase in eukaryotes that possesses helicase activity. However, it is also an error-prone polymerase. When DNA DSBs occur, a specialized network consisting of at least 4 pathways, including classical-non homologous end joining (C-NHEJ), homologous recombination (HR), single-strand annealing (SSA), and alternative-end joining (Alt-EJ), is responsible for repairing DNA damage caused by DSBs. In the absence of major DNA repair pathways like HR, cells rely on Alt-EJ pathway mediated by Polθ to repair damaged DNA and maintain genomic stability. Nevertheless, due to the low fidelity of Polθ, Alt-EJ repair often leads to errors. Depletion of Polθ has shown to increases DSB formation and compromise genomic stability. Conversely, overexpression of Polθ has been associated with increases DNA damage markers and impairs cell cycle progression. As a result, the impact of Polθ on genome stability remains controversial. Furthermore, overexpression of Polθ is frequently observed in cancer and is associated with a characteristic mutational signature and poor prognosis. Depleting Polθ in an HR-deficient background has been shown to impair cell viability, suggesting a synthetic lethal (SL) relationship between Polθ and HR factors. In recent years, targeted chemotherapy drugs that inhibit tumor growth have gained significant attention. However, off-target effects and drug resistance pose challenges for clinical application, particularly with poly-ADP-ribose polymerase inhibitor (PARPi). Blocking Polθ activity in HR-deficient tumor cells has been found to reverse PARPi resistance, making Polθ a very promising therapeutic target in cancer treatment. The availability of crystal structures for both helicase and polymerase domain has facilitated the design of potent inhibitors of Polθ. Currently, several highly specific and effective small molecule inhibitors targeting Polθ, such as Novobiocin, RP-6685, and ART558, have been reported to effectively block various cancers with HR deficiency. The initial success of these inhibitors points to new directions for treating BRCA1/2-mutated tumors. Additionally, reducing the Alt-EJ repair pathway mediated by Polθ can improve HR repair efficiency and increase the chance of exogenous gene target integration (TI), suggesting potential new applications for Polθ inhibitors. This article reviews the recent research progress on the molecular function of Polθ and its involvement in the Alt-EJ pathway modification mechanism, providing insights for a deeper understanding of this field.

Astrocyte elevated gene-1 serves as a target of miR542 to promote glioblastoma proliferation and invasion / 中华医学杂志(英文版)

BACKGROUND@#Epithelial to mesenchymal transition (EMT) is strongly linked with tumor invasion and metastasis, which performs a vital role in carcinogenesis and cancer progression. Emerging evidence suggests that microRNAs (miRNAs) expression are closely associated to EMT by regulating targeted genes. MiR542 has been found to be involved in the EMT program and bound up with various cancers. However, the functions of miR542 and its underlying mechanism in glioblastoma multiforme (GBM) remain largely unknown. In the current study, we investigated the effect of astrocyte elevated gene-1 (AEG-1) on U251 cells aggressiveness, proliferation, apoptosis, and cell cycle.@*METHODS@#The screening of targeted miRNAs was performed, as well as the functional roles and mechanisms of miR542 were explored.@*RESULTS@#MiR542 was selected as the target because of the most significantly differential expression and this high level of expression negatively correlated with cell migration and proliferation, which suggested that miR542 could be a novel tumor suppressor. Moreover, we confirmed that AEG-1 was a direct targeted gene of miR542 by luciferase activity assay, reverse transcription-polymerase chain reaction, and immunoblotting analysis. Furthermore, miR542 suppressed the expression of AEG-1, which upgraded the level of E-cadherin and degraded Vimentin expression contributing to retraining EMT.@*CONCLUSION@#The in vitro findings demonstrated that miR542 inhibited the migration and proliferation of U251 cells and suppressed EMT through targeting AEG-1, indicating that miR542 may be a potential anti-cancer target for GBM.

Evaluation of cytotoxicity of stearoyl gemcitabine-loaded PLGA nanoparticles to Lewis lung cancer cells / 中国免疫学杂志

Objective:To investigate the anti-proliferation effect of 4-(N)-stearoyl gemcitabine-loaded poly(lactic-co-glycolic) acid nanoparticles(GemC18-PLGA-NPs) on Lewis lung cancer cells(LLC) in vitro.Methods: Lewis cells were incubated with GemC18-PLGA-NPs,free GemC18,gemcitabine HCl(GemHCl) or GemC18-free blank nanoparticles(PLGA-NPs) respectively and cell viability was determined using an MTT assay after 24,48 or 72 h of incubation.The apoptosis rate after 48 and 72 h of incubation were measured by flow cytometry.Results:GemC18-PLGA-NPs,GemC18,and GemHCl all significantly inhibited the growth of LLC cells, and the survival rate of GemHCl group was lowest,GemC18-PLGA-NPs group had the highest survival rate.The cell survival rate of GemC18-PLGA-NPs after 72 h was significantly higher than that of GemHCl (P<0.05) at the concentration of 1 μmol/L,indicating that it had a significant drug release effect.PLGA-NPs group produced trifle inhibition on the Lewis cells without correlation to time or concentration.Conclusion:GemC18-PLGA-NPs have significant anti-proliferation effect on mouse Lewis lung cancer cells in vitro.

Cervical lymph node metastasis of hypopharyngeal carcinoma / 中华耳鼻咽喉头颈外科杂志

<p><b>OBJECTIVE</b>To investigate the characteristic of cervical lymph node metastasis of hypopharyngeal carcinoma and its influence to the prognosis.</p><p><b>METHODS</b>One hundred and eight hypopharyngeal carcinoma patients who accepted treatments in the 1st Affiliated Hospital of China Medical University from 1985 to 2000 were reviewed retrospectively. All of them accepted surgical treatment without pre-operative chemotherapy or radiotherapy. Stage was made according to the standard of International Union Against Cancer (UICC) in 1992. Specimens of the patients were carefully examined to confirm the primary site of the tumor and the distribution of cervical lymph node metastasis. Pathological differentiations of the tumor were classified into high, middle and low category. Kaplan-Meier method was used to estimate the 3rd, 5th years survival.</p><p><b>RESULTS</b>The rates of lymph node metastasis of was 45.8% for patients with TI and T2 disease, 79.8% for those with T3 and T4, and 75.0% (81/108)for the whole patients(P < 0.05). Patients with pyriform sinus cancer occupied 92.6% (100/108) of all the cases. Cervical lymph node metastasis rate of pyriform sinus cancer and posterior pharyngeal wall cancer were 74. 0% and 87. 5% respectively (P > 0.05). Cervical lymph node metastasis rate of patients with the high, middle and low differentiation tumor were 72. 2% , 67.6% and 85.7% respectively (P > 0.05). The 3rd and 5th years survival rates of all patients were 67.53% and 29.87% respectively. The occurrence of cervical lymph node metastasis was 76.5% in the level II and III, and 8.6% in the level V and VI. CONCLUSIONS Cervical lymph node metastasis rate of hypopharyngeal carcinoma is high. Cervical lymph node metastasis was one of the most significant prognostic factors of hypopharyngeal carcinoma. With the increase of the cervical node metastasis, the 3rd and 5th years survival of the patients declined gradually.</p>