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.

Biological function of myeloid-derived suppressor cells and their related inhibitors:research advances / 国际药学研究杂志

Myeloid-derived suppressor cells(MDSC)are heterogeneous cells with the myeloid progenitor cells and the imma-ture myeloid cells accumulated in pathological conditions.MDSC can inhibit the host immune response to tumors via inhibiting the pro-liferation and cytotoxicity of T cells as well as promoting the proliferation of protumorigenic T regulatory cells(Treg).In addition,MD-SC can also promote the angiogenesis and the tumor invasion and metastasis.Therefore,MDSC are potential therapeutic targets for a variety of tumors.This review summarizes the biological function of MDSC along with the MDSC-targeted inhibitors and their applica-tions in cancer immunotherapy.

Establishment and evaluation of experimental sepsis mouse model / 中国实验血液学杂志

After treating with chemotherapy or immunosuppressant, malignant diseases of hematopoietic system such as leukemia, malignant lymphoma and aplastic anemia usually induced severe infection such as sepsis. Sepsis which is hard to be diagnosed causes high death rate. This study was purposed to establish an experimental sepsis mouse model so as to provide a basis for pathogenesis and intervention study. A classic caecal ligation and puncture (CLP) was used to establish experimental sepsis model. ELISA was used to detect levels of C5a, IL-6, TNFalpha, and IFN-gamma. Flow Cytometry was applied to measure apoptosis of lymphocytes in thymus and mesentery. The pathologic changes of thymus and spleen were confirmed by HE staining. The results showed that almost 70%-80% mice died at 72 hours after CLP. Only approximate 20% animal survived during finite time, mice in CLP group had significant weight lose. Meanwhile large release of different inflammatory mediators which are related with sepsis (C5a, IL-6, TNF-alpha, and IFN-gamma) was observed after CLP. Apoptosis of lymphocytes in thymus and mesentery lymphonodus was enhanced markedly after CLP. Significantly pathologic injury was also observed in thymus and spleen. It is concluded that a mouse model of experimental sepsis was successfully established by caecal ligation and puncture which can well mimic the clinical symptom of sepsis. The experimental sepsis mouse model provides an excellent tool for exploring the pathogenesis and intervention ways for sepsis accompanied with complicated malignant hematological diseases in vivo.