Possible Role of Mural Cell–Covered Mature Blood Vessels in Inducing Drug Resistance in Cancer-Initiating Cells

Progression of m6A in the tumor microenvironment: hypoxia, immune and metabolic reprogramming

Recently, N6-methyladenosine (m6A) has aroused widespread discussion in the scientific community as a mode of RNA modification. m6A comprises writers, erasers, and readers, which regulates RNA production, nuclear export, and translation and is very important for human health. A large number of studies have found that the regulation of m6A is closely related to the occurrence and invasion of tumors, while the homeostasis and function of the tumor microenvironment (TME) determine the occurrence and development of tumors to some extent. TME is composed of a variety of immune cells (T cells, B cells, etc.) and nonimmune cells (tumor-associated mesenchymal stem cells (TA-MSCs), cancer-associated fibroblasts (CAFs), etc.). Current studies suggest that m6A is involved in regulating the function of various cells in the TME, thereby affecting tumor progression. In this manuscript, we present the composition of m6A and TME, the relationship between m6A methylation and characteristic changes in TME, the role of m6A methylation in TME, and potential therapeutic strategies to provide new perspectives for better treatment of tumors in clinical work.

Emerging role of interactions between tumor angiogenesis and cancer stem cells

Tumor angiogenesis and cancer stem cells (CSCs) are two major hallmarks of solid tumors. They have long received attention for their critical roles in tumor progression, metastasis and recurrence. Meanwhile, plenty of evidence indicates the close association between CSCs and tumor vasculature. CSCs are proven to promote tumor angiogenesis, and the highly vascularized tumor microenvironment further maintains CSCs growth in return, thereby forming a hard-breaking vicious circle to promote tumor development. Hence, though monotherapy targeting tumor vasculature or CSCs has been extensively studied over the past decades, the poor prognosis has been limiting the clinical application. This review summarizes the crosstalk between tumor vasculature and CSCs with emphasis on small-molecule compounds and the associated biological signaling pathways. We also highlight the importance of linking tumor vessels to CSCs to disrupt the CSCs-angiogenesis vicious circle. More precise treatment regimens targeting tumor vasculature and CSCs are expected to benefit future tumor treatment development.

The role of N6-methyladenosine mRNA in the tumor microenvironment

In recent years, the most widely distributed eukaryotic messenger RNA (mRNA) modification, N6-methyladenosine (m6A), has received a large amount of interest, in part due to the development and advances of high-throughput RNA sequencing. The effects of m6A mRNA on tumor progression have been the most widely studied, and large amounts of conflicting data have been reported due to differences in tumor contexts, cell types or cell states. The majority of these studies were related to the significance of m6A mRNA on tumor cells, including on proliferation, stemness, invasion capability, etc. However, it has been noted that tumorigenesis and tumor progression cannot occur without support from the tumor microenvironment (TME), which contains multiple types of stromal cells, such as infiltrating immune cells (IICs), vascular cells, mesenchymal stem cells (MSCs), cancer-associated fibroblasts (CAFs), and various environmental factors. Here, we summarized the contributions of abnormal m6A mRNA in stromal cells within the TME and described the effects of m6A mRNA on TME remodeling.

Embryonic expression of GINS members in the development of the mammalian nervous system

The GINS (Go, Ichi, Nii, and San) complex contains four protein subunits (PSF1, PSF2, PSF3, and SLD5) and has been identified as a factor essential for the initiation and elongation stages of the DNA replication process. A previous study indicated that PSF2 participated in the developing central nervous system (CNS) of Xenopus laevis. However, the expression and function of GINS members in the mammalian developing nervous system remains unclear. Here, we examined the expression of GINS members in mice during nervous system development via immunofluorescence staining. At the beginning of neural development, PSF1 and SLD5 were highly expressed in neuroepithelial stem cells (NSCs) of the inner surface of neural tube (NT) and overlapped with proliferation marker Ki67. After entering the mid- and late-phase of neural development, PSF1 and SLD5 changed their regions of expression. These genes were highly expressed in dorsal root ganglion (DRG) progenitors, but they showed no overlap with Ki67 positive cells. Instead, a reduction of SLD5 expression promoted neuronal differentiation and maturation in the late-phase. PSF2 and PSF3 showed no tissue-specificity. PSF2 was constitutively and highly expressed whereas PSF3 was expressed at very low levels during neural development. In this study, we demonstrated variations in proteins and expression regions of the GINS members during mammalian CNS development and revealed a correlation between GINS expression and cell proliferation. Furthermore, we have suggested a novel function of GINS member SLD5, which regulates the differentiation of neural stem/progenitors.

PSF1 (Partner of SLD Five 1) is a Prognostic Biomarker in Patients with Non-small Cell Lung Cancer Treated with Surgery Following Preoperative Chemotherapy or Chemoradiotherapy

BACKGROUND

PSF1 (Partner of SLD Five 1) is an evolutionarily conserved DNA replication factor that is part of the GINS (Go, Ichi, Nii, and San) complex . The objective of this study was to evaluate the relationship between PSF1 expression and prognosis in patients with non-small cell lung cancer (NSCLC) treated with surgery following preoperative chemotherapy or chemoradiotherapy.

METHODS

Sixty-nine patients with NSCLC treated with surgery following preoperative chemotherapy or chemoradiotherapy who did not achieve pathologic complete response were enrolled. The status of PSF1 expression was evaluated by immunohistochemistry, and the relationship between expression of PSF1 and Ki-67 was determined, as well as correlations between PSF1 expression and prognosis.

RESULTS

We found that 27 of 69 patients' tumors (39 %) were positive for PSF1 expression. The Ki-67 index was significantly higher in the PSF1-positive versus the PSF1-negative group (p = 0.0026). Five-year, disease-free survival of the PSF1-positive group was significantly worse (17.7 vs. 44.3 %, p = 0.0088), and the 5-year overall survival also was worse (16.6 vs. 47.2 %, p = 0.0059). Moreover, PSF1 expression was found to be a significant independent prognostic factor for shorter survival by Cox multivariate analysis (hazard ratio 2.43, 95 % confidence interval 1.27-4.60, p = 0.0076).

CONCLUSIONS

PSF1 is a useful prognostic biomarker to stratify NSCLC patients treated with surgery following preoperative chemotherapy or chemoradiotherapy.

Tumor microenvironment for cancer stem cells

Tumor tissues consist of heterogeneous cancer cells including cancer stem cells (CSCs) that can terminally differentiate into cancer cells. Tissue-specific stem cells in normal organs maintain their stemness in a specific microenvironment, the stem cell niche; several studies have suggested that there are specific microenvironments that maintain CSCs in an immature phenotype. Cell types in a CSC niche vary from fibroblasts, to endothelial cells, immune cells, and so on; these non-cancer cells have been suggested to change their original features in the normal tissue/organ and to acquire a phenotype that protects CSCs from anticancer therapies. Therefore, to kill CSCs, we need to understand the cellular and molecular mechanisms involved in the maintenance of the immature phenotype of CSCs and in drug resistance.

Knockdown of PSF1 expression inhibits cell proliferation in lung cancer cells in vitro

Partner of sld five 1 (PSF1) is a member of the heterotetrameric complex termed GINS. Previous studies have shown that PSF1 is unregulated in several cancer and associated with tumor malignant characters. However, the effects of PSF1 in lung cancer are still unclear. The goal of this study was to investigate the effects of PSF1 on the proliferation capacities of lung cancer. To start with, expression of PSF1 in 22 human lung cancer samples and adjacent non-tumor samples were detected by real-time RT-PCR and Western blotting. Our results showed that PSF1 was overexpressed in lung cancer samples compared to adjacent non-tumor samples. To achieve better insights of PSF1 functions in lung cancer cells, we used PSF1-specific small interfering RNA (siRNA) successfully inhibit the expression of PSF1 in messenger RNA (mRNA) and protein levels. In addition, we used lung cancer cell lines with different p53 gene background (p53 null and p53 wild-type). The results showed that knockdown of PSF1 inhibited cell proliferation and caused cell cycle arrest of lung cancer cells in a p53-independent manner. Our data indicated that PSF1 is functionally involved in lung cancer cell proliferation and is a potential target for lung cancer therapy.