To understand chemoresistance in the context of cancer stem cells (CSC), a cisplatin resistance model was developed using a high-grade serous ovarian cancer patient-derived, cisplatin-sensitive sample, PDX4. As a molecular subtype-specific stem-like cell line, PDX4 was selected for its representative features, including its histopathological and BRCA2 mutation status, and exposed to cisplatin in vitro. In the cisplatin-resistant cells, transcriptomics were carried out, and cell morphology, protein expression, and functional status were characterized. Additionally, potential signaling pathways involved in cisplatin resistance were explored. Our findings reveal the presence of distinct molecular signatures and phenotypic changes in cisplatin-resistant PDX4 compared to their sensitive counterparts. Surprisingly, we observed that chemoresistance was not inherently linked with increased stemness. In fact, although resistant cells expressed a combination of EMT and stemness markers, functional assays revealed that they were less proliferative, migratory, and clonogenic-features indicative of an underlying complex mechanism for cell survival. Furthermore, DNA damage tolerance and cellular stress management pathways were enriched. This novel, syngeneic model provides a valuable platform for investigating the underlying mechanisms of cisplatin resistance in a clinically relevant context, contributing to the development of targeted therapies tailored to combat resistance in stem-like ovarian cancer.

Background: High heterogeneity of mesenchymal stem/stromal cells (MSCs) due to different degrees of differentiation of cell subpopulations poses a considerable challenge in preclinical studies. The cells at a pluripotent-like stage represent a stem cell population of interest for many researchers worldwide, which is worthy of identification, isolation, and functional characterization. In the current study, we asked whether Wharton's jelly-derived MSCs (WJ-MSCs) which express stage-specific embryonic antigen-4 (SSEA-4) can be considered as a pluripotent-like stem cell population. Methods: SSEA-4 expression in different culture conditions was compared and the efficiency of two cell separation methods were assessed: Magnetic Activated Cell Sorting (MACS) and Fluorescence Activated Cell Sorting (FACS). After isolation, SSEA-4+ cells were analyzed for the following parameters: the maintenance of the SSEA-4 antigen expression after cell sorting, stem cell-related gene expression, proliferation potential, clonogenicity, secretome profiling, and the ability to form spheres under 3D culture conditions. Results: FACS allowed for the enrichment of SSEA-4+ cell content in the population that lasted for six passages after sorting. Despite the elevated expression of stemness-related genes, SSEA-4+ cells neither differed in their proliferation and clonogenicity potential from initial and negative populations nor exhibited pluripotent differentiation repertoire. SSEA-4+ cells were observed to form smaller spheroids and exhibited increased survival under 3D conditions. Conclusion: Despite the transient expression of stemness-related genes, our findings could not fully confirm the undifferentiated pluripotent-like nature of the SSEA-4+ WJ-MSC population cultured in vitro.
Copyright © 2024 Smolinska, Chodkowska, Kominek, Janiec, Piwocka, Sulejczak and Sarnowska.

Liver tumour-initiating cells (TICs) contribute to tumour initiation, metastasis, progression and drug resistance. Metabolic reprogramming is a cancer hallmark and plays vital roles in liver tumorigenesis. However, the role of metabolic reprogramming in TICs remains poorly explored. Here, we identify a mitochondria-encoded circular RNA, termed mcPGK1 (mitochondrial circRNA for translocating phosphoglycerate kinase 1), which is highly expressed in liver TICs. mcPGK1 knockdown impairs liver TIC self-renewal, whereas its overexpression drives liver TIC self-renewal. Mechanistically, mcPGK1 regulates metabolic reprogramming by inhibiting mitochondrial oxidative phosphorylation (OXPHOS) and promoting glycolysis. This alters the intracellular levels of α-ketoglutarate and lactate, which are modulators in Wnt/β-catenin activation and liver TIC self-renewal. In addition, mcPGK1 promotes PGK1 mitochondrial import via TOM40 interactions, reprogramming metabolism from oxidative phosphorylation to glycolysis through PGK1-PDK1-PDH axis. Our work suggests that mitochondria-encoded circRNAs represent an additional regulatory layer controlling mitochondrial function, metabolic reprogramming and liver TIC self-renewal.
© 2023. The Author(s).