miR-100-5p Enhances Cell Cycle-Mediated Chemoresistance by Modulating the CTDSPL/pRB/E2F1 Signaling Pathway in Oxaliplatin-Resistant Colorectal Cancer Cells

Objective: MicroRNAs (miRNAs) are small, non-coding RNAs that play a key role in the development of chemoresistance in various cancer types, including colorectal cancer (CRC). In this study, we aimed to study the underlying mechanisms of miRNA in chemotherapy-resistant CRC. Methods: LoVo CRC cell line was exposed to oxaliplatin at an increased dose, and cells were cultured in the presence of oxaliplatin to develop LoVoOXR cells. Microarray and Quantitative Reverse Transcription Polymerase Chain Reaction (qRT-PCR), western blot, and transwell assay were used to evaluate the chemoresistance in LoVoOXR CRC cells. Results: Microarray and qRT-PCR analysis showed an increased expression of miR-100-5p in LoVoOXR cells. MTT assay and flow cytometry analysis revealed less apoptosis and higher cell viability in LoVoOXR cells. mRNA prediction target gene analysis showed C-terminal domain small phosphatase-like (CTDSPL), a phosphatase-like tumor suppressor, as a key target of miR-100-5p. CTDSPL expression was low in LoVoOXR cells compared to LoVoWT cells. miR-100-5p regulates G1/S and S-phase transitions and inhibits differentiation by targeting the CTDSPL/pRB/E2F1 signaling pathway, which involves the modulation of cell cycle effectors in LoVoOXR cells. Further, we found that forkhead box P3 (FOXP3), as the upstream target of miR-100-5p, is highly expressed in LoVoOXR cells. Inhibiting miR-100-5p and FOXP3 down-regulates miR-100-5p expression, while increased CTDSPL expression contributed to reduced cell proliferation and promoted cell apoptosis in LoVoOXR CRC cells. Conclusions: miR-100-5p plays an oncogenic role in inducing chemoresistance through modulation of the CTDSPL/retinoblastoma protein (pRB)/E2F transcription factor 1 (E2F1) axis in CRC cells.