Elevated MCL1 expression drives esophageal squamous cell carcinoma stemness and induces resistance to radiotherapy.

Background: Esophageal squamous cell carcinoma (ESCC) stands as the sixth most common cause of cancer-related mortality on a global scale, with a strikingly high proportion-over half-of these fatalities occurring within China. The emergence of radiation resistance in ESCC patients significantly diminishes overall survival rates, complicating treatment regimens and reducing clinical outcomes. There is an urgent need to explore the molecular mechanisms that underpin radiation resistance in ESCC, which could lead to the identification of new therapeutic targets aimed at overcoming this resistance. This study aims to elucidate the role of myeloid cell leukemia-1 (MCL1) in ESCC and its association with radioresistance, thereby providing a novel strategy for enhancing the efficacy of radiotherapy.

Methods: We used The Cancer Genome Atlas (TCGA) database, Genotype-Tissue Expression (GTEx) project and real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) of 10 pairs of fresh endoscopic biopsy samples from patients with ESCC to analyze the messenger RNA (mRNA) expression levels of MCL1 in esophageal cancer tissues as compared to normal tissues. Immunohistochemistry (IHC) staining and Western blotting were performed using an anti-MCL1 antibody to visualize protein expression. The mechanism of radioresistance of ESCC was examined by combining bioinformatics analysis, Western blotting, and clone formation and stemness sphere formation assays.

Results: The analysis of TCGA database and the results of RT-qPCR indicated that the mRNA level of MCL1 was overexpressed in esophageal cancer tissues. Subsequently, the results of IHC and Western blotting showed that the protein level of MCL1 expression in cancer tissues was significantly higher than that in adjacent normal tissues. Moreover, there was a significant upregulation of MCL1 in ESCC tissues and in radioresistant tissues and cells, with its overexpression correlating with the acquisition of stemness properties in ESCC. In terms of mechanism, MCL1 induced cell cycle arrest by regulating the expression of cyclin D3 and p21 through the JAK-STAT signaling pathway. G0/G1 phase arrest contributed to the stem cell-like phenotype. Blocking JAK-STAT signaling significantly improved the efficacy of radiotherapy for ESCC.

Conclusions: These findings indicate that MCL1 is a critical cell cycle regulator that drives the stemness and radioresistance of ESCC and may thus be a potential target in a combined therapeutic strategy aimed at overcoming radioresistance.