[Methyltransferase-like protein 7B promotes glycolysis and malignant progression in papillary thyroid carcinoma cells via the USP28/HIF-1α axis].

OBJECTIVES: To investigate the expression of methyltransferase-like protein 7B (METTL7B) in papillary thyroid carcinoma (PTC) and elucidate its role and molecular mechanisms in tumor metabolic reprogramming and malignant progression.

METHODS: Public datasets from Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) were used to analyze METTL7B expression in PTC and its association with clinicopathological features. Immunohistochemistry on tissue microarrays was performed to validate METTL7B protein expression in clinical samples. Stable METTL7B-knockdown PTC cell lines were constructed, and knockdown efficiency was confirmed by quantitative real-time PCR (qRT-PCR) and Western blotting. Cell proliferation and clonogenic potential were evaluated using MTT and colony formation assays. Transcrip-tome sequencing was conducted in METTL7B-overexpressing cells to identify differentially expressed genes and enriched pathways, followed by qRT-PCR and Western blotting validation of METTL7B-mediated regulation of hypoxia-inducible factor 1α (HIF-1α). Cycloheximide chase and ubiquitination assays were used to assess the effect of METTL7B on HIF-1α protein stability, and the involvement of ubiquitin-specific protease 28 (USP28) was further examined. Lactate production and glucose uptake assays were performed to assess the impact of METTL7B and HIF-1α on glycolytic activity.

RESULTS: METTL7B was significantly upregulated in PTC tissues (P<0.05) and positively correlated with lymph node metastasis (P<0.05). METTL7B knockdown markedly suppressed PTC cell proliferation and colony formation (all P<0.05), and markedly reduced the growth rate of PTC xenograft tumors in nude mice, with tumor volumes smaller than those in the control group (P<0.05). Bioinformatics analysis suggested a strong association between METTL7B and the HIF-1α signaling pathway. METTL7B knockdown reduced HIF-1α protein levels without affecting its mRNA expression. Mechanistically, METTL7B inhibited the ubiquitination and degradation of HIF-1α, thereby maintaining its protein stability, and this process was mediated by USP28. Functional assays demonstrated that METTL7B enhanced glycolytic activity and malignant phenotypes of PTC cells by upregulating glycolysis-related genes through the USP28/HIF-1α axis.

CONCLUSIONS: METTL7B promotes glycolysis and malignant progression in PTC cells by stabilizing HIF-1α through USP28-mediated deubiquitination.