Studying genes involved in proteostasis is essential for understanding the mechanisms driving dedifferentiation in cancer, as this process enables tumor cells to acquire stem-like properties, promoting plasticity, resistance, and progression. In head and neck squamous cell carcinoma (HNSCC), a highly aggressive malignancy with poor prognosis, identifying molecular regulators of dedifferentiation is crucial for developing targeted therapies. PSMG2, a chaperone protein that forms a heterodimer with PSMG1, plays a key role in this context by facilitating the assembly of the 20S proteasome. Here, we characterized the role of PSMG2 in tumorigenesis and dedifferentiation in HNSCC cell lines.

Protein-protein interaction (PPI) analysis using IntAct and BioGRID identified key interactors of PSMG2, followed by functional enrichment via Gene Set Enrichment Analysis (GSEA). PSMG2 was overexpressed and downregulated in two HNSCC cell lines. Tumorigenesis was analysed using various functional assays, including growth curves, clonogenic assays, tumorsphere assays, and in vivo models. Molecular mechanisms such as apoptosis and autophagy were tested by flow cytometry, Western blotting, and immunofluorescence. Additionally, a reprogramming assay was conducted to assess the impact of gene downregulation on the dedifferentiation process.

High PSMG2 expression correlated with poor prognosis and reduced survival in HNSCC patients. To explore the molecular networks regulated by PSMG2, we analysed protein-protein interactions (PPI) identifying common interactors. GSEA revealed enrichment in proteostasis, unfolded protein response, and cancer-related signaling pathways. PSMG2 knockdown impaired cell proliferation both in vitro and in vivo and led to a significant reduction in stemness, dedifferentiation, and reprogramming properties. Mechanistically, PSMG2 reduction resulted in the accumulation of polyubiquitinated proteins, triggering endoplasmic reticulum (ER) stress and activating apoptosis and autophagy as compensatory mechanisms. Notably, PSMG2 downregulation enhanced the response to proteasome inhibitors, suggesting a potential therapeutic vulnerability.

Our findings demonstrate that PSMG2 is a key regulator of proteasome assembly, ER stress, and cellular homeostasis in HNSCC, linking proteostasis with dedifferentiation and therapy resistance. Targeting PSMG2 or the proteasome machinery may represent a promising therapeutic strategy for overcoming tumor plasticity and improving treatment outcomes in HNSCC patients.