The Clinical Significance of SPOP Upregulation and Nuclear Accumulation in Head and Neck Squamous Cell Carcinoma.

The speckle-type BTB/POZ protein (SPOP) is an E3 ubiquitin ligase adaptor typically considered a tumor suppressor, yet its role in head and neck squamous cell carcinoma (HNSCC) remains unclear. This study investigated SPOP expression, arecoline regulation, and its potential as a HNSCC biomarker. SPOP mRNA and its protein were quantified in HNSCC (FaDu, GMN, HSC-3, SAS, and A253) and normal oral epithelial (SG) cell lines via RT-qPCR and Western blot; arecoline's effect on SG, SAS, and A253 cells was evaluated. SPOP mRNA was analyzed using The Cancer Genome Atlas (TCGA) HNSCC cohort, and protein localization was assessed via immunohistochemistry (IHC) on tissue microarrays. SPOP mRNA was higher in some HNSCC lines; arecoline induced SPOP in SG cells, but not in HNSCC cell lines. TCGA confirmed SPOP mRNA upregulation in tumors correlating with grade. IHC showed SPOP upregulation in HNSCC, particularly in palate and pharynx/hypopharynx sites. The nuclear SPOP-positive ratio shifted from 12.14 ± 9.82% in normal tissues to 61.26 ± 33.03% in tumors (p < 0.0001), differentiating grades and sites better than total expression. SPOP is upregulated in HNSCC and inducible by arecoline. Enhanced nuclear SPOP localization indicates malignancy and progression, identifying it as a potential HNSCC diagnostic and progression biomarker.