Aims
(1) Investigate changes in S100A8/A9 expression as oral carcinogenesis progresses and (2) determine whether intracellular calprotectin can regulate epidermal growth factor receptor (EGFR), a negative prognostic factor, in HNSCC. Materials and
Conclusions
In HNSCC, S100A8/A9 is directly associated with cellular differentiation and appears to promote caspase-3/7-mediated cleavage of EGFR, which could explain why patients with S100A8/A9-high tumors survive longer.
Methods
Using immunohistochemistry (IHC), S100A8/A9 was analyzed in HNSCC specimens (N = 46), including well-differentiated (WD, N = 19), moderately-differentiated (MD, N = 14), poorly-differentiated (PD, N = 5) and non-keratinizing/basaloid (NK/BAS, N = 8), and premalignant epithelial dysplasias (PED, N = 16). Similarly, EGFR was analyzed in HNSCCs (N = 21). To determine whether calprotectin and EGFR expression are mechanistically linked, TR146 HNSCC cells that are S100A8/A9-expressing or silenced (shRNA) were compared for EGFR levels and caspase-3/7 activity using western blotting and immunofluorescence microscopy.
Results
In normal oral mucosal epithelium, S100A8/A9 stained strongly in the cytoplasm and nucleus of suprabasal cells; basal cells were consistently S100A8/A9 negative. In PED and HNSCC, S100A8/A9 expression was lower than in adjacent normal epithelial tissues (NAT) and declined progressively in WD, MD, PD and NK/BAS HNSCCs. S100A8/A9 and EGFR levels appeared inversely related, which was simulated in vitro when S100A8/A9 was silenced in TR146 cells. Silencing S100A8/A9 significantly reduced caspase-3/7 activity, whereas EGFR levels increased. Conclusions: In HNSCC, S100A8/A9 is directly associated with cellular differentiation and appears to promote caspase-3/7-mediated cleavage of EGFR, which could explain why patients with S100A8/A9-high tumors survive longer.