Iron-induced MMP-9 in squamous cell carcinoma via ERK/PI3K pathway

Objectives: Over-expression of matrix metalloproteinase-9 (MMP-9) and iron overload are associated with cancer progression. In the present study, we examined the effect of iron on MMP-9 expression and its molecular mechanism in head and neck squamous cell carcinoma (HNSCC). Methods: OM-2 and HN-22 cell lines were treated with ferric ammonium citrate (FAC) ranging from 5 to 25µg/ml. The expression of MMP-9 was examined by reverse transcription polymerase chain reaction (RT-PCR) and zymography. Specific inhibitors were used to determine the regulatory pathway. Electromobolity shift assay (EMSA) was performed to examine the promoter binding site. Results: FAC increased MMP-9 mRNA and protein in OM-2 and HN-22 in a dose dependent manner. Specific inhibitors to extracellular signal-regulated kinase (ERK), phosphatidylinnositol 3 kinase (PI3K) and Akt suppressed FAC-increased MMP-9. Analysis by EMSA demonstrated that iron mediated MMP-9 expression by activation of AP-1. Application of neutralizing antibody against transferrin receptor had no effect on the MMP-9 induction suggesting HN-22 cells used transferrin independent pathways for iron uptake. Conclusions: Iron increases MMP-9 expression through AP-1 via ERK and PI3K/Akt signaling pathways in HNSCC cell lines using a transferrin receptor independent pathway. We suggested that iron overload condition could support progression of HNSCC.