Mass Spectrometric Analysis of SOX11-Binding Proteins in Head and Neck Cancer Cells Demonstrates the Interaction of SOX11 and HSP90α

Deregulated expression of SOX11 has been shown to be involved in the progression of various types of cancer. However, the role of SOX11 in head and neck cancer remains largely unknown. In this study, coimmunoprecipitation (Co-IP) and liquid chromatography tandem mass spectrometry (LC-MS/MS) were performed to identify the proteins that bind to SOX11 at significantly higher levels in head and neck cancer cells than in normal human oral keratinocytes. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses indicated that many potential SOX11-binding partners were associated with protein synthesis, cell metabolism, and cell cell adhesion. One of the identified proteins, heat shock protein 90 alpha (HSP90 alpha), was selected for further investigation. The binding of HSP90 alpha with SOX11 in head and neck cancer cells was validated by Co-IP with western blotting. In addition, HSP90a was found to be remarkably overexpressed in head and neck cancer cell lines when compared to its level in normal human oral keratinocytes, and knockdown of HSP90a inhibited the proliferation and invasion capacity of these cancer cells. On the basis of The Cancer Genome Atlas (TCGA) data analysis, HSP9OAA1 gene was overexpressed in head and neck cancer tissues compared to normal controls and increased HSP9OAA1 gene expression was positively associated with extracapsular spread and clinical stage. Head and neck cancer patients with higher HSP9OAA1 expression had significantly poorer long-term overall and disease-free survival rates than those with lower HSP9OAA1 expression. Collectively, our studies indicate that SOX11 binds to HSP90 alpha, a highly overexpressed protein that may promote invasion and progression of head and neck cancer cells.