Quantitative Proteomic Analysis of Oral Brush Biopsies Identifies Secretory Leukocyte Protease Inhibitor as a Promising, Mechanism-Based Oral Cancer Biomarker

Abstract

A decrease in the almost fifty percent mortality rate from oral cancer is needed urgently. Improvements in early diagnosis and more effective preventive treatments could affect such a decrease. Towards this end, we undertook for the first time an in-depth mass spectrometry-based quantitative shotgun proteomics study of non-invasively collected oral brush biopsies. Proteins isolated from brush biopsies from healthy normal tissue, oral premalignant lesion tissue (OPMLs), oral squamous cell carcinoma (OSCC) and matched control tissue were compared. In replicated proteomic datasets, the secretory leukocyte protease inhibitor (SLPI) protein stood out based on its decrease in abundance in both OPML and OSCC lesion tissues compared to healthy normal tissue. Western blotting in additional brushed biopsy samples confirmed a trend of gradual decreasing SLPI abundance between healthy normal and OPML tissue, with a larger decrease in OSCC lesion tissue. A similar SLPI decrease was observed in-vitro comparing model OPML and OSCC cell lines. In addition, exfoliated oral cells in patients’ whole saliva showed a loss of SLPI correlated with oral cancer progression. These results, combined with proteomics data indicating a decrease in SLPI in matched healthy control tissue from OSCC patients compared to tissue from healthy normal tissue, suggested a systemic decrease of SLPI in oral cells correlated with oral cancer development. Finally, in-vitro experiments showed that treatment with SLPI significantly decreased NF-kB activity in an OPML cell line. The findings indicate anti-inflammatory activity in OPML, supporting a mechanistic role of SLPI in OSCC progression and suggesting its potential for preventative treatment of at-risk oral lesions. Collectively, our results show for the first time the potential for SLPI as a mechanism-based, non-invasive biomarker of oral cancer progression with potential in preventive treatment.

Secretory leukocyte protease inhibitor inhibits expression of polymeric immunoglobulin receptor via the NF-κB signaling pathway

“…Mean ± SD (n = 3). cells, and gingival squamous cell carcinoma-derived Ca9-22 cells (Yang et al, 2014). pIgR was not expressed in these cells.…”

“…Furthermore, we determined the effect of SLPI on pIgR expression by adding recombinant human SLPI (rhSLPI) to colorectal cancerderived HT-29 cells that constitutively express pIgR (Johansen et al, 1998). In addition, we used oral squamous cell carcinoma-derived Ca9-22 cells, which express SLPI but scarcely express pIgR (Yang et al, 2014), to generate SLPI-deficient ( SLPI) cells and investigated whether pIgR expression was induced in these cells.…”

Proteomic profile of saliva and plasma from women with impalpable breast lesions

“…The proteins present in the saliva and plasma, according to their functional class determined by the PANTHER program version 10.0, revealed immune system proteins, binding to nucleic acids and transportation proteins (data not shown), which are common among tumors (4,(25)(26)(27)(28)(29)(30). When observing the interactome, the highlighted proteins were involved in the initial process of carcinogenesis (data not shown), for example, the metalloproteinases and epidermal growth factor receptor (31).…”

Salivary secretory leukocyte protease inhibitor (SLPI) and head and neck cancer: The Cancer Prevention Study II Nutrition Cohort

“…Secretory leukocyte protease inhibitor (SLPI) is a defensin-like innate immunity-associated protein with broad antimicrobial and anti-inflammatory properties [4-6] that has been identified as a potential diagnostic and prognostic biomarker in HNC [7]. It is found in various bodily secretions, but is present in particularly high concentrations in the saliva [8].…”

“…The role of salivary SLPI in reducing transmission of HIV in the oral cavity has been well studied [9, 10], and there is growing evidence that SLPI may protect against oral HPV infection [11, 12]. Results from tumor studies suggest that SLPI may be associated with HNC carcinogenesis [7], metastasis [11, 13], and prognosis [14], although the exact mechanisms by which SLPI protects against HNC development and progression remain unclear. SLPI is believed to protect mucosal surfaces against proteolysis and epithelial tissue damage [15] by inhibiting neutrophil elastase, a serine protease produced by tumor and inflammatory cells that is known to induce tumor cell proliferation [16].…”