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Abstract
Squamous cell carcinoma of the head and neck (HNSCC) consist of two distinct biological entities. While the numbers of classical, tobacco-induced HNSCC are declining, tumors caused by human papillomavirus (HPV) infection are increasing in many countries. HPV-positive HNSCC mostly arise in the oropharynx and are characterized by an enhanced sensitivity towards radiotherapy and a favorable prognosis. To identify molecular differences between both entities on the protein level, we conducted a mass spectrometric comparison of eight HPV-positive and nine HPV-negative oropharyngeal tumors (OPSCC). Overall, we identified 2051 proteins, of which 31 were found to be differentially expressed. Seventeen of these can be assorted to three functional groups, namely DNA replication, nuclear architecture and cytoskeleton regulation, with the differences in the last group potentially reflecting an enhanced migratory and invasive capacity. Furthermore, a number of identified proteins have been described to directly impact on DNA double-strand break repair or radiation sensitivity (e.g., SLC3A2, cortactin, RBBP4, Numa1), offering explanations for the differential prognosis. The unequal expression of three proteins (SLC3A2, MCM2 and lamin B1) was confirmed by immunohistochemical staining using a tissue microarray containing 205 OPSCC samples. The expression levels of SLC3A2 and lamin B1 were found be of prognostic relevance in patients with HPV-positive and HPV-negative OPSCC, respectively.
Highlights
In recent decades, there has been an increase in the incidence of head and neck squamous cell carcinomas (HNSCC) with location in the oropharynx (OPSCC), whilst tumors arising from the larynx and hypopharynx have been declining
Center Hamburg-Eppendorf between August 2011 and March 2013 were reviewed for primary site and human papillomavirus (HPV)/p16 status within our clinical cancer database. p16 status had been determined by immunohistochemistry using a mouse anti-p16INK4a antibody and HPV status had been determined by genomic PCR using the MY09/11 primer set and subsequent sequencing of PCR products
Ten patients with HPV/p16-positive and 10 with HPV/p16-negative OPSCC with leftover formalin-fixed paraffin-embedded (FFPE) tumor tissue available from histopathological workup of the main tumor specimen were chosen for the mass spectrometric comparison
Summary
There has been an increase in the incidence of head and neck squamous cell carcinomas (HNSCC) with location in the oropharynx (OPSCC), whilst tumors arising from the larynx and hypopharynx have been declining. Sustained alcohol and tobacco consumption no longer represent the main risk factors for OPSCC in many countries as smoking cessation programs were implemented [1]. The rising numbers of OPSCC can be largely ascribed to an epidemic spread of human papillomavirus (HPV)-associated tumors mostly located at the tonsils and the base of the tongue. In the US, the incidence of HPV-positive OPSCC has increased by 225% between 1988 and 2004, and HPV-negative OPSCC declined by 50%. HPV-negative and HPV-positive HNSCC represent biologically and clinically distinct entities. The tumorigenesis of HPV-positive cancer is largely determined by the activity of the viral oncoproteins E6 and E7. E6 and E7 inhibit and degrade the tumor suppressors p53 and the retinoblastoma-associated protein (pRB), respectively
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