Remarkable progress has been made to identify genes expressed in
squamous cell carcinomas of the head and neck (
HNSCC). However, limited information is available on their corresponding
protein products, whose expression, post-translational modifications, and activity are ultimately responsible for the malignant behavior of this
tumor type. We have combined
laser-capture microdissection (LCM) with liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify
proteins expressed in histologically normal squamous epithelium and matching SCC. The
protein fraction from approximately 10,000-15,000 normal and
tumor cells was solubilized, digested with
trypsin, and the resulting
peptides were analyzed by LC-MS/MS. Database searching of the resulting sequence information identified 30-55
proteins per sample.
Keratins were the most abundant
proteins in both normal and
tumor tissues. Among the
proteins differentially expressed,
keratin 13 was much lower in
tumors, whereas heat-shock (Hsp) family members were highly expressed in neoplastic cells. Wnt-6 and Wnt-14 were identified in both normal and
tumor tissues, respectively, and placental
growth factor (PIGF) was detected only in
tumors. Immunohistochemical analysis of
HNSCC tissues revealed lack of
keratin 13 in
tumor tissues, and strong staining in normal epithelia, and high expression of Hsp90 in
tumors. Our study, by combining LCM and proteomic technologies, underscores the advantages of this approach to investigate complex changes at the
protein level in
HNSCC, thus complementing existing and emerging genomic technologies. These efforts may likely result in the identification of new
biomarkers for
HNSCC that can be used to diagnose disease, predict susceptibility, and monitor progression in individual patients.