Identification of squamous cell carcinoma associated proteins by proteomics and loss of beta tropomyosin expression in esophageal cancer

Aim: To assess the proteome of normal versus tumor tissue in squamous cell carcinoma of the esophagus (SCCE) in Iranian patients and compare our results with former reports by using proteomics. Methods: Protein was extracted from normal and tumor tissues. Two dimensional electrophoresis was carried out and spots with differential expression were identified with mass spectrometry. RNA extraction and RT-PCR along with immunodetection were performed. Results: Fourteen proteins were found whose expression levels differed in tumor compared to normal tissues. Mass spectrometric analysis resulted in the identification of β-tropomyosin (TMβ), myosin light chain 2 (and its isoform), myosin regulatory light chain 2, peroxyredoxin 2, annexin I and an unknown polypeptide as the down regulated polypeptides in tumor tissue. Heat shock protein 70 (HSP70), TPM4-ALK fusion oncoprotein 2, myosin light polypeptide 6, keratin I, GH16431p and calreticulin were the up-regulated polypeptides found in tumor tissue. Several of these proteins, such as TMβ, HSP70, annexin I, calreticulin, TPM4-ALK and isoforms of myosins, have been well recognized in tumorigenesis of esophageal or other types of cancers. Conclusion: Our study not only supports the involvement of some of the formerly reported proteins in SCCE but also introduces additional proteins found to be lost in SCCE, including TMβ.