Subcellular Proteomic Identification Of Uchl1 As A Potential Biomarker For Human Gastric Adenocarcinoma

Gastric cancer (GC) is one of the most severe malignant tumors that threatened public health.42% newly diagnosed gastric cancer worldwide comes from China, about 400 thousands cases. According to the third survey in 2008, the incidence and mortality rates of GC ranked 2 and 3 respectively. Because of the lack of specific markers for early diagnosis, most of GC patients were diagnosed at middle or late stages, when the best time of cure had been missed, and thus the 5-year survival rate was only about 20%. Therefore, screening for specific diagnostic markers for GC is important to improve early diagnoses and patients'survival.In this work, gastric adenocarcinoma cell line SGC7901 and immortalized normal gastric gland cell line GES were used as study models. Total proteins were fractionated by subcellular protein separation and the cytosol protein alterations between SGC7901 and GES were identified by using two-dimensional SDS-PAGE combined with MALDI-TOF/TOF-MS/MS. The alterations in expression were further confirmed in other three gastric adenocarcinoma cell lines AGS, BGC823 and MKN45, and gastric adenocarcinoma tissue and corresponding normal tissue.Totally,12 repeatable different protein spots with expression changes> 2-folds were obtained and 10 different proteins were identified, including UCHL1, GSTM3, S100-A11, SERPINB1, PSME1, HSPB1, LTA4H, FABP4, S100-A4 and S100-A6. Further confirmation revealed that UCHL1 (ubiquitin carboxyl terminal hydrolase L1) was obviously down-regulated in both protein and mRNA levels in gastric adenocarcinoma cell lines SGC7901, AGS, BGC823 and MKN45, compared with GES. And UCHL1 expression was also significantly lower in gastric cancer tissue compared with corresponding normal tissue.To investigate the function of UCHL1 in gastric cancer, the eukaryotic expression vector UCHL1/pcDNA3.1 was constructed, and transfected into SGC7901 with optimized conditions; and the efficient expression of UCHL1 was obtained.Our study provided a methodology reference for biomarker identification and suggested UCHL1 to be a potential biomarker for gastric adenocarcinoma. Further investigation on the function of UCHL1 in gastric adenocarcinoma is undergoing.