An approach to proteomic analysis of human tumors

Analysis of differentially expressed proteins in cancerous and normal colonic tissues

AIM: To identify and analyze the differentially expressed proteins in normal and cancerous tissues of four patients suffering from colon cancer.

METHODS: Colon tissues (normal and cancerous) were homogenized and the proteins were extracted using three protein extraction buffers. The extraction buffers were used in an orderly sequence of increasing extraction strength for proteins with hydrophobic properties. The protein extracts were separated using the SDS-PAGE method and the images were captured and analyzed using Quantity One software. The target protein bands were subjected to in-gel digestion with trypsin and finally analyzed using an ESI-ion trap mass spectrometer.

RESULTS: A total of 50 differentially expressed proteins in colonic cancerous and normal tissues were identified.

CONCLUSION: Many of the identified proteins have been reported to be involved in the progression of similar or other types of cancers. However, some of the identified proteins have not been reported before. In addition, a number of hypothetical proteins were also identified.

Screening of hepatocyte proteins binding to F protein of hepatitis C virus by yeast two-hybrid system

AIM: To investigate the biological function of F protein by yeast two-hybrid system.

METHODS: We constructed F protein bait plasmid by cloning the gene of F protein into pGBKT7, then recombinant plasmid DNA was transformed into yeast AH109 (a type). The transformed yeast AH109 was mated with yeast Y187 (α type) containing liver cDNA library plasmid in 2×YPDA medium. Diploid yeast was plated on synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) containing X-α-gal for selection and screening. After extracting and sequencing plasmids from positive (blue) colonies, we underwent sequence analysis by bioinformatics.

RESULTS: Thirty-six colonies were selected and sequenced. Among them, 11 colonies were zymogen granule protein, 5 colonies were zinc finger protein, 4 colonies were zinc-α-2-glycoprotein, 1 colony was sialyltransferase, 1 colony was complement control protein factor I, 1 colony was vitronectin, and 2 colonies were new genes with unknown function.

CONCLUSION: The yeast two-hybrid system is an effective method for identifying hepatocyte proteins interacting with F protein of hepatitis C virus. F protein may bind to different proteins.

Identification of tumor markers using two-dimensional electrophoresis in gastric carcinoma

AIM: To study the differential expression of proteins in normal and cancerous gastric tissues, and further identify new molecular markers for diagnosis and prognosis of gastric carcinoma, as well as develop new therapeutic targets of the disease.

METHODS: Matched pairs of tissues from 6 gastric cancer patients were analyzed for their two-dimensional electrophoresis (2DE) profiles. Soluble fraction proteins from human normal and cancerous gastric tissue were separated in the first dimension by isoelectric focusing on immobilized pH gradient (IPG, pH3-10) strips, and by 125 g/L sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) in the second dimension with silver nitrate staining. Protein differential expression was analyzed by use of image analysis software to find out candidates for gastric cancer-associated proteins.

RESULTS: Nine protein spots overexpressed in tumor tissues as compared with noncancerous regions. In the next step, 9 tumor-specific spots were cut off from Coomassie Brilliant Blue staining gels, digested in gel with L-1-tosylamide-2-phenylethyl chloromethyl ketone (TPCK)-trypsin. Protein identification was done by peptide mass fingerprinting with matrix assisted laser desorption/ ionization-time of flight-mass spectrometry (MALDI-TOF-MS). In total, 5 tumor-specific protein spots corresponding to 5 different polypeptide chains were identified, including annexin V, carbonic anhydrase, prohibitin, fibrin beta and fibrinogen fragment D. Among these 5 spots, the potential significance of the differential expressions is discussed.

CONCLUSION: Differential expression analysis of proteomes may be useful for the development of new molecular markers for diagnosis and prognosis of gastric carcinoma.

Using yeast two-hybrid system to identify ECRG2 associated proteins and their possible interactions with ECRG2 gene

AIM: To identify esophageal cancer related gene2 (ECRG2) associated proteins and their possible interactions with ECRG2 gene.

METHODS: In the yeast forward two-hybrid system, ECRG2 was fused with the DNA-binding domain (DBD) of Gal4 and human fetal liver cDNA library was fused with the transcriptional activation domain (AD) of Gal4. We performed a high-stringency scale procedure to screen ECRG2 against human fetal liver cDNA library and characterized positives by sequence analysis.

RESULTS: We found the following 9 putatively associated proteins. They were metallothionein2A, metallothionein1H, metallothionein1G, ferritin, erythrocyte membrane protein band4.2, mitochondrial ribosomal protein S12, hypothetical protein FLJ10101, and a novel gene whose cDNA was found to have no strong homology to any other previously characterized gene whose DDBJ/EMBL/GenBank accession number is AF422192 mapped to human chromosome 14q31.

CONCLUSION: MT, a potential interaction partner for ECRG2, might be involved in the regulation of cell proliferation and apoptosis, and in various physiological processes. Determination of a reliability score for each single protein-protein interaction, especially interaction of ECRG2 and MT, permits the assignment of ECRG2 and unannotated proteins to biological pathways. A further understanding of the association between ECRG2 and MT should facilitate the functions of ECRG2 gene.

Translocation of annexin I from cellular membrane to the nuclear membrane in human esophageal squamous cell carcinoma

AIM: To investigate the alteration of the annexin I subcellular localization in esophageal squamous cell carcinoma (ESCC) and the correlation between the translocation and the tumorigenesis of ESCC.

METHODS: The protein localization of annexin I was detected in both human ESCC tissues and cell line via the indirect immunofluorescence strategy.

RESULTS: In the normal esophageal epithelia the annexin I was mainly located on the plasma membrane and formed a consecutive typical trammels net. Annexin I protein also expressed dispersively in cytoplasm and the nuclei without specific localization on the nuclear membrane. In esophageal cancer annexin I decreased very sharply with scattered disappearance on the cellular membrane, however it translocated and highly expressed on the nuclear membrane, which was never found in normal esophageal epithelia. In cultured esophageal cancer cell line annexin I protein was also focused on the nuclear membrane, which was consistent with the result from esophageal cancer tissues.

CONCLUSION: This observation suggests that the translocation of annexin I protein in ESCC may correlate with the tumorigenesis of the esophageal cancer.