Overexpression of elongation factor-1γ protein in colorectal carcinoma

Abstract

BACKGROUND. Elongation factor-1 (EF-1) is a cellular protein that plays a role in protein synthesis by mediating the transfer of aminoacyl-tRNA to 80S ribosomes. It is comprised of four subunits: α, β, γ, and δ. EF-1γ is a substrate for the maturation-promoting factor, which determines entry into the M-phase of the cell cycle in all eukaryotic cells. Previously, the authors showed that EF-1γ RNA is overexpressed in a high proportion of colorectal carcinomas. At that time, there were no antibodies to EF-1γ, so the EF-1γ protein could not be examined. Because levels of RNA do not always parallel the levels of the protein it encodes, it was important to develop antibodies to EF-1γ to examine its expression at the protein level in colorectal carcinoma. METHODS. Twenty-nine patients undergoing surgical resection for colorectal adenocarcinoma were studied. A polyclonal antibody to EF-1γ in rabbit was prepared. Tumors and normal-appearing mucosa distant from the tumor (≤10 cm) were obtained from each patient. Cytosolic proteins were extracted from the tissues and examined by Western blot analysis with the EF-1γ antibody. Colonic tumors also were studied by immunohistochemical analysis with another EF-1γ polyclonal antibody. RESULTS. Using Western blot analysis, the authors observed greater expression of EF-1γ in the tumors than in the more distal normal-appearing mucosa. Overexpression was not observed in the patients with the two Dukes Stage A tumors, but was observed in four of ten patients with Dukes Stage B tumors, seven of eight patients with Dukes Stage C tumors, and six of nine patients with Dukes Stage D tumors. Overall, 17 of 29 patients (59%) were found to have overexpression of EF-1γ. Using immunohistochemical analysis, EF-1γ protein was shown to be located predominantly in tumor epithelium rather than the stroma or infiltrating mononuclear cells. CONCLUSIONS. Previous studies showed that EF- 1γ mRNA frequently is overexpressed in colorectal adenocarcinoma. This study showed that EF-1γ also was overexpressed at the protein level in colorectal adenocarcinoma relative to more distal normal-appearing mucosa from the same patient. Immunohistochemical analysis demonstrated that this protein was expressed predominantly in the tumor epithelial cells and therefore was not derived from cells involved in the desmoplastic response.