Overexpression of Glucose-regulated Protein 78 in Colon Cancer

Background: The 78 kDa glucose-regulated protein (GRP78) has been implicated in the development of tumorigenicity, drug resistance, and cytotoxic immunology. We investigated the expression pattern of GRP78 at the protein and mRNA level in human colon carcinoma, colon adenoma and normal colon mucosa.

Methods: Two-dimensional (2-D) gel electrophoresis, electrospray ionization tandem mass spectrometry, immunoblot analysis, reverse-transcriptase PCR and immunohistochemistry were used on colon normal and cancer tissues.

Results: Comparative 2-D gel electrophoresis of individual-matched colon normal and cancer tissues revealed 15 protein spots with concordantly increased and 20 protein spots with concordantly decreased intensity in tumor tissue. Fourteen of these proteins were identified by tandem mass spectrometry. One of the identified proteins, GRP78, exhibited a marked up-regulation in colon cancer tissue. This result was further confirmed by Western blot and immunohistochemical analysis. Immunohistochemistry also revealed increased cytoplasmic GRP78 expression with progression along the normal tissue-adenoma-carcinoma sequence. However, to our surprise, there was essentially no difference in the relative mRNA expression levels of GRP78 between normal and colon tumors.

Conclusions: Our findings indicate that overexpression of GRP78 protein may be an important biomarker for malignant transformation, and increased expression might be related with the posttranscriptional regulation of GRP78 in tumor tissues.