Potential role of herg1 gene and HERG1 protein in cancers of the gastrointestinal tract

E Lastraioli BSC^a, L Guasti BSC^a, O Crociani PhD^a, S Polvani PhD^a, G Hofmann PhD^a, M Paglierani BSC^b, M Calistri MD^c, A Taddei MD^d, MD Giani^d, L Bencini MD^c, L Messerini MD^b, H Witchel PhD^e, M Scatizzi MD^c, R Moretti MD^c, P Bechi MD^d, E Wanke BSC^f, GL Taddei MD^b, M Olivotto MD^a, G Mugnai MD^a, A Arcangeli MD PhD^a

^aDepartment of Experimental Pathology and Oncology, ^bDepartment of Human Pathology and Oncology, ^dSurgical Pathology I; University of Firenze, Firenze, Italy, ^cFirst Division of General Surgery and Transplantation, Careggi Hospital, Firenze, Italy, ^eDepartment of Physiology and Cardiovascular Research Laboratories, School of Medical Sciences, University of Bristol, Bristol, United Kingdom, ^fDepartment of Biotechnology and Biosciences, University of Milano Bicocca, Milano, Italy

AIM Acquisition of the capacity to invade surrounding tissues confers a more malignant phenotype to tumor cells, and is necessary for the establishment of metastases. It has been proposed that the altered setting of the plasma membrane electric potential (Vrest) of cancer cells can contribute to tumor growth. Our studies have shown that Vrest in tumor cells can often be modulated by the activity of K+ channels, encoded by the human eag-related gene (herg). The corresponding current, IHERG, can contribute to driving the Vrest of tumor cells to more depolarized values, due to IHERG’s peculiar biophysical properties. Both the herg gene and HERG protein are indeed expressed in tumor cell lines of differing histogenesis, as well as in primary human cancers. Based on these premises, we studied the expression of HERG channels and their role in the process of tumor progression in colorectal and gastric cancers. METHODS We analyzed colon (H630, HCT8, HCT116 and DLD1) and gastric (AKG118 and KKPCO2) cancer cell lines by means of the RNase Protection Assay and Western Blot. Experiments of cell migration through Matrigel in the presence of HERG specific inhibitors (Way 123.398 and E4031) were performed on the same cell lines used above. Using Reverse Transcription-Polymerase Chain reaction and immunohistochemistry we examined 64 samples of colorectal cancers and 25 samples of gastric adenocarcinomas displaying different locations and histopathological characteristics as well as the corresponding normal mucosa; in addition we also analyzed 11 colonic adenomas and 4 metastases (3 to liver and 1 to peritoneum) arising from primary colon cancer. RESULTS Through RPA and Western Blot experiments we demonstrated that the herg1 gene and the corresponding protein are expressed in many colon and gastric cancer cell lines. We showed that the activity of HERG1 modulates cancer cell invasiveness. Moreover, we selected different clones from H630 cells which displayed different amount of the HERG1 protein at the membrane level that is directly related to the invasive phenotype of colon cancer cells. Therefore we demonstrated that both the herg1 gene and HERG1 protein are expressed in a high percentage of primary human colorectal (80%) and gastric cancers (84%), while no expression could be detected in normal colonic and gastric mucosa. Among colorectal cancers the highest incidence of HERG expression occurs in metastatic adenocarcinomas (100%) and metastases as well (100%) and only in 1 adenoma (9%). CONCLUSIONS Basing on the previous results we can conclude that HERG expression is a peculiar characteristic of a neoplastic phenotype, with the highest incidence for the more aggressive tumor cells in the gastrointestinal tract. Moreover we demonstrated that invasive phenotype is strictly related to HERG expression at the plasma membrane level infact it increases with the amount of the protein and decreases by using specific inhibitors.This features could candidate herg1 as a potential oncogene and a new prognostic factor for these tumors.

Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in poster session 892 (Susceptibility genes).