P-199 - Degradation of CONNEXIN 43 in the plasma membrane by autophagy in colon cancer

Date 04 July 2015
Event WorldGI 2015
Session Posters
Topics Basic Science
Colon Cancer
Presenter J. Paulo
Citation Annals of Oncology (2015) 26 (suppl_4): 1-100. 10.1093/annonc/mdv233
Authors J. Paulo1, H. Gervasio2, J. Balça3, M. Areias1, L. André4, S. Catarino1, M. Zuzarte1, A. Cadime5, U. Schmidt Strassburger6, H. Girão1
  • 1Portuguese Institute of Oncology Francisco Gentil - Coimbra, Coimbra/PT
  • 2Portuguese Oncology Institute of Coimbra, Coimbra/PT
  • 3Faculty Medicine University of Coimbra - Polo III, Coimbra/PT
  • 4Portuguese Institute of Oncology Francisco Gentil, Coimbra/PT
  • 5Portugal, Coimbra/PT
  • 6Ulm University Medical Faculty Division of Learning and Teaching, Ulm/DE

Abstract

Introduction

Colorectal cancer (CRC) is a leading cause of cancer-related death in developed countries. Activation of autophagy by cancer cells under adverse conditions is often associated with tumour growth and resistance to therapeutics. Cx43, a membrane protein involved in GJIC, was down-regulated or aberrantly localized in CRC tumors, believed as a suppressor protein that predicts clinical outcome. One of the degradation mechanisms that have been involved in the regulation of Cx43 levels is autophagy, which is activated in tumor cells and contributes to cell proliferation and tumor growth. It was demonstrated that human CRC development is associated with either loss of Cx43 or relocalization of Cx43 from GJ plaques to intracellular compartments and that overexpression of Cx43 in colon cancer cell lines lacking Cx43 results in reduced growth and regression of tumour xenografts. Since upregulation of connexin expression has been found to result in reduced tumor growth in several cancer types, connexins have been suggested to represent potential target proteins in cancer prevention and therapy. The objective of this study is to evaluate whether activation of autophagy in colon cancer is associated with Cx43 degradation and if that degradation is made by autophagy. Also, study if there is a gradual difference between colon adenomas and colon cancer influencing GJIC's impairment and contributing to the progression of CRC and possible association to a poorer clinical outcome.

Methods

Fresh tissue samples of the 50 human colon cancer and colon polyps were collected from the patients who underwent diagnostic or revaluation colonoscopies. We analyzed: 1. connexin 43's localization by fluorescent immunostaining and determine its co-localization with autophagy markers LC3 and p62 (experiment 1); 2. We quantified a possible reduction in mRNA of connexin 43 from pre-malignant lesions comparing to malignant lesions, along with an increase of the autophagy markers' mRNA expression (experiment 2); 3. observed the cellular ultrastructure we aimed to compare the membranous structure between lesions and, if possible, find signs of autophagy involving the intercellular adhesion structures (experiment 3).

Results

In experiment 1 we've found compatible results as other authors where the sub-membranous location of connexin 43 in benign colon lesions and a merged cytoplasmic Cx43 distribution pattern in colon carcinoma. In experiment 2 we did not achieve any statistically significant reduction of connexin 43 mRNA levels comparing benign to malignant colon lesions, as it may be attributed to a eventual post-transcriptional regulation of this molecule. Furthermore, still in this experiment the autophagy marker was unexpectedly present in both samples, with an increasing trend in the malignant lesion. In experiment 3 our results were consistent with membrane ultrastructure disruption and loss of intercellular adhesion structures in colon carcinoma, along with a chaotic multi vesicle cellular structure.

Conclusion

Despite preliminary results we believe that autophagy might be the process involved in connexin 43 degradation. Furthermore, as several autophagy inhibitors are proven to be consistent therapeutic agents, an important subject for future studies will be to determine whether connexins are causally involved in the reduced neoplastic potential of cancer cells and if the process involved is autophagy.

Figure: P-199