Open Access Research article

Stat3 is a positive regulator of gap junctional intercellular communication in cultured, human lung carcinoma cells

Mulu Geletu1, Rozanne Arulanandam12, Samantha Greer13, Aaron Trotman-Grant1, Evangelia Tomai14 and Leda Raptis1*

Author Affiliations

1 Departments of Microbiology and Immunology and Pathology, Queen’s University, Kingston, Ontario, K7L3N6, Canada

2 Present address: Center for Innovative Cancer Research, Ottawa Hospital Research Institute, 501 Smyth Road, Ottawa, ON K1H 8L6, Canada

3 Present address: Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada, M5S1A8

4 Present address: Institute for Physiology and Pathophysiology, Medical Faculty, University of Heidelberg, Im Neuenheimer Feld 326, Heidelberg, D-69120, Germany

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BMC Cancer 2012, 12:605  doi:10.1186/1471-2407-12-605

Published: 18 December 2012

Abstract

Background

Neoplastic transformation of cultured cells by a number of oncogenes such as src suppresses gap junctional, intercellular communication (GJIC); however, the role of Src and its effector Signal transducer and activator of transcription-3 (Stat3) upon GJIC in non small cell lung cancer (NSCLC) has not been defined. Immunohistochemical analysis revealed high Src activity in NSCLC biopsy samples compared to normal tissues. Here we explored the potential effect of Src and Stat3 upon GJIC, by assessing the levels of tyr418-phosphorylated Src and tyr705-phosphorylated Stat3, respectively, in a panel of NSCLC cell lines.

Methods

Gap junctional communication was examined by electroporating the fluorescent dye Lucifer yellow into cells grown on a transparent electrode, followed by observation of the migration of the dye to the adjacent, non-electroporated cells under fluorescence illumination.

Results

An inverse relationship between Src activity levels and GJIC was noted; in five lines with high Src activity GJIC was absent, while two lines with extensive GJIC (QU-DB and SK-LuCi6) had low Src levels, similar to a non-transformed, immortalised lung epithelial cell line. Interestingly, examination of the mechanism indicated that Stat3 inhibition in any of the NSCLC lines expressing high endogenous Src activity levels, or in cells where Src was exogenously transduced, did not restore GJIC. On the contrary, Stat3 downregulation in immortalised lung epithelial cells or in the NSCLC lines displaying extensive GJIC actually suppressed junctional permeability.

Conclusions

Our findings demonstrate that although Stat3 is generally growth promoting and in an activated form it can act as an oncogene, it is actually required for gap junctional communication both in nontransformed lung epithelial cells and in certain lung cancer lines that retain extensive GJIC.

Keywords:
Stat3; Electroporation; Indium-Tin oxide; Gap junctions; Src; Cell to cell adhesion; Lung cancer