Connexin-43 upregulation in micrometastases and tumor vasculature and its role in tumor cell attachment to pulmonary endothelium.
BACKGROUND
The modulation of gap junctional communication between tumor cells and between tumor and vascular endothelial cells during tumorigenesis and metastasis is complex. The notion of a role for loss of gap junctional intercellular communication in tumorigenesis and metastasis has been controversial. While some of the stages of tumorigenesis and metastasis, such as uncontrolled cell division and cellular detachment, would necessitate the loss of intercellular junctions, other stages, such as intravasation, endothelial attachment, and vascularization, likely require increased cell-cell contact. We hypothesized that, in this multi-stage scheme, connexin-43 is centrally involved as a cell adhesion molecule mediating metastatic tumor attachment to the pulmonary endothelium.


METHODS
Tumor cell attachment to pulmonary vasculature, tumor growth, and connexin-43 expression was studied in metastatic lung tumor sections obtained after tail-vein injection into nude mice of syngeneic breast cancer cell lines, overexpressing wild type connexin-43 or dominant-negatively mutated connexin-43 proteins. High-resolution immunofluorescence microscopy and Western blot analysis was performed using a connexin-43 monoclonal antibody. Calcein Orange Red AM dye transfer by fluorescence imaging was used to evaluate the gap junction function.


RESULTS
Adhesion of breast cancer cells to the pulmonary endothelium increased with cancer cells overexpressing connexin-43 and markedly decreased with cells expressing dominant-negative connexin-43. Upregulation of connexin-43 was observed in tumor cell-endothelial cell contact areas in vitro and in vivo, and in areas of intratumor blood vessels and in micrometastatic foci.


CONCLUSIONS
Connexin-43 facilitates metastatic 'homing' by increasing adhesion of cancer cells to the lung endothelial cells. The marked upregulation of connexin-43 in tumor cell-endothelial cell contact areas, whether in preexisting 'homing' vessels or in newly formed tumor vessels, suggests that connexin-43 can serve as a potential marker of micrometastases and tumor vasculature and that it may play a role in the early incorporation of endothelial cells into small tumors as seeds for vasculogenesis.
Elzarrad
M Khair
MK
Department of Pharmacology and Center for Lung Biology, University of South Alabama, North University Boulevard, Mobile, AL 36688, USA. mke303@jaguar1.usouthal.edu
Haroon
Abu
A
Willecke
Klaus
K
Dobrowolski
Radoslaw
R
Gillespie
Mark N
MN
Al-Mehdi
Abu-Bakr
AB
D000818:Animals; D002448:Cell Adhesion / Q000235:genetics; D045744:Cell Line, Tumor; D018031:Connexin 43 / Q000096:biosynthesis / Q000097:blood / Q000235:genetics*; D004730:Endothelium, Vascular / Q000378:metabolism / Q000473:pathology; D005260:Female; D017629:Gap Junctions / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D008168:Lung / Q000473:pathology; D008175:Lung Neoplasms / Q000098:blood supply / Q000556:secondary*; D008325:Mammary Neoplasms, Experimental / Q000098:blood supply / Q000473:pathology*; D051379:Mice; D008819:Mice, Nude; D020125:Mutation, Missense; D009368:Neoplasm Transplantation; D009375:Neoplasms, Glandular and Epithelial / Q000098:blood supply / Q000556:secondary*; D009389:Neovascularization, Pathologic / Q000097:blood / Q000235:genetics* / Q000473:pathology*; D051381:Rats; D014162:Transfection
D018031:Connexin 43