Molecular plasticity of E-cadherin and sialyl lewis x expression, in two comparative models of mammary tumorigenesis

Abstract

Background: The process of metastasis involves a series of steps and interactions between the tumor embolus and the microenvironment. Key alterations in adhesion molecules are known to dictate progression from the invasive to malignant phenotype followed by colonization at a distant site. The invasive phenotype results from the loss of expression of the E-cadherin adhesion molecule, whereas the malignant phenotype is associated with an increased expression of the carbohydrate ligand-binding epitopes, (e.g. Sialyl Lewis (x/a)) that bind endothelial E-selectin of the lymphatics and vasculature.

Methodology: Our study analyzed the expression of two adhesion molecules, E-cadherin and Sialyl Lewis x (sLe(x)), in both a canine mammary carcinoma and human inflammatory breast cancer (IBC) model, using double labelled immunofluorescence staining.

Results: Our results demonstrate that canine mammary carcinoma and human IBC exhibit an inversely correlated cellular expression of E-cadherin and sLe(x) within the same tumor embolus.

Conclusions: Our results in these two comparative models (canine and human) suggest the existence of a biologically coordinated mechanism of E-cadherin and sLe(x) expression (i.e. molecular plasticity) essential for tumor establishment and metastatic progression.

Figure 1. Expression of E-cadherin and sLe^x in the MARY-X spheroid.

(A) MARY-X in vitro spheroid forms a compact, clump of cells due to over-expression of a key adhesion molecule, E-cadherin (light microscopy; 40× magnification). (B) Illustrates a heterogeneous population of cellular expression with a dominant population of cells expressing membrane-positioned E-cadherin (green) and a minority population of cells expressing sLe^x (red). (C & D) sLe^x was found to be either cytoplasmic- (long arrows) or membrane-positioned (blunt arrows).

Figure 2. Expression of E-cadherin and sLe^x throughout the metastatic progression of MARY-X and canine mammary carcinoma.

(A, B) Shows a heterogeneous population of cellular expression in both (A) MARY-X primary tumors and (B) canine primary tumors (carcinosarcoma and solid carcinoma) displaying a dominant population of cells with membrane-positioned E-cadherin (green) and smaller nests sLe^x (red) expressing cells (cytoplasmic or membrane-positioned). (A, B; middle panels) Magnified image shows the sLe^x found either cytoplasmic- (long arrows) or membrane-positioned (blunt arrows). Mary-X lung metastasis (MARY-X metastasis) displays a dominant population of cells expressing only E-cadherin (green), and a minority population of cells co-expressing cytoplasmic-positioned sLe^x (red) (long arrows). (B, C) Canine lung metastasis (Canine metastasis) displays a dominant population of cells expressing only E-cadherin (green), and minority populations of cells either co-expressing cytoplasmic-positioned sLe^x (red) (long arrows) or expressing only membrane-positioned sLe^x (red) (blunt arrows).

Figure 3. E-cadherin immunoprecipitation of CMT-U27 cell line.

The left lane shows the E-cadherin immunoprecipitate. The right lane shows the absence of sLe^x in the E-cadherin immunoprecipitate. The 50 kDa bands in both lanes are the immunoglobulin heavy chain.