Distinct kinetic and mechanical properties govern mucin 16- and podocalyxin-mediated tumor cell adhesion to E- and L-selectin in shear flow.

Daniel J Shea,Denis Wirtz,Kathleen J Stebe,Konstantinos Konstantopoulos

doi:10.18632/oncotarget.4704

Daniel J Shea, Denis Wirtz + Show 2 more

Open Access

https://doi.org/10.18632/oncotarget.4704

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Abstract

Selectin-mediated tumor cell tethering to host cells, such as vascular endothelial cells, is a critical step in the process of cancer metastasis. We recently identified sialofucosylated mucin16 (MUC16) and podocalyxin (PODXL) as the major functional E- and L-selectin ligands expressed on the surface of metastatic pancreatic cancer cells. While the biophysics of leukocyte binding to selectins has been well studied, little is known about the mechanics of selectin-mediated adhesion pertinent to cancer metastasis. We thus sought to evaluate the critical parameters of selectin-mediated pancreatic tumor cell tethering and rolling. Using force spectroscopy, we characterized the binding interactions of MUC16 and PODXL to E- and L-selectin at the single-molecule level. To further analyze the response of these molecular interactions under physiologically relevant regimes, we used a microfluidic assay in conjunction with a mathematical model to study the biophysics of selectin-ligand binding as a function of fluid shear stress. We demonstrate that both MUC16 and PODXL-E-selectin-mediated interactions are mechanically stronger than like L-selectin interactions at the single-molecule level, and display a higher binding frequency at all contact times. The single-molecule kinetic and micromechanical properties of selectin-ligand bonds, along with the number of receptor-ligand bonds needed to initiate tethering, regulate the average velocity of ligand-coated microspheres rolling on selectin-coated surfaces in shear flow. Understanding the biophysics of selectin-ligand bonds and their responses to physiologically relevant shear stresses is vital for developing diagnostic assays and/or preventing the metastatic spread of tumor cells by interfering with selectin-mediated adhesion.

Highlights

E- and L-selectins play a vital role in cell-cell interactions pertinent to cancer metastasis
E- or Lselectin-coated cantilevers were brought in contact with immunopurified mucin 16 (MUC16) or PODXL inserted in a lipid bilayer for a constant dwell time and retracted at designated retraction speeds
The adhesive interactions between selectins on host cells and their respective ligands expressed on tumor cells are known to facilitate tumor cell arrest in the microvasculature and promote cancer metastasis [1, 3]

Summary

Introduction

E- and L-selectins play a vital role in cell-cell interactions pertinent to cancer metastasis. E- and L-selectins share a similar structure, their binding kinetics and distribution differ considerably leading to distinct roles in cancer metastasis. Because the binding affinity of selectins for monocovalent sLex/a is low, it is vital to distinguish between structures that only interact with selectins in vitro and the functional selectin ligands [4] that interact with selectins selectively and with high affinity in vivo and whose depletion suppresses selectindependent binding. We recently identified sialofucosylated mucin 16 (MUC16) and podocalyxin (PODXL) as the major functional E- and L-selectin ligands expressed on the surface of metastatic pancreatic cancer cells [11, 12]

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