Glucose-limiting conditions induce an invasive population of MDA-MB-231 breast cancer cells with increased connexin 43 expression and membrane localization

Jennifer C Jones,Mallika A Jai,Mary M Chaudhry,Alan Lazzar,Vishnupriya Bodempudi,Brian Zanotti,Bradley S Taylor,Alexander E Urban,Ellen K Kohlmeir,Romel N Pancho,Chloe S Kaunitz,Thomas M Bodenstine,Amanda M Miceli,Sheeri Hanjra,Prarthana P Jain

doi:10.1007/s12079-020-00601-3

Abstract

Gap junctional intercellular communication (GJIC) is a homeostatic process mediated by membrane channels composed of a protein family known as connexins. Alterations to channel activity can modulate suppression or facilitation of cancer progression. These varying roles are influenced by the cancer cell genetic profile and the context-dependent mechanisms of a dynamic extracellular environment that encompasses fluctuations to nutrient availability. To better explore the effects of altered cellular metabolism on GJIC in breast cancer, we generated a derivative of the triple-negative breast cancer cell line MDA-MB-231 optimized for growth in low-glucose. Reduced availability of glucose is commonly encountered during tumor development and leads to metabolic reprogramming in cancer cells. MDA-MB-231 low-glucose adapted cells exhibited a larger size with improved cell–cell contact and upregulation of cadherin-11. Additionally, increased protein levels of connexin 43 and greater plasma membrane localization were observed with a corresponding improvement in GJIC activity compared to the parental cell line. Since GJIC has been shown to affect cellular invasion in multiple cancer cell types, we evaluated the invasive qualities of these cells using multiple three-dimensional Matrigel growth models. Results of these experiments demonstrated a significantly more invasive phenotype. Moreover, a decrease in invasion was noted when GJIC was inhibited. Our results indicate a potential response of triple-negative breast cancer cells to reduced glucose availability that results in changes to GJIC and invasiveness. Delineation of this relationship may help elucidate mechanisms by which altered cancer cell metabolism affects GJIC and how cancer cells respond to nutrient availability in this regard.

Highlights

The development and progression of cancer is affected by genetic alterations within cancer cells and an everchanging microenvironment that influences their behavior
We assessed markers for apoptosis and overall cellular integrity (SYTOX) by flow cytometry demonstrating greater than 90% viability in low-glucose media similar to that of MDA-MB-231 grown in control media (Fig. 1e)
Breast cancer cells exhibit a multitude of responses to the extracellular milieu in which they exist

Summary

Introduction

The development and progression of cancer is affected by genetic alterations within cancer cells and an everchanging microenvironment that influences their behavior. The ability of cancer cells to adapt to these changing conditions increases their potential to survive and proliferate This often requires utilization of secondary fuel sources for nitrogen and carbon and necessitates modifications to biochemical pathways (DeBerardinis and Chandel 2016; Pavlova and Thompson 2016). Gap junctions are intercellular channels mediated by a family of proteins known as connexins and support cellular homeostasis by allowing the regulated passage of ions, nutrients and signaling molecules (Nielsen et al 2012). This gap junctional intercellular communication (GJIC) is often dysregulated in cancer where it is frequently decreased due to downregulation of connexin genes, mislocalization of connexin proteins and changes to cellular adhesion junctions (Aasen et al 2016). GJIC remains a dynamic process in the cancer cell, consequences of which are influenced by context-dependent mechanisms that may suppress or promote cancer cell survival and function

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Conclusion