E-Cadherin Regulates HIF1-α In Vitro in Induced 3D Spheroid Models of Human Breast Cancer Through Both mTOR and Notch1 Signaling.

Background: Both spontaneous and induced 3D spheroid models are among many in vitro models that recapitulate aspects of in vivo cancers. Although numerous studies have described the spatiotemporal relevance of these 3D models, there has been a paucity of studies investigating the signaling pathways that are activated during spheroidgenesis. Methods: Since in vitro 3D spheroidgenesis is thought to reflect at least some of the in vivo aspects of cancer biology (which undoubtedly involve cell adhesion, metabolism, and hypoxia-related pathways) and since we previously investigated these pathways in a model of spontaneous spheroidgenesis, this present study investigates these pathways in a model of induced spheroidgenesis with comparative studies involving a series of well-known E-cadherin-positive (MCF-7, HTB-126, HTB-27) and E-cadherin-negative (MDA-MB-468, MDA-MB-231, BT-549) human breast carcinoma cell lines. Results: Our findings demonstrate that during early induced spheroidgenesis, E-cadherin regulates hypoxia-inducible factor 1-alpha (HIF-1α) predominantly through PI3K/AKT/mTOR signaling and to a lesser extent through Notch1 signaling. Both the knockout of E-cadherin and calpain-mediated E-cadherin proteolysis result in a remarkable reduction in HIF-1α. Conclusions: 3D spheroid models recapitulate, in part, some of the in vivo stages of cancer progression, which include primary tumor clusters, lymphovascular emboli, and micrometastases, the signaling pathways present in these 3D spheroid models likely have relevance in vivo.