Oncogenic extracellular HSP70 disrupts the gap-junctional coupling between capillary cells.

Dominique Thuringer,Eric Solary,Carmen Garrido,Gaetan Jego,Laurent Cronier,Kevin Berthenet

doi:10.18632/oncotarget.3522

Abstract

High levels of circulating heat shock protein 70 (HSP70) are detected in many cancers. In order to explore the effects of extracellular HSP70 on human microvascular endothelial cells (HMEC), we initially used gap-FRAP technique. Extracellular human HSP70 (rhHSP70), but not rhHSP27, blocks the gap-junction intercellular communication (GJIC) between HMEC, disrupts the structural integrity of HMEC junction plaques, and decreases connexin43 (Cx43) expression, which correlates with the phosphorylation of Cx43 serine residues. Further exploration of these effects identified a rapid transactivation of the Epidermal Growth Factor Receptor in a Toll-Like Receptor 4-dependent manner, preceding its internalization. In turn, cytosolic Ca2+ oscillations are generated. Both GJIC blockade and Ca2+ mobilization partially depend on ATP release through Cx43 and pannexin (Panx-1) channels, as demonstrated by blocking activity or expression of channels, and inactivating extracellular ATP. By monitoring dye-spreading into adjacent cells, we show that HSP70 released from human monocytes in response to macrophage colony-stimulating factor, prevents the formation of GJIC between monocytes and HMEC. Therapeutic manipulation of this pathway could be of interest in inflammatory and tumor growth.

Highlights

Heat shock protein 70 (HSP70) which was initially described as an intracellular protein [1,2,3] is released into the circulation under various stress conditions [4,5,6,7,8,9]
Because LPS or EGF induce Cx43 phosphorylation leading to gap junctional intercellular communication (GJIC) abrogation [28, 29], we examined whether extracellular HSP70, exogenously added or released from circulating monocytes, modulates GJIC and Cx43-hemichannel functions in human microvascular endothelial cells (HMEC) via the engagement of specific membrane receptor-associated signaling pathways in HMEC
We show that extracellular HSP70 decreases expression of Cx43 at the plasma membrane and induces hyperphosphorylation of Cx43 in a time-dependent manner, leading to GJIC blockage

Summary

Introduction

Heat shock protein 70 (HSP70) which was initially described as an intracellular protein [1,2,3] is released into the circulation under various stress conditions [4,5,6,7,8,9]. Circulating HSP70 is increased in pathological conditions including cancer cell invasiveness and metastasis [10,11,12]. Connexins expressed within the vasculature include Cx37, 40, 43 and 45 [15, 16] They are differentially expressed along the vascular tree, Cx43 is the most widely and highly expressed protein in all cell models and human tissues. The permeability of gap junctions can be affected by a number of mechanisms, including changes in cytosolic www.impactjournals.com/oncotarget ion concentrations and Cx43 phosphorylation [17]. Their aberrant function has been associated with a number of pathological conditions, including cancer and inflammation [18,19,20,21]

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Results

Conclusion