HIV-1 Tat and Heparan Sulfate Proteoglycans Orchestrate the Setup of in Cis and in Trans Cell-Surface Interactions Functional to Lymphocyte Trans-Endothelial Migration.

Chiara Urbinati,Maria Milanesi,Marco Rusnati,Nicola Lauro,Guido David,Paola Chiodelli,Cinzia Bertelli,Pasqualina D’Ursi

doi:10.3390/molecules26247488

Abstract

HIV-1 transactivating factor Tat is released by infected cells. Extracellular Tat homodimerizes and engages several receptors, including integrins, vascular endothelial growth factor receptor 2 (VEGFR2) and heparan sulfate proteoglycan (HSPG) syndecan-1 expressed on various cells. By means of experimental cell models recapitulating the processes of lymphocyte trans-endothelial migration, here, we demonstrate that upon association with syndecan-1 expressed on lymphocytes, Tat triggers simultaneously the in cis activation of lymphocytes themselves and the in trans activation of endothelial cells (ECs). This “two-way” activation eventually induces lymphocyte adhesion and spreading onto the substrate and vascular endothelial (VE)-cadherin reorganization at the EC junctions, with consequent endothelial permeabilization, leading to an increased extravasation of Tat-presenting lymphocytes. By means of a panel of biochemical activation assays and specific synthetic inhibitors, we demonstrate that during the above-mentioned processes, syndecan-1, integrins, FAK, src and ERK1/2 engagement and activation are needed in the lymphocytes, while VEGFR2, integrin, src and ERK1/2 are needed in the endothelium. In conclusion, the Tat/syndecan-1 complex plays a central role in orchestrating the setup of the various in cis and in trans multimeric complexes at the EC/lymphocyte interface. Thus, by means of computational molecular modelling, docking and dynamics, we also provide a characterization at an atomic level of the binding modes of the Tat/heparin interaction, with heparin herein used as a structural analogue of the heparan sulfate chains of syndecan-1.

Highlights

Heparan sulfate proteoglycans (HSPGs) are intimately associated with the cell surface and consist of multiple heparin-like glycosaminoglycan (GAG) chains attached to a core protein associated with the cell membrane either via a transmembrane protein domain or via a glycosyl-phosphatidyl-inositol anchor [1]
Extracellular Tat released by leukocytes acts in a paracrine manner on different uninfected cell types, including endothelial cells (ECs), where it interacts with HSPGs, inducing the in cis recruitment and activation of other signaling receptors, such as integrins, vascular endothelial growth factor receptor 2 (VEGFR2) and chemokine receptors [8,9]
These are B-lymphoid cells that, in their parental form or when transfected with an empty vector (EV-Namalwa cells (NCs)), do not express significant levels of HSPGs [24] on their surface and do not adhere to plastic-immobilized Tat or to an EC monolayer enriched with Tat, a capability that is instead acquired when transfected to overexpress syndecan-1 on their surface (SYN-NCs) [6]

Summary

Introduction

Heparan sulfate proteoglycans (HSPGs) are intimately associated with the cell surface and consist of multiple heparin-like glycosaminoglycan (GAG) chains attached to a core protein associated with the cell membrane either via a transmembrane protein domain or via a glycosyl-phosphatidyl-inositol anchor [1]. Tat and HSPGs orchestrate the setup of various in cis and in trans multimeric complexes involving different receptors, cytoskeleton components and second messengers that lead to the stimulation of both ECs and HIV+ lymphocytes, eventually leading to the extravasation of the latter. This favors HIV dissemination, the creation of reservoirs of infection in different organs [13] and the rise of AIDS-associated pathologies, such as lymphadenopathies, polyclonal B-cell activation, Kaposi sarcoma, and non-Hodgkin lymphoma [6,12]

Methods

Results

Conclusion