Fibroblast growth factor receptor-1 mediates internalization of pathogenic spotted fever rickettsiae into host endothelium

Abstract

Rickettsial infections continue to cause serious morbidity and mortality in severe human cases around the world. Host cell adhesion and invasion is an essential requisite for intracellular growth, replication, and subsequent dissemination of pathogenic rickettsiae. Heparan sulfate proteoglycans [HSPGs] facilitate the interactions between fibroblast growth factor(s) and their tyrosine kinase receptors resulting in receptor dimerization/activation and have been implicated in bacterial adhesion to target host cells. In the present study, we have investigated the contributions of fibroblast growth factor receptors [FGFRs] in rickettsial entry into the host cells. Inhibition of HSPGs by heparinase and FGFRs by AZD4547 (a selective small-molecule inhibitor) results in significant reduction in rickettsial internalization into cultured human microvascular endothelial cells (ECs), which represent the primary targets of pathogenic rickettsiae during human infections. Administration of AZD4547 during R. conorii infection in a murine model of endothelial-target spotted fever rickettsiosis also diminishes pulmonary rickettsial burden in comparison to mock-treated controls. Silencing of FGFR1 expression using a small interfering RNA also leads to similar inhibition of R. rickettsii invasion into ECs. Consistent with these findings, R. rickettsii infection of ECs also results in phosphorylation of tyrosine 653/654, suggesting activation of FGFR1. Using isobaric tag for relative and absolute quantitation [iTRAQ]-based proteomics approach, we further demonstrate association of β-peptide of rickettsial outer membrane protein OmpA with FGFR1. Mechanistically, FGFR1 binds to caveolin-1 and mediates bacterial entry via caveolin-1 dependent endocytosis. Together, these results identify host cell FGFR1 and rickettsial OmpA as another novel receptor-ligand pair contributing to the internalization of pathogenic rickettsiae into host endothelial cells and the potential application of FGFR-inhibitor drugs as adjunct therapeutics against spotted fever rickettsioses.

Comparative transcriptomic analysis of Rickettsia conorii during in vitro infection of human and tick host cells

“…At the end of incubation, monolayer was washed twice with sterile PBS and genomic DNA was extracted using a DNeasy blood and tissue kit (Qiagen) following the manufacturer's protocol. Absolute quantification of rickettsial load was performed by q-PCR using citrate synthase gene specific primers described previously [92,93].…”

FGFR1 clustering with engineered tetravalent antibody improves the efficiency and modifies the mechanism of receptor internalization

“…A number of proteins involved in CME of FGFR1 in response to FGF binding were identified,however, the exact role of a number of these factors in the receptor internalization is still largely mysterious [31,40–44]. Besides CME, clathrin‐independent endocytosis (CIE) may participate in FGFR1 internalization [34,45,46]. A mechanism determining which particular endocytic route(s) will be employed by FGFR1 is currently unknown.…”

Targeting Cellular Trafficking of Fibroblast Growth Factor Receptors as a Strategy for Selective Cancer Treatment

“…Rickettsia rickettsia , pathogenic Gram-nagative bacteria causing spotted fever in humans, interact with FGFR1 on the surface of the host cells. It is noteworthy that the bacteria are internalized via the FGFR1-dependent, caveolin-mediated endocytic pathway [150]. Syndecan-4 (S4) is a heparan sulfate proteoglycan involved in cell migration and adhesion.…”