A role for tetraspanin proteins in regulating fusion induced by Burkholderia thailandensis

Atiga Elgawidi,Muslim Idan Mohsin,Fawwaz Ali,Amyleigh Watts,Peter N Monk,Mark S Thomas,Lynda J Partridge

doi:10.1007/s00430-020-00670-6

Abstract

Burkholderia pseudomallei is the causative agent of melioidosis, a disease with high morbidity that is endemic in South East Asia and northern Australia. An unusual feature of the bacterium is its ability to induce multinucleated giant cell formation (MNGC), which appears to be related to bacterial pathogenicity. The mechanism of MNGC formation is not fully understood, but host cell factors as well as known bacterial virulence determinants are likely to contribute. Since members of the tetraspanin family of membrane proteins are involved in various types of cell:cell fusion, their role in MNGC formation induced by Burkholderia thailandensis, a mildly pathogenic species closely related to B. pseudomallei, was investigated. The effect of antibodies to tetraspanins CD9, CD81, and CD63 in MNGC formation induced by B. thailandensis in infected mouse J774.2 and RAW macrophage cell lines was assessed along with that of recombinant proteins corresponding to the large extracellular domain (EC2) of the tetraspanins. B. thailandensis-induced fusion was also examined in macrophages derived from CD9 null and corresponding WT mice, and in J774.2 macrophages over-expressing CD9. Antibodies to CD9 and CD81 promoted MNGC formation induced by B. thailandensis, whereas EC2 proteins of CD9, CD81, and CD63 inhibited MNGC formation. Enhanced MNGC formation was observed in CD9 null macrophages, whereas a decrease in MNGC formation was associated with overexpression of CD9. Overall our findings show that tetraspanins are involved in MNGC formation induced by B. thailandensis and by implication, B. pseudomallei, with CD9 and CD81 acting as negative regulators of this process.

Highlights

Melioidosis is a serious disease with a wide range of manifestations, depending on the route of infection
Our findings demonstrate that tetraspanins act to regulate multinucleated giant cell formation (MNGC) formation induced by B. thailandensis in mouse macrophages, with CD9 in particular acting as a negative regulator of this process
Our initial investigations showed that whilst undifferentiated or phorbol myristate acetate (PMA)-differentiated U937 cells and THP1 cells were infected by E264 and CDC72 strains of B. thailandensis, no MNGC formation was observed in these human mononuclear phagocyte cell lines

Summary

Introduction

Melioidosis is a serious disease with a wide range of manifestations, depending on the route of infection. The causative agent, Burkholderia pseudomallei, is a Gram-negative bacillus that is endemic in the tropics [1, 2]. The bacterium is normally resident in soil and acts as an opportunistic pathogen. There is little evidence of person:person transmission and infection occurs after exposure to contaminated soil/aerosols: increased risk factors for contracting the disease include diabetes and excessive alcohol consumption [3]. Most notified cases of melioidosis are in South East Asia and northern Australia, but underreporting is likely exacerbated by its similarity to other infectious conditions (notably tuberculosis). Despite recent estimates that it causes more fatalities (89,000 per annum) than Dengue fever [2], melioidosis has been relatively neglected and its prevalence underestimated.

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