Syndecan-1 Shedding Is Enhanced by LasA, a Secreted Virulence Factor of Pseudomonas aeruginosa

Abstract

Microbial pathogens frequently take advantage of host systems for their pathogenesis. Shedding of cell surface molecules as soluble extracellular domains (ectodomains) is one of the host responses activated during tissue injury. In this study, we examined whether pathogenic bacteria can modulate shedding of syndecan-1, the predominant syndecan of host epithelia. Our studies found that overnight culture supernatants of Pseudomonas aeruginosa and Staphylococcus aureus enhanced the shedding of syndecan-1 ectodomains, whereas culture supernatants of several other Gramnegative and Gram-positive bacteria had only low levels of activity. Because supernatants from all tested strains of P. aeruginosa (n ‫؍‬ 9) enhanced syndecan-1 shedding by more than 4-fold above control levels, we focused our attention on this Gram-negative bacterium. Culture supernatants of P. aeruginosa increased shedding of syndecan-1 in both a concentration-and time-dependent manner, and augmented shedding by various host cells. A 20-kDa shedding enhancer was partially purified from the supernatant through ammonium sulfate precipitation and gel chromatography, and identified by N-terminal sequencing as LasA, a known P. aeruginosa virulence factor. LasA was subsequently determined to be a syndecan-1 shedding enhancer from the findings that (i) immunodepletion of LasA from the partially purified sample resulted in abrogation of its activity to enhance shedding and (ii) purified LasA increased shedding in a concentration-dependent manner. Our results also indicated that LasA enhances syndecan-1 shedding by activation of the host cell's shedding mechanism and not by direct interaction with syndecan-1 ectodomains. Enhanced syndecan-1 shedding may be a means by which pathogenic bacteria take advantage of a host mechanism to promote their pathogenesis.

Innate immune signaling induces expression and shedding of the heparan sulfate proteoglycan syndecan‐4 in cardiac fibroblasts and myocytes, affecting inflammation in the pressure‐overloaded heart

“…100 Shedding of syndecan ectodomains occurs constitutively in some cultured cells, but is accelerated during wound healing and in response to pathological stimuli. [101][102][103][104] Indeed, syndecan ectodomains accumulate in wound fluids, consistent with a role in regulating pathophysiological events during inflammation.…”

“…[101][102][103][104] Thus, when studying the function of syndecans in disease, the picture is is likely to increase levels of shedding, was found to be protective in rat hearts post-MI. 207 Our findings in Paper II are the first to shed light on the functional effects of increased syndecan-4 shedding in the heart, indicating that during an acute inflammatory response, the increased shedding of syndecan-4 represents a protective mechanism that mitigates cardiac dysfunction and ensures a properly coordinated immune response by promoting recruitment of immune cells.…”

Enhanced bacterial virulence through exploitation of host glycosaminoglycans

“…Host HSPGs are used by pathogenic bacteria not only to mediate their attachment but also to enhance their virulence by a mechanism termed shedding, as recently described for Pseudomonas aeruginosa and Staphylococcus aureus (Park et al, 2000). The shedding mechanism involves cleavage of cell-surface proteins and release of their ectodomains from the surface as soluble effectors (Bernfield et al, 1999).…”

2-O-Sulfated Domains in Syndecan-1 Heparan Sulfate Inhibit Neutrophil Cathelicidin and Promote Staphylococcus aureus Corneal Infection

“…Syndecan-1 is the predominant HSPG of epithelial cells, a cell type that most bacteria first encounter during their pathogenesis (8). S. aureus (16), P. aeruginosa (17), and S. pneumoniae (18) induce the shedding of syndecan-1 ectodomains from the cell surface through specific virulence factors in cultured epithelial cells. Moreover, in mice, syndecan-1 ablation is a gain of function of mutation where the syndecan-1 null (Sdc1 Ϫ/Ϫ ) mice are significantly protected from P. aeruginosa (19) and S. aureus (20) lung infection, and S. aureus corneal infection (21) compared with wild type (Wt) mice, suggesting that syndecan-1 shedding promotes bacterial pathogenesis.…”