Abstract
BackgroundSeptins are conserved GTPases that form filaments and are required in many organisms for several processes including cytokinesis. We previously identified SEPT9 associated with phagosomes containing latex beads coated with the Listeria surface protein InlB.Methodology/Principal FindingsHere, we investigated septin function during entry of invasive bacteria in non-phagocytic mammalian cells. We found that SEPT9, and its interacting partners SEPT2 and SEPT11, are recruited as collars next to actin at the site of entry of Listeria and Shigella. SEPT2-depletion by siRNA decreased bacterial invasion, suggesting that septins have roles during particle entry. Incubating cells with InlB-coated beads confirmed an essential role for SEPT2. Moreover, SEPT2-depletion impaired InlB-mediated stimulation of Met-dependent signaling as shown by FRET.Conclusions/SignificanceTogether these findings highlight novel roles for SEPT2, and distinguish the roles of septin and actin in bacterial entry.
Highlights
Septins were originally identified in Saccharomyces cerevisiae as required for septum formation and cell division [1]
Fourteen human septin genes have been identified, and septins are classified on the basis of sequence identity into 4 groups consisting of the SEPT2 group, the SEPT3 group, the SEPT6 group, and the SEPT7 group [2,12]
Characterized complexes isolated from mammalian cells include SEPT2-SEPT6-SEPT7 [14,15] and SEPT7-SEPT9SEPT11 [17]
Summary
Septins were originally identified in Saccharomyces cerevisiae as required for septum formation and cell division [1]. Septin dysfunction has been associated with several human pathological conditions such as cancer [9], hereditary neuralgic amyotrophy [10], and Parkinson disease [11]. Despite these important implications, the molecular functions of septins are poorly understood. The structure demonstrated a central role for SEPT2 in filament formation, and definitively established that septins, as opposed to actin and microtubules, form non-polar filaments. Despite these and other structural insights [12,16], to what degree septins represent a distinct component of the cytoskeleton remains to be determined. We previously identified SEPT9 associated with phagosomes containing latex beads coated with the Listeria surface protein InlB
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