Ehrlichiasecretes Etf-1 to induce autophagy and capture nutrients for its growth through RAB5 and class III phosphatidylinositol 3-kinase

Abstract

Ehrlichia chaffeensis is an obligatory intracellular bacterium that causes a potentially fatal emerging zoonosis, human monocytic ehrlichiosis. E. chaffeensis has a limited capacity for biosynthesis and metabolism and thus depends mostly on host-synthesized nutrients for growth. Although the host cell cytoplasm is rich with these nutrients, as E. chaffeensis is confined within the early endosome-like membrane-bound compartment, only host nutrients that enter the compartment can be used by this bacterium. How this occurs is unknown. We found that ehrlichial replication depended on autophagy induction involving class III phosphatidylinositol 3-kinase (PtdIns3K) activity, BECN1 (Beclin 1), and ATG5 (autophagy-related 5). Ehrlichia acquired host cell preincorporated amino acids in a class III PtdIns3K-dependent manner and ehrlichial growth was enhanced by treatment with rapamycin, an autophagy inducer. Moreover, ATG5 and RAB5A/B/C were routed to ehrlichial inclusions. RAB5A/B/C siRNA knockdown, or overexpression of a RAB5-specific GTPase-activating protein or dominant-negative RAB5A inhibited ehrlichial infection, indicating the critical role of GTP-bound RAB5 during infection. Both native and ectopically expressed ehrlichial type IV secretion effector protein, Etf-1, bound RAB5 and the autophagy-initiating class III PtdIns3K complex, PIK3C3/VPS34, and BECN1, and homed to ehrlichial inclusions. Ectopically expressed Etf-1 activated class III PtdIns3K as in E. chaffeensis infection and induced autophagosome formation, cleared an aggregation-prone mutant huntingtin protein in a class III PtdIns3K-dependent manner, and enhanced ehrlichial proliferation. These data support the notion that E. chaffeensis secretes Etf-1 to induce autophagy to repurpose the host cytoplasm and capture nutrients for its growth through RAB5 and class III PtdIns3K, while avoiding autolysosomal killing.

Bartonella quintana type IV secretion effector BepE ‐induced selective autophagy by conjugation with K63 polyubiquitin chain

“…Modulation of the mTOR‐dependent pathway is the most classic way to regulate autophagy, how to regulate selective autophagy is still a challenge (Kirkin, McEwan, Novak, & Dikic, ). Unlike above‐mentioned Etf‐1‐induced autophagy that was reliant on mTOR pathway (Lin et al, ), we found that BepE‐induced autophagy is PI3K/mTOR‐independent because 3‐MA treatment failed to inhibit autophagosome formation. This was also observed in Vibrio VopQ‐induced autophagy that was not affected by treatment with wortmannin (a potent PI3K inhibitor; Burdette, Seemann, & Orth, ).…”

“…Autophagy, initiated by bacterial effector, was reported to capture nutrient and benefit bacterial growth (Lin et al, ; Niu & Rikihisa, ). Although we have identified Bqu ‐BepE activated cellular autophagy via its ubiquitination, it is not clear whether B .…”

“…Only two T4SS effectors Ats‐1 and Etf‐1 from obligate intracellular pathogens ( Anaplasma phagocytophilum and Ehrlichia chaffeensis ) are reported to induce cell autophagy directly. Ats‐1 and Etf‐1 bind to Beclin‐1 or Rab5 and Ptdlns3k complex and subsequently recruited autophagosomes to Anaplasma and Ehrlichia inclusions, respectively, to benefit the bacterial replication, respectively (Lin et al, ; Niu & Rikihisa, ). In addition, autophagy induced by bacterial cytotoxins acting as a host mechanism to protect from cell death was described for a cytolysin from Vibrio cholerae and vacuolating cytotoxin from Helicobacter pylori (Gutierrez et al, ).…”

“…Autophagy, initiated by bacterial effector, was reported to capture nutrient and benefit bacterial growth (Lin et al, 2016;Niu & Rikihisa, 2013 Figure 8a). On the contrary, we identified that cells with BepE-induced autophagy were about threefold more effective at engulfing B. quintana than cells with BepE-induced filopodia and membrane ruffles (Figure 8b-d).…”

Orientia tsutsugamushi Modulates Endoplasmic Reticulum-Associated Degradation To Benefit Its Growth

“…O. tsutsugamushi elicits but is not cleared by autophagy (56,57), autophagy is induced by and decreases ER stress (58), and amino acids resulting from autophagy benefit the intracellular growth of Anaplasma phagocytophilum and Ehrlichia chaffeensis (59,60), which are obligate intracellular bacteria that are in the order Rickettsiales with O. tsutsugamushi. Amino acids resulting from the autophagy response to O. tsutsugamushi-induced ER stress might a The predicted biological score (PBS) was calculated for each candidate protein to assess the reliability of each interaction, ranging from the highest probability of specificity (score of A) to the lowest probability of specificity (score of E) between two proteins.…”