{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,30]],"date-time":"2026-04-30T14:54:13Z","timestamp":1777560853152,"version":"3.51.4"},"reference-count":36,"publisher":"MDPI AG","issue":"19","license":[{"start":{"date-parts":[[2020,9,29]],"date-time":"2020-09-29T00:00:00Z","timestamp":1601337600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100000060","name":"National Institute of Allergy and Infectious Diseases","doi-asserted-by":"publisher","award":["1 R21 AI144888-01A1 and 5 R01 AI127899-03"],"award-info":[{"award-number":["1 R21 AI144888-01A1 and 5 R01 AI127899-03"]}],"id":[{"id":"10.13039\/100000060","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Institute for Human Infections and Immunity (IHII), University of Texas Medical Branch (UTMB)","award":["None"],"award-info":[{"award-number":["None"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>Attributed to the tropism for host microvascular endothelium lining the blood vessels, vascular inflammation and dysfunction represent salient features of rickettsial pathogenesis, yet the details of fundamentally important pathogen interactions with host endothelial cells (ECs) as the primary targets of infection remain poorly appreciated. Mechanistic target of rapamycin (mTOR), a serine\/threonine protein kinase of the phosphatidylinositol kinase-related kinase family, assembles into two functionally distinct complexes, namely mTORC1 (Raptor) and mTORC2 (Rictor), implicated in the determination of innate immune responses to intracellular pathogens via transcriptional regulation. In the present study, we investigated activation status of mTOR and its potential contributions to host EC responses during Rickettsia rickettsii and R. conorii infection. Protein lysates from infected ECs were analyzed for threonine 421\/serine 424 phosphorylation of p70 S6 kinase (p70 S6K) and that of serine 2448 on mTOR itself as established markers of mTORC1 activation. For mTORC2, we assessed phosphorylation of protein kinase B (PKB or Akt) and protein kinase C (PKC), respectively, on serine 473 and serine 657. The results suggest increased phosphorylation of p70 S6K and mTOR during Rickettsia infection of ECs as early as 3 h and persisting for up to 24 h post-infection. The steady-state levels of phospho-Akt and phospho-PKC were also increased. Infection with pathogenic rickettsiae also resulted in the formation of microtubule-associated protein 1A\/1B-light chain 3 (LC3-II) puncta and increased lipidation of LC3-II, a response significantly inhibited by introduction of siRNA targeting mTORC1 into ECs. These findings thus yield first evidence for the activation of both mTORC1 and mTORC2 during EC infection in vitro with Rickettsia species and suggest that early induction of autophagy in response to intracellular infection might be regulated by this important pathway known to function as a central integrator of cellular immunity and inflammation.<\/jats:p>","DOI":"10.3390\/ijms21197179","type":"journal-article","created":{"date-parts":[[2020,9,29]],"date-time":"2020-09-29T08:43:27Z","timestamp":1601369007000},"page":"7179","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Activation of Mechanistic Target of Rapamycin (mTOR) in Human Endothelial Cells Infected with Pathogenic Spotted Fever Group Rickettsiae"],"prefix":"10.3390","volume":"21","author":[{"given":"Abha","family":"Sahni","sequence":"first","affiliation":[{"name":"Department of Pathology, University of Texas Medical Branch (UTMB), Galveston, TX 77555-0609, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Hema P.","family":"Narra","sequence":"additional","affiliation":[{"name":"Department of Pathology, University of Texas Medical Branch (UTMB), Galveston, TX 77555-0609, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Sanjeev K.","family":"Sahni","sequence":"additional","affiliation":[{"name":"Department of Pathology, University of Texas Medical Branch (UTMB), Galveston, TX 77555-0609, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2020,9,29]]},"reference":[{"key":"ref_1","unstructured":"Gavins, F., and Stokes, K.Y. (2016). Endothelial activation and injury: The mechanisms of rickettsial vasculitis. Vascular Responses to Pathogens, Elsevier Press."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"753","DOI":"10.2217\/fmb-2019-0266","article-title":"Recent research milestones in the pathogenesis of human rickettsioses and opportunities ahead","volume":"15","author":"Narra","year":"2020","journal-title":"Future Microbiol."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"127","DOI":"10.1146\/annurev-pathmechdis-012418-012800","article-title":"Pathogenesis of rickettsial diseases: Pathogenic and immune mechanisms of an endotheliotropic infection","volume":"14","author":"Sahni","year":"2019","journal-title":"Annu. Rev. Pathol."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"960","DOI":"10.1016\/j.cell.2017.02.004","article-title":"mTOR signaling in growth, metabolism, and disease","volume":"168","author":"Saxton","year":"2017","journal-title":"Cell"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1061","DOI":"10.1007\/s00109-015-1326-7","article-title":"mTOR in health and in sickness","volume":"93","author":"Liko","year":"2015","journal-title":"J. Mol. Med."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"3589","DOI":"10.1242\/jcs.051011","article-title":"mTOR signaling at a glance","volume":"122","author":"Laplante","year":"2009","journal-title":"J. Cell Sci."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"767","DOI":"10.1038\/nri2161","article-title":"Unveiling the roles of autophagy in innate and adaptive immunity","volume":"7","author":"Levine","year":"2007","journal-title":"Nat. Rev. Immunol."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1465","DOI":"10.1016\/j.bbamcr.2009.03.003","article-title":"Autophagy in intracellular bacterial infection","volume":"1793","author":"Campoy","year":"2009","journal-title":"Biochim. Biophys. Acta."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"565","DOI":"10.1016\/j.immuni.2008.08.012","article-title":"The TSC-mTOR signaling pathway regulates the innate inflammatory response","volume":"29","author":"Weichhart","year":"2008","journal-title":"Immunity"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"203","DOI":"10.1196\/annals.1355.030","article-title":"Similarities and differences in host cell signaling following infection with different Rickettsia species","volume":"1063","author":"Rydkina","year":"2005","journal-title":"Ann. N. Y. Acad. Sci."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"303","DOI":"10.1111\/j.1469-0691.2008.02248.x","article-title":"Selective activation of signal transducer and activator of transcription (STAT) proteins STAT1 and STAT3 in human endothelial cells infected with Rickettsia rickettsii","volume":"15","author":"Sahni","year":"2009","journal-title":"Clin. Microbiol. Infect"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"274","DOI":"10.1016\/j.cell.2012.03.017","article-title":"mTOR signaling in growth control and disease","volume":"149","author":"Laplante","year":"2012","journal-title":"Cell"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"39","DOI":"10.1146\/annurev-immunol-020711-075024","article-title":"Regulation of immune responses by mTOR","volume":"30","author":"Powell","year":"2012","journal-title":"Annu. Rev. Immunol."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"6418","DOI":"10.1128\/IAI.67.12.6418-6423.1999","article-title":"Involvement of protein kinase C in Rickettsia rickettsii-induced transcriptional activation of the host endothelial cell","volume":"67","author":"Sahni","year":"1999","journal-title":"Infect Immun."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"599","DOI":"10.1038\/nri3901","article-title":"Regulation of innate immune cell function by mTOR","volume":"15","author":"Weichhart","year":"2015","journal-title":"Nat. Rev. Immunol."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"e00087-17","DOI":"10.1128\/IAI.00087-17","article-title":"Host serine\/threonine kinases mTOR and protein kinase C-\u03b1 promote InlB-mediated entry of Listeria monocytogenes","volume":"85","author":"Bhalla","year":"2017","journal-title":"Infect. Immun."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Ganesan, R., Hos, N.J., Gutierrez, S., Fischer, J., Stepek, J.M., Daglidu, E., Kr\u00f6nke, M., and Robinson, N. (2017). Salmonella Typhimurium disrupts Sirt1\/AMPK checkpoint control of mTOR to impair autophagy. PLoS Pathog., 13.","DOI":"10.1371\/journal.ppat.1006227"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"28171","DOI":"10.1038\/srep28171","article-title":"Autophagy induction targeting mTORC1 enhances Mycobacterium tuberculosis replication in HIV co-infected human macrophages","volume":"6","author":"Andersson","year":"2016","journal-title":"Sci. Rep."},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Lu, R., Herrera, B.B., Eshleman, H.D., Fu, Y., Bloom, A., Li, Z., Sacks, D.B., and Goldberg, M.B. (2015). Shigella Effector OspB activates mTORC1 in a manner that depends on IQGAP1 and promotes cell proliferation. PLoS Pathog., 11.","DOI":"10.1371\/journal.ppat.1005200"},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Edwards, M.W., Aultman, J.A., Harber, G., Bhatt, J.M., Sztul, E., Xu, Q., Zhang, P., Michalek, S.M., and Katz, J. (2013). Role of mTOR downstream effector signaling molecules in Francisella tularensis internalization by murine macrophages. PLoS ONE, 8.","DOI":"10.1371\/journal.pone.0083226"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"5097","DOI":"10.1242\/jcs.01382","article-title":"Early signaling events involved in the entry of Rickettsia conorii into mammalian cells","volume":"117","author":"Martinez","year":"2004","journal-title":"J. Cell Sci."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1287","DOI":"10.1016\/j.febslet.2010.01.017","article-title":"mTOR regulation of autophagy","volume":"584","author":"Jung","year":"2010","journal-title":"FEBS Lett."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"2145","DOI":"10.1080\/15548627.2016.1217369","article-title":"Ehrlichia secretes Etf-1 to induce autophagy and capture nutrients for its growth through RAB5 and class III phosphatidylinositol 3-kinase","volume":"12","author":"Lin","year":"2016","journal-title":"Autophagy"},{"key":"ref_24","first-page":"297","article-title":"Role and function of the type IV secretion system in Anaplasma and Ehrlichia species","volume":"413","author":"Rikihisa","year":"2017","journal-title":"Curr. Top. Microbiol. Immunol."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"20800","DOI":"10.1073\/pnas.1218674109","article-title":"Autophagosomes induced by a bacterial Beclin 1 binding protein facilitate obligatory intracellular infection","volume":"109","author":"Niu","year":"2012","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"942","DOI":"10.1038\/nature09076","article-title":"Termination of autophagy and reformation of lysosomes regulated by mTOR","volume":"465","author":"Yu","year":"2010","journal-title":"Nature"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"753","DOI":"10.1016\/j.cell.2004.11.038","article-title":"Autophagy is a defense mechanism inhibiting BCG and Mycobacterium tuberculosis survival in infected macrophages","volume":"119","author":"Gutierrez","year":"2004","journal-title":"Cell"},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Wang, J., Yang, K., Zhou, L., Wu, M., Wu, Y., Zhu, M., Lai, X., Chen, T., Feng, L., and Li, M. (2013). MicroRNA-155 promotes autophagy to eliminate intracellular mycobacteria by targeting Rheb. PLoS Pathog., 9.","DOI":"10.1371\/journal.ppat.1003697"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"11374","DOI":"10.1074\/jbc.M509157200","article-title":"Autophagy controls Salmonella infection in response to damage to the Salmonella-containing vacuole","volume":"281","author":"Birmingham","year":"2006","journal-title":"J. Biol. Chem."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"507","DOI":"10.1242\/jcs.094573","article-title":"Autophagy plays an essential role in the clearance of Pseudomonas aeruginosa by alveolar macrophages","volume":"125","author":"Yuan","year":"2012","journal-title":"J. Cell. Sci."},{"key":"ref_31","doi-asserted-by":"crossref","unstructured":"Owen, K.A., Meyer, C.B., Bouton, A.H., and Casanova, J.E. (2014). Activation of focal adhesion kinase by Salmonella suppresses autophagy via an Akt\/mTOR signaling pathway and promotes bacterial survival in macrophages. PLoS Pathog., 10.","DOI":"10.1371\/journal.ppat.1004159"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"e00690-17","DOI":"10.1128\/IAI.00690-17","article-title":"Ehrlichia activation of Wnt-PI3K-mTOR signaling inhibits autolysosome generation and autophagic destruction by the mononuclear phagocyte","volume":"85","author":"Lina","year":"2017","journal-title":"Infect Immun."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"654","DOI":"10.1016\/j.immuni.2010.04.011","article-title":"Human immunodeficiency virus-1 inhibition of immunoamphisomes in dendritic cells impairs early innate and adaptive immune responses","volume":"32","author":"Blanchet","year":"2010","journal-title":"Immunity"},{"key":"ref_34","doi-asserted-by":"crossref","unstructured":"Martin, S., Saha, B., and Riley, J.L. (2012). The battle over mTOR: An emerging theatre in host-pathogen immunity. PLoS Pathog., 8.","DOI":"10.1371\/journal.ppat.1002894"},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Sahni, A., Narra, H.P., Patel, J., and Sahni, S.K. (2018). MicroRNA-regulated rickettsial invasion into host endothelium via fibroblast growth factor 2 and its receptor FGFR1. Cells, 7.","DOI":"10.3390\/cells7120240"},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Sahni, A., Narra, H.P., Patel, J., and Sahni, S.K. (2017). MicroRNA signature of human microvascular endothelium infected with Rickettsia rickettsii. Int. J. Mol. Sci., 18.","DOI":"10.3390\/ijms18071471"}],"container-title":["International Journal of Molecular Sciences"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1422-0067\/21\/19\/7179\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T10:14:40Z","timestamp":1760177680000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1422-0067\/21\/19\/7179"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,9,29]]},"references-count":36,"journal-issue":{"issue":"19","published-online":{"date-parts":[[2020,10]]}},"alternative-id":["ijms21197179"],"URL":"https:\/\/doi.org\/10.3390\/ijms21197179","relation":{},"ISSN":["1422-0067"],"issn-type":[{"value":"1422-0067","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,9,29]]}}}