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Shigella Effector OspB Activates mTORC1 in a Manner That Depends on IQGAP1 and Promotes Cell Proliferation.

Lu R, Herrera BB, Eshleman HD, Fu Y, Bloom A, Li Z, Sacks DB, Goldberg MB - PLoS Pathog. (2015)

Bottom Line: We show that the effect on the area of bacterial spread is due to OspB triggering increased cell proliferation at the periphery of infected foci, thereby replacing some of the cells that die within infected foci and restricting the area of bacterial spread.OspB activation of mTORC1, and its effects on cell proliferation and bacterial spread, depends on IQGAP1.Our results identify OspB as a regulator of mTORC1 and mTORC1-dependent cell proliferation early during S. flexneri infection and establish a role for IQGAP1 in mTORC1 signaling.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Division of Infectious Diseases, Massachusetts General Hospital, Cambridge, Massachusetts, United States of America; Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, United States of America.

ABSTRACT
The intracellular bacterial pathogen Shigella infects and spreads through the human intestinal epithelium. Effector proteins delivered by Shigella into cells promote infection by modulating diverse host functions. We demonstrate that the effector protein OspB interacts directly with the scaffolding protein IQGAP1, and that the absence of either OspB or IQGAP1 during infection leads to larger areas of S. flexneri spread through cell monolayers. We show that the effect on the area of bacterial spread is due to OspB triggering increased cell proliferation at the periphery of infected foci, thereby replacing some of the cells that die within infected foci and restricting the area of bacterial spread. We demonstrate that OspB enhancement of cell proliferation results from activation of mTORC1, a master regulator of cell growth, and is blocked by the mTORC1-specific inhibitor rapamycin. OspB activation of mTORC1, and its effects on cell proliferation and bacterial spread, depends on IQGAP1. Our results identify OspB as a regulator of mTORC1 and mTORC1-dependent cell proliferation early during S. flexneri infection and establish a role for IQGAP1 in mTORC1 signaling. They also raise the possibility that IQGAP1 serves as a scaffold for the assembly of an OspB-mTORC1 signaling complex.

No MeSH data available.


Related in: MedlinePlus

OspB activation of mTORC1.(A-B) Phosphorylation of mTOR substrate S6K in the presence of OspB and dependent on IQGAP1. Representative western blot (A) and band densitometry of phospho-S6K signal normalized to total S6K (B). (C) Inhibition by rapamycin of OspB-induced and IQGAP1-dependent phosphorylation of S6K. (D-E) Reduced phosphorylation of Akt on Thr-308 in the presence of OspB and dependent on IQGAP1. Representative western blot (D), and band densitometry of phospho-Akt Thr-308 signal normalized to total Akt (E). Apparent MWs are indicated in Kd. Densitometry is mean ± S.D. Data represent three or more independent experiments. *, p < 0.05, Student’s two-tailed t test.
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ppat.1005200.g004: OspB activation of mTORC1.(A-B) Phosphorylation of mTOR substrate S6K in the presence of OspB and dependent on IQGAP1. Representative western blot (A) and band densitometry of phospho-S6K signal normalized to total S6K (B). (C) Inhibition by rapamycin of OspB-induced and IQGAP1-dependent phosphorylation of S6K. (D-E) Reduced phosphorylation of Akt on Thr-308 in the presence of OspB and dependent on IQGAP1. Representative western blot (D), and band densitometry of phospho-Akt Thr-308 signal normalized to total Akt (E). Apparent MWs are indicated in Kd. Densitometry is mean ± S.D. Data represent three or more independent experiments. *, p < 0.05, Student’s two-tailed t test.

Mentions: We tested whether OspB activated mTOR by examining the phosphorylation state of S6 kinase 1 (S6K), a substrate of mTOR kinase activity that controls cap-dependent translation elongation. Phosphorylation of S6K on Thr-389 was increased 2-fold (p<0.05) in the presence of OspB and in a manner that depended on IQGAP1 (Fig 4A and 4B). Phosphorylation of S6K by OspB was inhibited by rapamycin (Fig 4C). Together, these data establish that OspB activates mTOR.


Shigella Effector OspB Activates mTORC1 in a Manner That Depends on IQGAP1 and Promotes Cell Proliferation.

Lu R, Herrera BB, Eshleman HD, Fu Y, Bloom A, Li Z, Sacks DB, Goldberg MB - PLoS Pathog. (2015)

OspB activation of mTORC1.(A-B) Phosphorylation of mTOR substrate S6K in the presence of OspB and dependent on IQGAP1. Representative western blot (A) and band densitometry of phospho-S6K signal normalized to total S6K (B). (C) Inhibition by rapamycin of OspB-induced and IQGAP1-dependent phosphorylation of S6K. (D-E) Reduced phosphorylation of Akt on Thr-308 in the presence of OspB and dependent on IQGAP1. Representative western blot (D), and band densitometry of phospho-Akt Thr-308 signal normalized to total Akt (E). Apparent MWs are indicated in Kd. Densitometry is mean ± S.D. Data represent three or more independent experiments. *, p < 0.05, Student’s two-tailed t test.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4608727&req=5

ppat.1005200.g004: OspB activation of mTORC1.(A-B) Phosphorylation of mTOR substrate S6K in the presence of OspB and dependent on IQGAP1. Representative western blot (A) and band densitometry of phospho-S6K signal normalized to total S6K (B). (C) Inhibition by rapamycin of OspB-induced and IQGAP1-dependent phosphorylation of S6K. (D-E) Reduced phosphorylation of Akt on Thr-308 in the presence of OspB and dependent on IQGAP1. Representative western blot (D), and band densitometry of phospho-Akt Thr-308 signal normalized to total Akt (E). Apparent MWs are indicated in Kd. Densitometry is mean ± S.D. Data represent three or more independent experiments. *, p < 0.05, Student’s two-tailed t test.
Mentions: We tested whether OspB activated mTOR by examining the phosphorylation state of S6 kinase 1 (S6K), a substrate of mTOR kinase activity that controls cap-dependent translation elongation. Phosphorylation of S6K on Thr-389 was increased 2-fold (p<0.05) in the presence of OspB and in a manner that depended on IQGAP1 (Fig 4A and 4B). Phosphorylation of S6K by OspB was inhibited by rapamycin (Fig 4C). Together, these data establish that OspB activates mTOR.

Bottom Line: We show that the effect on the area of bacterial spread is due to OspB triggering increased cell proliferation at the periphery of infected foci, thereby replacing some of the cells that die within infected foci and restricting the area of bacterial spread.OspB activation of mTORC1, and its effects on cell proliferation and bacterial spread, depends on IQGAP1.Our results identify OspB as a regulator of mTORC1 and mTORC1-dependent cell proliferation early during S. flexneri infection and establish a role for IQGAP1 in mTORC1 signaling.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Division of Infectious Diseases, Massachusetts General Hospital, Cambridge, Massachusetts, United States of America; Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, United States of America.

ABSTRACT
The intracellular bacterial pathogen Shigella infects and spreads through the human intestinal epithelium. Effector proteins delivered by Shigella into cells promote infection by modulating diverse host functions. We demonstrate that the effector protein OspB interacts directly with the scaffolding protein IQGAP1, and that the absence of either OspB or IQGAP1 during infection leads to larger areas of S. flexneri spread through cell monolayers. We show that the effect on the area of bacterial spread is due to OspB triggering increased cell proliferation at the periphery of infected foci, thereby replacing some of the cells that die within infected foci and restricting the area of bacterial spread. We demonstrate that OspB enhancement of cell proliferation results from activation of mTORC1, a master regulator of cell growth, and is blocked by the mTORC1-specific inhibitor rapamycin. OspB activation of mTORC1, and its effects on cell proliferation and bacterial spread, depends on IQGAP1. Our results identify OspB as a regulator of mTORC1 and mTORC1-dependent cell proliferation early during S. flexneri infection and establish a role for IQGAP1 in mTORC1 signaling. They also raise the possibility that IQGAP1 serves as a scaffold for the assembly of an OspB-mTORC1 signaling complex.

No MeSH data available.


Related in: MedlinePlus