Toxoplasma gondiiRhoptry Discharge Correlates with Activation of the Early Growth Response 2 Host Cell Transcription Factor

Abstract

Toxoplasma gondii is a ubiquitous apicomplexan parasite that can cause severe disease in fetuses and immune-compromised patients. Rhoptries, micronemes, and dense granules, which are secretory organelles unique to Toxoplasma and other apicomplexan parasites, play critical roles in parasite growth and virulence. To understand how these organelles modulate infected host cells, we sought to identify host cell transcription factors triggered by their release. Early growth response 2 (EGR2) is a host cell transcription factor that is rapidly upregulated and activated in Toxoplasma-infected cells but not in cells infected with the closely related apicomplexan parasite Neospora caninum. EGR2 upregulation occurred only when live parasites were in direct contact with the host cell and not from exposure to cell extracts that contain dense granule or micronemal proteins. When microneme-mediated attachment was blocked by pretreating parasites with a calcium chelator, EGR2 expression was significantly reduced. In contrast, when host cells were infected with parasites in the presence of cytochalasin D, which allows rhoptry secretion but prevents parasite invasion, EGR2 was activated. Finally, we demonstrate that Toxoplasma activation of host p38 mitogen-activated protein kinase is necessary but not sufficient for EGR2 activation. Collectively, these data indicate that EGR2 is specifically upregulated by a parasite-derived secreted factor that is most likely a resident rhoptry protein.

Gene Expression Profiles in Genetically Different Mice Infected with Toxoplasma gondii: ALDH1A2, BEX2, EGR2, CCL3 and PLAU

“…In this study, EGR2 mRNA expression was rapidly upregulated in both strains of mice after T. gondii infection, especially high in the spleen and small intestine of T. gondii -infected C57BL/6 mouse as compared with those of BALB/c mice. These results are similar to previous studies suggesting that EGR1 and EGR2 transcription factors, as well as their downstream targets, were rapidly upregulated in Toxoplasma -infected cells [2,11], and that T. gondii increases the activity of transcription factors, including STAT3/6, hypoxia inducible factor and EGR2 [12]. Both our work and previous studies demonstrate that viable T. gondii acts as a powerful inducer of the transcriptional factor EGR2, especially in C57BL/6 mice, but the generated expression patterns differ from those induced by host factors.…”

Toxoplasma gondii Activates Hypoxia-inducible Factor (HIF) by Stabilizing the HIF-1α Subunit via Type I Activin-like Receptor Kinase Receptor Signaling

“…Luciferase Assays-HIF-1␣ WT cells were transfected using Lipofectamine (Invitrogen) as previously described (45). When infected cells were exposed to 3% O 2 , the parasites were allowed to invade for 1 h before transferring the infected cells to a hypoxia work station (Ruskinn, Cincinnati, OH).…”

The Role of Host‐ and Parasite‐Encoded Kinases inToxoplasma–Host Interactions

“…Both, EGR and SRF are MAPK-regulated TFs that are rapidly activated and subsequently shut off in response to growth factors and other external cues [50,51]. While many T. gondii strains similarly regulate SRF and EGR, the activity of these TFs continuously increases following infection with the Type I RH strain [49]. This difference is due to the non-RH strains expressing a rhoptry kinase, ROP38, that blocks the prolonged activation of host MAPK and subsequent downstream effectors [13].…”

“…gondii activates other host TFs such as early growth response (EGR) and serum response factor (SRF) [49]. Both, EGR and SRF are MAPK-regulated TFs that are rapidly activated and subsequently shut off in response to growth factors and other external cues [50,51].…”