Acanthamoeba induces cell-cycle arrest in host cells.
Acanthamoeba can cause fatal granulomatous amoebic encephalitis (GAE) and eye keratitis. However, the pathogenesis and pathophysiology of these emerging diseases remain unclear. In this study, the effects of Acanthamoeba on the host cell cycle using human brain microvascular endothelial cells (HBMEC) and human corneal epithelial cells (HCEC) were determined. Two isolates of Acanthamoeba belonging to the T1 genotype (GAE isolate) and T4 genotype (keratitis isolate) were used, which showed severe cytotoxicity on HBMEC and HCEC, respectively. No tissue specificity was observed in their ability to exhibit binding to the host cells. To determine the effects of Acanthamoeba on the host cell cycle, a cell-cycle-specific gene array was used. This screened for 96 genes specific for host cell-cycle regulation. It was observed that Acanthamoeba inhibited expression of genes encoding cyclins F and G1 and cyclin-dependent kinase 6, which are proteins important for cell-cycle progression. Moreover, upregulation was observed of the expression of genes such as GADD45A and p130 Rb, associated with cell-cycle arrest, indicating cell-cycle inhibition. Next, the effect of Acanthamoeba on retinoblastoma protein (pRb) phosphorylation was determined. pRb is a potent inhibitor of G1-to-S cell-cycle progression; however, its function is inhibited upon phosphorylation, allowing progression into S phase. Western blotting revealed that Acanthamoeba abolished pRb phosphorylation leading to cell-cycle arrest at the G1-to-S transition. Taken together, these studies demonstrated for the first time that Acanthamoeba inhibits the host cell cycle at the transcriptional level, as well as by modulating pRb phosphorylation using host cell-signalling mechanisms. A complete understanding of Acanthamoeba-host cell interactions may help in developing novel strategies to treat Acanthamoeba infections.
School of Biological and Chemical Sciences, Birkbeck College, University of London, London WC1E 7HX, UK 2Pediatric Infectious Diseases, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
James
J
Sissons
School of Biological and Chemical Sciences, Birkbeck College, University of London, London WC1E 7HX, UK 2Pediatric Infectious Diseases, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Selwa
S
Alsam
School of Biological and Chemical Sciences, Birkbeck College, University of London, London WC1E 7HX, UK 2Pediatric Infectious Diseases, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Samantha
S
Jayasekera
School of Biological and Chemical Sciences, Birkbeck College, University of London, London WC1E 7HX, UK 2Pediatric Infectious Diseases, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Kwang Sik
KS
Kim
School of Biological and Chemical Sciences, Birkbeck College, University of London, London WC1E 7HX, UK 2Pediatric Infectious Diseases, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Monique
M
Stins
School of Biological and Chemical Sciences, Birkbeck College, University of London, London WC1E 7HX, UK 2Pediatric Infectious Diseases, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Naveed Ahmed
NA
Khan
D000048:Acanthamoeba / Q000302:isolation & purification / Q000472:pathogenicity*; D000818:Animals; D002448:Cell Adhesion / Q000502:physiology; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics; D002478:Cells, Cultured; D056746:Cyclin G; D056766:Cyclin G1; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases / Q000096:biosynthesis / Q000235:genetics; D016213:Cyclins / Q000096:biosynthesis / Q000235:genetics; D042783:Endothelial Cells / Q000166:cytology / Q000469:parasitology*; D004847:Epithelial Cells / Q000166:cytology / Q000469:parasitology; D019573:Epithelium, Corneal / Q000166:cytology / Q000469:parasitology*; D016193:G1 Phase; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006801:Humans; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics; D010766:Phosphorylation; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics; D016160:Retinoblastoma Protein / Q000378:metabolism; D050717:Retinoblastoma-Like Protein p130; D016196:S Phase; D014158:Transcription, Genetic / Q000235:genetics; D000097642:GADD45 Proteins
D018797:Cell Cycle Proteins; D056746:Cyclin G; D056766:Cyclin G1; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases; D016213:Cyclins; D009687:Nuclear Proteins; D011506:Proteins; D016160:Retinoblastoma Protein; D050717:Retinoblastoma-Like Protein p130; C503669:CCNF protein, human; C534702:CCNG1 protein, human; C439070:GADD45A protein, human; D000097642:GADD45 Proteins; C493837:RBL2 protein, human; C495911:CDK6 protein, human