title: Legionella pneumophila requires polyamines for optimal intracellular growth.
abstract: The Gram-negative intracellular pathogen Legionella pneumophila replicates in a membrane-bound compartment known as the Legionella-containing vacuole (LCV), into which it abundantly releases its chaperonin, HtpB. To determine whether HtpB remains within the LCV or reaches the host cell cytoplasm, we infected U937 human macrophages and CHO cells with L. pneumophila expressing a translocation reporter consisting of the Bordetella pertussisa denylate cyclase fused to HtpB. These infections led to increased cyclic AMP levels, suggesting that HtpB reaches the host cell cytoplasm. To identify potential functions of cytoplasmic HtpB, we expressed it in the yeast Saccharomyces cerevisiae, where HtpB induced pseudohyphal growth. A yeast-two-hybrid screen showed that HtpB interacted with S-adenosylmethionine decarboxylase (SAMDC), an essential yeast enzyme (encoded by SPE2) that is required for polyamine biosynthesis. Increasing the copy number of SPE2 induced pseudohyphal growth in S. cerevisiae; thus, we speculated that (i) HtpB induces pseudohyphal growth by activating polyamine synthesis and (ii) L. pneumophila may require exogenous polyamines for growth. A pharmacological inhibitor of SAMDC significantly reduced L. pneumophila replication in L929 mouse cells and U937 macrophages, whereas exogenously added polyamines moderately favored intracellular growth, confirming that polyamines and host SAMDC activity promote L. pneumophila proliferation. Bioinformatic analysis revealed that most known enzymes required for polyamine biosynthesis in bacteria (including SAMDC) are absent in L. pneumophila, further suggesting a need for exogenous polyamines. We hypothesize that HtpB may function to ensure a supply of polyamines in host cells, which are required for the optimal intracellular growth of L. pneumophila.
authors: Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors: Gheyath K
authors: GK
authors: Nasrallah
authors: Angela L
authors: AL
authors: Riveroll
authors: Audrey
authors: A
authors: Chong
authors: Lois E
authors: LE
authors: Murray
authors: P Jeffrey
authors: PJ
authors: Lewis
authors: Rafael A
authors: RA
authors: Garduño
mesh_terms: D012437:Adenosylmethionine Decarboxylase / Q000378:metabolism; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D016466:CHO Cells; D049109:Cell Proliferation; D002470:Cell Survival; D018833:Chaperonins / Q000235:genetics / Q000378:metabolism*; D019295:Computational Biology; D006224:Cricetinae; D003412:Cricetulus; D003470:Culture Media; D003593:Cytoplasm / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006801:Humans; D016952:Legionella pneumophila / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D051379:Mice; D011073:Polyamines / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000254:growth & development / Q000378:metabolism; D020798:Two-Hybrid System Techniques; D020298:U937 Cells; D014617:Vacuoles / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D011073:Polyamines; D018833:Chaperonins; D012437:Adenosylmethionine Decarboxylase