Cyclic AMP inhibits developmental regulation of Chlamydia trachomatis

Abstract

The effect of cyclic AMP (cAMP) on the chlamydial growth cycle was studied with Chiamydia trachomatisinfected HeLa cells. At concentrations of 1 mM, cAMP had a profound effect on the chlamydial developmental cycle, resulting in small, immature inclusions. Immunoblot analysis revealed the absence of elementary body (EB)-specific antigens in the cAMP-treated cells. This effect was observed only if cAMP was added within the first 12 h of incubation and continued thereafter. Its withdrawal at any time from the medium led to the reappearance of fully mature, infectious organisms. Analogs or breakdown products of cAMP exerted no inhibitory effect on chlamydial development. Intracellular inclusions from the cAMP-treated cells were unable to infect fresh HeLa monolayers, in contrast to the completely infectious nontreated inclusions. Protein profiles of the cAMP-treated organisms (at any time point) resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis very closely resembled reticulate bodies (RB) and did not possess characteristic EB-binding proteins. Collectively, these observations suggest an inhibitory role for cAMP at the RB stage of intracellular development. We also identified a cAMP receptor protein which is associated with RB and not with EB, further supporting a role for this system in the developmental regulation of chlamydiae.Chlamydiae are obligate intracellular parasites of eucaryotic cells which have been implicated in a wide spectrum of human diseases (24). The developmental cycle of Chlamydia trachomatis proceeds by attachment to host cells, uptake, and enlargement of the infectious elementary bodies (EB) to form noninfectious, metabolically active reticulate bodies (RB). These RB divide within cytoplasmic inclusions by binary fission and then condense and subsequently rupture to release EB capable of infecting fresh host cells (16,17).The responsiveness of cells to a wide range of stimuli depends upon internal signalling systems such as cyclic AMP (cAMP) or cyclic GMP (cGMP) which regulate cellular activity. cAMP plays an important and multitudinous role in the regulation of both procaryotes and eucaryotes (6,21). In procaryotes, cAMP mainly acts through a cAMP receptor protein (CRP) which is capable of binding two molecules of cAMP (2). Ward and Salari (30) postulated a bidirectional cyclic nucleotide control of chlamydial infections with low levels of cGMP acting as a stimulator and high levels of cAMP acting as an inhibitor. Prostaglandins El and E2 and other compounds known to alter cyclic nucleotide levels in the cell also affect the susceptibility of cells to chlamydial infections. The possible mechanisms of cAMP-mediated inhibition of chlamydial infection include: (i) inhibition of binding and uptake of chlamydiae by HeLa cells, (ii) interference with EB growth subsequent to uptake, or (iii) developmental inhibition at the RB stage.To elucidate this mechanism, we added cAMP to the infectious system at different intervals after inoculation of HeLa cells with purified EB. cAMP was ...

Cloning and characterization of a Chlamydia psittaci gene coding for a protein localized in the inclusion membrane of infected cells

“…IncA is one of four chlamydial proteins which we have shown to be enriched in infected cells, relative to EBs. These studies complement and expand the existing literature describing polypeptide differences between EBs and RBs (Rockey and Rosquist, 1994;Kaul and Wenman, 1986;Hatch et al, 1984). Additionally, IncA is the first identified chlamydiai gene product which has an apparent function outside the chlamydial developmental form.…”

A monoclonal antibody to OspA inhibits association of Borrelia burgdorferi with human endothelial cells

“…MAbs generated. Six fusions which yielded 22 MAbs were performed. These MAbs were generated to four different borrelial proteins with apparent molecular masses by SDS-PAGE of 19, 31 (OspA), 34 (OspB), and 35 kDa (Fig.…”

Persistent chlamydiae: from cell culture to a paradigm for chlamydial pathogenesis.

“…Chlamydial development may be regulated by cyclic nucleotides, with cyclic GMP (cGMP) stimulating chlamydial growth and cAMP being inhibitory (123). Treatment of C. trachomatis L2-infected cells with cAMP reversibly interferes with the correct progression of chlamydiae through the developmental cycle (55,56). Inclusions are small and immature and remain noninfectious in the presence of cAMP.…”