In contrast to most bacterial pathogens, the chlamydial T3SS genes occur in clusters throughout the genome, rather than being concentrated on pathogenicity islands [11]. AC are associated with endemic, blinding trachoma, Serovars D K with sexually transmitted diseases, and serovars L1, L2, and L3 with lymphogranuloma venereum, a more systemic disease that is also sexually transmitted [1]. Chlamydiae have a unique biphasic developmental cycle consisting of cell types adapted for extracellular survival and intracellular growth. The developmental cycle ofChlamydiabegins when the metabolically inert, environmentally stable infectious particles, termed elementary bodies (EBs), invade target host cells. Once inside the host cell, the EBs differentiate into vegetative, non-infectious forms, termed reticulate bodies (RBs), which replicate within the membrane-bound parasitophorous vacuole called an inclusion [2]. Type III secretion systems (T3SSs) are known virulence determinants used by pathogenic Gram-negative bacteria to modulate the host cell environment by translocating bacterial effector proteins into the host cell [3]. The supramolecular structure of the T3SS apparatus resembles a needle complex Ciclesonide that spans the bacterial and host cell membranes [4]. The components of the secretion apparatus are generally conserved, however, the specific effector proteins delivered are typically unique to a species. The functions of these injected effectors are multitude. Many affect cellular signal transduction pathways to modulate cytoskeletal dynamics [5,6], inhibit cytokine production [7,8], inhibit,or promote apoptosis [7] and other cellular pathways to promote pathogen survival [9]. Chlamydiae encode the components of a type III secretion apparatus yet the full complement of effector proteins secreted remains unknown [10]. In contrast to most bacterial pathogens, the chlamydial T3SS genes occur in clusters throughout the genome, rather than being concentrated on pathogenicity islands [11]. While the majority of the T3SS genes are not expressed until middle to Ciclesonide late stage of the development cycle [12], proteomic analyses indicate that the essential components of the secretory apparatus are present on EBs [4]. Structurally, projections have been observed on the surface of both EBs and RBs in electron micrographs that may correspond to the T3SS apparatus [13,14]. Chlamydiae appear Ciclesonide to use type III secretion during at least two distinct stages in their development. During entry, extracellular, plasma membrane-associated EBs secrete a pre-existing effector protein, termed Tarp, for translocated actin recruiting protein, across the host cytoplasmic membrane whereC. trachomatisTarp is tyrosine-phosphorylated and functions in the nucleation of actin required for entry [15,16]. Once internalized, de novo synthesized effector proteins are also secreted across the inclusion membrane such that they are exposed to the cytosol [17,18]. Chlamydiae do not have two complete sets of secretion apparati, but certain individual components appear to be duplicated, thus the T3SSs operating at the distinct locations may be structurally distinct [19,20]. Due to limited genetic tools available inChlamydia, the putative T3SS effectors identified thus far have been confirmed using heterologous expression systems for T3SS effectors [10,12,2124]. Many intracellular and epicellular pathogens secrete type III effectors that alter cytoskeletal dynamics [9]. Typically, mutliple effector proteins are translocated upon contact. The only known effector secreted by chlamydiae immediately upon contact with host cells is Tarp [15]. It is likely that other, pre-existing effector molecules are also secreted upon contact with the host cell. The environmental signals that trigger secretion are poorly understood but there are many examples of induction of T3SS in the absence of host cells. Studies of Gram-negative organisms, includingShigella, Salmonella, Pseudomonas, Yersinia,andCampylobacter,have shown the following conditions are able to trigger induction of the T3SSs: temperature [25], low calcium [25], fetal bovine serum (FBS) [26], bovine serum albumin (BSA) [27], glutamate [27], congo red [28], and liposomes [29]. To date, the induction trigger of the T3SS inChlamdyiahas not been identified. Because of the limited opportunities for molecular genetic analysis of T3S in chlamydiae, we investigated several Rabbit Polyclonal to DNA-PK known inducers of T3SSs in an attempt to find some that induce secretion from EBs. Severalin vitroinducers of T3SSs functioned on EBs, and may provide a means to identify or confirm additional putative chlamydial type III effectors. == 2. Results == == 2.1. Induction of chlamydial EB type III secretion == It Ciclesonide was first necessary to determine a buffer in which the EBs would be stable with a minimum background release of proteins. We analyzed a variety of buffers, including 220 mM sucrose-50 mM sodium phosphate-5 mM glutamate, pH Ciclesonide 7.4 (SPG), Hanks balanced salt.