Abstract
We previously identified hypothetical protein Cpn1027 as a novel inclusion membrane protein that is unique to Chlamydia pneumoniae. In the current study, using a yeast-two hybrid screen assay, we identified host cell cytoplasmic activation/proliferation-associated protein 2 (Caprin2) as an interacting partner of Cpn1027. The interaction was confirmed and mapped to the C-termini of both Cpn1027 and Caprin2 using co-immunoprecipitation and GST pull-down assays. A RFP-Caprin2 fusion protein was recruited to the chlamydial inclusion and so was the endogenous GSK3β, a critical component of the β-catenin destruction complex in the Wnt signaling pathway. Cpn1027 also co-precipitated GSK3β. Caprin2 is a key regulator of the Wnt signaling pathway by promoting the recruitment of the β-catenin destruction complex to the cytoplasmic membrane in the presence of Wnt signaling while GSK3β is required for priming β-catenin for degradation in the absence of Wnt signaling. The Cpn1027 interactions with Caprin2 and GSK3β may allow C. pneumoniae to actively sequester the β-catenin destruction complex so that β-catenin is maintained even in the absence of extracellular Wnt activation signals. The maintained β-catenin can trans-activate Wnt target genes including Bcl-2, which may contribute to the chlamydial antiapoptotic activity. We found that the C. pneumoniae-infected cells were more resistant to apoptosis induction and the anti-apoptotic activity was dependent on β-catenin. Thus, the current study suggests that the chlamydial inclusion protein Cpn1027 may be able to manipulate host Wnt signaling pathway for enhancing the chlamydial anti-apoptotic activity.
Highlights
Chlamydia pneumoniae, a human respiratory pathogen, is associated with a spectrum of diseases such as atherosclerosis and asthma [1,2,3,4]
When yeasts co-transformed with pEXP-AD502-cytoplasmic activation/proliferation-associated protein 2 (Caprin2)(245–1128) as prey plus pDBLeu-Cpn1027(210– 527) as bait or the positive control prey Gal4AD-TRAF3 plus bait Gal4DB-LMP1 [34] or the negative control prey Gal4AD plus bait Gal4DB-LMP1 were grown on selective medium, the bait-prey interactions only occurred between Caprin2(245–1128) and Cpn1027(210–527) or TRAF3 and LMP1 but not Gal4AD alone and LMP1 (Fig 1A)
A red fluorescence protein (RFP)-Caprin2 (245–1128) fusion protein but not RFP alone was detected around C. pneumoniae inclusions (Fig 1D), suggesting that Caprin2 can be recruited by C. pneumoniae inclusion membrane proteins
Summary
A human respiratory pathogen, is associated with a spectrum of diseases such as atherosclerosis and asthma [1,2,3,4]. All Chlamydia species, including C. pneumoniae, possess a unique obligate intravacuolar biphasic life cycle [5]. The developmental cycle begins with attachment and entry of an extracellular infectious elementary body (EB) to a host cell, most likely via an induced endocytosis [6]. Throughout the chlamydial developmental cycle, chlamydial organisms remain within the cytosolic membrane-bound vacuole termed inclusion. The inclusion expands and is modified by the insertion of chlamydial inclusion membrane proteins (Incs). Many chlamydial proteins have been localized in the inclusion membrane, including the hypothetical protein Cpn1027 [15]. Cpn1027 possesses the structural features common to most Incs, with a N-terminal bi-lobed hydrophobic region that may be localized in the membrane and a hydrophilic c-terminus that may be exposed to the host cell cytosol
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