The inhibition of the apoptosis pathway by theCoxiella burnetiieffector protein CaeA requires the EK repetition motif, but is independent of survivin

Abstract

ABSRTACT Coxiella burnetii is an obligate intracellular bacterium that causes Query (Q) fever, a zoonotic disease. It requires a functional type IV secretion system (T4SS) which translocate bacterial effector proteins into the host cell cytoplasm and thereby facilitates bacterial replication. To date, more than 130 effector proteins have been identified, but their functions remain largely unknown. Recently, we demonstrated that one of these proteins, CaeA (CBU1524) localized to the host cell nucleus and inhibited intrinsic apoptosis of HEK293 or CHO cells. In the present study we addressed the question whether CaeA also affects the extrinsic apoptosis pathway. Ectopic expression of CaeA reduced extrinsic apoptosis and prevented the cleavage of the executioner caspase 7, but did not impair the activation of initiator caspase 9. CaeA expression resulted in an up-regulation of survivin (an inhibitor of activated caspases), which, however, was not causal for the anti-apoptotic effect of CaeA. Comparing the sequence of CaeA from 25 different C. burnetii isolates we identified an EK (glutamic acid/ lysine) repetition motif as a site of high genetic variability. The EK motif of CaeA was essential for the anti-apoptotic activity of CaeA. From these data, we conclude that the C. burnetii effector protein CaeA interferes with the intrinsic and extrinsic apoptosis pathway. The process requires the EK repetition motif of CaeA, but is independent of the upregulated expression of survivin.

Nuclear trafficking of the anti-apoptoticCoxiella burnetiieffector protein AnkG requires binding to p32 and Importin-α1

“…To gain further insight into AnkG function, we compared the anti‐apoptotic activities of AnkG alleles from different C. burnetii species. It had already been suggested that this might lead the path to characterizing effector proteins in more detail (Bisle et al ., ). We first analysed, whether the expression of AnkG from C. burnetii Nine Mile (AnkG NM ), which was used in all previous studies, exhibited a different anti‐apoptotic activity than the AnkG allele from C. burnetii Dugway (AnkG Dug ).…”

“…To gain further insight into AnkG function, we compared the anti-apoptotic activities of AnkG alleles from different C. burnetii species. It had already been suggested that this might lead the path to characterizing effector proteins in more detail (Bisle et al, 2016). We first analysed, whether the expression of AnkG from C. A. AnkG 1-42 (20 μg) and p32 (37.5 μg) were incubated overnight on ice, equal to a molar ratio of 3:1.…”

“…So far, we do not understand how exactly these three anti-apoptotic effector proteins interfere with the host cell apoptotic machinery. It was shown that CaeA inhibits intrinsic and extrinsic apoptosis, and an EK (glutamic acid-lysine) repeat was identified to be essential for anti-apoptotic activity (Bisle et al, 2016). CaeB prevents apoptosis at the mitochondrial level and ectopically expressed CaeB localizes to the host cell ER (Klingenbeck et al, 2013).…”

Increased levels of LAPTM4B, VEGF and survivin are correlated with tumor progression and poor prognosis in breast cancer patients

“…It potentially facilitates cell cycle processes and cell division and reduces apoptotic indices, which is strongly related with poor prognosis in breast cancer [13, 14]. Transcription from the survivin gene locus gives rise to 5 splice variants [15].…”

Right on Q: Genetics begin to Unravel Coxiella Burnetii host cell Interactions

“…A similar screen of known Coxiella effectors identified CBU1524 (CaeA) and CBU1532 (CaeB) as antiapoptotic effectors [87,126]. CaeA localizes to the nucleus and reduces both intrinsic and extrinsic apoptotic cascades between the initiator caspase-9 and the executioner caspase-7 by a mechanism requiring a CaeA glutamate/lysine repeat region [127]. More potent inhibition of intrinsic apoptosis is observed with CaeB that localizes to mitochondria and blocks mitochondrial outer membrane permeabilization in response to staurosporine treatment by a mechanism independent of p32 [126].…”