Ehrlichia chaffeensis TRP120 Effector Targets and Recruits Host Polycomb Group Proteins for Degradation To Promote Intracellular Infection

Abstract

has a group of well-characterized type I secreted tandem repeat protein (TRP) effectors that have moonlighting capabilities. TRPs modulate various cellular processes, reprogram host gene transcription as nucleomodulins, function as ubiquitin ligases, and directly activate conserved host cell signaling pathways to promote infection. One TRP-interacting host target is polycomb group ring finger protein 5 (PCGF5), a member of the polycomb group (PcG) protein family and a component of the polycomb repressive complex 1 (PRC1). The current study demonstrates that during early infection, PCGF5 strongly colocalizes with TRP120 in the nucleus and later dramatically redistributes to the ehrlichial vacuole along with other PCGF isoforms. Ectopic expression and immunoprecipitation of TRP120 confirmed the interaction of TRP120 with multiple different PCGF isoforms. At 48 h postinfection, a dramatic redistribution of PCGF isoforms from the nucleus to the ehrlichial vacuole was observed, which also temporally coincided with proteasomal degradation of PCGF isoforms and TRP120 expression on the vacuole. A decrease in PRC1-mediated repressive chromatin mark and an altered transcriptional activity in PRC1-associated Hox genes primarily from and clusters were observed along with the degradation of PCGF isoforms, suggesting disruption of the PRC1 ininfected cells. Notably, small interfering RNA (siRNA)-mediated knockdown of PCGF isoforms resulted in significantly increased infection. This study demonstrates a novel strategy in which manipulates PRC complexes through interactions between TRP120 and PCGF isoforms to promote infection.

Bacterial Factors Targeting the Nucleus: The Growing Family of Nucleomodulins

“…Recent results support a model in which, during E. chaffeensis infection, TRP120 relocalizes PCGF isoforms from the nucleus to the ehrlichial vacuole and induces their degradation [53] ( Figure 1C). This coincides with a decrease in the level of the PRC1-mediated epigenetic mark H2AK119Ub (histone H2A ubiquitinated at lysine 119) and in the transcriptional activation of PRC1 target genes, such as homeobox protein (HOX) encoding genes [53]. Knockdown of PCGF5 by small interfering RNAs (siRNAs) results in a significant increase in E. chaffeensis infection.…”

“…Furthermore, a HECT E3 (Homologous to E6AP C-terminal ubiquitin ligase) domain is present in the C-terminal region of TRP120 and targets PCGF5 for poly-ubiquitination [52]. Recent results support a model in which, during E. chaffeensis infection, TRP120 relocalizes PCGF isoforms from the nucleus to the ehrlichial vacuole and induces their degradation [53] ( Figure 1C). This coincides with a decrease in the level of the PRC1-mediated epigenetic mark H2AK119Ub (histone H2A ubiquitinated at lysine 119) and in the transcriptional activation of PRC1 target genes, such as homeobox protein (HOX) encoding genes [53].…”

Ehrlichia chaffeensis TRP120-mediated ubiquitination and proteasomal degradation of tumor suppressor FBW7 increases oncoprotein stability and promotes infection

“…Recent investigations of E. chaffeensis pathobiology have revealed how TRP effectors exploit host signaling and post translational pathways and other cellular processes in order to evade host innate immune mechanisms and establish intracellular infection [6,9,[42][43][44]. Specifically, E. chaffeensis has evolved mechanisms to avoid recognition by innate immune receptors and Lysates were treated with NEM (N-ethylmaleimide, equal mass amount to whole cell lysates used) and bortezomib (10ng/ml, 10 h) to prevent deubiquitination and proteasome degradation.…”

“…Notably, a TRP120 HECT ligase substrate (PCGF5) has been identified [10]. The interaction between TRP120 and PCGF5 has been shown to occur in the nucleus during early infection (24 h) and with cytoplasmic morulae during late infection (72 h) [6]; however, TRP120 appears to interact with FBW7 in the nucleus throughout the course of infection resulting in Ub-mediated degradation of FBW7.…”

“…One of the most studied E. chaffeensis effectors is TRP120, a moonlighting effector that has several defined functions. Early studies demonstrated that surface expressed TRP120 plays a role in host cell entry, but once ehrlichiae are internalized, TRP120 rapidly (<3 h) translocates to the host cell nucleus where it functions as a nucleomodulin, interacts with chromatin-associated proteins and directly binds genes associated with transcriptional regulation, signal transduction and apoptosis [6][7][8][9]. TRP120 is also a functional HECT E3 ligase that ubiquitinates host cell substrates including a known interacting partner, polycomb group ring finger protein 5 (PCGF5), a component of the nuclear polycomb repressive complex [10].…”