TRP120-dependent activation of noncanonical Wnt/NFAT signaling drives monocyte chemokine production in Ehrlichia chaffeensis infection

Ehrlichia chaffeensis is an obligately intracellular bacterium that repurposes multiple cellular signaling pathways, including Wnt, Hippo, Notch, and Hedgehog to evade innate immune defenses of mononuclear phagocytes. Although noncanonical Wnt signaling activation by E. chaffeensis induces nuclear factor of activated T-cells (NFAT) activity, the functional consequences of this response have remained unclear. Here, we demonstrate that E. chaffeensis exploits noncanonical Wnt/Ca²⁺ signaling to selectively activate NFATc1 and drive monocyte chemotactic chemokine production. In E. chaffeensis-infected THP-1 cells, NFATc1 was exclusively activated, which was recapitulated in cells treated with soluble recombinant TRP120 (rTRP120) or TRP120 Wnt ligand short linear motif (SLiM) peptide (QDVASH). Correspondingly, significant increases and similar chemokine expression profiles were detected in THP-1 cells infected with E. chaffeensis or treated with soluble rTRP120. Moreover, treatment with the NFATc1 peptide inhibitor (11R-VIVIT) significantly inhibited NFAT activation and chemokine expression. Consistent with a requirement for Wnt signaling, Frizzled 5 (FZD5)-deficient THP-1 cells exhibited reduced NFATc1 activation and diminished chemokine production and monocyte recruitment. Although the TRP120 Wnt ligand SLiM phenocopied E. chaffeensis-induced NFATc1 activation, it was insufficient to independently stimulate chemokine production. In contrast, ectopic expression of TRP120-induced chemokine expression, which was further amplified by TRP120 Wnt SLiM treatment, indicating both TRP120-directed extracellular Wnt signaling and intracellular mechanisms are required. Collectively, these findings define a previously unrecognized pathogen-driven strategy that co-opts non-canonical Wnt/NFAT signaling to promote monocyte chemotactic chemokine production.