Human Cytomegalovirus Utilizes a Nontraditional Signal Transducer and Activator of Transcription 1 Activation Cascade via Signaling through Epidermal Growth Factor Receptor and Integrins To Efficiently Promote the Motility, Differentiation, and Polarization of Infected Monocytes

Abstract

Human cytomegalovirus (HCMV) infects peripheral blood monocytes and triggers biological changes that promote viral dissemination and persistence. We have shown that HCMV induces a proinflammatory state in infected monocytes, resulting in enhanced monocyte motility and transendothelial migration, prolonged monocyte survival, and differentiation toward a long-lived M1-like macrophage phenotype. Our data indicate that HCMV triggers these changes, in the absence of de novo viral gene expression and replication, through engagement and activation of epidermal growth factor receptor (EGFR) and integrins on the surface of monocytes. We previously identified that HCMV induces the upregulation of multiple proinflammatory gene ontologies, with the interferon-associated gene ontology exhibiting the highest percentage of upregulated genes. However, the function of the HCMVinduced interferon (IFN)-stimulated genes (ISGs) in infected monocytes remained unclear. We now show that HCMV induces the enhanced expression and activation of a key ISG transcriptional regulator, signal transducer and activator of transcription (STAT1), via an IFN-independent but EGFR-and integrin-dependent signaling pathway. Furthermore, we identified a biphasic activation of STAT1 that likely promotes two distinct phases of STAT1-mediated transcriptional activity. Moreover, our data show that STAT1 is required for efficient early HCMV-induced enhanced monocyte motility and later for HCMV-induced monocyte-to-macrophage differentiation and for the regulation of macrophage polarization, suggesting that STAT1 may serve as a molecular convergence point linking the biological changes that occur at early and later times postinfection. Taken together, our results suggest that HCMV reroutes the biphasic activation of a traditionally antiviral gene product through an EGFRand integrin-dependent pathway in order to help promote the proviral activation and polarization of infected monocytes.

Interferon-Independent Innate Responses to Cytomegalovirus

“…Direct ISG induction by IRF3 is not the only pathway associated with the IFN-independent response to CMV. In human monocytes, IFN-independent, biphasic activation of STAT1 with differential phosphorylation at early (30 min) compared to late (24 h) time points post-HCMV infection appears to influence motility, migration, differentiation and polarization (156).…”

“…IFN-independent ISG induction can also be used to regulate the development of cells key to viral persistence and dissemination. In human monocytes infected with HCMV, ISGs are upregulated independently of IFN (4 hpi) that function to enhance monocyte motility and migration (156). This occurs in a STAT1-dependent manner that also suppresses transcription of anti-inflammatory M2-associated cytokines (IL-10 and CCL18), promoting polarization of macrophages toward a mixed M1/M2 phenotype (156).…”

“…In human monocytes infected with HCMV, ISGs are upregulated independently of IFN (4 hpi) that function to enhance monocyte motility and migration (156). This occurs in a STAT1-dependent manner that also suppresses transcription of anti-inflammatory M2-associated cytokines (IL-10 and CCL18), promoting polarization of macrophages toward a mixed M1/M2 phenotype (156). ISG15 was among the ISGs found to be upregulated in monocytes 4hpi with HCMV (156).…”

Leukemia Inhibitory Factor Signaling Enhances Production of Galactose-Deficient IgA1 in IgA Nephropathy

“…However, Src can be activated through integrin-driven adhesion, a process that has already been linked with STAT1 activation during monocyte to macrophage maturation [61]. A more recent report implicates both EGFR and integrin pathway with STAT1 activation in monocytes that further supports the potential for non-traditional activation of STAT1 [62]. As the abnormal phosphorylation of STAT1 in IgA1-secreting cells from patients with IgAN was not mediated by JAK2, it is possible that LIF activation involved SFKs and EGFR in IgA1-producing cells from IgAN patients [63][64][65].…”

EGR1 transcriptional control of human cytomegalovirus latency

“…To regulate the establishment of latency and the reactivation of replication, all herpesviruses rely on and manipulate cellular signaling pathways to regulate their viral lifecycle. CMV targets and manipulates EGFR and its downstream pathways to achieve this goal (11, 13, 15, 19, 24, 26). Stimulation of EGFR signaling upon entry into hematopoietic cells is important to establish an environment to support latency in CD34+ HPCs (10, 16, 45).…”