Toll-Like Receptor 4-Linked Janus Kinase 2 Signaling Contributes to Internalization of Brucella abortus by Macrophages

Abstract

e Brucella abortus is an intracellular pathogen that uses a crafty strategy to invade and proliferate within host cells, but the distinct signaling pathways associated with phagocytic mechanisms of B. abortus remain unclear. The present study was performed to test the hypothesis that Toll-like receptor 4 (TLR4)-linked signaling interacting with Janus kinase 2 (JAK2) plays an essential role in B. abortus phagocytosis by macrophages. The effects of TLR4-JAK2 signaling on B. abortus phagocytosis in murine macrophage RAW 264.7 cells were observed through an infection assay and confocal microscopy. We determined that the uptake of B. abortus was negatively affected by the dysfunction of TLR4 and JAK2. F-actin polymerization detected by flow cytometry and F-actin assay was amplified for B. abortus entry, whereas that event was attenuated by the disruption of TLR4 and JAK2. Importantly, JAK2 phosphorylation and actin skeleton reorganization were suppressed immediately after B. abortus infection in bone marrow-derived macrophages (BMDMs) from TLR4 ؊/؊ mice, showing the cooperation of JAK2 with TLR4. Furthermore, small GTPase Cdc42 participated in the intermediate pathway of TLR4-JAK2 signaling on B. abortus phagocytosis. Consequently, TLR4-associated JAK2 activation in the early cellular signaling events plays a pivotal role in B. abortus-induced phagocytic processes in macrophages, implying the pathogenic significance of JAK2-mediated entry. Here, we elucidate that this specific phagocytic mechanism of B. abortus might provide achievable strategies for inhibiting B. abortus invasion.

miR-15a/16 Regulates Macrophage Phagocytosis after Bacterial Infection

“…Furthermore, miR-15a/16 regulated the level of Rho GTPase Cdc42, a key participant in phagocytosis which spurs actin polymerization and subsequently enables the plasma membrane to encircle its target (31). GTPase Cdc42 has previously been reported to participate in the intermediate pathway of TLR4-JAK2 signaling on macrophage mediated phagocytosis (32). The TLR4 mediated pro-inflammatory cytokines and chemokines were also augmented in miR-15a/16 -/- cells in the early phase of infection, via regulating TLR4-associated TRAF6 (27).…”

Enhancement of LPS-Induced Microglial Inflammation Response via TLR4 Under High Glucose Conditions

“…It is known that the JAK2/STAT3 pathway plays a role in regulating the expression of TLR4 in macrophages [16]. Our previous study demonstrated that TLR4 can regulate microglia activation and inflammatory response [15].…”

“…These dimers are translocated to the nucleus where they directly bind to the promoter region and regulate transcription of specific target genes, many of which are involved in immune responses [23,24]. A previous study has indicated that JAK2, as the downstream signal of TLR4, plays an essential role in phagocytosis by macrophages [16]. The JAK2-STAT3 pathway is known to cause a pro-inflammatory response in activation of microglial cells [25,26].…”

Immune response triggered by Brucella abortus following infection or vaccination

“…Even though possibly not involved in resistance to infection, it is well established that the recognition of B. abortus PAMPs by both TLR2 and TLR4 induce the secretion of TNF-␣, IL-12 and IL-6 by murine cells [18,42,[48][49][50][53][54][55]. Interestingly, TLR4-linked signaling interacting with Janus kinase 2 (TLR4-JAK2) is also involved in B. abortus internalization by murine macrophages [56]. In contrast to TLR2 and TLR4, myeloid differentiation factor 88 (MyD88), an adapter molecule of all TLRs except TLR3, is critical for efficient clearance of B. abortus [53,57], besides mediating induction of IL-12p40 and TNF-␣ in mice [50].…”