Part:BBa_K2976002

Toll-like receptor 2

Toll-like receptor 2 (TLR2) is a transmembrane glycoprotein that participates in the innate immune response to microbial agents. TLR2 could form active heterodimers with TLR1 when exposed to some pathogen-associated molecular pattern molecules (PAMPs), and the heterodimers recognizes plenty of substance in lipoarabinomannan (LAM) biosynthesis with the help of CD14.

Usage

In 2019 CPU_CHINA project, TLR2 is expressed along with TLR1 and CD14 to form the TLR2:TLR1:CD14 cluster on the designer cell membrane. As a Mtb sensor, the complex could recognize the substances of Mtb and then stimulate the downstream signaling pathway. Then, activated NF-κB initiates transcription of the gene circuits to express other proteins in our project.

Biology

After being activated with Mtb, the activation cluster TLR2:TLR1:CD14 triggers NF-κB signaling pathways via MYD88 and TRAF6. NF-κB proteins exist in the cytoplasm in an inactive form because of their association with the IκB proteins. IκB proteins mask the nuclear-localization sequences (NLSs) of NF-κB subunits and retain it in the cytoplasm. Activation of TLR2:TLR1:CD14 cluster cause the degradation of IκB proteins by proteasomes. Then, NF-κB subunits could pass through the nuclear pore complex (NPC) and cause the expression of an array of pro-inflammatory cytokines and chemokines. Similarly, NF-κB subunits also can bind the NF-κB induced promoter and initiate transcription of the downstream genes behind these promoters.

Characterization

This year, we attempted to use immune-like cells to treat tuberculosis . To make the immune-like cells recognize M.tuberculosis, we expressed TLR2:TLR1:CD14 cluster on the designer cell membrane. And TLR2 forms active heterodimers with TLR1 to recognize substance in lipoarabinomannan (LAM) biosynthesis with the help of CD14. Thus, we conducted some researches on TLR2, the basic part and obtained valuable results.

Plasmid (TLR2-P2A-TLR1-T2A-CD14) was transfected into HEK293T cells. In order to determine whether TLR2 was successfully expressed on the membrane of the designer cells, we performed Western blotting assay and Flow cytometry analysis.

Figure 1.Western blot analysis of TLR2 expression and activation of TLR signaling pathway.

Western blot (Figure 1) result shows that TLR2 was successfully expressed in HEK293T cells after 48h transfection (A). In addition, we also investigated whether NF-κB signaling pathway could be activated in a TLR1/2 dependent pathway. Transfected cells were treated with Pam3Cys-Ser-(Lys)4. According to the results, phosphorylation of IκB was elevated and IκB was down-regulated, which indicate the activation of NF-κB signaling pathway in TLR1/TLR2/CD14 transfected HEK 293T cells, and the successful expression of TLR2 on the cell membrane.

Figure 2.Flow cytometry analysis of TLR2 expression.

Flow cytometry results (Figure 2) show that TLR2 was expressed on the membrane of artificial HEK293 cells, while strong fluorescence intensity was not observed. Combined with the result of successful activation, it is inferred that TLR1/2 heterodimer formation caused the fluorescence disappearance.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal BglII site found at 552
  
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]

MIT_MAHE 2020

Summary

Toll-like receptor 2 (TLR2) is a transmembrane glycoprotein that participates in the innate immune response. TLRs act as primary sensors of microbial products and activate signalling pathways that lead to the induction of immune and inflammatory genes.1 TLRs belong to a broader family of proteins, which include receptors for the proinflammatory cytokines interleukin (IL)-1 and IL-18. All members of this superfamily signal inflammation in a similar manner. 

References

1. Abend, J. R., Ramalingam, D., Kieffer-Kwon, P., Uldrick, T. S., Yarchoan, R., & Ziegelbauer, J. M. (2012). Kaposi's sarcoma-associated herpesvirus microRNAs target IRAK1 and MYD88, two components of the toll-like receptor/interleukin-1R signaling cascade, to reduce inflammatory-cytokine expression. Journal of virology, 86(21), 11663–11674. https://doi.org/10.1128/JVI.01147-12

2. Afraei, S., Azizi, G., Zargar, S. J., Sedaghat, R., & Mirshafiey, A. (2015). New therapeutic approach by G2013 in experimental model of multiple sclerosis. Acta neurologica Belgica, 115(3), 259–266. https://doi.org/10.1007/s13760-014-0392-x

3. Aisen, P. S., Schafer, K. A., Grundman, M., Pfeiffer, E., Sano, M., Davis, K. L., Farlow, M. R., Jin, S., Thomas, R. G., Thal, L. J., & Alzheimer's Disease Cooperative Study (2003). Effects of rofecoxib or naproxen vs placebo on Alzheimer disease progression: a randomized controlled trial. JAMA, 289(21), 2819–2826. https://doi.org/10.1001/jama.289.21.2819

4. Akira, S., Uematsu, S., & Takeuchi, O. (2006). Pathogen recognition and innate immunity. Cell, 124(4), 783–801. https://doi.org/10.1016/j.cell.2006.02.015