TRIB1 explained

Tribbles homolog 1 is a protein kinase that in humans is encoded by the TRIB1 gene.^{[1] [2] [3]} Orthologs of this protein pseudokinase (pseudoenzyme) can be found almost ubiquitously throughout the animal kingdom.^[4] It exerts its biological functions through binding to signalling proteins of the MAPKK level of the MAPK pathway, therefore eliciting a regulatory role in the function of this pathway which mediates proliferation, apoptosis and differentiation in cells. Tribbles-1 is encoded by the trib1 gene, which in humans can be found on chromosome 8 at position 24.13 on the longest arm (q). Recent crystal structures show that Tribbles 1 has an unusual 3D structure, containing a 'broken' C-helix region, a binding site for ubiquitinated substrates such as C/EBPalpha and a key regulatory C-tail region.^[5] Like TRIB2 and TRIB3, TRIB1 has recently been considered as a potential allosteric drug target.^[6]

Function

Tribbles-1 is one of three members of the Tribbles subfamily, which is a part of the CAMK Ser/Thr protein kinase family, of the protein kinase superfamily. The Tribbles subfamily is one of the pseudokinases, meaning that while expressing putative kinase regions in its structure, it is non-catalytic. The Tribbles subfamily lacks a functional ATP binding pocket, and therefore cannot phosphorylate its substrates; instead, Tribbles proteins function as scaffold proteins, which bind their substrates to localize them to or from their function ^[4]

Expression of Tribbles-1 is highly variable, constantly changing with respect to time and cell-type,^[7] which suggests a large amount of regulation that exists in the cell. The protein's primary structure contains a PEST region, indicative of proteins that are highly susceptible to degradation in the cell; Tribbles-1 plays a role in regulating its own expression by binding to its substrate, which not only produces its function on the MAPK pathway, but also works to protect it from degradation whilst binding. This, in part, creates a positive feedback loop in the function of Tribbles-1, as the function of Tribbles-1 directly aids in the increase of the amount of it. As positive feedback loops are often seen throughout biology in circumstances that require the alleviation of an external stimulus, the positive feedback loop exhibited by Tribbles-1 suggests that it plays a functional role in cell response.

Further reading

• Tang K, Finley RL, Nie D, Honn KV . Identification of 12-lipoxygenase interaction with cellular proteins by yeast two-hybrid screening . Biochemistry . 39 . 12 . 3185–91 . March 2000 . 10727209 . 10.1021/bi992664v .
• Wu M, Xu LG, Zhai Z, Shu HB . SINK is a p65-interacting negative regulator of NF-kappaB-dependent transcription . The Journal of Biological Chemistry . 278 . 29 . 27072–9 . July 2003 . 12736262 . 10.1074/jbc.M209814200 . free .
• Kiss-Toth E, Bagstaff SM, Sung HY, Jozsa V, Dempsey C, Caunt JC, Oxley KM, Wyllie DH, Polgar T, Harte M, O'neill LA, Qwarnstrom EE, Dower SK . 6 . Human tribbles, a protein family controlling mitogen-activated protein kinase cascades . The Journal of Biological Chemistry . 279 . 41 . 42703–8 . October 2004 . 15299019 . 10.1074/jbc.M407732200 . free . 2262/33449 . free .
• Xu C, Zhang J, Huang X, Sun J, Xu Y, Tang Y, Wu J, Shi Y, Huang Q, Zhang Q . 6 . Solution structure of human peptidyl prolyl isomerase-like protein 1 and insights into its interaction with SKIP . The Journal of Biological Chemistry . 281 . 23 . 15900–8 . June 2006 . 16595688 . 10.1074/jbc.M511155200 . free .
• Sung HY, Guan H, Czibula A, King AR, Eder K, Heath E, Suvarna SK, Dower SK, Wilson AG, Francis SE, Crossman DC, Kiss-Toth E . 6 . Human tribbles-1 controls proliferation and chemotaxis of smooth muscle cells via MAPK signaling pathways . The Journal of Biological Chemistry . 282 . 25 . 18379–87 . June 2007 . 17452330 . 2366084 . 10.1074/jbc.M610792200 . free .

Notes and References

1. Wilkin F, Suarez-Huerta N, Robaye B, Peetermans J, Libert F, Dumont JE, Maenhaut C . Characterization of a phosphoprotein whose mRNA is regulated by the mitogenic pathways in dog thyroid cells . European Journal of Biochemistry . 248 . 3 . 660–8 . September 1997 . 9342215 . 10.1111/j.1432-1033.1997.t01-1-00660.x . free .
2. Hegedus Z, Czibula A, Kiss-Toth E . Tribbles: novel regulators of cell function; evolutionary aspects . Cellular and Molecular Life Sciences . 63 . 14 . 1632–41 . July 2006 . 16715410 . 10.1007/s00018-006-6007-9 . 24556931 . 11136108 .
3. Web site: Entrez Gene: TRIB1 tribbles homolog 1 (Drosophila).
4. Eyers PA, Keeshan K, Kannan N . Tribbles in the 21st Century: The Evolving Roles of Tribbles Pseudokinases in Biology and Disease . Trends in Cell Biology . 27 . 4 . 284–298 . April 2017 . 27908682 . 5382568 . 10.1016/j.tcb.2016.11.002 .
5. Murphy JM, Nakatani Y, Jamieson SA, Dai W, Lucet IS, Mace PD . Molecular Mechanism of CCAAT-Enhancer Binding Protein Recruitment by the TRIB1 Pseudokinase . Structure . 23 . 11 . 2111–21 . November 2015 . 26455797 . 10.1016/j.str.2015.08.017 . free .
6. Foulkes DM, Byrne DP, Bailey FP, Eyers PA . Tribbles pseudokinases: novel targets for chemical biology and drug discovery? . Biochemical Society Transactions . 43 . 5 . 1095–103 . October 2015 . 26517930 . 10.1042/BST20150109 .
7. Sung HY, Francis SE, Crossman DC, Kiss-Toth E . Regulation of expression and signalling modulator function of mammalian tribbles is cell-type specific . Immunology Letters . 104 . 1–2 . 171–7 . April 2006 . 16364454 . 10.1016/j.imlet.2005.11.010 .