Tax1
The Tax1 is a PDZ domain containing oncoprotein encoded by HTLV-1.[1]
Disruption of tumor suppressors
[edit]Tax1 disrupts tumor suppressor pathways by using its PDZ-binding motif to interact with key scaffolding proteins such as Scribble and Erbin.[5][6][7]
Summary
[edit]Tax1 contains a conserved PDZ-binding motif at its C-terminus that allows it to bind multiple PDZ domains in host proteins.[7][6] These interactions interfere with tumor suppressor functions, disrupting epithelial cell polarity through Scribble and enhancing growth signaling via Erbin.[5][6][7] By mimicking endogenous ligands, Tax1 alters normal scaffolding networks, contributing to abnormal cell proliferation through pathways like Ras–Raf–MEK–ERK.[5][6] Structural studies show that Tax1 binds each PDZ domain in Scribble with distinct affinities and can compete with native proteins.[6] The interaction is also subject to regulation through phosphorylation, revealing a potential control point in this oncogenic mechanism.[6]
Structural features of the PDZ-binding motif
[edit]The PDZ-binding motif of Tax1 is a short amino acid sequence located at its C-terminus that fits a common class I motif, usually ending in threonine–glutamate–valine.[6] This conserved structure allows Tax1 to bind with high specificity to PDZ domains—modular protein regions involved in organizing signaling complexes.[6] Tax1's PDZ binding motif mimics cellular ligands, enabling it to fit into the grooves of multiple PDZ domains without requiring major conformational changes.[6]
Scribble binding and loss of cell polarity
[edit]Scribble is a scaffold protein that helps maintain cell polarity and limits cell growth.[6][7] Tax1 binds all four of Scribble's PDZ domains with differing strengths: PDZ1 (KD = 7.8 μM), PDZ2 (15.4 μM), PDZ3 (9.1 μM), and PDZ4 (40.2 μM).[6] These interactions prevent Scribble from forming complexes with its normal partners, such as β-PIX and Vangl2, leading to disrupted polarity signaling.[6] As a result, Scribble becomes mislocalized within the cell, weakening its tumor suppressor role.[6] Research also shows that phosphorylation of Tax1 at a specific threonine residue (Thr351) reduces its ability to bind PDZ domains, indicating that this interaction may be regulated by cellular signaling.[6]
Interaction with Erbin and enhanced growth signaling
[edit]Erbin is another PDZ domain-containing tumor suppressor that plays a role in localizing and regulating the Ras–Raf–MEK–ERK pathway, a major driver of cell growth.[5][7] In cells where Erbin is present, Tax1 binding leads to increased activation of Ras and Raf proteins, enhancing downstream ERK signaling.[5] This sustained activation can drive cell division beyond normal controls and supports the growth of transformed cells.[5][6]
Conclusion
[edit]Tax1 hijacks host signaling networks by using its conserved C-terminal PDZ-binding motif to bind tumor suppressor proteins like Scribble and Erbin.[5][6][7] These interactions disrupt pathways responsible for cell polarity and growth regulation, including the Ras–Raf–MEK–ERK signaling cascade.[5][6][7] By mimicking cellular ligands and targeting PDZ domains with specific binding affinities, Tax1 reprograms scaffolding proteins in a way that supports oncogenic transformation.[5][6][7]
References
[edit]- ↑ Boxus M, Twizere JC, Legros S, Dewulf JF, Kettmann R, Willems L (2008). "The HTLV-1 Tax interactome". Retrovirology. 5: 76. doi:10.1186/1742-4690-5-76. PMC 2533353. PMID 18702816.
- 1 2 Bank, RCSB Protein Data. "RCSB PDB Group Summary: P03409". www.rcsb.org. Retrieved 2025-05-10.
- ↑ Bank, RCSB Protein Data. "RCSB PDB - 8CN3: hDLG1-PDZ2 in complex with a TAX1 peptide from HTLV-1". www.rcsb.org. Retrieved 2025-05-10.
- ↑ "UniProt". UniProt. Retrieved 2025-05-11.
- 1 2 3 4 5 6 7 8 9 Hirata, Akira; Higuchi, Masaya; Niinuma, Akiko; Ohashi, Minako; Fukushi, Masaya; Oie, Masayasu; Akiyama, Tetsu; Tanaka, Yuetsu; Gejyo, Fumitake; Fujii, Masahiro (January 2004). "PDZ domain-binding motif of human T-cell leukemia virus type 1 Tax oncoprotein augments the transforming activity in a rat fibroblast cell line". Virology. 318 (1): 327–336. doi:10.1016/j.virol.2003.10.006.
- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Javorsky, Airah; Maddumage, Janesha C.; Mackie, Emily R. R.; Soares da Costa, Tatiana P.; Humbert, Patrick O.; Kvansakul, Marc (February 2023). "Structural insight into the Scribble PDZ domains interaction with the oncogenic Human T‐cell lymphotrophic virus‐1 (HTLV ‐1) Tax1 PBM". The FEBS Journal. 290 (4): 974–987. doi:10.1111/febs.16607. ISSN 1742-464X. PMC 10952772. PMID 36029163.
- 1 2 3 4 5 6 7 8 Song, Chunjiao; Wang, Weimin; Li, Meng; Liu, Yanxin; Zheng, Dexian (June 2009). "Tax1 enhances cancer cell proliferation via Ras–Raf–MEK–ERK signaling pathway". IUBMB Life. 61 (6): 685–692. doi:10.1002/iub.221. ISSN 1521-6543.