Molecular determinants of PDLIM2 in suppressing HTLV-I Tax-mediated tumorigenesis
1University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
Abstract:
Human T-cell leukemia virus type I (HTLV-I) encodes a Tax oncoprotein that has crucial roles in both virus replication and cell transformation. Our recent studies suggest that the counterbalance between HTLV-I/Tax and PDZ-LIM domain-containing protein PDLIM2 may determine the outcome of HTLV-I infection. Although HTLV-I represses PDLIM2 epigenetically and specifically in transformed cells, PDLIM2 shuttles Tax into the nuclear matrix for ubiquitination-mediated proteasomal degradation, thereby suppressing the transforming ability of HTLV-I. Here, we have further shown that PDLIM2 binds to Tax directly, which was mediated by a putative α-helix motif of PDLIM2 at amino acids 236-254. Consistently, selective disruption of this short-helix crippled PDLIM2 in shutting Tax to the nuclear matrix for ubiquitination-mediated degradation, therefore, PDLIM2 lost the ability in tumor suppression. Although the C-terminal LIM domain of PDLIM2 was not required for Tax binding, it was important for PDLIM2 to interact with the nuclear matrix. Accordingly, the LIM domain was essential for PDLIM2-mediated Tax repression. On the contrary, the N-terminal PDZ domain of PDLIM2 was dispensable for all these events, although the PDZ domain was involved in PDLIM2 binding to cytoskeleton. These studies dissect functional sequences within PDLIM2 and their distinct roles in Tax regulation.
Insights
Human T-cell leukemia virus type I (HTLV-I) Tax protein's transforming ability is suppressed by PDZ-LIM domain-containing protein PDLIM2. PDLIM2 directly binds Tax via an alpha-helix motif, shuttling it for degradation and inhibiting tumor formation.
Area of Science:
- Molecular biology
- Virology
- Cancer research
Background:
- Human T-cell leukemia virus type I (HTLV-I) Tax oncoprotein drives viral replication and cell transformation.
- The balance between HTLV-I/Tax and PDLIM2 influences HTLV-I infection outcomes.
- HTLV-I epigenetically represses PDLIM2 in transformed cells.
Purpose of the Study:
- To investigate the molecular mechanisms of PDLIM2 in regulating HTLV-I Tax.
- To identify specific functional domains within PDLIM2 responsible for Tax interaction and degradation.
- To elucidate the role of PDLIM2 in suppressing HTLV-I-mediated transformation.
Main Methods:
- Direct binding assays to confirm PDLIM2-Tax interaction.
- Site-directed mutagenesis to disrupt PDLIM2 functional motifs (alpha-helix, LIM, PDZ domains).
- Cellular localization studies to track Tax and PDLIM2.
- Ubiquitination and proteasomal degradation assays.
- Tumorigenesis assays to assess PDLIM2's tumor suppressive function.
Main Results:
- PDLIM2 directly binds to the HTLV-I Tax oncoprotein.
- A specific alpha-helix motif (amino acids 236-254) in PDLIM2 is essential for Tax binding and nuclear matrix shuttling.
- Disruption of this motif abolishes PDLIM2's ability to degrade Tax and suppress tumors.
- The C-terminal LIM domain of PDLIM2 is crucial for nuclear matrix interaction and Tax repression, but not Tax binding.
- The N-terminal PDZ domain of PDLIM2 is dispensable for Tax regulation but involved in cytoskeleton interaction.
Conclusions:
- PDLIM2 directly interacts with HTLV-I Tax via a critical alpha-helix motif.
- PDLIM2 mediates Tax ubiquitination and proteasomal degradation, thereby suppressing HTLV-I-driven cell transformation.
- Distinct domains of PDLIM2 (LIM for nuclear localization, alpha-helix for binding) play specific roles in regulating Tax activity and tumor suppression.
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