Thyroid hormone receptor β suppresses SV40-mediated tumorigenesis via novel nongenomic actions

Area of Science:

• Oncology
• Molecular Biology
• Endocrinology

Background:

• Thyroid hormone receptor β (TRβ) is implicated as a tumor suppressor, but its precise mechanisms in inhibiting tumorigenesis remain unclear.
• Simian virus-40 large T antigen (SV40Tag) is an oncoprotein known to inactivate tumor suppressors p53 and retinoblastoma protein (Rb), promoting thyroid tumor development.

Purpose of the Study:

• To elucidate the molecular mechanisms by which TRβ suppresses thyroid tumor development induced by SV40Tag.
• To investigate TRβ's role in counteracting the oncogenic effects of SV40Tag on p53 and Rb.

Main Methods:

• Utilized mouse xenograft models with SV40Tag-immortalized human thyroid epithelial (HTori) cells.
• Assessed the impact of stably expressed TRβ on tumor development in these models.
• Examined protein-protein interactions between TRβ, SV40Tag, p53, and Rb.

Main Results:

• Stable expression of TRβ completely blocked tumor development in SV40Tag-induced mouse xenografts.
• TRβ competed with p53 and Rb for binding to SV40Tag, preventing their inactivation.
• TRβ-SV40Tag interaction reactivated Rb, inhibiting cell cycle progression.
• TRβ-SV40Tag interaction reactivated p53, increasing Pten expression and attenuating PI3K-AKT signaling, leading to reduced proliferation and apoptosis.

Conclusions:

• TRβ functions as a potent tumor suppressor in the context of SV40Tag-induced thyroid tumorigenesis.
• TRβ's tumor-suppressive activity is mediated by direct protein-protein interaction with SV40Tag, disrupting the oncoprotein's binding to p53 and Rb.
• This interaction reactivates Rb and p53 pathways, ultimately inhibiting cell proliferation and promoting apoptosis, thereby blocking tumor development.