Oncogenic mutations of thyroid hormone receptor β

Area of Science:

• Molecular Biology
• Oncology
• Endocrinology

Background:

• The C-terminal frame-shift mutant of thyroid hormone receptor beta 1 (TRβ1), known as PV, exhibits oncogenic properties.
• The specific sequence responsible for the oncogenic activity of mutated TRβ1 remains an important research question.

Purpose of the Study:

• To investigate whether the oncogenic activity of TRβ1 mutants is solely dependent on the PV mutation.
• To explore the role of the C-terminal region in the oncogenic actions of TRβ1 mutants.

Main Methods:

• Utilized four C-terminal frame-shift mutants (PV, Mkar, Mdbs, AM) of TRβ1.
• Employed mouse xenograft models to assess tumor growth.
• Conducted molecular analyses, including GST-binding assays and cell-based interaction studies with p85α subunit of PI3K.

Main Results:

• All four C-terminal mutants induced comparable tumor growth in mouse xenograft models.
• Mutants demonstrated similar physical interactions with the p85α regulatory subunit of PI3K.
• Mutants exhibited high-avidity binding to the C-terminal Src-homology 2 (CSH2) domain of p85α, leading to sustained PI3K-AKT-ERK/STAT3 pathway activation.
• This signaling cascade promoted cell proliferation and invasion while inhibiting apoptosis.

Conclusions:

• The oncogenic activity of TRβ1 mutants is not uniquely dependent on the PV sequence.
• These mutants facilitate a C-terminal conformation that binds to the p85α CSH2 domain, initiating PI3K activation and downstream signaling.
• The mutated C-terminal region of TRβ1 may function as an "onco-domain," identifying TRβ1 as a potential therapeutic target in cancer.