Aberrant accumulation of PTTG1 induced by a mutated thyroid hormone β receptor inhibits mitotic progression
Hao Ying, … , Mark C. Willingham, Sheue-yann Cheng
Hao Ying, … , Mark C. Willingham, Sheue-yann Cheng
Published November 1, 2006
Citation Information: J Clin Invest. 2006;116(11):2972-2984. https://doi.org/10.1172/JCI28598.
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Research Article Oncology

Aberrant accumulation of PTTG1 induced by a mutated thyroid hormone β receptor inhibits mitotic progression

Abstract

Overexpression of pituitary tumor–transforming 1 (PTTG1) is associated with thyroid cancer. We found elevated PTTG1 levels in the thyroid tumors of a mouse model of follicular thyroid carcinoma (TRβPV/PV mice). Here we examined the molecular mechanisms underlying elevated PTTG1 levels and the contribution of increased PTTG1 to thyroid carcinogenesis. We showed that PTTG1 was physically associated with thyroid hormone β receptor (TRβ) as well as its mutant, designated PV. Concomitant with thyroid hormone–induced (T3-induced) degradation of TRβ, PTTG1 proteins were degraded by the proteasomal machinery, but no such degradation occurred when PTTG1 was associated with PV. The degradation of PTTG1/TRβ was activated by the direct interaction of the liganded TRβ with steroid receptor coactivator 3 (SRC-3), which recruits proteasome activator PA28γ. PV, which does not bind T3, could not interact directly with SRC-3/PA28γ to activate proteasome degradation, resulting in elevated PTTG1 levels. The accumulated PTTG1 impeded mitotic progression in cells expressing PV. Our results unveil what we believe to be a novel mechanism by which PTTG1, an oncogene, is regulated by the liganded TRβ. The loss of this regulatory function in PV led to an aberrant accumulation of PTTG1 disrupting mitotic progression that could contribute to thyroid carcinogenesis.

Authors

Hao Ying, Fumihiko Furuya, Li Zhao, Osamu Araki, Brian L. West, John A. Hanover, Mark C. Willingham, Sheue-yann Cheng

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Figure 2

Analysis of the interaction of PTTG1 with TRβ1 or PV by GST pull-down assays.

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Analysis of the interaction of PTTG1 with TRβ1 or PV by GST pull-down as...
(A) [35S]-labeled PTTG1 (20 μl) prepared by in vitro transcription/translation was incubated with agarose beads (lane 2), agarose-GST (lane 3), or GST-TRβ1 (lane 4) as described in Methods. Lane 1 shows the input (1 μl) of [35S]-labeled PTTG1. (B). Binding of truncated [35S]-labeled TRβ1 to GST-PTTG1. Lanes 1–5 show the input of [35S]-labeled TRβ1 and truncated TRβ1 proteins as marked (10% of that in lanes 6–10). Lanes 6 and 7 show the binding of the full-length and truncated (domains C+D+E) TRβ1, respectively. The volumes of programmed lysates were adjusted such that equal amounts of full-length TRβ1, ED41, MD32, KD25, and KP24 protein were used in the binding assay. (C) Schematic representation of full-length and truncated TRβ1 proteins, with domains and boundaries indicated. (D) Binding of [35S]-labeled TRβ1 (10 μl) or [35S]-labeled PV (10 μl) to GST-PTTG1 and GST-PTTG1ΔC in the presence (lanes 6, 8, 10, and 12) and absence (lanes 5, 7, 9, and 11) of T3 (1 μM). Inputs (lanes 1 and 2) were 10% of that used in the binding experiments (lanes 5–12). The binding site of PTTG1 with TRβ1 and PV was located in the aminoterminal domain of PTTG1 (lanes 5–12). (E). Schematic representation of full-length and truncated PTTG1 proteins, with boundaries indicated.