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 9

Protein abundance (A) and interaction (B) of PTTG1, TRβ1, and PV at different cell cycles.

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Protein abundance (A) and interaction (B) of PTTG1, TRβ1, and PV at diff...
(A) FH-TRβ1 and FH-PV cells were synchronized in the G0/G1, S, and G2/M phases as described in Methods. Asynchronized cells (AS) and synchronized cells at different phases of the cell cycle were confirmed by fluorescence-activated cell sorting analysis, and the expression of cell cycle markers (cyclin D1, cyclin A, and cyclin B1 for the G0/G1, S, and G2/M phases, respectively) was determined. The protein abundance of cyclin D1, cyclin A, and cyclin B1 were determined by Western blot analysis using anti–cyclin D1 (1:1,000 dilution), anti–cyclin A (1:1,000 dilution), and anti–cyclin B1 (1:2,000 dilution) antibodies, respectively. The protein abundance of PTTG1, F-TRβ1, F-PV, and the loading control α-tubulin was determined by Western blot analysis similar to that in Figure 5. (B). Cell lysates (1 mg) prepared from FH-TRβ1 cells (lanes 1–4) and FH-PV cells (lanes 5–10) not synchronized (lanes 1, 5, and 9) or synchronized at the G0/G1, S and G2/M phase (lanes 2–4, 6–8, and 10) were analyzed for the interaction of the endogenous PTTG1 with F-TRβ1 or F-PV by coimmunoprecipitation. Cell lysates were first immunoprecipitated with anti-Flag antibodies followed by Western blot analysis with anti-PTTG1. Lane 11 is the negative control using HEK293 cells that did not have TRs. Lanes 9 and 10 show the direct Western blot analysis using anti-PTTG1 antibodies, indicating the input (25 μg of cell lysates).