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Oncogenic mutations of thyroid hormone receptor β.

Park JW, Zhao L, Willingham M, Cheng SY - Oncotarget (2015)

Bottom Line: Thus, these results argue against the oncogenic activity of PV being uniquely dependent on the PV mutated sequence.Rather, these four mutants could favor a C-terminal conformation that interacted with the CSH2 domain of p85α to initiate activation of PI3K to relay downstream signaling to promote tumorigenesis.Thus, we propose that the mutated C-terminal region of TRβ1 could function as an "onco-domain" and TRβ1 is a potential therapeutic target.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.

ABSTRACT
The C-terminal frame-shift mutant of the thyroid hormone receptor TRβ1, PV, functions as an oncogene. An important question is whether the oncogenic activity of mutated TRβ1 is uniquely dependent on the PV mutated sequence. Using four C-terminal frame-shift mutants-PV, Mkar, Mdbs, and AM-we examined that region in the oncogenic actions of TRβ1 mutants. Remarkably, these C-terminal mutants induced similar growth of tumors in mouse xenograft models. Molecular analyses showed that they physically interacted with the p85α regulatory subunit of PI3K similarly in cells. In vitro GST-binding assay showed that they bound to the C-terminal Src-homology 2 (CSH2) of p85α with markedly higher avidity. The sustained association of mutants with p85α led to activation of the common PI3K-AKT-ERK/STAT3 signaling to promote cell proliferation and invasion and to inhibit apoptosis. Thus, these results argue against the oncogenic activity of PV being uniquely dependent on the PV mutated sequence. Rather, these four mutants could favor a C-terminal conformation that interacted with the CSH2 domain of p85α to initiate activation of PI3K to relay downstream signaling to promote tumorigenesis. Thus, we propose that the mutated C-terminal region of TRβ1 could function as an "onco-domain" and TRβ1 is a potential therapeutic target.

No MeSH data available.


Related in: MedlinePlus

Key downstream regulators of the PI3K signaling pathway are constitutively activated by C-terminal mutants of TRβ1A. I. Western blot analysis of key regulators, AKT (panels a & b), m-TOR (panels c & d), ERK (panels e & f) and MMP2 (panel g) and MMP9 (panel h) of the PI3K signaling pathway in tumors. Tumors were excised from the injection sites (hind flanks) of athymic nude mice, and the Western blot analysis was carried as described in Materials and Methods. A. II. The band intensities of the protein detected in A-I were quantified and compared. The data are shown as mean ± SE (n = 2). B.I. Western blot analysis of key regulators, STAT3 (panels a &b) and BIM (panel c) of the PI3K signaling pathway in tumors. B. II. The band intensities of the protein detected in B-I were quantified and compared. The data are shown as mean ± SE (n = 2).
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Figure 8: Key downstream regulators of the PI3K signaling pathway are constitutively activated by C-terminal mutants of TRβ1A. I. Western blot analysis of key regulators, AKT (panels a & b), m-TOR (panels c & d), ERK (panels e & f) and MMP2 (panel g) and MMP9 (panel h) of the PI3K signaling pathway in tumors. Tumors were excised from the injection sites (hind flanks) of athymic nude mice, and the Western blot analysis was carried as described in Materials and Methods. A. II. The band intensities of the protein detected in A-I were quantified and compared. The data are shown as mean ± SE (n = 2). B.I. Western blot analysis of key regulators, STAT3 (panels a &b) and BIM (panel c) of the PI3K signaling pathway in tumors. B. II. The band intensities of the protein detected in B-I were quantified and compared. The data are shown as mean ± SE (n = 2).

Mentions: The strong sustained interaction of mutant proteins with the CSH2 domain of p85α shown in vitro would predict that the PI3K downstream pathway leads to higher PI3K signaling. We therefore tested this prediction by carrying out Western blot analyses of the downstream key regulators in the PI3K signaling pathway. Figure 8A-I-ashows that reduced phosphorylated AKT (p-AKT) was detected in the tumors induced by MDA-TRβ1cells (lanes 3 & 4), while p-AKT protein abundance in cells expressing mutants (lanes 5-12, two tumors for each mutant expressing cells) was similarly high as that in the control Neo cells (lanes 1 & 2), without significantly affecting the total AKT levels (panel b). Higher levels of p-mTOR, a downstream effector of p-AKT, were detected in all tumors derived from cells expressing mutants (lanes 5-12, panel c) than in tumors derived from MDA-TRβ1 cells (lanes 3 & 4, panel c). No apparent changes were found in total m-TOR (panel d) in all tumors. The ratios of p-AKT/Total AKT and p-mTOR/Total mTOR were quantified from the band intensities to indicate that a higher activation of AKT-mTOR signaling in all tumors derived from cells expressing mutants than from MDA-TRβ1 cells (Figure 8A-II, panels a & b).


Oncogenic mutations of thyroid hormone receptor β.

Park JW, Zhao L, Willingham M, Cheng SY - Oncotarget (2015)

Key downstream regulators of the PI3K signaling pathway are constitutively activated by C-terminal mutants of TRβ1A. I. Western blot analysis of key regulators, AKT (panels a & b), m-TOR (panels c & d), ERK (panels e & f) and MMP2 (panel g) and MMP9 (panel h) of the PI3K signaling pathway in tumors. Tumors were excised from the injection sites (hind flanks) of athymic nude mice, and the Western blot analysis was carried as described in Materials and Methods. A. II. The band intensities of the protein detected in A-I were quantified and compared. The data are shown as mean ± SE (n = 2). B.I. Western blot analysis of key regulators, STAT3 (panels a &b) and BIM (panel c) of the PI3K signaling pathway in tumors. B. II. The band intensities of the protein detected in B-I were quantified and compared. The data are shown as mean ± SE (n = 2).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4480739&req=5

Figure 8: Key downstream regulators of the PI3K signaling pathway are constitutively activated by C-terminal mutants of TRβ1A. I. Western blot analysis of key regulators, AKT (panels a & b), m-TOR (panels c & d), ERK (panels e & f) and MMP2 (panel g) and MMP9 (panel h) of the PI3K signaling pathway in tumors. Tumors were excised from the injection sites (hind flanks) of athymic nude mice, and the Western blot analysis was carried as described in Materials and Methods. A. II. The band intensities of the protein detected in A-I were quantified and compared. The data are shown as mean ± SE (n = 2). B.I. Western blot analysis of key regulators, STAT3 (panels a &b) and BIM (panel c) of the PI3K signaling pathway in tumors. B. II. The band intensities of the protein detected in B-I were quantified and compared. The data are shown as mean ± SE (n = 2).
Mentions: The strong sustained interaction of mutant proteins with the CSH2 domain of p85α shown in vitro would predict that the PI3K downstream pathway leads to higher PI3K signaling. We therefore tested this prediction by carrying out Western blot analyses of the downstream key regulators in the PI3K signaling pathway. Figure 8A-I-ashows that reduced phosphorylated AKT (p-AKT) was detected in the tumors induced by MDA-TRβ1cells (lanes 3 & 4), while p-AKT protein abundance in cells expressing mutants (lanes 5-12, two tumors for each mutant expressing cells) was similarly high as that in the control Neo cells (lanes 1 & 2), without significantly affecting the total AKT levels (panel b). Higher levels of p-mTOR, a downstream effector of p-AKT, were detected in all tumors derived from cells expressing mutants (lanes 5-12, panel c) than in tumors derived from MDA-TRβ1 cells (lanes 3 & 4, panel c). No apparent changes were found in total m-TOR (panel d) in all tumors. The ratios of p-AKT/Total AKT and p-mTOR/Total mTOR were quantified from the band intensities to indicate that a higher activation of AKT-mTOR signaling in all tumors derived from cells expressing mutants than from MDA-TRβ1 cells (Figure 8A-II, panels a & b).

Bottom Line: Thus, these results argue against the oncogenic activity of PV being uniquely dependent on the PV mutated sequence.Rather, these four mutants could favor a C-terminal conformation that interacted with the CSH2 domain of p85α to initiate activation of PI3K to relay downstream signaling to promote tumorigenesis.Thus, we propose that the mutated C-terminal region of TRβ1 could function as an "onco-domain" and TRβ1 is a potential therapeutic target.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.

ABSTRACT
The C-terminal frame-shift mutant of the thyroid hormone receptor TRβ1, PV, functions as an oncogene. An important question is whether the oncogenic activity of mutated TRβ1 is uniquely dependent on the PV mutated sequence. Using four C-terminal frame-shift mutants-PV, Mkar, Mdbs, and AM-we examined that region in the oncogenic actions of TRβ1 mutants. Remarkably, these C-terminal mutants induced similar growth of tumors in mouse xenograft models. Molecular analyses showed that they physically interacted with the p85α regulatory subunit of PI3K similarly in cells. In vitro GST-binding assay showed that they bound to the C-terminal Src-homology 2 (CSH2) of p85α with markedly higher avidity. The sustained association of mutants with p85α led to activation of the common PI3K-AKT-ERK/STAT3 signaling to promote cell proliferation and invasion and to inhibit apoptosis. Thus, these results argue against the oncogenic activity of PV being uniquely dependent on the PV mutated sequence. Rather, these four mutants could favor a C-terminal conformation that interacted with the CSH2 domain of p85α to initiate activation of PI3K to relay downstream signaling to promote tumorigenesis. Thus, we propose that the mutated C-terminal region of TRβ1 could function as an "onco-domain" and TRβ1 is a potential therapeutic target.

No MeSH data available.


Related in: MedlinePlus