The telomerase inhibitor PinX1 is a major haploinsufficient tumor suppressor essential for chromosome stability in mice
Xiao Zhen Zhou, … , Roderick Bronson, Kun Ping Lu
Xiao Zhen Zhou, … , Roderick Bronson, Kun Ping Lu
Published March 23, 2011
Citation Information: J Clin Invest. 2011;121(4):1266-1282. https://doi.org/10.1172/JCI43452.
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Research Article

The telomerase inhibitor PinX1 is a major haploinsufficient tumor suppressor essential for chromosome stability in mice

Abstract

Telomerase is activated in most human cancers and is critical for cancer cell growth. However, little is known about the significance of telomerase activation in chromosome instability and cancer initiation. The gene encoding the potent endogenous telomerase inhibitor PinX1 (PIN2/TRF1-interacting, telomerase inhibitor 1) is located at human chromosome 8p23, a region frequently exhibiting heterozygosity in many common human cancers, but the function or functions of PinX1 in development and tumorigenesis are unknown. Here we have shown that PinX1 is a haploinsufficient tumor suppressor essential for chromosome stability in mice. We found that PinX1 expression was reduced in most human breast cancer tissues and cell lines. Furthermore, PinX1 heterozygosity and PinX1 knockdown in mouse embryonic fibroblasts activated telomerase and led to concomitant telomerase-dependent chromosomal instability. Moreover, while PinX1-null mice were embryonic lethal, most PinX1+/– mice spontaneously developed malignant tumors with evidence of chromosome instability. Notably, most PinX1 mutant tumors were carcinomas and shared tissues of origin with human cancer types linked to 8p23. PinX1 knockout also shifted the tumor spectrum of p53 mutant mice from lymphoma toward epithelial carcinomas. Thus, PinX1 is a major haploinsufficient tumor suppressor essential for maintaining telomerase activity and chromosome stability. These findings uncover what we believe to be a novel role for PinX1 and telomerase in chromosome instability and cancer initiation and suggest that telomerase inhibition may be potentially used to treat cancers that overexpress telomerase.

Authors

Xiao Zhen Zhou, Pengyu Huang, Rong Shi, Tae Ho Lee, Gina Lu, Zhihong Zhang, Roderick Bronson, Kun Ping Lu

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Figure 5

TERT knockdown or knockout rescues telomerase activation and telomere elongation and abrogates anaphase bridges and chromosome instability in PinX1+/– MEFs.

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TERT knockdown or knockout rescues telomerase activation and telomere el...
(A and B) TERT knockdown. PinX1+/+ and PinX1+/– MEFs were stably infected with 2 different TERT shRNA or control lentiviruses, followed by quantitative TERT RT-PCR analysis with actin as a control (A) and TRAP assay (B, Supplemental Figure 2D, and E). Data are represented as mean ± SD. (C–F) TERT knockdown rescues telomere lengthening in PinX1+/– MEFs at late passage. Stable cells were continuously cultured for 20 passages and then subjected to telomere qFISH. TERT knockdown had no effects on telomere length in PinX1+/+ MEFs under the same conditions (Supplemental Figure 3). (G and H) TERT knockdown rescues anaphase bridges, lagging chromosomes, and aneuploidy in PinX1+/– MEFs. PinX1+/+ and PinX1+/– MEFs expressing TERT shRNAs or control vector were fixed at 20 passages, followed by scoring for the frequency of anaphase bridges and/or lagging chromosomes (G) or aneuploidy (H). (I–L) TERT knockdown rescues abnormal DNA content in PinX1+/– MEFs. PinX1+/+ and PinX1+/– MEFs expressing TERT shRNAs or control were fixed at 20 passages, followed by flow cytometry to determine the DNA content. Green and red arrows point to the DNA contents expected for diploid and tetraploid cells, respectively. (M) Generation of TERT and PinX1 double-knockout MEFs. 2 MEF lines of each group derived from Tert–/– and PinX1+/+ or PinX1+/– embryos at E12.5 were subjected to PCR genotyping and confirmed by RT-PCR. (N and O) TERT knockout prevents telomere elongation in PinX1+/– MEFs at late passage, as determined by qFISH. (P) TERT knockout prevents anaphase bridges and/or lagging chromosomes in PinX1+/– MEFs at late passage.