The telomerase inhibitor PinX1 is a major haploinsufficient tumor suppressor essential for chromosome stability in mice
Xiao Zhen Zhou, Pengyu Huang, Rong Shi, Tae Ho Lee, Gina Lu, Zhihong Zhang, Roderick Bronson, Kun Ping Lu
Xiao Zhen Zhou, Pengyu Huang, Rong Shi, Tae Ho Lee, Gina Lu, Zhihong Zhang, Roderick Bronson, Kun Ping Lu
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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 3

PinX1 heterozygous knockout leads to telomere elongation in MEFs and mice.

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PinX1 heterozygous knockout leads to telomere elongation in MEFs and mic...
(A–F) Telomere elongation in PinX1+/– MEFs at late passage, as determined by qFISH. PinX1+/+ and PinX1+/– MEFs at early (from 3 to 5) (A–C) and late (~30) (D–F) passage were fixed and hybridized with a FITC-labeled PNA (CCCTAA)3 probe, followed by quantifying TFUs in approximately 2,000 telomeres, with a telomere distribution curve being shown in C and F. (G and H) Telomere elongation in PinX1+/– MEFs at late passage, as determined by telomere Southern blot. Multiple independent clones of PinX1+/+ and PinX1+/– MEFs were cast into plug molds, lysed, and digested, followed by Southern blot analysis using a TTAGGG repeat as a probe. Prior to hybridization, the gels were stained with ethidium bromide to insure equal loading of total DNA, with a segment of the gels being shown in lower panels (G), with average TRF lengths from 3 independent MEF lines being quantified using ImageQuant (H). (I and J) Telomere elongation at old (10–13 months) (J), but not young age (6–10 weeks) (I) of PinX1+/– mice, as determined by qFISH. (K and L) Telomere elongation at old, but not young age of PinX1+/– mice, as determined by Southern blot analysis of splenocytes (K), with average TRF lengths from 5–6 littermates being quantified using ImageQuant (L). The lanes were run on the same gel, but were noncontiguous. **P < 0.01. Data are represented as mean ± SD.