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 2

PinX1 expression is gene-dosage–dependent, and PinX1 heterozygous knockout reduces PinX1 expression and increases telomerase activity in vitro and in vivo.

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PinX1 expression is gene-dosage–dependent, and PinX1 heterozygous knocko...
(A) Construction of the PinX1 targeting vector and deletion of the PinX1 gene by Cre- and loxP-mediated homologous recombination. Cre-mediated deletion of the PinX1rec allele generates the PinX1– allele. (B) Identification of PinX1-KO mice, as confirmed by genomic Southern analysis using a 5′ probe. Black and red arrows point to the expected products of WT and KO alleles. (C) Identification of PinX1 KO mice by 2 different sets of PCR amplification using 3 primers each. (D) Gene-dosage–dependent expression of PinX1 mRNA in mouse embryos, as determined by qRT-PCR amplification of 1-kb full-length PinX1 mRNA in PinX1+/+, PinX1+/–, and PinX1–/– embryos at E9.5. (E and F) Gene-dosage–dependent expression of PinX1 protein in liver tissues of adult PinX1+/+ and PinX1+/– mice (E) and MEFs derived from PinX1+/+ and PinX1+/– embryos at E12.5 (F), as determined by immunoblotting using anti-PinX1 antibodies. Unrelated proteins (E, marked by asterisks) and/or actin (E and F) were used as loading controls. (G and H) Elevated telomerase activity in primary PinX1+/– MEFs. Telomerase-containing fractions were subject to the standard TRAO assay, stained with SYBR green (G), and semiquantified as ratios between telomerase products and the internal control (IC, arrow) (H). B. lys, boiled lysates. (I and J) Elevated telomerase activity in young PinX1+/– testes tissues. Telomerase-containing fractions isolated from 3 PinX1+/– or PinX1+/+ littermates were subject to the standard TRAP assay (I) and semiquantified, with PinX1+/+ telomerase activity being set at 100% (J). Data are represented as mean ± SD.