54984

PINX1

LPTL|LPTS;PIN2/TERF1 interacting, telomerase inhibitor 1;PINX1;PIN2/TERF1 interacting, telomerase inhibitor 1

67-11-3 protein|PIN2 interacting protein 1|PIN2-interacting protein 1|PIN2/TERF1-interacting telomerase inhibitor 1|TRF1-interacting protein 1|hepatocellular carcinoma-related putative tumor suppressor|liver-related putative tumor suppressor|pin2-interact

8p23

protein-coding

Human chromosome 8p23 is known as a region that is associated with loss of heterozygosity (LOH), which is frequently deleted in hepatocellular carcinoma (HCC) tissues. We report here the characterization of a gene for a liver-related putative tumor suppressor (LPTS) localized at 8p23, that was isolated by allelic-loss mapping and positional candidate cloning. The expression of the gene for LPTS was ubiquitous in normal human tissues, albeit at relatively low levels, whereas levels appeared to be significantly reduced, or sometimes undetectable in HCC cells and neoplastic tissues. Thus, it appeared that LPTS might be involved in the control of cell proliferation. Indeed, we observed the significant suppression of growth and growth arrest of SMMC-7721 HCC cells after introduction of the gene for LPTS. We also used antisense oligodeoxynucleotides (AS-ODNs) to suppress the expression of LPTS in normal liver cells L02. Several AS-ODNs specific for LPTS mRNA significantly enhanced cell growth, whereas control oligodeoxynucleotides (ODNs) did not. Our results suggest that LPTS might be a growth-inhibitory protein in human hepatocytes.

AIM: To find the point mutations meaningful for inactivation of liver-related putative tumor suppressor gene (LPTS) gene, a human novel liver-related putative tumor suppressor gene and telomerase inhibitor in hepatocellular carcinoma. METHODS: The entire coding sequence of LPTS gene was examined for mutations by single strand conformation polymorphism (SSCP) assay and PCR products direct sequencing in 56 liver cancer cell lines, 7 ovarian cancer and 7 head neck tumor cell lines and 70 pairs of HCC tissues samples. The cDNA fragment coding for the most frequent mutant protein was subcloned into GST fusion expression vector. The product was expressed in E.coli and purified by glutathione-agarose column. Telomeric repeat amplification protocol (TRAP) assays were performed to study the effect of point mutation to telomerase inhibitory activity. RESULTS: SSCP gels showed the abnormal shifting bands and DNA sequencing found that there were 5 different mutations and/or polymorphisms in 12 tumor cell lines located at exon2, exon5 and exon7. The main alterations were A(778)A/G and A(880)T in exon7. The change in site of 778 could not be found in HCC tissue samples, while the mutation in position 880 was seen in 7 (10 %) cases. The mutation in the site of 880 had no effect on telomerase inhibitory activity. CONCLUSION: Alterations identified in this study are polymorphisms of LPTS gene. LPTS mutations occur in HCC but are infrequent and of little effect on the telomerase inhibitory function of the protein. Epigenetics, such as methylation, acetylation, may play the key role in inactivation of LPTS.

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.