Loss of heterozygosity and histone hypoacetylation of the PINX1 gene are associated with reduced expression in gastric carcinoma

Abstract

The expression of PINX1, a possible telomerase inhibitor and a putative tumor suppressor, has not been studied in human cancers, including gastric cancer (GC). We examined expression of PINX1 by quantitative reverse transcription (RT)-PCR in 73 cases of GC, and 45 of these cases were further studied for loss of heterozygosity (LOH) by PCR with microsatellite marker D8S277. Reduced expression (tumor vs normal ratioo0.5) of PINX1 was detected in 50 (68.5%) of 73 cases of GC. GC tissues with reduced expression of PINX1 showed significantly higher telomerase activities as measured by telomeric repeat amplification protocol than those with normal expression of PINX1 (P ¼ 0.031). LOH of PINX1 locus was detected in 15 (33.3%) of 45 cases of GC and was correlated significantly with reduced expression of PINX1 (P ¼ 0.031). Expression of PINX1 in a GC cell line, MKN-74, was induced by treatment with trichostatin A (TSA) or nicotinamide (NAM). Chromatin immunoprecipitation assay of MKN-74 cells revealed that acetylation of histone H4 in the 5 0 untranslated region (UTR) of PINX1 was enhanced by treatment with TSA or NAM, whereas acetylation of histone H3 was not changed by TSA or NAM. In addition, TSA or NAM treatment led to inhibition of telomerase activity in MKN-74 cells. These results indicate that LOH of PINX1 locus and hypoacetylation of histone H4 in the 5 0 UTR of PINX1 are associated with reduced expression of PINX1 in GC.

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

“…In addition, although telomere loss in cancers has been well studied, telomere elongation is quite common in human cancers, e.g., in more than 40% of liver cancer (65), esophageal cancer (66), and brain tumors (67), and also correlates with advanced stages and/or poor survival in some cancers (65,66,68,69). Together with previous findings that reducing PinX1 potently increases tumorigenicity of human cancer cells (45) and that PinX1 is reduced in the majority of liver and gastric cancers (8,9,50), these results indicate that PinX1 is a major haploinsufficient tumor suppressor whose reduction may contribute to tumorigenesis by activating telomerase and promoting chromosome instability. Given telomerase activation in most human cancers, loss of PinX1 function likely contributes to the pathogenesis of many cancers and might have important therapeutic implications.…”

“…Although further experiments are needed to elucidate whether chromosome instability is related to telomere-dependent, and/or -independent functions of telomerase or PinX1, we have focused our effort on determining whether reducing PinX1 levels leads to cancer development. This question is important because PinX1 is located at 8p23 in humans, a frequent LOH region in many epithelial cancers, and depleting PinX1 increases tumorigenicity of cancer cells (8,9,45,50). Moreover, it might offer new insights into the development and treatment of human cancers.…”

“…These results suggest that PinX1 might be a putative tumor suppressor. Subsequent PinX1 studies on human cancer samples provide some supportive evidence (9,50) and contradictory results (51,52). Furthermore, the interpretation of these expression results is complicated because they all used RT-PCR analyses that could detect other alternatively spliced PinX1 variants and a potential PinX1 pseudogene in the genome.…”

“…Chromosome 8p23 is one of the most frequent LOH regions in common human adult epithelial malignancies, including breast, liver, lung, and gastrointestinal cancers. For example, up to 70% of hepatocellular carcinomas (4)(5)(6)(7)(8) and 60% of human gastric cancer (9) exhibit LOH at 8p23 near the marker D8S277. 8p23 is also a common integration site for HBV, a well-known major risk factor in liver cancer (5,10).…”

Gene expression profiling with microarray and SAGE identifies PLUNC as a marker for hepatoid adenocarcinoma of the stomach

“…1 Cancer develops as a result of multiple genetic and epigenetic alterations. [2][3][4] Better knowledge of the changes in gene expression that occur during gastric carcinogenesis may lead to improvements in diagnosis, treatment, and prevention. Identification of novel biomarkers for cancer diagnosis and novel targets for treatment are the major goals in this field.…”