Identification of PITX1 as a TERT Suppressor Gene Located on Human Chromosome 5

Abstract

Telomerase, a ribonucleoprotein enzyme that maintains telomere length, is crucial for cellular immortalization and cancer progression. Telomerase activity is attributed primarily to the expression of telomerase reverse transcriptase (TERT). Using microcell-mediated chromosome transfer (MMCT) into the mouse melanoma cell line B16F10, we previously found that human chromosome 5 carries a gene, or genes, that can negatively regulate TERT expression (H. Kugoh, K. Shigenami, K. Funaki, J. Barrett, and M. Oshimura, Genes Chromosome Cancer 36:37-47, 2003). To identify the gene responsible for the regulation of TERT transcription, we performed cDNA microarray analysis using parental B16F10 cells, telomerase-negative B16F10 microcell hybrids with a human chromosome 5 (B16F10MH5), and its revertant clones (MH5R) with reactivated telomerase. Here, we report the identification of PITX1, whose expression leads to the downregulation of mouse tert (mtert) transcription, as a TERT suppressor gene. Additionally, both human TERT (hTERT) and mouse TERT (mtert) promoter activity can be suppressed by PITX1. We show that three and one binding site within the hTERT and mtert promoters, respectively, that express a unique conserved region are responsible for the transcriptional activation of TERT. Furthermore, we showed that PITX1 binds to the TERT promoter both in vitro and in vivo. Thus, PITX1 suppresses TERT transcription through direct binding to the TERT promoter, which ultimately regulates telomerase activity.

PITX1 is a novel predictor of the response to chemotherapy in head and neck squamous cell carcinoma

“…The present study demonstrated that the expression of PITX1 was downregulated in HNSCC samples compared with that in normal pharyngeal samples, suggesting that PITX1 may act as a tumor suppressor and a possible novel biomarker in HNSCC and other human malignancies (8)(9)(10)(11)(12)(13)(14)(15)(16)(17). A previous study demonstrated that a low expression of PITX1 is associated with a poor prognosis in colorectal carcinoma (16) and hepatocellular carcinoma (15).…”

“…Amplification of unmutated KRAS2 in HNSCC contributes to tumor growth (28). It was also reported that PITX1 suppresses TERT by directly binding to the TERT promoter (8), which is known to be a component of the telomerase enzyme and is necessary for cancer cell immortalization and proliferation (29). Previously, Ohira et al (30) reported that the mRNA expression level of PITX1 is directly suppressed by microRNA-19b, followed by the upregulation of TERT expression in melanoma cells (30).…”

“…Previously, it was reported that PITX1 is a negative regulator of telomerase, due to transcriptional repression of the promoter of telomerase reverse transcriptase (TERT) (8). Downregulation of PITX1 is consistently associated with the malignancy of various human cancer types, including oral squamous cell carcinoma (9), malignant melanoma (10), esophageal (11), gastric (8,12), lung (13), breast (14), hepatic (15), colorectal (16), and prostate (17) cancer, suggesting that PITX1 may be a tumor suppressor gene. By contrast, an association between PITX1 and HNSCC, including pharyngeal or laryngeal carcinoma, remains to be identified.…”

miR-886-3p upregulation in clear cell renal cell carcinoma regulates cell migration, proliferation and apoptosis by targeting PITX1

“…5A). Furthermore, PITX1 has been identified as a tumor suppressor and is associated with the progression and development in various cancers (21)(22)(23)(24)(25).…”

Combinations of chromosome transfer and genome editing for the development of cell/animal models of human disease and humanized animal models

“…This technique has been used for the identification of genes related to tumor suppression [13,14], genomic imprinting [15,16], DNA repair [17][18][19], metastasis and genomic instability [20], telomerase regulation [21][22][23], mitochondrial disorders [24], and lysosomal storage diseases [25]. MMCT has also been applied to investigate chromosomal functions such as kinetochore assembly, telomere function, and high-order chromosome architecture [8,26,27].…”