Over-expression of LPTS-L in hepatocellular carcinoma cell line SMMC-7721 induces crisis

PinX1 plays multifaceted roles in human cancers: a review and perspectives

BACKGROUND

Pin2/TRF1 interacting protein X1 (PinX1), a telomerase inhibitor, is located at human chromosome 8p23. This region is important for telomere length maintenance and chromosome stability, both of which are essential for regulating human ageing and associated diseases.

METHODS AND RESULTS

We investigated the research progress of PinX1 in human cancers. In cancers, the expression levels of PinX1 mRNA and protein vary according to cancer cell types, and PinX1 plays a critical role in the regulation of cancer development and progression. Additionally, a review of the literature indicates that PinX1 is involved in mitosis and affects the sensitivity of cancer cells to radiation-induced DNA damage. Therefore, PinX1 has therapeutic potential for cancer, and understanding the function of PinX1 in the regulation of cancers is crucial for improving treatment. In this review, we discuss the expression level of PinX1 in a variety of cancers and how it affects the implicated pathways. Additionally, we outline the function of PinX1 in cancer cells and provide a theoretical basis for PinX1-related cancer therapy.

CONCLUSIONS

PinX1 has promising prospects in future cancer therapeutics. This review may provide theoretical support for researchers in this field.

Hesperidin Inhibits Lung Cancer In Vitro and In Vivo Through PinX1

New drugs or active leads with high efficiency and low toxicity are needed in the treatment of lung cancer. Natural products are an important source of anti-tumor drugs. At present, there are many molecular-targeted anti-tumor drugs derived from natural products or their derivatives for tumor treatment or in clinical trials. Hesperidin is a flavanone isolated from the Rutaceae plant lime Citrus aurantium L. or Citrus sinensis Osbeck. It has been considered to inhibit cancer cell viability in vitro. However, the effect of hesperidin on lung cancer and its underlying mechanism remain unclear. In this study, we found that the pinX1 expression level is closely related to overall survival and plays an important role in regulating lung cancer cell proliferation, migration, invasion, and senescence. More importantly, hesperidin significantly increased pinX1 protein expression, and knockdown pinX1 by its specific siRNA blocked the protective effects of hesperidin. Moreover, we also assessed that hesperidin at 100 mg/kg is safe in vivo. These findings showed that hesperidin is a potential therapeutic candidate for preventing the progression of lung cancer.

A scalable and reproducible preparation for the antitumor protein TLC, a human-derived telomerase inhibitor

Telomerase, which is overexpressed in approximately 90% of liver cancer cells, is an ideal target for anti-liver cancer therapy. LPTS, a putative liver tumor suppressor, is the only human-derived protein that can bind telomerase directly and inhibit the extension of telomere activity. Our previous studies demonstrated that TAT-LPTS-LC (TLC), a recombinant protein fused by the C-terminal 133-328 fragment of LPTS and TAT peptides, could be delivered into cells to inhibit telomerase-positive hepatoma cell growth in vitro and in vivo with very low toxicity. In the present study, E. coli strains which expressed TLC in abundance were screened and cultured in a laboratory bioreactor. A reproducible protein separation process was built, and this process was suitable for industrial amplification. The yields of TLC protein were up to 184 mg in one batch with a purity of approximately 95%. The purified TLC protein had a similar inhibitory effect on telomerase activity in vitro compared with those purified by Ni-affinity chromatography. Furthermore, TLC protein could be delivered into the cell nucleus to increase the doubling time of the cell and suppress cell growth in telomerase-positive liver cancer cell lines. Cell growth inhibition was negatively correlated with telomere length, suggesting that TLC is a highly targeted telomerase-telomere anticancer agent. These results will contribute to future preclinical studies of the TLC protein.

Oncogenic role of PinX1 in prostate cancer cells through androgen receptor dependent and independent mechanisms

Coregulators play an important role in prostate cancer (PCa), modulating androgen receptor (AR) action and representing a possible cause of androgen deprivation therapy failure. Pin2-interacting protein X1 (PinX1) is a nucleolar protein described as a steroid hormone receptor coregulator in breast cancer cell lines. In this work, we studied the effect of PinX1 on AR action in PCa. Our results demonstrate that PinX1 acts as an AR coactivator, increasing its transcriptional activity and target gene expression, as well as proliferation, migration and colony formation in PCa cell lines. These effects are observed in the presence and absence of AR agonist and antagonists, suggesting a possible androgen independent pathway for PinX1. We present the first oncogenic roles described for PinX1, acting as a coactivator of the AR.

Insufficient PINX1 expression stimulates telomerase activation by direct inhibition of EBV LMP1-NF-κB axis during nasopharyngeal carcinoma development

OBJECTIVE

Early malignant transformation of nasopharyngeal carcinoma(NPC) is associated with Epstein-Barr virus(EBV) infection and telomerase activation. The EBV latent membrane protein 1(LMP1) regulates expression of various genes by triggering NF-κB signaling pathway. PINX1 is a well-identified tumor suppressor gene by inhibiting telomerase activity and cancer cell growth. However, whether and how EBV inhibit PINX1 expression and activate telomerase in NPC is still incompletely elucidated.

METHODS

Immunohistochemistry, real-time PCR and Western blotting were utilized to explore the expression of PINX1. Chromatin immunoprecipitation(ChIP) and Dual-luciferase reporter assay were used to elucidate the regulatory mechanism between NF-κB and PINX1. TRAP-SYBR Green assay and Southern blotting were utilized to detect telomerase activity and telomere length. CCK8 and EdU tests were conducted to measure proliferation ability.

RESULTS

We demonstrated that PINX1 is down-regulated in NPC for the first time. Mechanistically, we found that LMP1 could inhibit the transcriptional activity of PINX1 by promoting the binding of p65 to three specific sites in PINX1 promoter, significantly, two(-1698/-1689, tgcaatttcc; -206/-197, cgggctttac) of which have not been reported. In addition, we also observed that LMP1 overexpression resulted in increased telomerase activity, prolonged telomere length and enhanced proliferation.

CONCLUSION

We first discovered EBV led to reduced PINX1 expression through LMP1-NF-κB-PINX1 axis, which up-regulated telomerase activity in NPC. And hence, the tumor cells acquired the ability to proliferate more exuberantly. This signaling pathway illustrates the relationship between EBV latent infection and telomerase activation, and further provides new thinking for early diagnosis and treatment in NPC.

Efficient expression of recombinant human telomerase inhibitor 1 (hPinX1) in Pichia pastoris

PinX1 encoded by a remarkable tumor suppressor gene and located in human chromosome 8p23 is known as telomerase inhibitor. In recent years, this protein has been of interest as clinically tumor suppressor. Pichia pastoris expression system is preferred to produce heterologous proteins and is suitable for industrial and research purposes. In the present study, human PinX1 gene (hPinX1) was cloned in E. coli One Shot TOP10 cells and overexpressed in P. pastoris strain X-33 intracellularly, using a strong AOX (alcohol oxidase) promoter. The recombinant cells were grown in shaking flask. Induction time, methanol concentration and initial pH were optimized for obtaining high levels of hPinX1 protein production. Recombinant protein production was confirmed by Western blot analysis and the relative expression levels of rhPinX1 were quantified. According to Western blot analysis, molecular mass of produced hPinX1 was determined as 47.5 kDa. At the end of optimization studies, the best fermentation conditions were determined as induction time 48 h, methanol concentration 3% and initial culture pH 5.0. This process would be an applicable way for obtaining recombinant hPinX1 using P. pastoris expression system. This is the first report on recombinant production of hPinX1 in P. pastoris.

PinX1: structure, regulation and its functions in cancer

PIN2/TRF1-interacting telomerase inhibitor 1 (PinX1) is a novel cloned gene located at human chromosome 8p23, playing a vital role in maintaining telomeres length and chromosome stability. It has been demonstrated to be involved in tumor genesis and progression in most malignancies. However, some researches showed opposing molecular status of PinX1 gene and its expression patterns in several other types of tumors. The pathogenic mechanism of PinX1 expression in human malignancy is not yet clear. Moreover, emerging evidence suggest that PinX1 (especially its TID domain) might be a potential new target cancer treatment. Therefore, PinX1 may be a new potential diagnostic biomarker and therapeutic target for human cancers, and may play different roles in different human cancers. The functions and the mechanisms of PinX1 in various human cancers remain unclear, suggesting the necessity of further extensive works of its role in tumor genesis and progression.

Biological significance of PinX1 telomerase inhibitor in esophageal carcinoma treatment

In the present study, to investigate the expression of PinX1 gene and its functional effects in human esophageal carcinoma (Eca)-109 cell line, expression vectors of human PinX1 (pEGFP-C3-PinX1) and its small interfering RNA (PinX1-FAM-siRNA) were constructed and transfected into Eca-109 cells using Lipofectamine 2000. Firstly, the mRNA expression level of PinX1 was examined using reverse transcription-polymerase chain reaction (RT-PCR). Once successful transfection was achieved, the effects on the mRNA level of human telomerase reverse transcriptase (hTERT), telomerase activity, cell proliferation and apoptosis were examined by semi-quantitative RT-PCR, stretch PCR, MTT assay and flow cytometry, respectively. Analysis of restriction and sequencing demonstrated that the recombining plasmids were successfully constructed. The results also indicated that transfection with pEGFP-C3-PinX1 and PinX1-FAM-siRNA into Eca-109 cells significantly increased PinX1 mRNA, decreased hTERT mRNA by 29.9% (P<0.05), and significantly reduced telomerase activity (P<0.05), inhibited cell growth, and increased the cell apoptotic index from 19.27±0.76 to 49.73±2%. The transfected PinX1-FAM-SiRNA exhibited PinX1 mRNA expression levels that were significantly decreased by 70% (P<0.05), whereas the remaining characteristics of Eca-109 cells, including cell growth, mRNA level of hTERT, telomerase activity and cell apoptotic index were not altered. Exogenous PinX1 has been demonstrated to be highly expressed in human Eca. PinX1 can inhibit human telomerase activity and the expression of hTERT mRNA, reduce tumor cell growth and induce apoptosis. Notably, these inhibitory functions were inhibited by silencing PinX1 in Eca with PinX1-FAM-siRNA. PinX1 was successfully increased and decreased in the present study, demonstrating that it may be a potential telomerase activity inhibitor. As PinX1 is an endogenous telomerase inhibitor, it may be used as a novel tumor-targeted gene therapy.

Expression and mechanism of PinX1 and telomerase activity in the carcinogenesis of esophageal epithelial cells

Esophageal tissues were collected from an esophageal carcinoma high-risk area of China and were used to detect the telomere length and the expression of human telomerase reverse transcriptase (hTERT) by immuhistochemistry and fluorescence in situ hybridization; esophageal carcinoma tissues, paired-adjacent mucosa and paired normal mucosa were obtained from resected surgical specimens of esophageal squamous cell carcinoma in order to determine telomerase activity and expression of hTERT and Pin2/TRF1 interacting protein X1 (PinX1) by telomeric repeat amplification protocol-silver staining, RT-PCR and flow cytometry (FCM). The cell proliferation and apoptosis of Eca109 cells were analyzed by FCM and MTT assay. We found that the length of telomere DNA decreased and hTERT protein expression increased in the carcinogenesis of esophageal epithelial cells; telomerase activity was significantly upregulated followed by a decrease of PinX1 expression in esophageal carcinoma compared with dysplasia and normal patients, which notably correlated with grade and lymph node metastasis. Overexpression of PinX1 inhibited cell growth, arrested cells at the G0/G1 stage and induced cell apoptosis in Eca109 cells. In addition, PinX1 overexpression significantly inhibited telomerase activity. In conclusion, the length shortening of telomere was an important characteristic in the carcinogenesis of esophageal epithelial cells, followed by increase of telomerase activity and downregulation of PinX1. Overexpression of PinX1 blocked Eca109 cell proliferation and induced cell apoptosis by downregulating telomerase activity.

PinX1: a sought-after major tumor suppressor at human chromosome 8p23

Human chromosome 8p23 is a region that has the most frequent heterozygosity in common human adult epithelial malignancies, but its major tumor suppressor gene(s) remain to be identified. 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 and highly conserved endogenous telomerase inhibitor PinX1 is located at human chromosome 8p23. However, the role of PinX1 in telomerase regulation and cancer development is not clear. Recent works from our group indicate that PinX1 is critical for maintaining telomere length at the optimal length. Furthermore, PinX1 is reduced in a large subset of human breast cancer tissues and cells. Significantly, PinX1 inhibition activates telomerase, and elongates telomeres, eventually leading to chromosome instability, all of which are abrogated by telomerase knockdown or knockout. Moreover, PinX1 allele loss causes majority of mice to develop a variety of epithelial cancers, which display chromosome instability and recapitulate to 8p23 allele loss in humans. These results indicate that PinX1 is a sought-after major tumor suppressor at human chromosome 8p23 that is essential for regulating telomerase activity and maintaining chromosome stability. These results suggest that inhibition of telomerase using PinX1 especially its telomerase inhibitory fragment or other methods might be used to treat cancers that have telomerase activation.

PinX1 regulation of telomerase activity and apoptosis in nasopharyngeal carcinoma cells

BACKGROUND

Human interacting protein X1 (PinX1) has been identified as a critical telomerase inhibitor and proposed to be a putative tumor suppressor gene. Loss of PinX1 has been found in a large variety of malignancies, however, its function in inhibiting telomerase activity of tumor cells is not well documented. Here we show that PinX1 is essential for down-regulation telomerase activity of nasopharyngeal carcinoma.

METHODS

Expression vectors of human PinX1 (pEGFP-C3-PinX1) and its small interfering RNA (PinX1-FAM-siRNA) were constructed and transfected into NPC. Their effects on mRNA of telomerase catalytic subunit (hTERT), telomerase activity, cell proliferation, cell migration, wound healing, cell cycles and apoptosis were examined using semi-quantitative RT-PCR, stretch PCR, MTT assay, Transwell, scratch assay and flow cytometry, respectively.

RESULTS

Transfection of pEGFP-C3-PinX1 and PinX1-FAM-siRNA increased and reduced PinX1 mRNA by 1.6-fold and 70%, respectively. Over-expression of PinX1 decreased hTERT mRNA by 21%, reduced telomerase activity, inhibited cell growth, migration and wound healing ability, arrested cells in G0/G1 phase, and increased apoptotic index. In contrast, down-regulation of PinX1 did not alter the above characteristics.

CONCLUSIONS

PinX1 may play important roles in NPC proliferation, migration and apoptosis and has application potential in tumor-targeted gene therapy.

HIV-Tat-mediated delivery of an LPTS functional fragment inhibits telomerase activity and tumorigenicity of hepatoma cells

BACKGROUND & AIMS

Human liver-related putative tumor suppressor (LPTS) is a gene that encodes a telomerase inhibitory protein that is similar to human Pin2/TRF1-interacting protein. The LPTS protein binds directly to the telomerase catalytic subunit (human telomerase reverse transcriptase) and suppresses telomerase activity. Telomere maintenance and telomerase activity are required for long-term proliferation of cancer cells, so LPTS might be used in anticancer strategies.

METHODS

The carboxy-terminal (functional) fragment of LPTS was fused to the transactivator of transcription of human immunodeficiency virus (Tat)-an 11-amino acid peptide that translocates across the cell membrane; the TAT-fused C-terminal of LPTS (TAT-LPTS-LC) was purified and transduced into cells. Telomerase activity was identified by using the telomeric repeat amplification protocol. The effects of the TAT-LPTS-LC protein on cell proliferation and death were evaluated by colorimetric tetrazolium salt and flow cytometry analyses. Tumor growth was analyzed in nude mice.

RESULTS

The purified TAT-LPTS-LC protein was efficiently delivered into the cells, where it suppressed telomerase activity and shortened telomere length. TAT-LPTS-LC inhibited proliferation of telomerase-positive hepatocellular carcinoma BEL-7404 and hepatoblastoma HepG2cells and induced their death; however, it had no effect on telomerase-negative liver cell line L02 and osteosarcoma cell line Saos-2. In mice, tumor formations by BEL-7404 cells were suppressed by TAT-LPTS-LC treatments.

CONCLUSIONS

Transduction of hepatoma cells with a fusion protein that contains the C-terminal, functional fragment of LPTS and human immunodeficiency virus Tat (TAT-LPTS-LC) causes telomere shortening, limits proliferation, and inhibits growth of tumors from these cells in mice. TAT-LPTS-LC inhibits telomerase activity and might be developed as an anticancer agent.

Telomerase inhibitor PinX1 provides a link between TRF1 and telomerase to prevent telomere elongation

Telomere maintenance is essential for protecting chromosome ends. Aberrations in telomere length have been implicated in cancer and aging. Telomere elongation by human telomerase is inhibited in cis by the telomeric protein TRF1 and its associated proteins. However, the link between TRF1 and inhibition of telomerase elongation of telomeres remains elusive because TRF1 has no direct effect on telomerase activity. We have previously identified one Pin2/TRF1-interacting protein, PinX1, that has the unique property of directly binding and inhibiting telomerase catalytic activity (Zhou, X. Z., and Lu, K. P. (2001) Cell 107, 347-359). However, nothing is known about the role of the PinX1-TRF1 interaction in the regulation of telomere maintenance. By identifying functional domains and key amino acid residues in PinX1 and TRF1 responsible for the PinX1-TRF1 interaction, we show that the TRF homology domain of TRF1 interacts with a minimal 20-amino acid sequence of PinX1 via hydrophilic and hydrophobic interactions. Significantly, either disrupting this interaction by mutating the critical Leu-291 residue in PinX1 or knocking down endogenous TRF1 by RNAi abolishes the ability of PinX1 to localize to telomeres and to inhibit telomere elongation in cells even though neither has any effect on telomerase activity per se. Thus, the telomerase inhibitor PinX1 is recruited to telomeres by TRF1 and provides a critical link between TRF1 and telomerase inhibition to prevent telomere elongation and help maintain telomere homeostasis.

C-terminal amino acids 290-328 of LPTS/PinX1 confer telomerase inhibition

LPTS/PinX1, a telomerase inhibitor composed of 328 amino acids, binds to the telomere associated protein Pin2/TRF1 and to the telomerase catalytic subunit hTERT. However, the mechanism by which LPTS/PinX1 regulates telomerase activity remains unclear. Here we show, for the first time, that LPTS/PinX1 uses different domains to interact with Pin2/TRF1 and hTERT. The LPTS/PinX1(254-289) fragment specifically binds to Pin2/TRF1, and LPTS/PinX1(290-328) can associate with hTERT. Compared with the full-length LPTS/PinX1 protein, LPTS/PinX1(290-328) shows stronger in vitro telomerase inhibitory activity. Moreover, the LPTS/PinX1 protein was recruited to telomeres for binding to Pin2/TRF1. Overexpression of LPTS/PinX1(290-328), which contains a nucleolus localization signal, in cells resulted in telomere shortening and progressive cell death. Conversely, telomere elongation was induced by expression of the dominant-negative LPTS/PinX1(1-289). Our results suggest that the C-terminal fragment of LPTS/PinX1 (LPTS/PinX1(290-328)) contains a telomerase inhibitory domain that is required for the inhibition of telomere elongation and the induction of cell crisis. Our studies also provide evidence that LPTS/PinX1 interaction with Pin2/TRF1 may play a role in the stabilization of telomeres.

Human MCRS2, a cell-cycle-dependent protein, associates with LPTS/PinX1 and reduces the telomere length

Human LPTS/PinX1 is a telomerase-inhibitory protein, which binds to the telomere protein Pin2/TRF1 and the catalytic subunit hTERT of telomerase. To explore the proteins that might be involved in the telomerase pathway, we performed a yeast two-hybrid screening with LPTS/PinX1 as the bait. A novel gene, MCRS2, encoding for an isoform of MCRS1/p78 and MSP58 was isolated. The expression of MCRS2 protein is cell-cycle dependent, accumulating in the very early S phase. MCRS2 interacts with LPTS/PinX1 in vitro, in vivo and colocalizes with LPTS/PinX1 in cells. MCRS2 and its amino terminus inhibit telomerase activity in vitro and long-term overexpression of MCRS2 in SMMC-7721 cells results in a gradual and progressive shortening of telomeres. Our findings suggest that MCRS2 might be a linker between telomere maintenance and cell-cycle regulation.

Cloning and characterization of the promoter region of human LPTS/PinX1 gene

The gene for LPTS/PinX1 encodes a potent telomerase inhibitor and suppresses tumor cell growth. In order to investigate the transcriptional regulation of this gene, we isolated its 5'-flanking region from the human genomic BAC clone and identified a major transcriptional initiation site. The sequence of the 5'-flanking region is GC-rich, lacks canonical TATA box, but contains potential binding sites for a variety of transcription factors. The deletion analysis indicated that the proximal 100 bp (from nt -66 to +34) is essential for minimal promoter activity and the regions of promoter from nt -1272 to -573 and nt -330 to -66 are required for maximal expression of the LPTS/PinX1 gene. Four DNase I hypersensitive sites (DHS1-4) mapping to the regions of transcription initiation and promoter in LPTS/Pinx1 gene were also revealed.

Effect of arsenic trioxide on rat hepatocarcinoma and its renal cytotoxicity

AIM: To study the effect of arsenic trioxide (As₂O₃) on rat experimental hepatocarcinoma and its renal cytotoxicity.

METHODS: The hepatocarcinoma model was established by diethaylnitrosamine perfusion in stomach of 120 Wistar rats, and the treatment began at the end of 20 weeks. Before the treatment, the rat models were randomly divided into 5 groups. In the treatment groups, three doses of As₂O₃ were injected into rat abdominal cavity, the total time of drug administration was 4 weeks. Cisplatin control or the blank group was injected into abdominal cavity with equal amount of cisplatin or saline at the same time, respectively. On the 7^th, 14^th and 28^th day after the treatment, the hepatocarcinoma nodules were obtained and the morphologic changes of hepatocarcinoma cells were observed under light and electron microscopes; Immunohistochemistry (S-P methods) was employed to detect the expression of bcl-2, bax and PCNA in hepatocarcinoma tissues; flow cytometry (TUNEL assay) was used to detect the apoptosis of liver cancer cells and the change of cytokinetics. On the 28^th day, the kidneys were obtained and their histologic changes were observed under light microscope, and immunohistochemistry (SP stain) was also employed to detect the expression of bcl-2 and PCNA. Cisplatin and saline solution were used as the control.

RESULTS: As₂O₃ could induce the apoptosis of rat liver cancer cells and exhibited typical morphologic changes. The incidence of apoptosis of hapatocarcinoma cells was elevated (P = 0.001). The elevation was the most higher in the group of middle-dose of As₂O₃ (1 mg·kg^-1), significantly higher than that of the other arsenic groups and the controls (P = 0.001). Large dose of As₂O₃ (5 mg·kg^-1) was able to arise the incidence of apoptosis, but also produced a large amount of necrosis and inflammatory reaction. Middle dose of As₂O₃ dramatically increased the cell number in G2/M phase (P = 0.0001), and apoptosis happened apparently. The expression of bcl-2 and bax was related to the dose of As₂O₃. With the up-regulation of apoptotic incidence, the ratio of bcl-2/bak decreased. But the incidence of apoptosis was not the highest status and the ratio of bcl-2/bax was at the lowest when the highest-dose of As₂O₃ was used. There was significant difference among the PCNA indexes (PCNA L1) of the five groups. Of them, three arsenic groups all showed decrease of different degrees, and this down-regulation was most obvious in group A. There was significant difference among the three groups (P = 0.016). Under the light microscope, the rat kidney in the cisplatin group exhibited tubular epithelium swelling and degeneration, protein casts in collecting tubules; While all arsenic groups didn’t show the significant changes (P = 0.013). In the arsenic groups, the expression of bcl-2 in the renal tubular epithelium was increased (P = 0.005), no obvious changes happened to PCNA L1. But in the group of cisplatin, the PCNA L1 increased significantly (P = 0.001).

CONCLUSION: As₂O₃ can induce apoptosis of rat hepatocellular carcinoma cells. And there is optimum dose; too high dose will induce the cytotoxic effect, while certain dose of As₂O₃ is able to block the cell cycle at G2/M phase. As₂O₃ had the most remarkable influence on G2/M cells, and it can also induce apoptosis to cells at other phases. As₂O₃ can restrain the proliferation of rat hepatocellular carcinoma cells, in a dose-time dependent manner. Compared with cisplatin, As₂O₃ didn’t show obvious renal toxicity, which was related to the increasing expression of bcl-2 in renal tubular epithelium, the inhibition of apoptosis and the anti-oxidation effects.