PINX1 explained

PIN2/TERF1-interacting telomerase inhibitor 1, also known as PINX1, is a human gene.^[1] PINX1 is also known as PIN2 interacting protein 1. PINX1 is a telomerase inhibitor and a possible tumor suppressor.

Interactions

PINX1 has been shown to interact with MCRS1,^[2] TERF1^[3] and telomerase reverse transcriptase.^[3]

Structure

There are two known variants of PINX1. The second variant “lacks an exon in the 3’ coding region which results in a frameshift compared to variant 1. The encoded isoform is shorter and has a distinct C-terminus compared to isoform 1.”^[4] There are three PINX1 cDNA clones. The longest one encodes a 328 amino acid 45kDa protein which contains an N-terminal Gly-rich patch and a C-terminal TID domain (telomerase inhibitory domain). The TRF1 binding domain is in the C-terminal 75 amino acids of PINX1. Mouse PINX1 is 74% identical to human PINX1. In other eukaryotes, including yeast, there is an overall 50% similarity to human PINX1.^[5]

Function

Over-expression of PINX1 results in decreased telomerase activity, telomere shortening, and induction of crisis. Reduction of PINX1 leads to an increase in telomerase activity and elongation of telomeres. PINX1 differs from other proteins that regulate telomere length in that it acts on telomerase while other proteins adjust telomere length without affecting telomerase activity.

The PINX1 budding yeast orthologue Gnop1 inhibits telomerase by isolating the uncomplexed TERT protein so that it cannot associate with the telomerase template RNA, which prevents telomerase from being assembled. However, in humans, PINX1 impedes already assembled telomerase. PINX1 binds to N-terminus of hTERT and binds to hTR in the presence of hTERT. PINX1 binding to hTR “is correlated to the repressive function of PINX1 on telomerase, implying that the mode of enzyme telomerase inhibition by PINX1 may involve an associated with hTR....The effect of hPINX1 on telomerase appears to be exclusive of the G-patch region and is mediated instead by the C terminus of the protein. This suggests that hPINX1 may have functionally separable cellular effects in which the N terminus is involved in RNA processing via the G-patch, and the C terminus is involved in telomere dynamics.” It is suggested that “PINX1 represses telomerase activity in vivo by binding to the assembled hTERT-hTR complex.” ^[6]

The TID domain of PINX1 is likely what binds to hTERT. In cells, full-length PINX1 is not as strong as just the TID domain at inhibiting telomerase. This may be due to full-length PINX1 being subject to “endogenous regulation such as posttranslational modifications to reduce its inhibitory activity.” Or it may be due to a reduction of the TID domain to bind and inhibit telomerase as a result of proteins interacting with PINX1, such as PIN2/TRF1 which colocalizes PINX1 in cells.

There are two types of PINX1: nuclear PINX1 which is associates with telomeres and CAC repeats and nucleolar PINX1 does not bind directly to the telomeres, but instead interacts with TRF1. Nucleolar hPINX1 mediates the movement of hTERT and TRF1 to the nucleolus. Over-expression of nucleolar hPINX1 leads to increased TRF1 in the nucleolus and binding to telomeres. However, this accumulation in the nucleolus was not found in ALT (alternative lengthening of telomeres) cells indicating that PINX1 function is telomerase dependent.^{[7] [8]}

hPINX1 is found more in the nucleoplasm during the S phase which is also when telomerase is released into the nucleoplasm indicating that hPINX1 may inhibit telomerase during the S phase.

Cancer

PINX1 is located at 8p23. Heterozygosity of this area is frequently lost in tumors including liver, prostate, prostate, colorectal, lung, and head and neck. Most PINX1 mutant tumors are carcinomas. PINX1 expression is significantly reduced in these tumors. This significance was shown with HT1080 cells, which increased tumorigenicity with decreased PINX1 expression. Over-expression of PINX1 in HT1080 cells did not allow them to form tumors in mice. Therefore, PINX1 may be a tumor suppressor.^[9]

PINX1 expression is a predictor of cervical squamous cell carcinoma (CSCC) cells response to cisplatin/paclitaxel chemotherapy. High levels of PINX1 correlated to response. But the levels of PINX1 were only associated with cytotoxicity of paclitaxel. Reduced levels of PINX1 led to increased paclitaxel cytotoxicity. “The ability of PINX1 to stabilize the tension between sister kinetochores and maintain the spindle assembly checkpoint was the main reason CSCC cells undergo apoptosis when treated with paclitaxel.”^[10]

Chemoradiotherapy is a standard treatment for advanced esophageal squamous cell carcinoma (ESCC). Reduced PINX1 expression did not affect ESCC cells response to 5-fluorouracil and cisplatin, but did increase efficacy of radiation therapy. High levels of PINX1 led to reduced cell death due to radiation. “PINX1 resistance to radiotherapy (RT) was attributed to PINX1 maintaining telomere stability, reducing ESCC cell death by RT-induced mitosis catastrophe.”^[11] High levels of PINX1 is a predictor of short disease-specific survival.

PINX1 levels were found to be reduced in urothelial carcinoma of the bladder (UCB) compared to normal urothelial bladder epithelium. “PINX1 levels were inversely correlated with tumor multiplicity, advanced N classification, high proliferation index, and poor survival.”^[12] Over-expression of PINX1 reduced UCB cell proliferation and G1/S phase arrest. Knockdown PINX1 led to increased cell proliferation and accelerated G1/S transition.

PinX1 in other cancers:

• Ovarian^[13]
  • PINX1 in 100% of normal ovarian tissue and 66.2% of ovarian carcinomas
  • Decreased PINX1 expression related to poor prognostic factors and presence of lymph node metastasis
• Gastric^{[14] [15] [16]}
  • Loss of heterozygosity of PINX1 gene more common in lymph node metastasis and higher TNM stage
  • Microstatellite instability of PINX1 gene less frequent in cases with lymph node metastasis
  • Suppression of telomerase activity mediated by Mad1/c-Myc pathway
• Esophageal^[17]
  • Over-expression of PINX1 inhibited cell growth, arrested cells at G0/G1, and induced apoptosis
• Nasopharyngeal^[18]
  • Over-expression of PINX1 decreased hTERT mRNA, reduced telomerase activity, inhibited cell growth, migration and would healing ability, arrested cells in G0/G1 phase, increased apoptosis
  • Down-regulation of PINX1 did not alter any of these characteristics
• Colorectal^[19]
  • Intact PINX1 and PINX1 without G-patch motif induce apoptosis, G1 arrest, and cellular senescence
  • Truncated PINX1 does not affect telomerase
• Cervical^[20]
  • Regulated by p53

Further reading

• Liao C . Identification of the gene for a novel liver-related putative tumor suppressor at a high-frequency loss of heterozygosity region of chromosome 8p23 in human hepatocellular carcinoma . Hepatology . 32 . 4 Pt 1 . 721–7 . 2000 . 11003615 . 10.1053/jhep.2000.17967 . vanc. Zhao M . Song H . 3 . Uchida . K . Yokoyama . KK . Li . T .
• Zhou XZ, Lu KP . The Pin2/TRF1-interacting protein PinX1 is a potent telomerase inhibitor . Cell . 107 . 3 . 347–59 . 2001 . 11701125 . 10.1016/S0092-8674(01)00538-4 . 6822193 . free .
• Guglielmi B, Werner M . The yeast homolog of human PinX1 is involved in rRNA and small nucleolar RNA maturation, not in telomere elongation inhibition . J. Biol. Chem. . 277 . 38 . 35712–9 . 2002 . 12107183 . 10.1074/jbc.M205526200 . free .
• Liao C . Over-expression of LPTS-L in hepatocellular carcinoma cell line SMMC-7721 induces crisis . World J. Gastroenterol. . 8 . 6 . 1050–2 . 2003 . 12439923 . 4656378 . 10.3748/wjg.v8.i6.1050. vanc. Zhao MJ . Zhao J . 3 . Jia . D . Song . H . Li . ZP . free .
• Strausberg RL . Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences . Proc. Natl. Acad. Sci. U.S.A. . 99 . 26 . 16899–903 . 2003 . 12477932 . 10.1073/pnas.242603899 . 139241 . vanc. Feingold EA . Grouse LH . 3 . Derge . JG . Klausner . RD . Collins . FS . Wagner . L . Shenmen . CM . Schuler . GD . 2002PNAS...9916899M. free .
• Liao C . Mutation analysis of novel human liver-related putative tumor suppressor gene in hepatocellular carcinoma . World J. Gastroenterol. . 9 . 1 . 89–93 . 2003 . 12508358 . 4728256 . 10.3748/wjg.v9.i1.89. vanc. Zhao MJ . Zhao J . 3 . Song . H . Pineau . P . Marchio . A . Dejean . A . Tiollais . P . Wang . HY . free .
• Ota T . Complete sequencing and characterization of 21,243 full-length human cDNAs . Nat. Genet. . 36 . 1 . 40–5 . 2004 . 14702039 . 10.1038/ng1285 . vanc. Suzuki Y . Nishikawa T . 3 . Otsuki . Tetsuji . Sugiyama . Tomoyasu . Irie . Ryotaro . Wakamatsu . Ai . Hayashi . Koji . Sato . Hiroyuki . free .
• Wang S, Liao C, Li T, Zhao M . Cloning and characterization of the promoter region of human LPTS/PinX1 gene . Biochim. Biophys. Acta . 1676 . 3 . 261–5 . 2004 . 14984932 . 10.1016/j.bbaexp.2003.12.002 .
• Song H . Human MCRS2, a cell-cycle-dependent protein, associates with LPTS/PinX1 and reduces the telomere length . Biochem. Biophys. Res. Commun. . 316 . 4 . 1116–23 . 2004 . 15044100 . 10.1016/j.bbrc.2004.02.166 . vanc. Li Y . Chen G . 3 . Xing . Zhen . Zhao . Jing . Yokoyama . Kazunari K . Li . Tsaiping . Zhao . Mujun .
• Banik SS, Counter CM . Characterization of interactions between PinX1 and human telomerase subunits hTERT and hTR . J. Biol. Chem. . 279 . 50 . 51745–8 . 2005 . 15381700 . 10.1074/jbc.M408131200 . free .
• Gerhard DS . The Status, Quality, and Expansion of the NIH Full-Length cDNA Project: The Mammalian Gene Collection (MGC) . Genome Res. . 14 . 10B . 2121–7 . 2004 . 15489334 . 10.1101/gr.2596504 . 528928 . vanc. Wagner L . Feingold EA . 3 . Shenmen . CM . Grouse . LH . Schuler . G . Klein . SL . Old . S . Rasooly . R .
• Kondo T . Loss of heterozygosity and histone hypoacetylation of the PINX1 gene are associated with reduced expression in gastric carcinoma . Oncogene . 24 . 1 . 157–64 . 2005 . 15637589 . 10.1038/sj.onc.1207832 . vanc. Oue N . Mitani Y . 3 . Kuniyasu . Hiroki . Noguchi . Tsuyoshi . Kuraoka . Kazuya . Nakayama . Hirofumi . Yasui . Wataru .
• Rual JF . Towards a proteome-scale map of the human protein-protein interaction network . Nature . 437 . 7062 . 1173–8 . 2005 . 16189514 . 10.1038/nature04209 . vanc. Venkatesan K . Hao T . 3 . Hirozane-Kishikawa . Tomoko . Dricot . Amélie . Li . Ning . Berriz . Gabriel F. . Gibbons . Francis D. . Dreze . Matija . 2005Natur.437.1173R. 4427026 .
• Ewing RM . Large-scale mapping of human protein–protein interactions by mass spectrometry . Mol. Syst. Biol. . 3 . 1. 89 . 2007 . 17353931 . 10.1038/msb4100134 . 1847948 . vanc. Chu P . Elisma F . 3 . Li . Hongyan . Taylor . Paul . Climie . Shane . McBroom-Cerajewski . Linda . Robinson . Mark D . O'Connor . Liam .

Notes and References

1. Web site: Entrez Gene: PINX1 PIN2-interacting protein 1.
2. Song . Hai . Li Yiliang . Chen Guoyuan . Xing Zhen . Zhao Jing . Yokoyama Kazunari K . Li Tsaiping . Zhao Mujun . Apr 2004 . Human MCRS2, a cell-cycle-dependent protein, associates with LPTS/PinX1 and reduces the telomere length . Biochem. Biophys. Res. Commun. . 316 . 4 . 1116–23 . 0006-291X. 15044100 . 10.1016/j.bbrc.2004.02.166 .
3. Zhou . X Z . Lu K P . Nov 2001 . The Pin2/TRF1-interacting protein PinX1 is a potent telomerase inhibitor . Cell . 107 . 3 . 347–59 . 0092-8674. 11701125 . 10.1016/S0092-8674(01)00538-4 . 6822193 . free .
4. Web site: PINX1 PIN2/TERF1 interacting, telomerase inhibitor 1 [Homo sapiens (human) ]]. 2015-04-08. NCBI.
5. Telomerase Inhibitor PinX1 Provides a Link between TRF1 and Telomerase to Prevent Telomere Elongation. Soohoo. C.Y.. November 2010. Journal of Biological Chemistry. 10.1074/jbc.M110.180174. 21119197. Shi. R.. Lee. T.H.. Huang. P.. Lu. K.P.. Zhou. X.Z.. 286. 5. 3894–906. 3030390. free.
6. Characterization of Interactions between PinX1 and Human Telomerase Subunits hTERT and hTR. Banik. S.S.R.. September 2004. Journal of Biological Chemistry. 10.1074/jbc.M408131200. 15381700. Counter. C.M.. 279. 50. 51745–8. free.
7. Human PinX1 Mediates TRF1 Accumulation in Nucleolus and Enhances TRF1 Binding to Telomeres. Yoo. J.E.. March 2009. Journal of Molecular Biology. 10.1016/j.jmb.2009.02.051. 19265708. Oh. B.K.. Park. Y.N. . 388 . 5. 928–940.
8. PinX1, a Telomere Repeat-binding Factor 1 (TRF1)-interacting Protein, Maintains Telomere Integrity by Modulating TRF1 Homeostasis, the Process in Which Human Telomerase Reverse Transcriptase (hTERT) Plays Dual Roles. Yoo. J.E.. January 2014. Journal of Biological Chemistry. 10.1074/jbc.M113.506006. 24415760. Park. Y.N.. Oh. B.K. . 289 . 10. 6886–6898 . 3945350. free.
9. The telomerase inhibitor PinX1 is a major haploinsufficient tumor suppressor essential for chromosome stability in mice. Zhou. X.Z.. April 2011. Journal of Clinical Investigation. 10.1172/JCI43452. 21436583. Huang. P.. Shi. R.. Lee. T.H.. Lu. G.. Zhang. Z.. Bronson. R.. Lu. K.P.. 121. 4. 1266–82. 3069765.
10. The telomere/telomerase binding factor PinX1 regulates paclitaxel sensitivity depending on spindle assembly checkpoint in human cervical squamous cell carcinomas. Tian. X.P.. July 2014. Cancer Letters. 10.1016/j.canlet.2014.07.012. 25045845. Qian. D.. He. L.R.. Huang. H.. Mai. S.J.. Li. C.P.. Huang. X.X.. Cai. M.Y.. Liao. Y.J.. 353. 1. 104–14.
11. The telomere/telomerase binding factor PinX1 is a new target to improve the radiotherapy effect of oesophageal squamous cell carcinomas. Qian. D.. February 2013. Journal of Pathology. 10.1002/path.4163. 23341363. Zhang. B.. He. L.R.. Cai. M.Y.. Mai. S.J.. Liao. Y.J.. Liu. Y.H.. Lin. M.C.. Bian. X.W.. 229. 5. 765–74. 206326137.
12. PinX1 suppresses bladder urothelial carcinoma cell proliferation via the inhibition of telomerase activity and p16/cyclin D1 pathway. Liu. J.Y.. November 2013. Molecular Cancer. 10.1186/1476-4598-12-148. 24268029. Qian. D.. He. L.R.. Li. Y.H.. Liao. Y.J.. Mai. S.J.. Tian. X.P.. Liu. Y.H.. Zhang. J.X.. 12. 1. 148. 4176126 . free .
13. Decreased expression of PinX1 protein is correlated with tumor development and is a new independent poor prognostic factor in ovarian carcinoma. Cai. MY. June 2010. Cancer Science. 10.1111/j.1349-7006.2010.01560.x. 20367640. Zhang. B.. He. W.P.. Yang. G.F.. Rao. H.L.. Rao. Z.Y.. Wu. Q.L.. Guan. X.Y.. Kung. H.F. . 101 . 6. 1543–1549. 34290765. free. 11159430.
14. The correlation of genetic instability of PINX1 gene to clinico-pathological features of gastric cancer in the Chinese population. Ma. Y.. March 2009. Journal of Cancer Research and Clinical Oncology. 10.1007/s00432-008-0471-6. 18784941. Wu. L.. Liu. C.. Xu. L.. Li. D.. Li. J.C. . 135 . 3. 431–437. 24420150.
15. Loss of heterozygosity and histone hypoacetylation of the PINX1 gene are associated with reduced expression in gastric carcinoma. Kondo. T. January 2005. Oncogene. 24. 1. 157–164. 10.1038/sj.onc.1207832 . 15637589. Oue. N.. Mitani. Y.. Kuniyasu. H.. Noguchi. T.. Kuraoka. K.. Nakayama. H.. Yasui. W..
16. PinX1 inhibits telomerase activity in gastric cancer cells through Mad1/c-Myc pathway. Wang. H.B.. August 2010. Journal of Gastrointestinal Surgery. 10.1007/s11605-010-1253-4. 20544396. Wang. X.W.. Zhou. G.. Wang. W.Q.. Sun. Y.G.. Yang. S.M.. Fang. D.C. . 14 . 8. 1227–1234. 1549235.
17. Expression and mechanism of PinX1 and telomerase activity in the carcinogenesis of esophageal epithelial cells. Zuo. J.. October 2013. Oncology Reports. 30. 4. 1823–1831. 10.3892/or.2013.2649. 23912465. Wang. D.H.. Zhang. Y.J.. Liu. L.. Liu. F.L.. Liu. W.. free.
18. PinX1 regulation of telomerase activity and apoptosis in nasopharyngeal carcinoma cells. Lai. X.F.. February 2012. Journal of Experimental & Clinical Cancer Research. 10.1186/1756-9966-31-12. 22316341. Shen. C.X.. Wen. Z.. Qian. Y.H.. Yu. C.S.. Wang. J.Q.. Zhong. P.N.. Wang. H.L. . 31 . 1 . 12. 3296635 . free .
19. PinX1 without the G-patch motif suppresses proliferation, induces senescence, but does not inhibit telomerase activity in colorectal cancer SW480 cells. Zhang. R.. July 2014. Oncology Reports. 32. 1. 286–292. 10.3892/or.2014.3199. 24839934. Zhao. J.. Wang. X.. Wang. L.L.. Xu. J.. Song. C.. free.
20. PinX1, a novel target gene of p53, is suppressed by HPV16 E6 in cervical cancer cells. Wu. G.. February 2014. 10.1016/j.bbagrm.2014.01.004. 24412852. Liu. D.. Jiang. K.. Zhang. L.. Zeng. Y.. Zhou. P.. Zhong. D.. Gao. M.. He. F. . Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanisms. 1839 . 2. 88–96.