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Gene Review

TOPORS  -  topoisomerase I binding, arginine/serine...

Homo sapiens

Synonyms: E3 ubiquitin-protein ligase Topors, LUN, P53BP3, RP31, SUMO1-protein E3 ligase Topors, ...
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Disease relevance of TOPORS


High impact information on TOPORS


Biological context of TOPORS

  • These results suggest that topors functions as a negative regulator of cell growth, and possibly as a tumor suppressor [1].
  • Additional studies indicate that forced expression of topors inhibits cellular proliferation and is associated with an accumulation of cells in the G(0)/G(1) phase of the cell cycle [1].
  • The corresponding full-length protein, named topors, contains a consensus RING zinc finger domain and nuclear localization signals in addition to the arginine-serine-rich region [5].

Anatomical context of TOPORS

  • By contrast, topors mRNA and protein levels are decreased or undetectable in colon adenocarcinomas relative to normal colon tissue, and expression of the topors protein is not detectable in several colon cancer cell lines [1].
  • In HeLa cells, Topors induced p53 sumoylation was accompanied by an increase in endogenous p53 protein levels [6].
  • Studies using isogenic PML+/+ and PML-/- murine embryonic fibroblasts indicate that the punctate nuclear localization of topors is dependent on PML [7].
  • We present the development of a vision-feedback method to characterize how selective paralysis distorts the three-dimensional (3D) volume representing digit-tip force production capability and its application to healthy individuals producing thumb-tip force with and without simulated low ulnar nerve palsy (LUNP) [8].

Physical interactions of TOPORS


Regulatory relationships of TOPORS

  • Here, we demonstrate that Topors also enhances the conjugation of the small ubiquitin-like modifier 1 (SUMO-1) to p53 in vivo and in a reconstituted in vitro system [6].
  • LUN is a novel RING finger protein that is highly expressed in the lung and might be a transcriptional regulator of E-cadherin [J. Biol. Chem. 276 (2001) 14004] [10].

Other interactions of TOPORS

  • A subset of these Topors' nuclear speckles were closely associated with the PML nuclear bodies (POD, ND10) [9].
  • In addition, the mean LUN/GAPDH ratio in lung cancer tissues was significantly lower than that in normal lung tissues (0.072 versus 0.162; P < 0.001) [10].
  • When expressed in HeLa cells as a green fluorescent protein fusion, topors localizes in the nucleus in a punctate pattern and co-immunoprecipitates with topoisomerase I. These data suggest that topors is involved in trans-cription, possibly recruiting topoisomerase I to RNA polymerase II transcriptional complexes [5].

Analytical, diagnostic and therapeutic context of TOPORS

  • In protocol 78 LUN 328, radiotherapy was given between courses of chemotherapy, and in protocol LUN 81343, it was given simultaneously [11].


  1. The topoisomerase I- and p53-binding protein topors is differentially expressed in normal and malignant human tissues and may function as a tumor suppressor. Saleem, A., Dutta, J., Malegaonkar, D., Rasheed, F., Rasheed, Z., Rajendra, R., Marshall, H., Luo, M., Li, H., Rubin, E.H. Oncogene (2004) [Pubmed]
  2. Cloning and characterization of LUN, a novel ring finger protein that is highly expressed in lung and specifically binds to a palindromic sequence. Chu, D., Kakazu, N., Gorrin-Rivas, M.J., Lu, H.P., Kawata, M., Abe, T., Ueda, K., Adachi, Y. J. Biol. Chem. (2001) [Pubmed]
  3. Topors functions as an E3 ubiquitin ligase with specific E2 enzymes and ubiquitinates p53. Rajendra, R., Malegaonkar, D., Pungaliya, P., Marshall, H., Rasheed, Z., Brownell, J., Liu, L.F., Lutzker, S., Saleem, A., Rubin, E.H. J. Biol. Chem. (2004) [Pubmed]
  4. Topors, a p53 and topoisomerase I binding protein, interacts with the adeno-associated virus (AAV-2) Rep78/68 proteins and enhances AAV-2 gene expression. Weger, S., Hammer, E., Heilbronn, R. J. Gen. Virol. (2002) [Pubmed]
  5. Interaction between human topoisomerase I and a novel RING finger/arginine-serine protein. Haluska, P., Saleem, A., Rasheed, Z., Ahmed, F., Su, E.W., Liu, L.F., Rubin, E.H. Nucleic Acids Res. (1999) [Pubmed]
  6. Topors acts as a SUMO-1 E3 ligase for p53 in vitro and in vivo. Weger, S., Hammer, E., Heilbronn, R. FEBS Lett. (2005) [Pubmed]
  7. The topoisomerase I-binding RING protein, topors, is associated with promyelocytic leukemia nuclear bodies. Rasheed, Z.A., Saleem, A., Ravee, Y., Pandolfi, P.P., Rubin, E.H. Exp. Cell Res. (2002) [Pubmed]
  8. Quantifying deficits in the 3D force capabilities of a digit caused by selective paralysis: application to the thumb with simulated low ulnar nerve palsy. Kuxhaus, L., Roach, S.S., Valero-Cuevas, F.J. Journal of biomechanics. (2005) [Pubmed]
  9. The DNA topoisomerase I binding protein topors as a novel cellular target for SUMO-1 modification: characterization of domains necessary for subcellular localization and sumolation. Weger, S., Hammer, E., Engstler, M. Exp. Cell Res. (2003) [Pubmed]
  10. Expression of LUN gene that encodes a novel RING finger protein is correlated with development and progression of non-small cell lung cancer. Oyanagi, H., Takenaka, K., Ishikawa, S., Kawano, Y., Adachi, Y., Ueda, K., Wada, H., Tanaka, F. Lung Cancer (2004) [Pubmed]
  11. Patterns of failure in combined chemotherapy and radiotherapy for limited small cell lung cancer: Southeastern Cancer Study Group experience. Birch, R., Omura, G.A., Greco, F.A., Perez, C.A. NCI monographs : a publication of the National Cancer Institute. (1988) [Pubmed]
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