BMI1 and KAP1 interaction and function: BMI1 capped by KAP1?

  • J. van Haasteren


The Polycomb-repressive complex 1 (PRC1) protein BMI1 is of major importance in the epigenetic regulation of gene expression. The repression of important tumour suppressor genes (such a P16INK4a and P14ARF) by means of chromatin remodeling has marked BMI1 as a proto-oncoprotein. We previously found evidence that posttranslational modification by phosphorylation may be implicated in the stability and functioning of BMI1. Furthermore, we found that KAP1, through direct interaction with BMI1, may be implicated in regulation of BMI1 functioning. I here begin to elucidate how phosphorylation affects BMI1 and how KAP1 regulates BMI1. Several U2OS or TIG3ER cell lines were created that overexpressed BMI1 wild type and mutants that either contain phospho-mimic or phospho-null mutations. shRNA’s were used to effectively knockdown KAP1 expression. The effect of BMI1 mutant overexpression and/or KAP1 knock down on proliferation was measured under cell stress conditions induced by arsenite, selenite or etoposide. The effect of KAP1 knock down and mutant KAP1 lacking the RingFinger domain (KAP1-DeltaRF) on sub-cellular localization was assessed in U2OS cells. Finally functional interaction between KAP1 and PRC1 was measured by analysis of transcriptional induction of the PRC1-target gene ATF3 upon mitogenic stimulation. BMI1 overexpression partially rescues arsenite induced senescence; this rescue activity is affected by its phosphorylation status. KAP1 knockdown increases the effect of BMI1 overexpression on proliferation under arsenite induced cell stress but ablates the differences observed between different BMI1 phospho-mutants. KAP1 induced increases of ATF3 induction point towards a functional interaction between KAP1 and PRC1. My experiments provide experimental indication that BMI1 affects proliferation under arsenite induced cell stress condition. This effect was enhanced by KAP1 knockdown suggesting that KAP1 inhibits the pro-proliferative effects of BMI1. Increased ATF3 induction in the presence of KAP1-DeltaRF mutant protein suggests that the KAP1 negatively controls expression of ATF3 in a RF-dependent manner. Further research is required to elucidate the exact molecular mechanisms underlying the function interaction of BMI1 and KAP1. 


Sparmann A, van Lohuizen M. Polycomb silencers control cell fate, development and cancer. Nature reviews Cancer. 2006;6(11):846-56.

Posfai E, Kunzmann R, Brochard V, Salvaing J, Cabuy E, Roloff TC, et al. Polycomb function during oogenesis is required for mouse embryonic development. Genes & development. 2012;26(9):920-32.

Surface LE, Thornton SR, Boyer LA. Polycomb group proteins set the stage for early lineage commitment. Cell stem cell. 2010;7(3):288-98.

Francis NJ, Kingston RE. Mechanisms of transcriptional memory. Nature Reviews Molecular Cell Biology. 2001;2(6):409-21.

Gunster MJ, Raaphorst FM, Hamer KM, den Blaauwen JL, Fieret E, Meijer CJ, et al. Differential expression of human Polycomb group proteins in various tissues and cell types. Journal of cellular biochemistry Supplement. 2001;Suppl 36:129-43.

Simon JA, Kingston RE. Mechanisms of polycomb gene silencing: knowns and unknowns. Nature reviews Molecular cell biology. 2009;10(10):697-708.

Czermin B, Melfi R, McCabe D, Seitz V, Imhof A, Pirrotta V. Drosophila Enhancer of Zeste/ESC Complexes Have a Histone H3 Methyltransferase Activity that Marks Chromosomal Polycomb Sites. Cell. 2002;111(2):185-96.

Wang H, Wang L, Erdjument-Bromage H, Vidal M, Tempst P, Jones RS, et al. Role of histone H2A ubiquitination in Polycomb silencing. Nature. 2004;431(7010):873-8.

Cao R, Tsukada Y, Zhang Y. Role of Bmi-1 and Ring1A in H2A ubiquitylation and Hox gene silencing. Molecular cell. 2005;20(6):845-54.

Alchanati I, Teicher C, Cohen G, Shemesh V, Barr HM, Nakache P, et al. The E3 Ubiquitin-Ligase Bmi1/Ring1A Controls the Proteasomal Degradation of Top2- Cleavage Complex–A Potentially New Drug Target. PloS one. 2009;4(12):e8104.

Ismail IH, Andrin C, McDonald D, Hendzel MJ. BMI1-mediated histone ubiquitylation promotes DNA doublestrand break repair. The Journal of Cell Biology. 2010;191(1):45-60.

Vonlanthen S, Heighway J, Altermatt H, Gugger M, Kappeler A, Borner M, et al. The bmi-1 oncoprotein is differentially expressed in non-small cell lung cancer and correlates with INK4A-ARF locus expression. British journal of cancer. 2001;84(10):1372.

Kim JH, Yoon SY, Kim C-N, Joo JH, Moon SK, Choe IS, et al. The Bmi-1 oncoprotein is overexpressed in human colorectal cancer and correlates with the reduced p16INK4a/p14ARF proteins. Cancer letters. 2004;203(2):217-24.

Niessen HE, Demmers JA, Voncken JW. Talking to chromatin: post-translational modulation of polycomb group function. Epigenetics & chromatin. 2009;2(1):10.

Voncken JW, Niessen H, Neufeld B, Rennefahrt U, Dahlmans V, Kubben N, et al. MAPKAP kinase 3pK phosphorylates and regulates chromatin association of the polycomb group protein Bmi1. The Journal of biological chemistry. 2005;280(7):5178-87.

Yadav AK, Sahasrabuddhe AA, Dimri M, Bommi PV, Sainger R, Dimri GP. Research Deletion analysis of BMI1 oncoprotein identifies its negative regulatory domain. Molecular cancer. 2010;9.

Spivakov M, Fisher AG. Epigenetic signatures of stem-cell identity. Nature Reviews Genetics. 2007;8(4):263-71.

Bracken AP, Dietrich N, Pasini D, Hansen KH, Helin K. Genome-wide mapping of Polycomb target genes unravels their roles in cell fate transitions. Genes & development. 2006;20(9):1123-36.

O’Geen H, Squazzo SL, Iyengar S, Blahnik K, Rinn JL, Chang HY, et al. Genome-wide analysis of KAP1 binding suggests autoregulation of KRAB-ZNFs. PLoS genetics. 2007;3(6):e89.

Lu J, Kaeck M, Jiang C, Wilson AC, Thompson HJ. Selenite induction of DNA strand breaks and apoptosis in mouse leukemic L1210 cells. Biochemical pharmacology. 1994;47(9):1531-5.

d’Adda di Fagagna F. Living on a break: cellular senescence as a DNA-damage response. Nature reviews Cancer. 2008;8(7):512-22.

Burden DA, Kingma PS, Froelich-Ammon SJ, Bjornsti M-A, Patchan MW, Thompson RB, et al. Topoisomerase II· etoposide interactions direct the formation of drug-induced enzyme-DNA cleavage complexes. Journal of Biological Chemistry. 1996;271(46):29238-44.

Wang C, Ivanov A, Chen L, Fredericks WJ, Seto E, Rauscher FJ, 3rd, et al. MDM2 interaction with nuclear corepressor KAP1 contributes to p53 inactivation. The EMBO journal. 2005;24(18):3279-90.