Bmi-1 in Cancer Cancer genetics 2012/04/16 20128085 전종철 Good afternoon. I’m Jongcheol Jeon. And I will present about the Bmi-1 in cancer

Contents Introduction Functions of Bmi-1 in cancer Mechanisms of Bmi-1 action Current studies of Bmi-1 This page shows the contents of my presentation First I briefly introduce the Bmi-1 Then study the functions and mechanisms of Bmi1. at the end, I will cover the current studies of Bmi-1

Introduction

What is the Bmi-1 B cell-specific Mo-MLV integration site 1 (1991) Human chromosome 10p11.23 36.9-kDa nuclear protein The polycomb group protien RING finger domain in its N-terminal end and a central helix-turn-helix-turn-helix-turn motif(H-T-H-T) Bmi-1 is abbreviation of the B cell–specific Mo-MLV integration site 1. Mo-MLV is a virus that integrates into three genes. Bmi-1 is One of the those genes. It is 36.9 kilo dalton nuclear protein and Bmi1 gene is located in human chromosome 10 petit 11.23 And It is a polycomb group protein which will be explained in next page. Bmi-1 has RING finger domain which plays a key role in the ubiquitination and HTHT motif which acts as a DNA binding domain. And it has also NLSs. So this protein is localized in nucleus. Red arrow point out the Bmi1 ribbon structure, Yellow one is RING1 which interact with Bmi-1. Ginjala, V., et al., Molecular and Cellular Biology, 2011. Li, Z., et al., Journal of Biological Chemistry, 2006.

Polycomb group protein The polycomb group(PcG) protiens are epigenetic chromatin modifiers involved in cancer development and also in the maintenance of embryonic and adult stem cells The polycomb group protiens are epigenetic chromatin modifiers involved in cancer development and also in the maintenance of embryonic and adult stem cells. They may act as a transcription repressor. At least two types of Polycomb recessive complex exist in human. PRC1 is the complex which includes PSC proteins. Bmi-1 is one of the six PSC proteins(BMI1, MEL18, MBLR, NSPC1, RNF159 and RNF3) PRC1 recognizes the H3K27 methylation. And then, RING proteins that have E3 ubiquitin ligase activity can ubiquitylate the H2AK119. This ubiqutination leads the transcriptional inactivation. Bracken, A.P. and K. Helin,. Nature Reviews Cancer, 2009.

Functions of the Bmi-1 Oncogenic activities Silencing tumor suppressor genes Protection of cells from apoptosis Promote EMT pathway Induce telomerase activity Self-renewal, Proliferation and Differentiation Maintain self-renewal property Hox gene silencing Developmental regulators and differentiation factors (TIMP-3, HHIP, INHBA) DNA damage protection Bmi1 has many functions. It has ongogenic activities such as Silencing of tumor suppressors, anti apoptotic activity, promotion of the EMT pathway and Induction of telomerase activity. And it regulates self-renewal property of stem cells, and affects proliferation and differentiation of many kinds of cell types. Moreover it is related to DNA damage protection. 1. Bmi1-deficient mice suffer from progressive loss of hematopoietic cells and cerebellar neurons 2. Implicated in the self-renewal of multiple stem cells as well as the proliferation of early cerebellar progenitors 3. BMI1-induced EMT and enhanced the motility and invasiveness of human nasopharyngeal epithelial cells, whereas silencing endogenous BMI1 expression reversed EMT and reduced motility. They demonstrated that BMI1 transcriptionally downregulated expression of the tumor suppressor PTEN in tumor cells through direct association with the PTEN locus. 4. Bmi-1 with c-myc can induce telomerase activity and immortalization of human epithelial cells 5. Matrix metalloproteinase 3, hedgehog interacting protein, and inhibin A genes

Functions of BMI1 in cancer

Silencing of tumor suppressor genes(TSG) Hedgehog SALL4 Myc … … RING-1 p19ARF Bmi-1 p16INK4a Mel18 Bmi-1 act as a silencer of tumor suppressor genes! Bmi-1 can be activated by Hedgehog signaling, SALL4, and Myc. And then Bmi-1 suppress the transcription of p19arf and p16Ink4a. Ring-1 and mel18 are partners of the Bmi1 functions.

Rb E2F p16INK4a Cdk4, 6 Cyclin D Rb P E2F Bmi-1 G1 phase S phase P16 ink4a is the repressor of cdks. So it make the G1/S cell cycle arrest. P19 stabilizes p53 by antagonizing MDM2 and activating p53-dependent transcription. So this protein induces G2/M cell cycle arrest. But these two proteins are inhibited by Bmi1. Therefore cell proliferation is activated. Cell cycle arrest p19ARF Mdm2 p53 G2/M stabilizing

Regulation of BMI1 expression and downstream signaling pathways This figure summarizes the regulation of Bmi1 expression and downstream signaling pathways. Bmi1 is activated by Akt signaling via the phosphorylation. Activated Bmi1 induces the DNA damage repair and represses the transcription of Ink4a/Arf, PTEN and other TSGs. Increasing of self renewal and proliferation, decreasing of senescence and apoptosis are results of Bmi-1 functions. Cao, L., et al., Journal of Cellular Biochemistry, 2011.

Bmi1 affects proliferation and apoptosis These figures show that Bmi1 affects proliferation and apoptosis. OA and TPA make DNA damage stress condition in cells. In contrast to control cells, Bmi-1 overexpressed cells can proliferate though they have DNA damage stresses OA : okadaic acid TPA: 2-O-tetradecanoylphorbol-13-acetate Lee, K., et al., Journal of Investigative Dermatology, 2007.

Mechanisms of BMI1 action Next is mechanisms of Bmi1 action Mechanisms of BMI1 action

PcG recruitment and displacement Bmi1 act as a component of polycomb group complex. Cell fate transcription factors can recruit or displace PcG proteins. Long ncRNA(non coding) also can recruits PcGs to target genes. And recruited PcG represses transcription of target gene *CTTF: cell fate transcription factor Bracken, A.P. and K. Helin,. Nature Reviews Cancer, 2009.

Bmi-1 plays a role in H2A ubiquitination This western data shows that Bmi1 and ring1B do the ubiqutinations in H2A by dose dependent manner. Upper one is in vitro test using purified proteins. The other is in vivo test. Cao, R., Y. Tsukada, and Y. Zhang, Molecular cell, 2005.

Bmi-1 plays a key role in regulation of the Ink4a/Arf locus This data is obtained by ChIP assay. Blue dots reveal primer sites of the ChIP. Number 5 is control. Bmi1 is associated with Ink4a/Arf locus If Bmi1 is defected, H2A ubuquitination in Ink4a/Arf locus is decreased. Dhawan, S., S.I. Tschen, and A. Bhushan, Genes & development, 2009.

Scheme of the Bmi-1 action PRC1 binds to H3K27 methylation site Bmi1 and other proteins perform ubiquitination in H2A Repression of TSGs of the cancer Occurrence It is summary of the Bmi1 action. First PRC1 binds to H3K27 methylation site by CFTFs. Then, PRC1 that includes Bmi1 and other proteins perform ubiquitination in H2A. So TSGs are repressed, and cancer will occur.

Current studies of Bmi1 and its applications

DNA damage specific localization of the Bmi-1 If there are DNA DSBs which are induced by laser scissors, Histone H2AX is rapidly phosphorylated near sites of DNA breaks by ATM, ATR, and DNA-PK. These fluorescence microscopy data show that Bmi1 is localized in DNA damage sites. And merged with pH2AX sites BMI1-mediated H2AK119 ubiquitination at sites of DNA breaks plays a role in facilitating HR-mediated repair. DNA damage sites requires signaling through ATM/ATR pathway but is independent of 53BP1 and proximal to BRCA1 Ginjala, V., et al., Molecular and Cellular Biology, 2011.

Protection against oxidative and DNA damage stresses Bmi1 protects cells against oxidative and DNA damage stresses. mediator(s) in this question mark should be investigated. Ginjala, V., et al., Molecular and Cellular Biology, 2011.

Bmi-1 is a drug target HDAC inhibitors: butyrate and valproic acid Inhibit the Bmi-1 expression: siRNA and Artemisinin Post-transcriptional regulation: MAPKAP kinase or Akt inhibitors

Reference Jiang, L., J. Li, and L. Song, Bmi-1, stem cells and cancer. Acta biochimica et biophysica Sinica, 2009. 41(7): p. 527-534. Valk-Lingbeek, M.E., S.W.M. Bruggeman, and M. van Lohuizen, Stem cells and cancer: the polycomb connection. Cell, 2004. 118(4): p. 409-418. Li, Z., et al., Structure of a Bmi-1-Ring1B polycomb group ubiquitin ligase complex. Journal of Biological Chemistry, 2006. 281(29): p. 20643. Ginjala, V., et al., BMI1 is recruited to DNA breaks and contributes to DNA damage-induced H2A ubiquitination and repair. Molecular and Cellular Biology, 2011. 31(10): p. 1972-1982. Bracken, A.P. and K. Helin, Polycomb group proteins: navigators of lineage pathways led astray in cancer. Nature Reviews Cancer, 2009. 9(11): p. 773-784. Lee, K., et al., Expression of Bmi-1 in epidermis enhances cell survival by altering cell cycle regulatory protein expression and inhibiting apoptosis. Journal of Investigative Dermatology, 2007. 128(1): p. 9-17. Dhawan, S., S.I. Tschen, and A. Bhushan, Bmi-1 regulates the Ink4a/Arf locus to control pancreatic β-cell proliferation. Genes & development, 2009. 23(8): p. 906-911. Cao, L., et al., BMI1 as a novel target for drug discovery in cancer. Journal of Cellular Biochemistry, 2011. 112(10): p. 2729-2741. Cao, R., Y. Tsukada, and Y. Zhang, Role of Bmi-1 and Ring1A in H2A ubiquitylation and Hox gene silencing. Molecular cell, 2005. 20(6): p. 845-854. 

Implicated in the self-renewal of multiple stem cells Ex) hematopoietic stem cell Cell 130, 403-404 (2007)