648

BMI1

BMI1 proto-oncogene, polycomb ring finger;BMI1;BMI1 proto-oncogene, polycomb ring finger

B lymphoma Mo-MLV insertion region 1 homolog|BMI1 polycomb ring finger oncogene|BMI1 polycomb ring finger proto-oncogene|flvi-2/bmi-1|murine leukemia viral (bmi-1) oncogene homolog|polycomb complex protein BMI-1|polycomb group RING finger protein 4|polyco

10p11.23

protein-coding

cellular senescence of biliary epithelial cells with p16INK4a and p21WAF1/Cip expression in damaged small bile ducts may be critical for progressive bile duct loss in primary biliary cirrhosis. We investigated the involvement of bmi1, a polycomb group gene repressing p16INK4a expression, in the pathogenesis of biliary cellular senescence. Bmi1 expression was examined immunohistochemically in livers taken from the patients with primary biliary cirrhosis (n=18) and other diseased (n=19) and normal livers (n=16). We examined the effect of oxidative stress and a short interference RNA (siRNA) targeting bmi1 on cellular senescence in cultured mouse biliary epithelial cells. Bmi1 was widely expressed in the nuclei of biliary epithelial cells in the control livers. In contrast, bmi1 expression was significantly decreased in damaged small bile ducts in 43% of livers with primary biliary cirrhosis of stage 1/2, coordinating with the increased p16INK4a expression. In cultured biliary epithelial cells, oxidative stress by H2O2 treatment significantly decreased bmi1 expression, followed by increased P16INK4a expression. A knockdown of bmi1 induced increased p16INK4a expression, decreased cell proliferation, and increased cellular senescence. In conclusion, the decreased bmi1 expression caused by oxidative stress may be involved in the pathogenesis of cellular senescence of biliary epithelial cells in primary biliary cirrhosis.

Activation of telomerase is sufficient for immortalization of some types of human cells but additional factors may also be essential. It has been proposed that stress imposed by inadequate culture conditions induces senescence due to accumulation of p16(INK4a). Here, we present evidence that many human cell types undergo senescence by activation of the p16(INK4a)/Rb pathway, and that introduction of Bmi-1 can inhibit p16(INK4a) expression and extend the life span of human epithelial cells derived from skin, mammary gland and lung. Introduction of p16(INK4a)-specific short hairpin RNA, as well as Bmi-1, suppressed p16(INK4a) expression in human mammary epithelial cells without promoter methylation, and extended their life span. Subsequent introduction of hTERT, the telomerase catalytic subunit, into cells with low p16(INK4a) levels resulted in efficient immortalization of three cell types without crisis or growth arrest. The majority of the human mammary epithelial cells thus immortalized showed almost normal ploidy as judged by G-banding and spectral karyotyping analysis. Our data suggest that inhibition of p16(INK4a) and introduction of hTERT can immortalize many human cell types with little chromosomal instability.

Polycomb-group proteins Bmi1 is regarded as a "stemness" gene involved in the maintenance of stem cells, malignant transformation, and biologic aggressiveness of several human carcinomas. We examined the significance of the Bmi1 expression in intrahepatic cholangiocarcinoma. The expression of Bmi1 was examined in intrahepatic cholangiocarcinoma (n = 30; 9 bile ductular carcinoma, 8 intrahepatic cholangiocarcinoma of peripheral type, and 13 of hilar type) by using immunohistochemistry and real-time polymerase chain reaction. The expression level of Bmi1 was assessed in 7 cholangiocarcinoma cell lines. The effect of Bmi1 knockdown was examined in cultured cholangiocarcinoma cells (HuCCT1 and TFK-1) using small interfering RNA. Bmi1 was consistently expressed in nonneoplastic biliary epithelial cells and in ALL intrahepatic cholangiocarcinoma, irrespective of the location and histological degree of differentiation. The level of mRNA expression was significantly higher in 13 (81.3%) of 16 intrahepatic cholangiocarcinoma compared with the corresponding nonneoplastic tissues. ALL 7 cultured cholangiocarcinoma cells overexpressed Bmi1 to various degrees. The knockdown of Bmi1 resulted in decreased colony formation, decreased cell proliferation activities, and increased cellular senescence. The overexpression of polycomb-group protein Bmi1 is essential for colony formation and cell proliferation, probably by the repression of cellular senescence in intrahepatic cholangiocarcinoma.

PURPOSE: Determine cyclin-dependent kinase inhibitor 2A (p16(Ink4a)) and polycomb ring finger oncogene (Bmi1) expression in corneal endothelium samples from different age groups and test whether the expression of p16(INK4a) and Bmi1 are associated with endothelial cellular senescence in human cornea. METHODS: Samples were selected from an eyebank of healthy human corneal endothelial cells (HCECs). Donor human corneas were divided into three age-groups: age /=50 years. The expression of p16(INK4a) and Bmil were analyzed by real-time PCR, immunohistochemistry, and immunofluorescence. RESULTS: Through real-time PCR, we detected less than threefold decreases in Bmi1 expression and greater than fivefold increases in p16(INK4a) expression associated with aging. Bmi1 expression was significantly down-regulated with increasing donor age. The number of p16(INK4a)-positive cells was significantly higher and the number of Bmi1-positive cells was significantly lower in older donors compared to the younger age groups. Our immunohistochemistry experiments showed that the expression of p16(INK4a) in older donors was stronger than that in younger donors and the expression of Bmi1 in older donors was weaker than that in younger donors. Results from both the immunohistochemistry and real-time PCR experiments confirmed increased expression of p16(INK4a) and decreased expression of Bmi1 with age in HCECs. Additionally, the results of immunofluorescence double-staining for p16(INK4a) and Bmi1 further validated the immunocytochemistry and real-time PCR results. CONCLUSIONS: Our data are the first to demonstrate that high expression of p16(INK4a) and low expression of Bmi1 are associated with endothelial cellular senescence in human cornea. Our findings are not just for cornea transplantation but also for a better understanding of the cornea senescence and the process of aging in this specific human organ.