Sesamin is a major lignan constituent of sesame and possesses multiple functions such as antihypertensive, cholesterol-lowering, lipid-lowering and anticancer activities. Several groups have previously reported that sesamin induces growth inhibition in human cancer cells. However, the nature of this growth inhibitory mechanism remains unknown. The authors here report that sesamin induces growth arrest at the G1 phase in cell cycle progression in the human breast cancer cell line MCF-7. Furthermore, sesamin dephosphorylates tumor-suppressor retinoblastoma protein (RB). It is also shown that inhibition of MCF-7 cell proliferation by sesamin is correlated with down-regulated cyclin D1 protein expression, a proto-oncogene that is overexpressed in many human cancer cells. It was found that sesamin-induced down-regulation of cyclin D1 was inhibited by proteasome inhibitors, suggesting that sesamin suppresses cyclin D1 protein expression by promoting proteasome degradation of cyclin D1 protein. S esamin is a major lignan constituent of sesame and sesame oil, which have been traditional health foods in eastern countries for thousands of years. Many studies have revealed that sesamin is effective in preventing hypertension, thrombogenesis, (1) and hypercholesteremia by increasing hepatic fatty acid oxidation. (2,3) Additionally, sesamin exhibits antioxidative properties, by reducing peroxidation products in the plasma and liver of rats, (4 -6) and exerts an inhibitory effect on chemically induced cancers. Several groups have previously reported that treatment with sesamin induces growth inhibition and apoptosis in human lymphoid leukemia Molt 4B cells and human stomach cancer KATO III cells, respectively.(8,9) Furthermore, sesamin inhibits the incorporation of tritiated thymidine into human leukemia (HL-60) cells.(10) However, the growth inhibitory mechanism of sesamin remains to be elucidated.Cell cycle progression is regulated by cyclin-dependent kinases (CDK) that form complexes with cyclin in a phase-specific manner during the cell cycle.(11) Cyclin D1/D2/D3-CDK4/6 and cyclin E/A-CDK2 play important roles in promoting the G1-to-S phase transition of the cell cycle by phosphorylating tumor-suppressor retinoblastoma protein (RB). (11,12) Activation of cyclins/ CDK is counterbalanced by CDK inhibitors (CKI). The first family of CKI, referred to as the CIP/ KIP family, consists of the related proteins known as p21 WAF1/Cip1 , p27 Kip1 and p57 Kip2 , and each member inhibits cyclin E /A-CDK2 complexes. (13,14) The second family of CDK inhibitors is called the INK4 family of proteins. The four members of the INK4 family, p16INK4a , p15 INK4b , p18INK4c and p19 INK4d , specifically and directly bind to CDK4/6 and inhibit their activities. (14)(15)(16) In the present study, it is shown that sesamin induces growth arrest at the G1 phase and dephosphorylates RB protein in the human breast cancer cell line MCF-7. It is also shown that sesamin specifically down-regulates the expression of cyclin D1 protein among the cell-cycl...

Histone deacetylase (HDAC) inhibitors are known to arrest human tumor cells at the G1 phase of the cell cycle and activate the cyclin-dependent kinase inhibitor, p21 WAF1/Cip1 . However, several studies have suggested the existence of a p21-independent molecular pathway. We report here that HDAC inhibitors activate a member of the INK4 family, the INK4d gene, causing G1 phase arrest, in the human T cell leukemia cell line, Jurkat. One of the major Trichostatin A (TSA)-responsive elements is a specific Sp1 binding site in the INK4d promoter. Electrophoretic mobility-shift assay revealed that Sp1 and Sp3 can specifically interact with this Sp1 binding site. Furthermore, using chromatin immunoprecipitation assay, we demonstrated that HDAC2 was present in the INK4d proximal promoter region in the absence, but not the presence, of TSA. Taken together, these results suggest that treatment with TSA transcriptionally activates INK4d by releasing HDAC2 from the histone-DNA complex at the INK4d promoter. Using a p21 WAF1/Cip1 -deleted human colorectal carcinoma cell line, HCT116 p21 (À/À), we show that upregulation of p19INK4d by TSA is associated with inhibition of cell proliferation. Moreover, mouse embryo fibroblasts lacking Ink4d were resistant to the growth inhibitory effects of TSA as compared to their wild-type counterpart. Our findings suggest that p19INK4d in addition to p21is an important molecular target of HDAC inhibitors inducing growth arrest.

Histone deacetylase (HDAC) inhibitors arrest human tumor cells at the G1 phase of the cell cycle and activate the cyclin-dependent kinase inhibitor, p21WAF1=Cip1 . However, several studies have suggested the existence of a p21WAF1=Cip1 -independent molecular pathway. We report here that HDAC inhibitors, trichostatin A (TSA) and sodium butyrate, activate the p15INK4b gene, a member of the INK4 gene family, through its promoter in HaCaT cells. Furthermore, we show that upregulation of p15INK4b by TSA is associated with cell growth inhibition of HCT116 p21 (3 3/3 3) cells. Our ¢ndings suggest that p15INK4b is one of the important molecular targets of HDAC inhibitors.

The INK4 family members p16INK4a and p15 INK4b negatively regulate cell cycle progression by inhibition of cyclin-dependent kinase (CDK) 4/6. Loss of p16INK4a functional activity is frequently observed in tumor cells, and is thought to be one of the primary causes of carcinogenesis. In contrast, despite the biochemical similarity to p16 INK4a, the frequency of defects in p15INK4b was found to be lower than in p16 INK4a, suggesting that p15 INK4b-inductive agents may be useful for tumor suppression. Here we report the discovery of a novel pyrido-pyrimidine derivative, JTP-70902, which exhibits p15