p21 and p27 induction by silibinin is essential for its cell cycle arrest effect in prostate carcinoma cells

Abstract

Recent studies have shown that silibinin induces p21/Cip1 and p27/Kip1 and G 1 arrest in different prostate cancer cells irrespective of p53 status; however, biological significance and mechanism of such induction have not been studied. Here, using two different prostate cancer cell lines DU145 and 22Rv1, representing androgen-independent and androgen-dependent stages of malignancy, first we investigated the importance of p21 and p27 induction in silibininmediated G 1 arrest. Silencing p21 and p27 individually by RNA interference showed marked reversal in G 1 arrest; however, their simultaneous ablation showed additional reversal of G 1 arrest in 22Rv1 but not DU145 cells. These results suggest that whereas relative importance of these molecules might be cell line specific, their induction by silibinin is essential for its G 1 arrest effect. Next, studies were done to examine mechanisms of their induction where cycloheximide-chase experiments showed that silibinin increases p21 and p27 protein half-life. This effect was accompanied by strong reduction in Skp2 level and its binding with p21 and p27 together with strong decrease in phosphorylated Thr 187 p27 without considerable change in proteasomal activity, suggesting a posttranslational mechanism. Skp2 role was further elucidated using Skp2-small interfering RNA -transfected cells, where decreased G 1 arrest and attenuated Cip/Kip induction were observed with silibinin treatment. Further, silibinin caused a marked increase in p21 and p27 mRNA levels together with an increase in their promoter activity, also indicating a transcriptional mechanism. Together, our results for the first time identify a central role of p21 and p27 induction and their regulatory mechanism in silibinin-mediated cell cycle arrest. [Mol Cancer Ther 2007;6(10):2696 -707]

Epigenetic modifications and p21-cyclin B1 nexus in anticancer effect of histone deacetylase inhibitors in combination with silibinin on non-small cell lung cancer cells

“…3D). In cancer cells, p21 binds and inactivates cyclin/Cdk complexes primarily mediating a G 1 arrest, 32 but recent studies have also suggested a role in inducing G 2 arrest, either by interfering with the phosphorylation at Tyr 161 of Cdc2-cyclin B1 complex or by limiting the supply of cyclin B1 by causing its proteasomal degradation. 33,34 Since p21 increase correlated with a decrease in cyclin B1 levels by combination treatments (Fig.…”

“…38 For p21 mRNA level, RNA was isolated by Trizol R method, and specific primers for p21 and β-actin were used for amplification by RT-PCR. 32,43 Tumor xenograft study. Six week old athymic (nu/nu) male nude mice, (NCI-Frederick) were subcutaneously injected with ~three million exponentially growing H1299 cells mixed with equal volume (1:1) of matrigel (BD Biosciences) on the right flank of each mouse.…”

Upregulation of manganese superoxide dismutase (SOD2) is a common pathway for neuroendocrine differentiation in prostate cancer cells

“…24 Polyphenolic flavonoid silibinin induces G1 arrest by decreasing CDK and cyclin D1 and inducing p21 and p27 which is essential for its anti-proliferative action in PCa. 40,41 Similarly, the indole melatonin reduces cell proliferation by increasing p21 and p53. 24 To some extent, both antioxidants seem to work similarly; they share p21 induction and prevention of NFjB activation induced by TNF, sensitizing PCa cell to apoptosis induced by this cytokine.…”

Silibinin: An Inhibitor of Mir-181a Gene Expression in Sk-Br-3 Breast Cancer Cell Line

“…[21][22][23][24][25] It has been shown to modulate the expression of large numbers of miRNAs, small [22][23][24][25] nucleotides long non-coding RNAs, in cancer cells that lead to reduction of tumor growth. [26][27][28] Also, miRNAs play an important role in the modulation of chemosensitivity of tumor cells.…”