Apigenin-induced Cell Cycle Arrest is Mediated by Modulation of MAPK, PI3K-Akt, and Loss of Cyclin D1 Associated Retinoblastoma Dephosphorylation in Human Prostate Cancer Cells

Abstract

Apigenin, a dietary plant-flavonoid has shown anti-proliferative and anticancer properties, however the molecular basis of this effect remains to be elucidated. We studied the molecular events of apigenin action in human prostate cancer cells. Treatment of LNCaP and PC-3 cells with apigenin causes G0-G1 phase arrest, decrease in total Rb protein and its phosphorylation at Ser780 and Ser807/811 in dose- and time-dependent fashion. Apigenin treatment caused increased phosphorylation of ERK1/2 and JNK1/2 and this sustained activation resulted in decreased ELK-1 phosphorylation and c-FOS expression thereby inhibiting cell survival. Use of kinase inhibitors induced ERK1/2 phosphorylation, albeit at different levels, and did not contribute to cell cycle arrest in comparison to apigenin treatment. Despite activation of MAPK pathway, apigenin caused a significant decrease in cyclin D1 expression that occurred simultaneously with the loss of Rb phosphorylation and inhibition of cell cycle progression. The reduced expression of cyclin D1 protein correlated with decrease in expression and phosphorylation of p38 and PI3K-Akt, which are regulators of cyclin D1 protein. Interestingly, apigenin caused a marked reduction in cyclin D1, D2 and E and their regulatory partners CDK 2, 4 and 6, operative in G0-G1 phase of the cell cycle. This was accompanied by a loss of RNA polymerase II phosphorylation, suggesting the effectiveness of apigenin in inhibiting transcription of these proteins. This study provides an insight into the molecular mechanism of apigenin in modulating various tyrosine kinases and perturbs cell cycle progression, suggesting its future development and use as anticancer agent in humans.

Apigenin suppresses the senescence-associated secretory phenotype and paracrine effects on breast cancer cells

“…At 10 μM, apigenin significantly and near-maximally reduced IL-6 secretion by these normal cells. Because apigenin was shown to induce apoptosis and inhibit cell proliferation in cancer cell lines (Reiners et al 1999, Gupta et al 2001, Way et al 2004, Brusselmans et al 2005, Shukla and Gupta 2007, Jayasooriya et al 2012, we tested it for these activities in normal human fibroblasts. At 10 μM, apigenin did not induce apoptosis in non-senescent or senescent normal cells and, while robustly reducing IL-6 secretion, only decreased proliferation of non-senescent cells by ∼25% while the flavonoid was present.…”

“…d IRAK4 phosphorylation in response to apigenin treatment was compared between senescent and non-senescent BJ fibroblasts (Freund et al 2011). Apigenin was shown to inhibit p38MAPK phosphorylation in prostate cancer cells, albeit at a higher concentration (40 μM) (Shukla and Gupta 2007). To determine whether apigenin alters IRAK1/IRAK4/p38MAPK phosphorylation in normal cells at a concentration that inhibited the SASP (10 μM), we stimulated non-senescent BJ fibroblasts with IL-1A in the presence of the phosphatase inhibitor calyculin.…”

Acacia honey and chrysin reduce proliferation of melanoma cells through alterations in cell cycle progression

“…Other secondary metabolites of class of flavones, such as apigenin, luteolin and tangertin, with anticancer properties blocked the cell cycle either in the G 0 /G1 phase (33,34) or in the G 2 /M phase (35)(36)(37). Since most of the antineoplastic drugs in clinical use block the cell cycle in the S or G 2 /M phases whereas chrysin blocks the cell cycle in the G 1 phase, a combination of chrysin with currently used drugs might possibly improve melanoma therapies.…”

Role of RHOB in the antiproliferative effect of glucocorticoid receptor on macrophage RAW264.7 cells

“…It has been reported that Akt regulated cell growth progress by controlling the expression and activity of multiple cell cycle regulatory proteins, such as cyclin D1, cyclin E, CDK2, CDK4, and cyclin-dependent kinase inhibitors CDKN1B and CDKN1A (Shukla & Gupta 2007, Lee et al 2008, Seo et al 2008. Wu et al (2008) reported that PRKCA, a regulator of cell proliferation, was highly expressed in the poorly differentiated hepatocellular carcinoma cell lines and the reduction in PRKCA expression resulted in a decrease in the growth rate and the level of cyclin D1 in these cells.…”