Mechanism of Sulforaphane-Induced Cell Cycle Arrest and Apoptosis in Human Colon Cancer Cells

Abstract

Sulforaphane (SFN) is a natural micronutrient found in cruciferous vegetables that has been shown to possess antitumoral properties in carcinogen-treated rats. In vitro, SFN regulates phase II enzymes, cell cycle, and apoptosis. In the present study, we investigated the relationship between SFN induction of apoptosis and cell cycle arrest in HT29 human colon carcinoma cells. In previously published data, a significant increase in the G2/M phase of the cell cycle has been observed in SFN-treated cells that was associated with increased cyclin B1 protein levels. In the present study, our results show that SFN induced p21 expression. Moreover, preincubation of HT29 cells with roscovitine, a specific cdc2 kinase inhibitor, blocked the G2/M phase accumulation of HT29 cells treated with SFN and abolished its apoptotic effect (22.2 +/- 4 of floating cells in SFN-treated cells vs. 6.55 +/- 2 in cells treated with both SFN and roscovitine). These results suggest that the cdc2 kinase could be a key target for SFN in the regulation of G2/M block and apoptosis. Moreover, in SFN-treated cells the retinoblastoma tumor suppressor protein (Rb) is highly phosphorylated. Inhibition of the cdc2 kinase by roscovitine did not change the phosphorylation status of Rb in SFN-treated cells, suggesting that this cyclin-dependent kinase may not be involved. In our study, we did not observe any significant change in the proteasomal activity between control and SFN-treated cells. Moreover, inhibition of proteasomal activity through the use of MG132 diminished SFN-induced HT29 cell death, suggesting that the apoptotic effect of SFN requires a functional proteasome-dependent degradation system. In summary, we have elucidated part of the mechanism of action of SFN in the concomitant regulation of intestinal cell growth and death.

Chemoprotection by sulforaphane: Keep one eye beyond Keap1

“…Further work established an IC 50 of 15 μM SFN in HT-29 cells and 50 μM in CaCo-2 cells, suggesting possible selective effects toward undifferentiated versus differentiated cells, respectively [36]. Alterations in cell cycle progression also have been reported in HT-29 cells treated with SFN, with a decrease in the percentage of cells in G1 and an increase in G2/M, as well as increases in cyclin A and cyclin B1 protein levels [37], and hyperphosphorylation of the retinoblastoma tumor suppressor protein (Rb) [38]. Furthermore, there was an increase in Bax protein expression, loss of cytochrome c from mitochondria, and concomitant elevation of cytosolic cytochrome c [37].…”

“…First, two groups demonstrated that SFN maintains Cdc2 kinase in its active form, which was correlated with induction of apoptosis [38,43]. However, another study reported reduction of Cdc25C, a phosphatase responsible for activation of Cdc2; this reduction of Cdc25C by SFN was mediated via activation of checkpoint 2 kinase (Chk2) [41].…”

Sulforaphane inhibits hypoxia-induced HIF-1α and VEGF expression and migration of human colon cancer cells

“…In the last decade, many studies revealed that sulforaphane acts as a chemopreventive agent by inducing apoptosis and cell cycle arrest and inhibiting proliferation. In colon cancer cells, sulforaphane induced apoptosis and G2/M phase cell cycle arrest (15)(16)(17)(18)(19). In vivo studies showed that sulforaphane suppressed azoxymethane-induced colonic aberrant crypt foci (ACF) (20) and prevented polyps in Apc/Min mice (21).…”

The Mediterranean Diet in the Prevention of Degenerative Chronic Diseases

“…The abundance of fruits and vegetables, along with extra-virgin olive oil, red wine, aromatic herbs (oregano, parsley, and rosemary), garlic, onion, and pepper (ingredients generously used in Mediterranean cuisine), ofers a number of phenolic compounds with a strong antioxidant action that is hardly possible to achieve with other types of diet. Examples are allyl sulides, which are present in garlic and raw onions, give cardiovascular beneits, improve cognitive ability, and have chemopreventive activity; it was shown that certain isothiocyanates (degradation products of glucosinolates, compounds present in caper berries) can afect the cell cycle and induce apoptosis in HT-29 human colon cancer cells and other isothiocyanates, present in high concentration in cruciferous vegetables (cabbage and broccoli) [24,25], have the capacity to modulate the metabolism of carcinogens; kaemferolo and lavonoids quercetin and hydrocinnamic acids from capers have well-known anti-inlammatory and antioxidant efects and chives also rich in phenolic compounds with diuretic, antihypertensive, anti-inlammatory, and antioxidant substances [26][27][28]; catechins fruit (e.g., apple skin and grape) antioxidant molecules prevent the production of reactive oxygen species generated by oxidative stress; the anthocyanins, plant pigments, give the red or blue color to fruits and vegetables (berries, eggplant, black grapes, and red beet), are antioxidants, photoprotective, and are able to inhibit angiogenesis. One other major constituent of MD is vitamin E, which contains a group of eight isomers: four tocopherols (α, β, γ, δ-tocopherol) and four tocotrienols (α, β, γ, δ-tocotrienol).…”