Diallyl disulfide induces ERK phosphorylation and alters gene expression profiles in human colon tumor cells.

Diallyl disulfide (DADS), a compound found in processed garlic, has been shown to arrest unsynchronized human colon tumor cells (HCT-15) in the G(2)/M phase of the cell cycle. The present studies were designed to examine whether this cell cycle block related to alterations in protein kinase C (PKC), Ca(2+)/calmodulin-dependent protein kinase II (CAMK II) or extracellular signal-regulated kinase (ERK) activity. Exposing double thymidine synchronized HCT-15 cells to DADS (25, 50 and 100 micromol/L) for 4 h increased the G(2)/M population by 30, 31 and 63%, respectively, compared with controls (P < 0.05). PKC and CAM KII activities were not influenced by increasing DADS exposure and thus did not correlate with the block of cells in the G(2)/M phase. Although ERK activity increased by 44 and 60% after treatment with 100 and 500 micromol/L DADS (P < 0.05), it was not influenced by exposure to 25 or 50 micromol/L DADS. Western blot analysis revealed that although DADS (25, 50, 100 and 500 micromol/L) did not influence the quantity of ERK protein expressed, it did increase its phosphorylation by 39, 52, 73 and 61%, respectively, compared with controls (P < 0.05). These studies provide evidence that early alterations in ERK pathway signaling may contribute to the G(2)/M arrest observed after DADS exposure. Preliminary data generated using the Clonetech Atlas Human Cancer cDNA Expression Array suggest that alterations in cell cycle, DNA repair and cellular adhesion factors accompany DADS exposure and may also be involved in mediating the block in G(2)/M progression.