The ERK pathway involves positive and negative regulations of HT-29 colorectal cancer cell growth by extracellular zinc

Dietary zinc is an important trace element in the body and is related to both cell proliferation and growth arrest. A recent study found that extracellular zinc-sensing receptors trigger intracellular signal transduction in HT-29 human colorectal cancer cells. However, the signaling mechanism causing this growth regulation by extracellular zinc is not clearly understood. At 10- and 100-microM levels of ZnCl2 treatment, HT-29 cell growth and proliferation increased and decreased, respectively, in a minimally serum-starved medium (MSSM). A lack of significant increase in intracellular zinc levels after zinc treatment suggested that this differential growth regulation of HT-29 cells by extracellular zinc is acquired by receptor-mediated signal transduction. Moreover, this zinc-induced growth regulation was differentially affected by PD-98059, suggesting the involvement of the ERK pathway. Transient ERK activation and subsequent cyclin D1 induction were observed on adding 10 microM ZnCl2 in MSSM in the presence of cell proliferation. On the other hand, prolonged ERK activity was observed with a subsequent increase of cyclin D1 and p21(Cip/WAF1) on adding 100 microM ZnCl2 in MSSM, and this was associated with nonproliferation. Moreover, this ERK activation and cyclin D1 and p21(Cip/WAF1) induction were abolished by PD-98059 pretreatment. The differential regulations of cell growth, ERK activities, and cyclin D1 and p21(Cip/WAF1) inductions were also observed in serum-enriched medium containing higher zinc concentrations. Therefore, differential cell cycle regulator induction occurs by a common ERK pathway in the differential growth regulation of HT-29 cells by extracellular zinc.