Grifolin, a secondary metabolite isolated from the fresh fruiting bodies of the mushroom Albatrellus confluens, has been shown to inhibit the growth of some
cancer cell lines in vitro by induction of apoptosis in previous studies of our group. However, the mechanisms of action are not completely understood. An apoptosis-related gene expression profiling analysis provided a clue that
death-associated protein kinase 1 (dapk1) gene was upregulated at least twofold in response to
grifolin treatment in
nasopharyngeal carcinoma cell CNE1. Here, we further investigated the role of DAPK1 in apoptotic effect induced by
grifolin. We observed that
protein as well as
mRNA level of DAPK1 was induced by
grifolin in a dose-dependent manner in
nasopharyngeal carcinoma cell CNE1. We found that
grifolin increased both Ser392 and Ser20 phosphorylation levels of
transcription factor p53
protein, which could promote its transcriptional activity. Moreover, induced by
grifolin, the recruitment of p53 to dapk1 gene promoter was confirmed to enhance markedly using EMSA and ChIP assays analysis. The involvement of DAPK1 in
grifolin-induced apoptosis was supported by the studies that introducing
siRNA targeting DAPK1 to CNE1 cells remarkably interfered
grifolin-caused apoptotic effect as well as the activation of
caspase-3.
Grifolin induced upregulation of DAPK1 via p53 was also observed in tumour cells derived from human
breast cancer and human
colon cancer. The findings suggest that upregulation of DAPK1 via p53-DAPK1 pathway is an important mechanism of
grifolin contributing to its ability to induce apoptotic effect. Since growing evidence found a significant loss of DAPK1 expression in a large variety of tumour types,
grifolin may represent a promising candidate in the intervention of
cancer via targeting DAPK1.