VDR independent induction of acid-sphingomyelinase by 1,23(OH)2 D3 in gastric cancer cells: Impact on apoptosis and cell morphology.

1 alpha,25-dihydroxyvitamin D3 (1,23(OH)2 D3) is known to play a dual role in cancer, by promoting or inhibiting carcinogenesis via 1,23(OH)2 D3 receptor (VDR) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Fok I polymorphism of VDR may indirectly influence the receptor levels through autoregulation. The involvement of neutral sphingomyelinase in the non-classic VDR-mediated genomic pathway response to 1,23(OH)2 D3 treatment has been reported. Until now no information were reported about Fok I polymorphism of VDR in NCI-N87 human gastric cancer cells and the relation between acid sphingomyelinase and 1,23(OH)2 D3. Herein, we showed that NCI-N87 human gastric cancer cells are homozygous for the Fok I 'C' allele; resulting in a three amino acid-truncated protein form of the VDR. Surprisingly 1,23(OH)2 D3 treatments strongly down-regulated the expression of VDR whereas acid sphingomyelinase and PTEN expression were upregulated. No changes of neutral sphingomyelinase expression were observed after 1,23(OH)2 D3 treatment, whereas acid sphingomyelinase activity increased. Furthermore 1,23(OH)2 D3 induced over-expression of caspase 8, CDKN2B, MAP3K5, cytochrome C apoptotic genes. Morphological analysis highlighted some very large round or oval cells and small cells with angular or fusiform extensions, confirmed by MIB-1 immunodetection and Hercep test. Taken together our results indicated that the action of 1,23(OH)2 D3 in gastric cancer cells was independent on 1,23(OH)2 D3 receptor and suggested the acid sphingomyelinase as a possible target to induce molecular events.