Modulators of intracellular Ca2+ and the calmodulin inhibitor W-7 alter the expression of metastasis-associated genes MTS1 and NM23 in metastatic variants of the B16 murine melanoma.

MTS1 is a metastasis-associated gene highly expressed in highly metastatic tumours. NM23 has been described as a putative metastasis suppressor gene. Here we show that thapsigargin (which raises intracellular calcium [Ca2+]i from intracellular stores) and verapamil (which blocks Ca2+ influx) both down-regulate MTS1 and NM23 gene expression in the poorly metastatic F1 and highly metastatic ML8 variants of the B16 murine melanoma without altering their metastatic behaviour. The data presented here suggest that Ca2+ released from intracellular stores could be functionally differentiated from influxed Ca2+ and could be activating different components of the Ca2+ signalling system. Many of the cellular responses to calcium are mediated through calmodulin. We have therefore further investigated the role of Ca2+ in the regulation of the MTS1 and NM23 genes using the calmodulin inhibitor W-7. Both these genes were down-regulated after treatment of the F1 and ML8 cell variants. We have shown previously that retinoic acid reduces lung colonization by the highly metastatic variant ML8 and that melanocyte stimulating hormone (MSH) enhances lung colonization by the poorly metastatic variant F1, with corresponding changes in the relative expression of NM23 and MTS1. Here we have found that verapamil and thapsigargin have no effect on lung colonization, possibly due to both genes being down-regulated. These data support the concept that NM23 and MTS1 gene expression is linked and that metastatic potential may be determined by their relative expression.