[Regulation of protein S100 expression during transcription]

The S100 protein family is a group of homologous, small, calcium-binding proteins expressed in a cell specific manner. In man, the genes coding the majority of these proteins are localized in a cluster on chromosome 1. The cell specific expression of these proteins is mainly attained at the transcriptional level. It appears that the promoters of some S100 genes (rat S100A4, mouse and human S100B and rat CALB3) contain inhibitory sequences which reduce transcription level. Their effect may be counteracted by an interaction with cell specific transcription factor(s), which allows transcription in certain cell types. In other cases (human S100A2, mouse S100A4 and human S100A6), the main mechanism controlling cell specific expression seems to be methylation of the promoter or intronic sequences leading to gene silencing in some cells. The level of protein expression might be further modulated by different regulatory sequences that respond, via interactions with specific transcription factors, to various extracellular stimuli.