HSG cells, a model in the submandibular clock

Circadian rhythm of vital processes is essential to health, and various tissues show unique peripheral rhythms. HSG is the human submandibular gland cell line that has been used for analysing the effects of steroids and growth factors. In the present study, we analysed the transcriptional regulation of the BMAL1 gene, a critical component of the mammalian clock system to investigate the possibility of using HSG cells as a model system of the submandibular clock. The BMAL1 gene was expressed with circadian oscillation after stimulation with dexamethasone, and its regulatory region contained two recognition motifs for ROR (retinoic acid-receptor-related orphan receptor) and ROREs [ROR alpha (ROR alpha-subunit)binding elements] in hypomethylated CpG islands with an open chromatin structure. REV-ERB alpha was expressed with circadian oscillation, and knockdown experiments suggested that REV-ERB alpha is involved in circadian transcription of the BMAL1 gene in HSG cells. These results are similar to those in NIH 3T3 cells, a standard model for the circadian system, whereas ROR alpha required for REV-ERB alpha antagonism was expressed very little in HSG cells. These findings show that in the salivary gland cell line HSG there is a rhythm in the core oscillator components BMAL1 and REV-ERB alpha, indicating that circadian-based transcriptional regulation can be modelled in this peripheral cell type.