Whether the diurnal rhythm of cell cycle is associated with that of interferon-α/β receptor (IFNAR) expression was investigated in implanted-tumor cells. The expression of IFNAR mRNA significantly increased when the proportion of tumor cells in DNA synthesis (S) phase increased in vitro. A diurnal rhythm was observed for cell cycle distribution in implanted-tumor cells. The specific binding of interferon-α to receptor and IFNAR mRNA increased when the proportion of tumor cells in S phase increased in vivo. The time-dependent expression of IFNAR was supported by that of transcription factor level induced by interferon-β. The present result suggests that the rhythm of IFNAR expression is closely related to that of cell cycle distribution in implanted-tumor cells.
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