Recently, probiotics, including Bifidobacterium, Lactobacillus, and Enterococcus, among other organisms, have been clinically applied for their enhancing effects on defense mechanisms. It is reported that gene expression in somatic cells can be activated by autoinducers, which are hormone-like molecules produced in a microbial QS system. In the present study, based on a hypothesis that a low-molecular substance related to the QS system is involved in the probiotics effects of Bifidobacterium, we intended to extract the low-molecular substance. As a result, we successfully isolated the peptide p(CHWPR), which was composed of five amino acids including Cys, His, Trp, Pro, and Arg, and found that the peptide was produced in the stationary phase of bacterial growth and that it could enhance the gene expression of oxalyl-CoA decarboxylase (Oxc). p(CHWPR) enhanced the gene expression of c-myc and interleukin (IL)-6 in an established cell line, HL-60. We demonstrated that p(CHWPR) penetrates the cell membrane and binds specifically to RORgamma, which is a cytosolic nuclear receptor. This suggests that RORgamma bound to p(CHWPR) would bind to promoter regions of the c-myc gene. Furthermore, we found that p(CHWPR) also bound to a transcriptional avtivation subunit, CRSP70; this suggests that p(CHWPR), RORgamma, and CRSP70 in combination enhance transcription activity.