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Title: Retinoic acid-induced growth inhibition of a human myeloma cell line via down-regulation of IL-6 receptors. Author: Sidell N, Taga T, Hirano T, Kishimoto T, Saxon A. Journal: J Immunol; 1991 Jun 01; 146(11):3809-14. PubMed ID: 2033252. Abstract: In this report we demonstrate that retinoic acid (RA) down-regulated the number of IL-6R on human leukocyte cell lines, including the myeloma cell line AF10, and two B cell hybridomas that correspond to cells at earlier stages of B cell development. Using AF10 cells, whose growth was determined to be mediated by the autocrine action of IL-6, we found that RA reduction of IL-6R was concentration-dependent over a range of 10(-11) to 10(-5) M and corresponded to the ability of the retinoid to inhibit cell proliferation. The down-regulation of IL-6R number by RA was accompanied by reduced IL-6R mRNA expression. RA did not affect endogeneous IL-6 synthesis or secretion from AF10 cells. However, addition of exogenous rIL-6 could overcome RA-induced growth inhibition. Menthol, a structurally unrelated compound to RA, also suppressed IL-6R expression and, correspondingly, inhibited cell growth. Taken together, our results suggest that the antiproliferative action of RA on AF10 cells is caused by reduction of IL-6R expression and subsequent inhibition of IL-6-mediated autocrine growth. These findings suggest the possibility that down-regulation of IL-6R is a means by which RA can modulate immune function.[Abstract] [Full Text] [Related] [New Search]