Differentiation-dependent expression of retinoid-proteins in BFC-1β adipocytes (original) (raw)

Journal of Biological Chemistry

Recently, we demonstrated that adipose tissue plays an important role in retinol storage and retinol-binding protein (RBP) synthesis. Our data suggested that RBP expression in adipose tissue is dependent on the state of adipocyte differentiation. To examine this possibility, we explored the differentiation-dependent expression of RBP using BFC-1 j 3 preadipocytes, which can be stimulated to undergo adipose differentiation. Total RNA was isolated from undifferentiated (preadipocytes) and differentiated (adipocytes) BFC-1j3 cells and analyzed by Northern blotting. RBP mRNA was not detected in the preadipocytes, but considerable RBP mRNA was present in differentiated BFC-lj3 cells. In BFC-1j3 cells, induced to differentiate with insulin and thyroid hormone, RBP mRNA was first detected after 4 days, reached a maximum level by day 10, and remained at this maximum level for at least 2 more days. Cellular retinol-binding protein was expressed at low levels in the BFC-1B preadipocytes and the level of expression increased for 6 days after induction to differentiate and slowly declined on later days. Neither the maximum level of RBP expression nor the day on which this level was reached was influenced by the level of retinol provided in the BFC-1j3 culture medium. BFC-lj3 cells secreted newly synthesized RBP into the culture medium at a rate of 43 2 14 ng RBP/24 h/106 adipocytes. When the BFC-lj3 adipocytes were provided 1.0 PM retinol in the medium, they accumulated the retinol and synthesized retinyl esters. These studies with BFC-lj3 cells confirm that RBP synthesis and secretion and retinol accumulation are intrinsic properties of differentiated adipocytes. Furthermore, they suggest that RBP and cellular retinolbinding protein gene expression are regulated as part of a package of genes which are modulated during adipocyte differentiation.

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