A putative white adipose tissue specific nuclear orphan receptor that interacts with the cAMP-response element of the human β3-adrenergic receptor gene

The authors previously reported that one of the cAMP-response elements (CREs) of the human β3-AR gene, β3CRE2, interacts with a nuclear factor which is distinct from CREB/ATF family. We named this factor WATSF-1 (white adipose tissue specific factor-1) since it is preferentially expressed in WAT. In this work, we have shown the absence of DNA binding or transcriptional activity of this factor in several non-adipose cells tested. By computer analysis, βCRE2 was found to constitute an octameric element that is highly homologous to the binding site for some members of the nuclear hormone receptor superfamily. Using the response elements of other adipocyte- specific nuclear receptors as competitors, a 'cross-talk' between WATSF-1 and these response elements has been demonstrated. However, the affinity of WATSF-1 for these response elements differs from that for β3CRE2 (self), implying that WATSF-1 is distinct from these adipocyte-specific nuclear receptors. Furthermore the DNA-binding activity of WATSF-1 was shown to be enhanced by phosphatase treatment, suggesting that phosphorylation may play an important role in the functional modulation of this factor. In an effort to prove that it is indeed an adipocyte-specific factor, we used 3T3-L1 cells, a cellular model of WAT, that can undergo differentiation into adipocytes. The DNA binding and transcriptional activity of this factor appeared during differentiation of the cells. Taken together, these results demonstrate that WATSF-1 is a putative white adipocyte-specific nuclear orphan receptor induced during adipogenesis and is a transcriptional activator through one of the CREs of the human β3-AR gene. Targeting this factor may be a novel therapeutic approach to stimulation of the β3-AR signal transduction pathway in adipose tissues. (C) 2000 Published by Elsevier Science Ireland Ltd.