Extracellular stimuli trigger adipocyte differentiation by inducing the com
plex cascades of transcription. Transcription factors CCAAT enhancer-bindin
g proteins (C/EBPs) and peroxisome proliferator-activated receptor gamma (P
PAR gamma) play crucial roles in this process. Although ectopic expression
of these factors in NIH-3T3 cells, a multipotential mesenchymal stem cell l
ine, results in adipogenic conversion, little is known as to hormonal facto
rs that regulate adipogenesis in these cells. In this report we demonstrate
that PRL, a lactogenic hormone, enhances C/EBP beta and PPAR gamma mRNA ex
pression and augments adipogenic conversion of NIH-3T3 cells. Moreover, we
show that ectopic expression of the PRL receptor in NIH-3T3 cells results i
n efficient adipocyte conversion when stimulated with PRL and a PPAR gamma
ligand, as evidenced by expression of the adipocyte differentiation-specifi
c genes as well as the presence of fat-laden cells. We further demonstrate
that signal transducer and activator of transcription 5 (Stat5), a PRL sign
al transducer, activates aP2 promoter in a PRL-dependent manner. These resu
lts suggest that PRL acts as an adipogenesis-enhancing hormone in NIH-3T3 c
ells.