NOREPINEPHRINE-DEPENDENT SELECTION OF BROWN ADIPOCYTE CELL-LINES

A transgenic mouse carrying a simian virus-40 T-antigen gene under con trol of a mouse urinary protein promoter induced the formation of a br own fat tumor. In tissue culture, these tumor cells expressed the brow n fat-specific mitochondrial uncoupling protein (Ucp) gene when stimul ated by norepinephrine. To develop cell lines for the analysis of Ucp expression, we investigated growth conditions that would maintain expr ession. We found that the addition of 10(-7)-10(-6) M norepinephrine w as critical for establishing cells with high Ucp expression, mitochond rial content, and adipogenesis. Norepinephrine exerts its effects by s electively stimulating the proliferation of brown fat cells. Results w ith receptor-specific agonists and antagonists indicate that norepinep hrine interacts with the beta(1)-adrenergic receptor to stimulate cell proliferation. The capacity of these brown fat cells to respond to no repinephrine by proliferating seems to be a manifestation of a normal physiological response of brown fat cells, because exposing an animal to the cold increases cell proliferation. Thus, this system indicates that two independent pathways for cell proliferation coexist in parall el, one based on transformation of the cell by the simian virus-40 T-a ntigen and the other on the normal response of the cell to stimulation by norepinephrine. Several clonal lines have been isolated that have similar levels of marker gene expression for adipogenesis and mitochon driogensis, but differ in the level of Ucp expression and the fact tha t the expression of Ucp in brown fat is not coordinately linked to tha t of other nuclear genes which encode proteins associated with thermog enesis.