The role of β-estradiol (E2) in lipoprotein metabolism in mammary tumors is unclear, therefore, we investigated the effect of E2 on the secretion of lipoprotein lipase (LPL) from mouse mammary tumor FM3A cells. E2-treated cells increased the secretion of active LPL from FM3A cells in a time- and dose-dependent manner. Activity of mitogen-activated protein kinase (MAPK) was increased in the tumor cells treated with E2, and enhanced secretion of LPL was suppressed by MAPK kinase 1/2 inhibitor, PD98059, extracellular signal-regulated kinase (ERK) 1/2 inhibitor, FR180204, p38 MAPK inhibitor, SB202190, and phosphatidyl inositol 3-kinase (PI3K) inhibitor, LY294002. In addition, the effect of E2 on LPL secretion was markedly suppressed by an inhibitor of mammalian target of rapamycin complex (mTORC) 1 and 2, KU0063794, but were not by a mTORC1 inhibitor, rapamycin. Furthermore, a small interfering RNA (siRNA)-mediated decrease in the expression of rapamycin-insensitive companion of mTOR (Rictor), a pivotal component of mTORC2, suppressed secretion of LPL by E2. These results suggest that the stimulatory secretion of LPL by E2 from the tumor cells is closely associated with an activation of mTORC2 rather than mTORC1 possibly via the MAPK cascade.
Keywords: lipoprotein lipase; mammalian target of rapamycin; mammary tumor; mitogen activated-protein kinase; β-estradiol.