Both microglia, the resident myeloid cells of the CNS parenchyma, and infiltrating blood-derived macrophages participate in inflammatory responses in the CNS. Macrophages can be polarized into M1 and M2 phenotypes, which have been linked to functional properties including production of inflammation association molecules and phagocytic activity. We compare phenotypic and functional properties of microglia derived from the adult human CNS with macrophages derived from peripheral blood monocytes in response to M1 and M2 polarizing conditions. Under M1 conditions, microglia and macrophages upregulate expression of CCR7 and CD80. M2 treatment of microglia-induced expression of CD209 but not additional markers CD23, CD163, and CD206 expressed by M2 macrophages. M1-polarizing conditions induced production of IL-12p40 by both microglia and macrophages; microglia produced higher levels of IL-10 under M1 conditions than did macrophages. Under M2 conditions, microglia 6 LPS produced comparable levels of IL-10 under M1 conditions whereas IL-10 was induced by LPS in M2 macrophages. Myelin phagocytosis was greater in microglia than macrophages under all conditions; for both cell types, activity was higher for M2 cells. Our findings delineate distinctive properties of microglia compared with exogenous myeloid cells in response to signals derived from an inflammatory environment in the CNS. V

Active-site mTOR inhibitors (asTORi) hold great promise for targeting dysregulated mTOR signaling in cancer. Because of the multifaceted nature of mTORC1 signaling, identification of reliable biomarkers for the sensitivity of tumors to asTORi is imperative for their clinical implementation. Here, we show that cancer cells acquire resistance to asTORi by downregulating eukaryotic translation initiation factor (eIF4E)-binding proteins (4E-BPs-EIF4EBP1, EIF4EBP2). Loss of 4E-BPs or overexpression of eIF4E renders neoplastic growth and translation of tumor-promoting mRNAs refractory to mTOR inhibition. Conversely, moderate depletion of eIF4E augments the anti-neoplastic effects of asTORi. The anti-proliferative effect of asTORi in vitro and in vivo is therefore significantly influenced by perturbations in eIF4E/4E-BP stoichiometry, whereby an increase in the eIF4E/4E-BP ratio dramatically limits the sensitivity of cancer cells to asTORi. We propose that the eIF4E/4E-BP ratio, rather than their individual protein levels or solely their phosphorylation status, should be considered as a paramount predictive marker for forecasting the clinical therapeutic response to mTOR inhibitors. Cancer Res; 72(24); 6468-76. Ó2012 AACR.

Metformin inhibits the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway, which is frequently upregulated in hepatocellular carcinoma (HCC). Metformin has also been shown to induce apoptosis in this cancer. Here, we investigate whether metformin-induced apoptosis in HCC is mediated by the downstream mTORC1 effectors eukaryotic initiation factor 4E and (eIF4E)-binding proteins (4E-BPs). Further, we ask whether changes in 4E-BPs activity during metformin treatment negatively regulate translation of the anti-apoptotic myeloid cell leukemia 1 (Mcl-1) mRNA. A genetic HCC mouse model was employed to assess the ability of metformin to reduce tumor formation, induce apoptosis, and control 4E-BP1 activation and Mcl-1 protein expression. In parallel, the HCC cell line Huh7 was transduced with scrambled shRNA (control) or shRNAs targeting 4E-BP1 and 4E-BP2 (4E-BP knock-down (KD)) to measure differences in mRNA translation, apoptosis, and Mcl-1 protein expression after metformin treatment. In addition, immunohistochemical staining of eIF4E and 4E-BP1 protein levels was addressed in a HCC patient tissue microarray. We found that metformin decreased HCC tumor burden, and tumor tissues showed elevated apoptosis with reduced Mcl-1 and phosphorylated 4E-BP1 protein levels. In control but not 4E-BP KD Huh7 cells, metformin induced apoptosis and repressed Mcl-1 mRNA translation and protein levels. Immunostaining of HCC patient tumor tissues revealed a varying ratio of eIF4E/4E-BP1 expression. Our results propose that metformin induces apoptosis Research PaperOncotarget 50543 www.impactjournals.com/oncotarget in mouse and cellular models of HCC through activation of 4E-BPs, thus tumors with elevated expression of 4E-BPs may display improved clinical chemopreventive benefit of metformin.