RAPAMYCIN INHIBITS SUBSTANCE-P-INDUCED PROTEIN-SYNTHESIS AND PHOSPHORYLATION OF PHAS-I (4E-BP1) AND P70 S6 KINASE (P70(S6K)) IN HUMAN ASTROCYTOMA-CELLS

The mitogenic substance P receptor (NK-1 subtype) is expressed in many primary human tumors with the highest frequency of expression appeari ng in astrocytomas and glioblastomas (75% and 100%, respectively). Rec ently, we showed that substance P neuropeptide induces DNA synthesis i n the human astrocytoma U-373MG cells by activating the mitogen-activa ted protein (MAP) kinase pathway leading to the induction of c-Fos and c-Myc expression. The induction of these immediate early genes is nec essary for the progression of cells form G1 to S phase of the cell cyc le. In this study, we demonstrate that U-373MG cells are highly sensit ive to the growth-inhibitory action of rapamycin at nanomolar concentr ations (IC50 <1 ng/ml). We also show that SP peptide stimulates protei n synthesis in the U-373MG cell line by activating a rapamycin-sensiti ve signaling pathway. Further, we demonstrate that SP is potent in sti mulating PHAS-I protein (also known as 4E-BP1) phosphorylation and p70 S6 kinase (p70(S6K)) phosphorylation and enzymatic activity, and that this stimulation is inhibited by subnanomolar concentrations of rapam ycin. In contrast, rapamycin was not at all effective in repressing SP -induced activation of MAP kinase pathway, c-Fos phosphoprotein expres sion, and DNA synthesis in U-373MG astrocytoma cells.