SUBSTANCE-P-INDUCED MITOGENESIS IN HUMAN ASTROCYTOMA-CELLS CORRELATESWITH ACTIVATION OF THE MITOGEN-ACTIVATED PROTEIN-KINASE SIGNALING PATHWAY

The neuropeptide substance P (SP) regulates many biological processes through binding to and activating the SP receptor (NK-1 subtype). Acti vation of the SP receptor induces mitogenesis in several cell types. I n this study, we characterized the mitogenic response induced by SP pe ptide in the U-373MG astrocytoma cell line and showed that activation of the SP receptor induces [H-3]thymidine incorporation into DNA. We a lso found that SP potently induces c-myc mRNA and protein in the U-373 MG cells. Tyrphostin A25, which blocks activity of tyrosine kinases, s ignificantly inhibited SP-induced mitogenesis, suggesting that the mit ogenic response induced by SP peptide involves phosphorylation by tyro sine kinases. Furthermore, stimulation of the SP receptor activates ty rosine phosphorylation and enzymatic activity of extracellular signal- regulated kinases (Erk1 and Erk2), also called the mitogen-activated p rotein kinases (MAPKs). This result suggests that MAPKs participate in the SP peptide-induced signaling pathway. The addition of CP 96,345 - 2-(diphenylmethyl)-N-[(2-metoxyphenyl)-methyl]-1- azabicyclo[2.2.2]oct an-3-amine]; an NK-1 receptor antagonist) or PD 098059 (MEK1 inhibitor ) inhibited both DNA synthesis and activation of the MAPK pathway, sub stantiating that SP stimulates mitogenesis by activating the MAPK path way through receptors of the NK-1 subtype. Our results demonstrate tha t SP peptide is a strong mitogen in the U-373MG astrocytoma cell line and establish a clear correlation between SP-induced mitogenesis and a ctivation of MAPK signaling pathway.