title: RasGRP1 confers the phorbol ester-sensitive phenotype to EL4 lymphoma cells.
abstract: The murine EL4 lymphoma cell line exists in variants that are either sensitive or resistant to the tumor promoter phorbol 12-myristate 13-acetate (PMA). In sensitive EL4 cells, PMA causes robust Erk mitogen-activated protein kinase activation that results in growth arrest. In resistant cells, PMA induces minimal Erk activation, without growth arrest. PMA stimulates IL-2 production in sensitive, but not resistant, cells. The role of RasGRP1, a PMA-activated guanine nucleotide exchange factor for Ras, in EL4 phenotype was examined. Endogenous RasGRP1 protein is expressed at much higher levels in sensitive than in resistant cells. PMA-induced Ras activation is observed in sensitive cells but not in resistant cells lacking Ras-GRP1. PMA induces down-regulation of RasGRP1 protein in sensitive cells but increases RasGRP1 in resistant cells. Transfection of RasGRP1 into resistant cells enhances PMA-induced Erk activation. In the reverse experiment, introduction of small interfering RNA (siRNA) for RasGRP1 suppresses PMA-induced Ras and Erk activations in sensitive cells. Sensitive cells incubated with siRNA for RasGRP1 exhibit the PMA-resistant phenotype, in that they are able to proliferate in the presence of PMA and do not secrete IL-2 when stimulated with PMA. These studies indicate that the PMA-sensitive phenotype, as previously defined for the EL4 cell line, is conferred by endogenous expression of RasGRP1 protein.
authors.affiliation: Department of Pharmaceutical Sciences, Washington State University, Pullman, WA 99164-6534, USA.
authors.forename: Shujie
authors.initials: S
authors.lastname: Han
authors.forename: Stewart M
authors.initials: SM
authors.lastname: Knoepp
authors.forename: Mark A
authors.initials: MA
authors.lastname: Hallman
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Meier
mesh_terms: D000818:Animals; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D020662:Guanine Nucleotide Exchange Factors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D007700:Kinetics; D008223:Lymphoma; D051379:Mice; D010641:Phenotype; D034741:RNA, Small Interfering / Q000235:genetics; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D034741:RNA, Small Interfering; C112278:Rasgrp1 protein, mouse; D013755:Tetradecanoylphorbol Acetate