EL4 is a murine lymphoma cell line developed in 1945 by treating C57 black mice with 9:10-dimethyl-1:2-benzanthracene (1). The cells were originally propagated in animal hosts, prior to adaptation to cell culture. EL4 cells were used for many years as a source of interleukin-2 (IL2), which they secrete when treated with phorbol 12-myristate 13-acetate (PMA).The EL4 cell line originally provided to us, by a colleague at the University of Washington, was heterogeneous with respect to PMA response. We, therefore, developed and characterized EL4 sub-lines. Wild-type (WT)-derived cell lines, which are PMA responsive, grow readily in suspension culture as did the original strain. Variant (V)-derived (PMA-resistant) sub-lines were selected for enhanced adhesion to tissue culture plastic (2). Clonal lines were developed from both cell types by limiting dilution (3). The PMA sensitivity of WT-derived cells, as reflected by PMA-induced IL2 production and mitogen-activated protein kinase (ERK1/2) activation, has been attributed to expression of Ras guanyl nucleotide releasing protein 1 (RasGRP1), which binds PMA and directly activates Ras (4); V-derived cells do not express RasGRP1.Clonal EL4 cell lines were used for experimental metastasis studies in syngeneic mice, with WT2 and V7 as prototypes (5, 6). WT2 cells do not form tumors (nonmetastatic), while V7 cells form liver tumors (metastatic) after tail vein injection. 'Metastasis' more strictly refers to tumorigenesis in this model, since circulating EL4 cells home to the liver to form tumors (5). The clonal C5 cell line was developed after stably overexpressing human hemagllutinin (HA)-tagged phospholipase D2 (PLD2) in V7 cells in order to characterize the signaling role of PLD2 using a cell line expressing little or no endogenous PLD2 (5). As compared to V7, C5 cells exhibit increased cell migration (7) and tumor growth (5), providing an early example of the positive role of PLD2 in tumorigenesis.This report presents data from microarray analyses comparing transcripts expressed by these three EL4 cell types, with the goal of further defining their phenotypes.