SYK MUTATION IN JURKAT E6-DERIVED CLONES RESULTS IN LACK OF P72(SYK) EXPRESSION

The human leukemic Jurkat cell line is commonly used as a model cellul ar system to study T lymphocyte signal transduction. Various clonal de rivatives of Jurkat T cells exist which display different characterist ics with regard to responses to external stimuli, Among these, the E6- 1 clone of Jurkat T cells has been used as a parental line from which numerous important somatic mutant clones have been generated, During t he course of experiments examining signals initiated by the T cell ant igen receptor in an E6-1-derived Jurkat cell clone J.CaM1, we observed that the 72-kilodalton Syk protein tyrosine kinase previously found i n other Jurkat cells was not detected, Upon further analysis it was de termined that Syk transcripts from the J.CaM1 cells as well as the par ental E6-1 cells contain a single guanine nucleotide insertion at posi tion 92. This nucleotide insertion results in a shift in the Syk open reading frame leading to alternate codon usage as well as the generati on of a termination codon at position 109. Thus, Syk transcripts in E6 -1 cells and E6-1-derived clones are predicted to be capable of encodi ng only the first 33 amino acids of the 630-amino acid wild type Syk, These findings are incompatible with a recently proposed model of T ce ll antigen receptor signal transduction based, in part, on experiments conducted using E6-1-derived cells, suggesting that Syk might play a role upstream of Lck and Zap70.