Interaction between growth arrest-DNA damage protein 34 and Src kinase Lynnegatively regulates genotoxic apoptosis

Genotoxic stresses activate intracellular signaling molecules, which lead t o growth arrest, DNA repair, and/or apoptosis. Among these molecules are th e growth arrest and DNA damage protein 34 (GADD34) and the Src-related prot ein tyrosine kinase Lyn. Here, we report that these two proteins physically and functionally interact to regulate DNA damage-induced apoptosis. Multip le isolates of GADD34 and the related murine protein MyD1 16 were identifie d as binding partners of Lyn in a yeast two-hybrid screen. The specific int eraction was confirmed by in vitro association of GADD34 with glutathione S -transferase fusion proteins containing the Src Homology 3 (SH3) domain of Lyn, as well as coimmunoprecipitation of GADD34 and Lyn from mammalian cell s. GADD34 was tyrosine-phosphorylated in vivo in a Lyn-dependent manner. Ly n efficiently phosphorylated affinity-purified GADD34 in vitro. Lyn negativ ely regulated the proapoptotic function of GADD34 in a kinase-dependent man ner. Expression of wild-type, but not kinase-inactive, Lyn weakened promoti on of apoptosis by GADD34 following treatment with methyl-methanesulfonate or ionizing radiation in HEK293 and HeLa cells. In contrast, pretreatment o f cells with the Src-specific tyrosine kinase inhibitor PP1 strengthened pr omotion of apoptosis by GADD34. We propose that Lyn regulates the proapopto tic function of GADD34 by binding and phosphorylating it.