Death-associated protein kinase (DAPK) is a death domain-containing serine/threonine kinase, and participates in various apoptotic paradigms. Here, we identify the extracellular signal-regulated kinase (ERK) as a DAPKinteracting protein. DAPK interacts with ERK through a docking sequence within its death domain and is a substrate of ERK. Phosphorylation of DAPK at Ser 735 by ERK increases the catalytic activity of DAPK both in vitro and in vivo. Conversely, DAPK promotes the cytoplasmic retention of ERK, thereby inhibiting ERK signaling in the nucleus. This reciprocal regulation between DAPK and ERK constitutes a positive feedback loop that ultimately promotes the apoptotic activity of DAPK. In a physiological apoptosis system where ERK-DAPK interplay is reinforced, downregulation of either ERK or DAPK suppresses such apoptosis. These results indicate that bidirectional signalings between DAPK and ERK may contribute to the apoptosis-promoting function of the death domain of DAPK.

Death-associated protein kinase (DAPK) is a calmodulin-regulated serine/threonine kinase and elicits tumor suppression function through inhibiting cell adhesion/migration and promoting apoptosis. Despite these biological functions, the signaling mechanisms through which DAPK is regulated remain largely elusive. Here, we show that the leukocyte common antigen-related (LAR) tyrosine phosphatase dephosphorylates DAPK at pY491/492 to stimulate the catalytic, proapoptotic, and antiadhesion/antimigration activities of DAPK. Conversely, Src phosphorylates DAPK at Y491/492, which induces DAPK intra-/intermolecular interaction and inactivation. Upon EGF stimulation, a rapid Src activation leads to subsequent LAR downregulation, and these two events act in synergism to inactivate DAPK, thereby facilitating tumor cell migration and invasion toward EGF. Finally, DAPK Y491/492 hyperphosphorylation is found in human cancers in which Src activity is aberrantly elevated. These results identify LAR and Src as a DAPK regulator through their reciprocal modification of DAPK Y491/492 residues and establish a functional link of this DAPK-regulatory circuit to tumor progression.