Structural and functional analysis of the apoptosis-associated tyrosine kinase (AATYK) family

Apoptosis-associated tyrosine kinase (AATYK) is a protein kinase that is predominantly expressed in the nervous system and is involved in apoptosis and neurite growth of cerebellar granule cells. In this study, we cloned three new members of the mouse AATYK family, AATYK1B, AATYK2 and AATYK3. AATYK1B is a splicing variant of the previously reported AATYK1 (referred to as AATYK1A hereafter). In comparison with AATYK1A, these three AATYK members were characterized by having an extra N-terminal region that consists of a signal peptide-like sequence and a predicted transmembrane (TM) region, which is followed by a kinase domain and a long C-terminal domain. Both TM-containing AATYK isoforms (AATYK(+)TM: AATYK1B, 2, and 3) and TM-lacking isoform (AATYK(-)TM: AATYK1A) were recovered in membrane fractions, suggesting that AATYK(+)TM and AATYK(-)TM are transmembrane- and peripheral-membrane protein kinases, respectively. AATYK1A was recovered in the soluble fraction when the cells were treated with 2-bromo palmitate, suggesting that AATYK1A associates with membrane via palmitoylation. The kinase domain was highly conserved among all AATYK members and was shown to be catalytically active. Three AATYK family members were predominantly expressed in adult mouse brains with almost similar expression profiles: widespread distribution over the various brain regions, especially in the cerebellum and hippocampus, and up-regulated expression during development of the cerebellum. In cultured cerebellar granule cells, AATYK1 was abundantly localized in both soma and axons, AATYK2 distribution was restricted to soma, and AATYK3 was punctately present over the cells. AATYK1 was concentrated in the central domain of growth cones of dorsal root ganglion neurons. Our results indicate that AATYK family members are brain-dominant and membrane-associated kinases with slightly different distribution patterns in the developing and adult mouse brain, which may be involved in fine regulation of neuronal functions including neurite extension and apoptosis.