The c-Abl Tyrosine Kinase Phosphorylates the Fe65 Adaptor Protein to Stimulate Fe65/Amyloid Precursor Protein Nuclear Signaling

Abstract

The amyloid precursor protein (APP) is proteolytically processed to release a C-terminal domain that signals to the nucleus to regulate transcription of responsive genes. The APP C terminus binds to a number of phosphotyrosine binding (PTB) domain proteins and one of these, Fe65, stimulates APP nuclear signaling. Fe65 is an adaptor protein that contains a number of protein-protein interaction domains. These include two PTB domains, the second of which binds APP, and a WW domain that binds proline-rich ligands. One ligand for the Fe65WW domain is the tyrosine kinase c-Abl. Here, we show that active c-Abl stimulates APP/Fe65-mediated gene transcription and that this effect is mediated by phosphorylation of Fe65 on tyrosine 547 within its second PTB domain. The homologous tyrosine within the motif Tyr-(Leu/Met)-Gly is conserved in a variety of PTB domains, and this suggests that PTB tyrosine phosphorylation occurs in other proteins. As such, PTB domain phosphorylation may represent a novel mechanism for regulating the function of this class of protein.The amyloid precursor protein (APP) 1 is a type-1 membrane protein with a large ectodomain and a smaller C-terminal intracellular domain. APP undergoes proteolytic processing by enzymes termed secretases. ␣,␤-Secretases cleave at sites that are N-terminal to the membrane-spanning domain, and subsequently ␥-secretase cleaves APP within the membrane. The results of these activities are secreted products that include the large APP extracellular domain, the 40 -42-amino acid residue A␤ peptide that is deposited in the brains of patients with Alzheimer's disease, and the remaining intracellular APP Cterminal domain (1). This C-terminal fragment contains a YENPTY motif and through this, APP binds to a number of phosphotyrosine binding (PTB) domain proteins. These include the Fe65s, X11s (also known as munc-18-interacting proteins, mints), c-Jun N-terminal kinase (JNK)-interacting protein-1 (JIP-1), Numb, ShcA, and disabled (2-16).The functions of APP are not properly understood, although recently its proteolytically processed C-terminal domain has been shown to translocate to the nucleus to regulate transcription (17-24). To do so, it complexes with a number of nuclear proteins, one of which is the adaptor protein Fe65. Fe65 contains a variety of protein-protein interaction domains including two C-terminal PTB domains (the second of which binds APP) and a WW domain that interacts with proline-rich ligands. The first Fe65 PTB domain binds to two transcription factors, the histone acetyltransferase Tip60 and CP2/LSF/LBP1, and Tip60 stimulates APP/Fe65 transcriptional activity (19,25). The full complement of binding partners for the Fe65WW domain are not known, but include the mammalian homologue of Drosophila enabled (Mena) and the c-Abl tyrosine kinase (26, 27). The molecular mechanisms that control APP/Fe65 nuclear signaling are not properly understood and indeed, APP can function to inhibit Fe65 nuclear translocation (28). However, the Fe65WW domain is required for potent ...

Dexras1 Interacts with FE65 to Regulate FE65-Amyloid Precursor Protein-dependent Transcription

“…5C). This is similar to previous observations in other cultured cell types (42). Dexras1 reduced the transcription further in both FE65 wild-type and FE65-Y547F co-transfected cells (Fig.…”

“…FE65 and AICD have been shown to form a transcription stimulation complex for a GAL4-dependent reporter (3,42). In the present study, we have shown that Dexras1 binds to and co-localizes with FE65 in the nucleus.…”

“…Plasmids-Mammalian expression constructs for myctagged FE65, APP695, and GAL4-AICD were as described (42,44). Wild-type Tau 2N4R construct was as described (45).…”

“…(60,61). GSK3␤ is one of the FE65-APP-regulated genes that has been reported by several different groups (42,54,62,63). We therefore determined if Dexras1 modulates FE65-APP-mediated GSK3␤ promoter activity.…”

Fe65 matters: New light on an old molecule

“…The WW domain of FE65 binds the prolinecontaining motif of Mena, the mammalian homolog of enabled, which is involved in the control of cell motility through regulation of the actin cytoskeleton (16). Another ligand of the WW domain is the c-Abl tyrosine kinase, which phosphorylates APP on Tyr-682 (17,18) and Fe65 on Tyr-547, within the PTB2 domain (19). The member of INHAT complex SET/TAF1-b binds to a region of Fe65 overlapping the WW domain (20).…”