Characterization of APPBP2/PAT1a and Analysis of its interaction with APP family Proteins
The physiological function and pathogenic role of the Amyloid Precursor Protein (APP) and its homologues, Amyloid Precursor Protein like protein 1 and 2 (APLP1, APLP2), correlate strongly to their subcellular localization. Lines of evidences from Pimplikar and co-workers showed a kinesin light chain (KLC) like protein, termed PAT1 (protein interacting with APP tail 1), interacts with both microtubules and the intracellular domain of APP, in addition, a neuronal function in the microtubule plus end directed translocation of APP toward the plasma membrane was proposed along within their study. However neither expression nor functional studies in neuronal system for PAT1 were done to date. In this study, we found that the PAT1 sequence exhibits 7 nucleotide exchanges resulting in 6 non-homologous amino acid substitutions, which are likely due to a rarely occurring polymorphism in the APPBP2 gene, therefore in this study, APPBP2 was used to perform further investigation on the interaction with APP and APLPs. Characterization by Northern analysis reveals that APPBP2/PAT1a is ubiquitously expressed in all tissues examined from Human and Mouse. In situ hybridization and immunohistochemical analysis clearly show a wide overlap of APPBP2/PAT1a with APP/APLPs in mouse brain, and is predominantly expressed by neurons. Further, this study shows the existence of a common complex containing APP family members and APPBP2/PAT1a in mouse brain. In primary cultured neurons, APPBP2/PAT1a is partly associated with vesicular membranes among soma and neurites, bearing APP, APLP1 and APLP2 suggesting that APPBP2/PAT1a is implicated in the intraneuronal transport of APP/APLPs. The highest degree of colocalization in neurons was observed for APLP2 in comparison to the other family members indicating that APPBP2/PAT1a might interact preferentially with APLP2 in vivo. Moreover, data in this study also showed that the PAT1a protein level affects APP/APLPs processing and alters Ab secretion in stably transfected SH-SY5Y cells. All together, these data reveal the expression pattern of PAT1a in situ in mouse brain and various tissues among human and mouse, the in vivo interaction of APPBP2/PAT1a with all APP family members in mouse CNS, and co-distribution in late secretory pathway in primary neurons. Besides, this study shows that APPBP2/PAT1a has a regulatory function in APP/APLPs processing and Ab production suggesting that APPBP2/PAT1a shall be considered as a alternative novel target for analyzing physiological functions of APP family proteins and further, a potential target for therapeutic approaches to facilitate Ab production in Alzheimer’s disease.
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