Functional characterization of the interactions between endosomal adaptor protein APPL1 and the NuRD co-repressor complex

Abstract

Multifunctional adaptor protein APPL1 [adaptor protein containing PH (pleckstrin homology) domain, PTB (phosphotyrosine binding) domain and leucine zipper motif] belongs to a growing group of endocytic proteins which actively participate in various stages of signalling pathways. Owing to its interaction with the small GTPase Rab5, APPL1 localizes predominantly to a subpopulation of early endosomes but is also capable of nucleocytoplasmic shuttling. Among its various binding partners, APPL1 was reported to associate with the nuclear co-repressor complex NuRD (nucleosome remodelling and deacetylase), containing both nucleosome remodelling and HDAC (histone deacetylase) activities, but the biochemical basis or functional relevance of this interaction remained unknown. Here we characterized the binding between APPL1 and NuRD in more detail, identifying HDAC2 as the key NuRD subunit responsible for this association. APPL1 interacts with the NuRD complex containing enzymatically active HDAC2 but not HDAC1 as the only deacetylase. However, the cellular levels of HDAC1 can regulate the extent of APPL1–NuRD interactions, which in turn modulates the nucleocytoplasmic distribution of APPL1. Increased binding of APPL1 to NuRD upon silencing of HDAC1 promotes the nuclear localization of APPL1, whereas HDAC1 overexpression exerts an opposite effect. Moreover, we also uncovered a NuRD-independent interaction of APPL1 with HDAC1. APPL1 overexpression affects the composition of the HDAC1-containing NuRD complex and the expression of HDAC1 target p21WAF1/CIP1. Cumulatively, these data reveal a surprising complexity of APPL1 interactions with HDACs, with functional consequences for the modulation of gene expression. In a broader sense, these results contribute to an emerging theme of endocytic proteins playing alternative roles in the cell nucleus.

Rab5a overexpression promoting ovarian cancer cell proliferation may be associated with APPL1‐related epidermal growth factor signaling pathway

“…It was previously documented that APPL1 interacts with the NuRD complex depending on the HDAC2 subunit. ( 15,27 ) In the present study, we observed APPL1 could colocalize with MTA2, HDAC1, and HDAC2 by confocal microscopy, and we also found the that three subunits could be pulled down by APPL1 with immunoprecipitation analysis. These results further confirmed Miaczynska’s theory that APPL1 interacted with the NuRD complex rather than a single component in the nucleus.…”

EHD2 shuttles to the nucleus and represses transcription

“…Dab1 and Dab2, plasma membrane associated adaptors that are involved in endocytosis, were also shown to traffic to the nucleus [42,43], where Dab2 functions as a co-activator of TGFβ-dependent transcription [43]. On the other hand, APPL1 (adaptor protein, phosphotyrosine interaction, pleckstrin homology domain and leucine zipper containing 1), which associates with endosomal membranes and promotes membrane bending through its BAR (Bin/amphiphysin/Rvs) domain [44], was shown to interact in the nucleus with the NuRD (nucleosome remodelling and histone deacetylase) corepressor complex [45][46][47]. Thus endocytic proteins that shuttle to the nucleus may serve as co-activators or corepressors.…”

Multifunctional protein APPL2 contributes to survival of human glioma cells

“…Intriguingly, these activities appear independent of endosomal localization of APPL2 and therefore could be mediated by its nuclear or cytoplasmic, but not endosomal, binding partners. Among others, APPL proteins interact with the nuclear proteins, such as nucleosome remodeling and histone deacetylase complex NuRD (Banach‐Orlowska et al., 2009; Miaczynska et al., 2004) or the multifunctional transcriptional regulator Reptin (Rashid et al., 2009). In the cytoplasm, APPL1 binds TRAF2 adapter protein which affects NF‐κB‐dependent transcription (Hupalowska et al., 2012).…”

“…Indeed, the involvement of many endocytic proteins in the pathogenesis of cancer has been reported (Mosesson et al., 2008; Pyrzynska et al., 2009). Two homologous proteins APPL1 and APPL2 (adapter proteins containing pleckstrin homology domain, phosphotyrosine binding domain and leucine zipper motif) represent good examples of proteins actively participating in both endocytosis and cellular signaling (Banach‐Orlowska et al., 2009; Miaczynska et al., 2004; Rashid et al., 2009). In addition, some lines of evidence suggest a possible role of these proteins in cancer development and/or progression.…”