Alternative splicing affecting the SH3A domain controls the binding properties of intersectin 1 in neurons

Institute of Molecular Biology and Genetics, 150 Zabolotnogo Street, Kyiv 03143, Ukraine.
Biochemical and Biophysical Research Communications (Impact Factor: 2.3). 09/2008; 372(4):929-34. DOI: 10.1016/j.bbrc.2008.05.156
Source: PubMed


Intersectin 1 (ITSN1) is a conserved adaptor protein implicated in endocytosis, regulation of actin cytoskeleton rearrangements and mitogenic signaling. Its expression is characterized by multiple alternative splicing. Here we show neuron-specific expression of ITSN1 isoforms containing exon 20, which encodes five amino acid residues in the first SH3 domain (SH3A). In vitro binding experiments demonstrated that inclusion of exon 20 changes the binding properties of the SH3A domain. Endocytic proteins dynamin 1 and synaptojanin 1 as well as GTPase-activating protein CdGAP bound the neuron-specific variant of the SH3A domain with higher affinity than ubiquitously expressed SH3A. In contrast, SOS1, a guanine nucleotide exchange factor for Ras, and the ubiquitin ligase Cbl mainly interact with the ubiquitously expressed isoform. These results demonstrate that alternative splicing leads to the formation of two pools of ITSN1 with potentially different properties in neurons, affecting ITSN1 function as adaptor protein.

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    ABSTRACT: Intersectin 1 (ITSN1) is an adaptor protein involved in clathrin-mediated endocytosis, apoptosis, signal transduction and cytoskeleton organization. Here, we show that ITSN1 forms a complex with adaptor protein Ruk/CIN85, implicated in downregulation of receptor tyrosine kinases. The interaction is mediated by the SH3A domain of ITSN1 and the third or fourth proline-rich blocks of Ruk/CIN85, and does not depend on epidermal growth factor stimulation, suggesting a constitutive association of ITSN1 with Ruk/CIN85. Moreover, both proteins colocalize in MCF-7 cells with their common binding partner, the ubiquitin ligase c-Cbl. The possible biological role of the interaction between ITSN1 and Ruk/CIN85 is discussed.
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    ABSTRACT: Intersectin 1 (ITSN1) is an evolutionarily conserved adaptor protein that functions in clathrin-mediated endocytosis, cell signalling and cytoskeleton rearrangements. The ITSN1 gene encodes two main isoforms: a short form (ITSN1-s), which is ubiquitously expressed and consists of two Eps15 homology (EH) domains and five Src homology 3 (SH3) domains, and a long form (ITSN1-l), which is predominantly expressed in the brain and contains three additional domains, a Dbl homology (DH) domain, a Pleckstrin homology (PH) domain and a C2 domain. Using computational analysis of the EST database and 3' RACE we determined the length of the 3' untranslated region of ITSN1-l and demonstrated that the polyadenylation site is located 11,559 nt downstream of the stop codon of the ITSN1-l mRNA. Recently, additional splicing events affecting ITSN1 transcripts were reported, but full-length transcriptional isoforms with different combinations of alternatively spliced exons remained unknown. Here we report the identification of fifteen novel transcriptional isoforms of the human ITSN1 gene with full-length coding sequences that are the result of different combinations of the alternatively spliced exons 5, 6/6', 20, 23, 25, 26, 26a and 35. The isoforms identified differ in domain organization and expression level in different tissues and more likely contribute to the modulation of many complex protein interactions in which ITSN1 participates.
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