The central proline rich region of POB1/REPS2 plays a regulatory role in epidermal growth factor receptor endocytosis by binding to 14-3-3 and SH3 domain-containing proteins.
BACKGROUND
The human POB1/REPS2 (Partner of RalBP1) protein is highly conserved in mammals where it has been suggested to function as a molecular scaffold recruiting proteins involved in vesicular traffic and linking them to the actin cytoskeleton remodeling machinery. More recently POB1/REPS2 was found highly expressed in androgen-dependent prostate cancer cell lines, while one of its isoforms (isoform 2) is down regulated during prostate cancer progression.


RESULTS
In this report we characterize the central proline rich domain of POB1/REPS2 and we describe for the first time its functional role in receptor endocytosis. We show that the ectopic expression of this domain has a dominant negative effect on the endocytosis of activated epidermal growth factor receptor (EGFR) while leaving transferrin receptor endocytosis unaffected. By a combination of different approaches (phage display, bioinformatics predictions, peptide arrays, mutagenic analysis, in vivo co-immunoprecipitation), we have identified two closely spaced binding motifs for 14-3-3 and for the SH3 of the proteins Amphiphysin II and Grb2. Differently from wild type, proline rich domains that are altered in these motifs do not inhibit EGFR endocytosis, suggesting that these binding motifs play a functional role in this process.


CONCLUSIONS
Our findings are relevant to the characterization of the molecular mechanism underlying the involvement of POB1/REPS2, SH3 and 14-3-3 proteins in receptor endocytosis, suggesting that 14-3-3 could work by bridging the EGF receptor and the scaffold protein POB1/REPS2.
Tomassi
Laura
L
Department of Biology, University of Rome Tor Vergata, Via della Ricerca Scientifica, 00133 Rome, Italy. tomassi@uniroma2.it
Costantini
Anna
A
Corallino
Salvatore
S
Santonico
Elena
E
Carducci
Martina
M
Cesareni
Gianni
G
Castagnoli
Luisa
L
D048948:14-3-3 Proteins / Q000378:metabolism*; D000595:Amino Acid Sequence; D002135:Calcium-Binding Proteins; D004705:Endocytosis / Q000235:genetics*; D066246:ErbB Receptors / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011392:Proline / Q000235:genetics; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs / Q000235:genetics; D015398:Signal Transduction; D014162:Transfection; D018909:src Homology Domains / Q000235:genetics*
D048948:14-3-3 Proteins; D002135:Calcium-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; C489722:REPS2 protein, human; D011392:Proline; D066246:ErbB Receptors