The Na ؉ ͞H ؉ exchanger regulatory factor (NHERF) binds to the tail of the ␤ 2 -adrenergic receptor and plays a role in adrenergic regulation of Na ؉ ͞H ؉ exchange. NHERF contains two PDZ domains, the first of which is required for its interaction with the ␤ 2 receptor. Mutagenesis studies of the ␤ 2 receptor tail revealed that the optimal C-terminal motif for binding to the first PDZ domain of NHERF is D-S͞T-x-L, a motif distinct from those recognized by other PDZ domains. The first PDZ domain of NHERF-2, a protein that is 52% identical to NHERF and also known as E3KARP, SIP-1, and TKA-1, exhibits binding preferences very similar to those of the first PDZ domain of NHERF. The delineation of the preferred binding motif for the first PDZ domain of the NHERF family of proteins allows for predictions for other proteins that may interact with NHERF or NHERF-2. For example, as would be predicted from the ␤ 2 receptor tail mutagenesis studies, NHERF binds to the tail of the purinergic P2Y1 receptor, a seven-transmembrane receptor with an intracellular C-terminal tail ending in D-T-S-L. NHERF also binds to the tail of the cystic fibrosis transmembrane conductance regulator, which ends in D-T-R-L. Because the preferred binding motif of the first PDZ domain of the NHERF family of proteins is found at the C termini of a variety of intracellular proteins, NHERF and NHERF-2 may be multifunctional adaptor proteins involved in many previously unsuspected aspects of intracellular signaling.PDZ domains are conserved protein modules that mediate protein-protein interactions (1-3). The term ''PDZ'' is derived from the first letters in the names of the three proteins in which these modules were originally characterized: PSD-95, Dlg, and ZO-1. PDZ domains bind to the C-terminal tails of target proteins, and the binding preferences of a number of PDZ domains have been characterized (4-7). Such characterization is useful because it allows for predictions regarding the set of proteins to which a given PDZ domain may potentially bind.A PDZ domain-containing protein, the Na ϩ ͞H ϩ exchanger regulatory factor (NHERF), has been recently characterized (8) and found to regulate the Na ϩ ͞H ϩ exchanger type 3 (NHE3) (8-9) via an interaction which does not involve binding of the NHE3 C terminus to the NHERF PDZ domains (9). The function and preferences of the two NHERF PDZ domains were unknown until NHERF was identified as a binding partner of the ␤ 2 -adrenergic receptor (10). The interaction of NHERF with the ␤ 2 receptor is mediated via binding of the first PDZ domain of NHERF to the last few amino acids of the ␤ 2 receptor tail (10). In the present study, we characterize this interaction via mutagenesis of the ␤ 2 receptor tail and saturation NHERF-binding studies. We furthermore demonstrate that NHERF-2, a close relative of NHERF, specifically binds to the ␤ 2 receptor tail and exhibits binding specificity similar to NHERF. Moreover, we demonstrate how the binding preferences of the first PDZ domain of the NHERF family of protein...

Platelet-derived growth factor (PDGF) is a potent mitogen for many cell types. The PDGF receptor (PDGFR) is a receptor tyrosine kinase that mediates the mitogenic effects of PDGF by binding to and/or phosphorylating a variety of intracellular signaling proteins upon PDGF-induced receptor dimerization. We show here that the Na ؉ /H ؉ exchanger regulatory factor (NHERF; also known as EBP50), a protein not previously known to interact with the PDGFR, binds to the PDGFR carboxyl terminus (PDGFR-CT) with high affinity via a PDZ (PSD-95/Dlg/Z0-1 homology) domain-mediated interaction and potentiates PDGFR autophosphorylation and extracellular signal-regulated kinase (ERK) activation in cells. A point-mutated version of the PDGFR, with the terminal leucine changed to alanine (L1106A), cannot bind NHERF in vitro and is markedly impaired relative to the wild-type receptor with regard to PDGF-induced autophosphorylation and activation of ERK in cells. NHERF potentiation of PDGFR signaling depends on the capacity of NHERF to oligomerize. NHERF oligomerizes in vitro when bound with PDGFR-CT, and a truncated version of the first NHERF PDZ domain that can bind PDGFR-CT but which does not oligomerize reduces PDGFR tyrosine kinase activity when transiently overexpressed in cells. PDGFR activity in cells can also be regulated in a NHERF-dependent fashion by stimulation of the ␤ 2 -adrenergic receptor, a known cellular binding partner for NHERF. These findings reveal that NHERF can directly bind to the PDGFR and potentiate PDGFR activity, thus elucidating both a novel mechanism by which PDGFR activity can be regulated and a new cellular role for the PDZ domain-containing adapter protein NHERF.Receptor tyrosine kinases (RTKs) are a large family of transmembrane proteins that transduce signals from the extracellular environment to the cell interior. RTKs are typically activated by ligand-induced dimerization or oligomerization, which leads to stimulation of their intrinsic tyrosine kinase activity. Platelet-derived growth factor (PDGF) activates an RTK known as the PDGF receptor (PDGFR), which can comprise ␣ and/or ␤ subunits. Following PDGF-induced dimerization, the PDGFR autophosphorylates and then associates via its large intracellular carboxyl terminus (CT) with a variety of intracellular proteins in order to mediate its effects on cell growth, motility, and proliferation (20).Nearly a decade ago, it was reported that removal of the last several dozen amino acids from the PDGFR-␤ CT could result in a significant decrease in receptor autophosphorylation and signaling (40). Such a minimal truncation of the CT would not be expected to block the interaction of the PDGFR with most known PDGFR-associated proteins except possibly for phospholipase C␥ (39, 40). Since point mutations that block phospholipase C␥ binding to the PDGFR do not reduce PDGFR tyrosine kinase activity (39), however, the reduction in the tyrosine kinase activity of minimally truncated PDGFR has remained an unexplained finding.We recently described an interaction b...

OBJECTIVE To evaluate the cause, diagnosis, management and complications of self‐inserted urethral foreign bodies in men, reviewing a 17‐year experience. PATIENTS AND METHODS From November 1986 to January 2004, 17 men were treated for self‐inflicted urethral foreign bodies; the records were analysed retrospectively for presentation, diagnosis, management and complications. RESULTS In all 17 patients the foreign bodies were clearly palpable. Objects included speaker wire, an AAA battery, open safety pins, a plastic cup, straws, a marble, and a cotton‐tipped swab. The most common symptom was frequency with dysuria, but there was sometimes gross haematuria and urinary retention. The cause for inserting the foreign body varied; psychiatric disorder was the most common, followed by intoxication, and erotic stimulation was the cause in only five patients. All patients had diagnostic imaging; plain pelvic images were sufficient in 14, ultrasonography or computed tomography was needed in three. Endoscopic retrieval was successful in all but one patient, where a perineal urethrotomy was required. The most common complications were mucosal tears and false passages. Urethral strictures were associated with multiple attempts to insert the foreign body. CONCLUSION Self‐inflicted urethral foreign‐body insertion in men is unusual. A radiological evaluation is necessary to determine the exact size, location and number of foreign bodies. Endoscopic retrieval is usually successful, and antibiotic coverage is necessary. A psychiatric evaluation is recommended for all patients, with appropriate medical therapy when indicated. Late manifestation has included urethral stricture disease, and a close follow‐up, albeit difficult in these patients, is desirable.