FAN-PH mutants with a non-functional PtdIns(4,5)P binding site were unable to mediate TNF-induced filopodia formation

FAN-PH mutants with a non-functional PtdIns(4,5)P binding site were unable to mediate TNF-induced filopodia formation. cytoskeleton reorganization. as His-tag fusion protein and affinity purified (Figure 5E). In a lipid overlay assay, membranes spotted with different lipids were incubated with recombinant FAN-PH protein and bound protein was detected by Western blot using anti-His antibody. As shown in Figure 5F, the recombinant FAN-PH-domain protein bound specifically to PtdIns(4,5)P. No binding could be observed either to related phosphoinositides or to different phospholipids like phosphatidylcholin or phosphatidylethanolamine. It has been proposed that positively charged conserved residues in the basic binding pocket of several PH domains mediate the interaction of PH domains with phosphoinositides (Lemmon and Ferguson, 2000; Cozier F-actin binding assay using recombinant FAN-GST and F-actin. As shown in Figure 7C, FAN-GST but not GST alone was co-sedimented with F-actin, demonstrating a direct F-actin binding capability of FAN. The observed interactions provide a functional link between FAN and the actin cytoskeleton machinery, which may result in co-precipitation of proteins involved in filopodia formation like VASP, as shown in Figure 7A and B. Further investigations on the impact of the PH domain of FAN on the actin binding capacity in HEK 293 cells revealed that deletion of the PH domain, which abrogates plasma membrane Tal1 association of FAN (Figure 5C) also abolished the interaction of FAN with actin, whereas binding to TNF-RI remained unaffected (Figure 7D). Finally, no actin binding was detected with FAN-PH alone, suggesting that PH modulates FAN actin binding by promoting correct subcellular localization at the plasma membrane. Discussion In contrast to other TNF receptor adaptor proteins such as TRADD, FADD, RIP or TRAF2, FAN does not bind to, or interact with death domains, and its precise function in specific cellular responses to TNF remained largely unclear. Here, we show that FAN is crucial for the formation of filopodia and actin cytoskeleton reorganization induced by TNF. A major finding of our study demonstrates specific binding of the FAN PH domain to PtdIns(4,5)P, which directs FAN to the plasma membrane. Additionally, FAN binds to the actin cytoskeleton machinery upon TNF treatment, which is modulated by PH action. FAN-PH mutants with a non-functional PtdIns(4,5)P binding site were unable to mediate TNF-induced filopodia formation. Furthermore, disruption of the intramolecular interaction between the PH and BEACH domains abrogated the actin modulatory function of FAN without affecting membrane localization. Thus, the molecular mode of PH domain action in FAN signaling is defined by two independent functional features, that is, targeting of FAN to the plasma membrane and correct interdomain interaction between BEACH and PH regulating FAN function. Several proteins involved in modulating the actin cytoskeleton via regulation of Rho GTPases 1-Methyladenosine contain PH or PH-like domains with lipid binding properties (Bellanger (2001) have previously reported that 1-Methyladenosine exogenous sphingomyelinase and synthetic C2-ceramide induce membrane association of Rho GTPases like Cdc42 and phosphorylation of paxillin and focal adhesion kinase. Thus, 1-Methyladenosine it will be interesting to test a possible functional link between FAN and nSMase3 in TNF-induced activation of Cdc42 and subsequent formation of filopodia. This idea is supported by the observation that mutations of PH or BEACH that disrupt the interaction between the PH and BEACH domains not only block TNF-induced filopodia formation but also destroy FAN-mediated activation of nSMase (Jogl at 1-Methyladenosine 37C for 3 h. Soluble protein was bound to nickelCagarose affinity resin (Novagen/Merck Biosciences, Darmstadt, Germany) and eluted as described by the manufacturer in a buffer containing 20 mM TrisCHCl (pH 7.5), 500 mM NaCl, 1 mM PMSF and 100 mM imidazole. For production of FAN-GST, FAN cloned into pGEX-4T3 vector was expressed in at 25C for 5 h and purified.