Indiana University-Purdue University Indianapolis (IUPUI) / Knowledge of the molecular and cellular mechanisms of ischemic injury is necessary for understanding acute kidney injury and devising optimal treatment regimens. The cortical actin cytoskeleton in the proximal tubule epithelial cells of the kidney nephron, playing an important role in both the establishment and maintenance of cell polarity, is drastically disrupted by the onset of ischemia. We found that in LLC-PK cells (a porcine kidney proximal tubule epithelial cell line), cortactin, an important regulator of actin assembly and organization, translocated from the cell cortex to the cytoplasmic regions upon ischemia/ATP-depletion. Meanwhile both the tyrosine phosphorylation level of cortactin and cortactin’s interaction with either F-actin or the actin nucleator Arp2/3 complex were down-regulated upon ischemia/ATP-depletion or inhibition of Src kinase activity. These results suggest that tyrosine phosphorylation plays an important role in regulating cortactin’s cellular function and localization in the scenario of kidney ischemia. The Rho GTPase signaling pathways is also a critical mediator of the effects of ATP depletion and ischemia on the actin cytoskeleton, but the mechanism by which ATP depletion leads to altered RhoA and Rac1 activity is unknown. We propose that ischemia and ATP depletion result in activation of AMP-activated protein kinase (AMPK) and that this affects Rho GTPase activity and cytoskeletal organization (possibly via TSC1/2 complex and/or mTOR complex). We found that AMPK was rapidly activated (≤5 minutes) by ATP depletion in S3 epithelial cells derived from the proximal tubule in mouse kidney, and there was a corresponding decrease in RhoA and Rac1 activity. During graded ATP-depletion, we found intermediate levels of AMPK activity at the intermediate ATP levels, and that the activity of RhoA and Rac1 activity correlated inversely with the activity of AMPK. Activation of AMPK using two different drugs suppressed RhoA activity, and also led to morphological changes of stress fibers. In addition, the inhibition of AMPK activation partially rescued the disruption of stress fibers caused by ATP-depletion. This evidence supports our hypothesis that the activation of AMPK is upstream of the signaling pathways that eventually lead to RhoA inactivation and cytoskeletal dysregulation during ATP-depletion.

Embargoed until 1 January 2011 / The filamin family act as scaffolding proteins associating with actin filmanents, acting through a highly conserved actin binding domain (ABD). The ABD of the filamins is homologous to that found in other F-actin binding proteins such as dystrophin. Mutations in the filamin A gene cause a wide range of disease symptoms in humans reflecting the diversity of the roles that filamin A has in cell structure and signalling pathways. The diseases fall into two separate phenotypic groups. Periventricular nodular heterotopia (PVNH) generally results from the complete loss of filamin A protein, and affects the central nervous system. The clinically separate otopalatodigital disorders (OPD) spectrum disorders are skeletal disorders and were hypothesised to be gain of function phenotype diseases. At the beginning of this work, there was very little structural data available for the human filamins, and none for the crucial highly conserved actin binding domain. This lack of structural data limited the interpretation of the biochemical and genetic data and constrained our understanding of the disease associated mutations that cluster in this domain. These studies aimed to provide insights into the structure and mechanism of actin binding domains, and thus provide a better understanding of the diseases caused when this domain is mutated. A secondary structural analysis and crystal structures of the wildtype and OPD2 associated mutant ABDs were obtained. The overall fold of the three proteins was equivalent as determined by circular dichroism spectroscopy and x-ray crystallography. The ABD from filamin A E254K showed 3.7 fold increased F-actin affinity, accompanied by a reduced thermostability (of 5.6 °C). Western blotting of OPD2, frontometaphyseal dysplasia (FMD) and PVNH patient fibroblast lysates showed similar levels of filamin A compared to the control cells. In addition the OPD and PVNH patient fibroblasts were able to adhere to fibronectin and migrate with an equivalent rate to control cells. Together these results have allowed correlations to be developed between structure, protein stability, actin affinity, cellular phenotype and the overall clinical phenotype. Showing that, at least in one example, OPD2 may be due to an increased actin affinity providing further evidence for a gain of function mechanism of OPD2.

Embargoed until 1 January 2011 / The filamin family act as scaffolding proteins associating with actin filmanents, acting through a highly conserved actin binding domain (ABD). The ABD of the filamins is homologous to that found in other F-actin binding proteins such as dystrophin. Mutations in the filamin A gene cause a wide range of disease symptoms in humans reflecting the diversity of the roles that filamin A has in cell structure and signalling pathways. The diseases fall into two separate phenotypic groups. Periventricular nodular heterotopia (PVNH) generally results from the complete loss of filamin A protein, and affects the central nervous system. The clinically separate otopalatodigital disorders (OPD) spectrum disorders are skeletal disorders and were hypothesised to be gain of function phenotype diseases. At the beginning of this work, there was very little structural data available for the human filamins, and none for the crucial highly conserved actin binding domain. This lack of structural data limited the interpretation of the biochemical and genetic data and constrained our understanding of the disease associated mutations that cluster in this domain. These studies aimed to provide insights into the structure and mechanism of actin binding domains, and thus provide a better understanding of the diseases caused when this domain is mutated. A secondary structural analysis and crystal structures of the wildtype and OPD2 associated mutant ABDs were obtained. The overall fold of the three proteins was equivalent as determined by circular dichroism spectroscopy and x-ray crystallography. The ABD from filamin A E254K showed 3.7 fold increased F-actin affinity, accompanied by a reduced thermostability (of 5.6 °C). Western blotting of OPD2, frontometaphyseal dysplasia (FMD) and PVNH patient fibroblast lysates showed similar levels of filamin A compared to the control cells. In addition the OPD and PVNH patient fibroblasts were able to adhere to fibronectin and migrate with an equivalent rate to control cells. Together these results have allowed correlations to be developed between structure, protein stability, actin affinity, cellular phenotype and the overall clinical phenotype. Showing that, at least in one example, OPD2 may be due to an increased actin affinity providing further evidence for a gain of function mechanism of OPD2.

Embargoed until 1 January 2011 / The filamin family act as scaffolding proteins associating with actin filmanents, acting through a highly conserved actin binding domain (ABD). The ABD of the filamins is homologous to that found in other F-actin binding proteins such as dystrophin. Mutations in the filamin A gene cause a wide range of disease symptoms in humans reflecting the diversity of the roles that filamin A has in cell structure and signalling pathways. The diseases fall into two separate phenotypic groups. Periventricular nodular heterotopia (PVNH) generally results from the complete loss of filamin A protein, and affects the central nervous system. The clinically separate otopalatodigital disorders (OPD) spectrum disorders are skeletal disorders and were hypothesised to be gain of function phenotype diseases. At the beginning of this work, there was very little structural data available for the human filamins, and none for the crucial highly conserved actin binding domain. This lack of structural data limited the interpretation of the biochemical and genetic data and constrained our understanding of the disease associated mutations that cluster in this domain. These studies aimed to provide insights into the structure and mechanism of actin binding domains, and thus provide a better understanding of the diseases caused when this domain is mutated. A secondary structural analysis and crystal structures of the wildtype and OPD2 associated mutant ABDs were obtained. The overall fold of the three proteins was equivalent as determined by circular dichroism spectroscopy and x-ray crystallography. The ABD from filamin A E254K showed 3.7 fold increased F-actin affinity, accompanied by a reduced thermostability (of 5.6 °C). Western blotting of OPD2, frontometaphyseal dysplasia (FMD) and PVNH patient fibroblast lysates showed similar levels of filamin A compared to the control cells. In addition the OPD and PVNH patient fibroblasts were able to adhere to fibronectin and migrate with an equivalent rate to control cells. Together these results have allowed correlations to be developed between structure, protein stability, actin affinity, cellular phenotype and the overall clinical phenotype. Showing that, at least in one example, OPD2 may be due to an increased actin affinity providing further evidence for a gain of function mechanism of OPD2.

Embargoed until 1 January 2011 / The filamin family act as scaffolding proteins associating with actin filmanents, acting through a highly conserved actin binding domain (ABD). The ABD of the filamins is homologous to that found in other F-actin binding proteins such as dystrophin. Mutations in the filamin A gene cause a wide range of disease symptoms in humans reflecting the diversity of the roles that filamin A has in cell structure and signalling pathways. The diseases fall into two separate phenotypic groups. Periventricular nodular heterotopia (PVNH) generally results from the complete loss of filamin A protein, and affects the central nervous system. The clinically separate otopalatodigital disorders (OPD) spectrum disorders are skeletal disorders and were hypothesised to be gain of function phenotype diseases. At the beginning of this work, there was very little structural data available for the human filamins, and none for the crucial highly conserved actin binding domain. This lack of structural data limited the interpretation of the biochemical and genetic data and constrained our understanding of the disease associated mutations that cluster in this domain. These studies aimed to provide insights into the structure and mechanism of actin binding domains, and thus provide a better understanding of the diseases caused when this domain is mutated. A secondary structural analysis and crystal structures of the wildtype and OPD2 associated mutant ABDs were obtained. The overall fold of the three proteins was equivalent as determined by circular dichroism spectroscopy and x-ray crystallography. The ABD from filamin A E254K showed 3.7 fold increased F-actin affinity, accompanied by a reduced thermostability (of 5.6 °C). Western blotting of OPD2, frontometaphyseal dysplasia (FMD) and PVNH patient fibroblast lysates showed similar levels of filamin A compared to the control cells. In addition the OPD and PVNH patient fibroblasts were able to adhere to fibronectin and migrate with an equivalent rate to control cells. Together these results have allowed correlations to be developed between structure, protein stability, actin affinity, cellular phenotype and the overall clinical phenotype. Showing that, at least in one example, OPD2 may be due to an increased actin affinity providing further evidence for a gain of function mechanism of OPD2.

Embargoed until 1 January 2011 / The filamin family act as scaffolding proteins associating with actin filmanents, acting through a highly conserved actin binding domain (ABD). The ABD of the filamins is homologous to that found in other F-actin binding proteins such as dystrophin. Mutations in the filamin A gene cause a wide range of disease symptoms in humans reflecting the diversity of the roles that filamin A has in cell structure and signalling pathways. The diseases fall into two separate phenotypic groups. Periventricular nodular heterotopia (PVNH) generally results from the complete loss of filamin A protein, and affects the central nervous system. The clinically separate otopalatodigital disorders (OPD) spectrum disorders are skeletal disorders and were hypothesised to be gain of function phenotype diseases. At the beginning of this work, there was very little structural data available for the human filamins, and none for the crucial highly conserved actin binding domain. This lack of structural data limited the interpretation of the biochemical and genetic data and constrained our understanding of the disease associated mutations that cluster in this domain. These studies aimed to provide insights into the structure and mechanism of actin binding domains, and thus provide a better understanding of the diseases caused when this domain is mutated. A secondary structural analysis and crystal structures of the wildtype and OPD2 associated mutant ABDs were obtained. The overall fold of the three proteins was equivalent as determined by circular dichroism spectroscopy and x-ray crystallography. The ABD from filamin A E254K showed 3.7 fold increased F-actin affinity, accompanied by a reduced thermostability (of 5.6 °C). Western blotting of OPD2, frontometaphyseal dysplasia (FMD) and PVNH patient fibroblast lysates showed similar levels of filamin A compared to the control cells. In addition the OPD and PVNH patient fibroblasts were able to adhere to fibronectin and migrate with an equivalent rate to control cells. Together these results have allowed correlations to be developed between structure, protein stability, actin affinity, cellular phenotype and the overall clinical phenotype. Showing that, at least in one example, OPD2 may be due to an increased actin affinity providing further evidence for a gain of function mechanism of OPD2.

Enterohemorrhagic Escherichia coli O157:H7 (EHEC) is an attaching and effacing pathogen that upon attachment to host cells, induce characteristic attaching and effacing lesions and formation of F-actin rich pedestals beneath sites of bacterial attachment. EHEC harbors a Type III secretion system through which it delivers dozens of effectors into the host cell. The two secreted effectors critical for EHEC-mediated actin pedestal formation are the translocated intimin receptor (Tir) and EspFU. EspFU consists of an N-terminal secretion signal and a C-terminus containing six tandem 47-residue proline-rich repeats, each of which can bind and activate the actin nucleation promoting factor N-WASP. Structural and functional analyses described here have identified the mechanism of N-WASP activation by EspFU and the minimal domains and specific residues required for this activity. While EspFU and Tir are the only bacterial effectors required for F-actin pedestal formation, recruitment of EspFU to Tir is mediated by an unidentified putative host factor. To identify the host factor responsible for linking these two effectors, a combination of in vitro and functional assays were used to identify the host factor, IRTKS and the residues required for these interactions were defined. Further, the presence of at least two 47-residue repeats in all characterized clinical isolates of canonical EHEC strains led us to address the minimal requirements for EspFU functional domains to promote recruitment to Tir and N-WASP activation. Here we show that two proline-rich elements of EspFU are required for recruitment of EspFU by IRTKS to sites of bacterial attachment. Furthermore, once artificially clustered at the membrane, a single N-WASP binding element of EspFU can induce actin pedestal formation.

Crucial to a cell’s ability to migrate is the organization of its plasma membrane and associated proteins in a polarized manner to interact with and respond to its surrounding environment. Cells interact with the extracellular matrix (ECM) through specialized contact sites, including podosomes and invadopodia. Tumor cells use F-actin-rich invadopodia to degrade ECM and invade tissues; related structures, termed podosomes, are sites of dynamic ECM interaction and degradation. We show here that supervillin (SV), a peripheral membrane protein that binds F-actin and myosin II,reorganizes the actin cytoskeleton and potentiates invadopodial function. Overexpressed SV increases the number of F-actin punctae, which are highly dynamic and co-localize with markers of podosomes and invadopodia. Endogenous SV localizes to the cores of Src-generated podosomes in COS-7 cells and with invadopodia in MDA-MB-231 cells. EGFP-SV overexpression increases the average amount of matrix degradation; RNAi-mediated downregulation of SV decreases degradation. Cortactin, an essential component of both podosomes and invadopodia, binds SV sequences in vitro and contributes to the formation of EGFP-SV induced punctae. Additionally, SV affects cortactin localization,which could provide a mechanism for SV action at invadopodia. The formation of cholesterol-rich membrane rafts is one method of plasma membrane organization. A property of membrane rafts is resistance to extraction with cold Triton X-100 and subsequent flotation to low buoyant densities. The actin cytoskeleton has been implicated in many signaling events localized to membrane rafts, but interactions between actin and raft components are not well characterized. Our laboratory isolated a heavy detergent resistant membrane fraction from neutrophils, called DRM-H, that contains at least 23 plasma membrane proteins. DRM-H is rich in cytoskeletal proteins, including fodrin, actin, myosin II, as well as supervillin. DRM-H also contains proteins implicated in both raft organization and membrane-mediated signaling. DRM-H complexes exhibit a higher buoyant density than do most DRMs (referred to as DRM-L), which are deficient in cytoskeletal proteins. By using similar purification methods, I find that COS-7 cells also contain cytoskeleton-associated DRMs. In addition, when transfected into COS-7 cells, estrogen receptor (ER)α associates with DRM-H, while ERβ is seen in both DRM-L and DRM-H populations, suggesting a role for DRM-H in nongenomic estrogen signaling. Thus, the cytoskeleton-associated DRM-H not limited to hematopoietic cells and could constitute a scaffold for membrane raftcytoskeleton signaling events in many cells. Taken together, our results show that SV is a component of cytoskeleton-associated membrane rafts as well as podosomes and invadopodia, and that SV plays a role in invadopodial function. SV, with its connections to both membrane rafts and the cytoskeleton, is well situated to mediate cortactin localization, activation state, and/or dynamics of matrix metalloproteases at the ventral cell surface for proper matrix degradation through invadopodia. The molecular dissection of invadopodia formation and function may contribute to a greater understanding of in vivo invasion, and thus, tumor cell metastasis.

Salmonella enterica subtype Typhimurium (S. Typhimurium) is one of many non-typhoidal Salmonella enterica strains responsible for over one million cases of salmonellosis in the United States each year. These Salmonella strains are also a leading cause of diarrheal disease in developing countries. Nontyphoidal salmonellosis induces gastrointestinal distress that is characterized histopathologically by an influx of polymorphonuclear leukocytes (PMNs), the non-specific effects of which lead to tissue damage and contribute to diarrhea. Prior studies from our lab have demonstrated that the type III secreted bacterial effector SipA is a key regulator of PMN influx during S. Typhimurium infection and that its activity requires processing by caspase-3. Although we established caspase-3 activity is required for the activation of inflammatory pathways during S. Typhimurium infection, the mechanisms by which caspase-3 is activated remain incompletely understood. Most challenging is the fact that SipA is responsible for activating caspase-3, which begs the question of how SipA can activate an enzyme it requires for its own activity. In the present study, we describe our findings that the eukaryotic tetraspanning membrane protein PERP is required for the S. Typhimuriuminduced influx of PMNs. We further show that S. Typhimurium infection induces PERP accumulation at the apical surface of polarized colonic epithelial cells, and that this accumulation requires SipA. Strikingly, PERP accumulation occurs in the absence of caspase-3 processing of SipA, which is the first time we have shown SipA mediates a cellular event without first requiring caspase-3 processing. Previous work demonstrates that PERP mediates the activation of caspase-3, and we find that PERP is required for Salmonella-induced caspase-3 activation. Our combined data support a model in which SipA triggers caspase-3 activation via its cellular modulation of PERP. Since SipA can set this pathway in motion without being cleaved by caspase-3, we propose that PERP-mediated caspase-3 activation is required for the activation of SipA, and thus is a key step in the inflammatory response to S. Typhimurium infection. Our findings further our understanding of how SipA induces inflammation during S. Typhimurium infection, and also provide additional insight into how type III secreted effectors manipulate host cells.