Coiled-coil interaction of N-terminal 36 residues of cyclase-associated protein with adenylyl cyclase is sufficient for its function in Saccharomyces cerevisiae ras pathway

Disease association of cyclase-associated protein (CAP): Lessons from gene-targeted mice and human genetic studies

Cyclase-associated protein (CAP) is an actin binding protein that has been initially described as partner of the adenylyl cyclase in yeast. In all vertebrates and some invertebrate species, two orthologs, named CAP1 and CAP2, have been described. CAP1 and CAP2 are characterized by a similar multidomain structure, but different expression patterns. Several molecular studies clarified the biological function of the different CAP domains, and they shed light onto the mechanisms underlying CAP-dependent regulation of actin treadmilling. However, CAPs are crucial elements not only for the regulation of actin dynamics, but also for signal transduction pathways. During recent years, human genetic studies and the analysis of gene-targeted mice provided important novel insights into the physiological roles of CAPs and their involvement in the pathogenesis of several diseases. In the present review, we summarize and discuss recent progress in our understanding of CAPs' physiological functions, focusing on heart, skeletal muscle and central nervous system as well as their involvement in the mechanisms controlling metabolism. Remarkably, loss of CAPs or impairment of CAPs-dependent pathways can contribute to the pathogenesis of different diseases. Overall, these studies unraveled CAPs complexity highlighting their capability to orchestrate structural and signaling pathways in the cells.

CAP1 binds and activates adenylyl cyclase in mammalian cells

CAP1 (Cyclase-Associated Protein 1) is highly conserved in evolution. Originally identified in yeast as a bifunctional protein involved in Ras-adenylyl cyclase and F-actin dynamics regulation, the adenylyl cyclase component seems to be lost in mammalian cells. Prompted by our recent identification of the Ras-like small GTPase Rap1 as a GTP-independent but geranylgeranyl-specific partner for CAP1, we hypothesized that CAP1-Rap1, similar to CAP-Ras-cyclase in yeast, might play a critical role in cAMP dynamics in mammalian cells. In this study, we report that CAP1 binds and activates mammalian adenylyl cyclase in vitro, modulates cAMP in live cells in a Rap1-dependent manner, and affects cAMP-dependent proliferation. Utilizing deletion and mutagenesis approaches, we mapped the interaction of CAP1-cyclase with CAP's N-terminal domain involving critical leucine residues in the conserved RLE motifs and adenylyl cyclase's conserved catalytic loops (e.g., C1a and/or C2a). When combined with a FRET-based cAMP sensor, CAP1 overexpression-knockdown strategies, and the use of constitutively active and negative regulators of Rap1, our studies highlight a critical role for CAP1-Rap1 in adenylyl cyclase regulation in live cells. Similarly, we show that CAP1 modulation significantly affected cAMP-mediated proliferation in an RLE motif-dependent manner. The combined study indicates that CAP1-cyclase-Rap1 represents a regulatory unit in cAMP dynamics and biology. Since Rap1 is an established downstream effector of cAMP, we advance the hypothesis that CAP1-cyclase-Rap1 represents a positive feedback loop that might be involved in cAMP microdomain establishment and localized signaling.

CAPt'n of Actin Dynamics: Recent Advances in the Molecular, Developmental and Physiological Functions of Cyclase-Associated Protein (CAP)

Cyclase-associated protein (CAP) has been discovered three decades ago in budding yeast as a protein that associates with the cyclic adenosine monophosphate (cAMP)-producing adenylyl cyclase and that suppresses a hyperactive RAS2 variant. Since that time, CAP has been identified in all eukaryotic species examined and it became evident that the activity in RAS-cAMP signaling is restricted to a limited number of species. Instead, its actin binding activity is conserved among eukaryotes and actin cytoskeleton regulation emerged as its primary function. However, for many years, the molecular functions as well as the developmental and physiological relevance of CAP remained unknown. In the present article, we will compile important recent progress on its molecular functions that identified CAP as a novel key regulator of actin dynamics, i.e., the spatiotemporally controlled assembly and disassembly of actin filaments (F-actin). These studies unraveled a cooperation with ADF/Cofilin and Twinfilin in F-actin disassembly, a nucleotide exchange activity on globular actin monomers (G-actin) that is required for F-actin assembly and an inhibitory function towards the F-actin assembly factor INF2. Moreover, by focusing on selected model organisms, we will review current literature on its developmental and physiological functions, and we will present studies implicating CAP in human pathologies. Together, this review article summarizes and discusses recent achievements in understanding the molecular, developmental and physiological functions of CAP, which led this protein emerge as a novel CAPt'n of actin dynamics.

The Cytoskeletal Protein Cyclase-Associated Protein 1 (CAP1) in Breast Cancer: Context-Dependent Roles in Both the Invasiveness and Proliferation of Cancer Cells and Underlying Cell Signals

As a conserved actin-regulating protein, CAP (adenylyl Cyclase-Associated Protein) functions to facilitate the rearrangement of the actin cytoskeleton. The ubiquitously expressed isoform CAP1 drives mammalian cell migration, and accordingly, most studies on the involvement of CAP1 in human cancers have largely been based on the rationale that up-regulated CAP1 will stimulate cancer cell migration and invasiveness. While findings from some studies reported so far support this case, lines of evidence largely from our recent studies point to a more complex and profound role for CAP1 in the invasiveness of cancer cells, where the potential activation of cell adhesion signaling is believed to play a key role. Moreover, CAP1 was also found to control proliferation in breast cancer cells, through the regulation of ERK (External signal-Regulated Kinase). Alterations in the activities of FAK (Focal Adhesion Kinase) and ERK from CAP1 depletion that are consistent to the opposite adhesion and proliferation phenotypes were detected in the metastatic and non-metastatic breast cancer cells. In this review, we begin with the overview of the literature on CAP, by highlighting the molecular functions of mammalian CAP1 in regulating the actin cytoskeleton and cell adhesion. We will next discuss the role of the FAK/ERK axis, and possibly Rap1, in mediating CAP1 signals to control breast cancer cell adhesion, invasiveness, and proliferation, largely based on our latest findings. Finally, we will discuss the relevance of these novel mechanistic insights to ultimately realizing the translational potential of CAP1 in targeted therapeutics for breast cancer.

Conserved hydrophobic residues in the CARP/β-sheet domain of cyclase-associated protein are involved in actin monomer regulation

Cyclase-associated protein (CAP) is a multidomain protein that promotes actin filament dynamics. The C-terminal region of CAP contains a CAP and X-linked retinitis pigmentosa 2 protein (CARP) domain (or a β-sheet domain), which binds to actin monomer and is essential for enhancing exchange of actin-bound nucleotides. However, how the CARP domain binds to actin is not clearly understood. Here, we report that conserved hydrophobic residues in the CARP domain play important roles in the function of CAP to regulate actin dynamics. Single mutations of three conserved surface-exposed hydrophobic residues in the CARP domain of CAS-2, a Caenorhabditis elegans CAP, significantly reduce its binding to actin monomers and suppress its nucleotide exchange activity on actin. As a result, these mutants are weaker than wild-type to compete with ADF/cofilin to promote recycling of actin monomers for polymerization. A double mutation (V367A/I373A) eliminates these actin-regulatory functions of CAS-2. These hydrophobic residues and previously identified functional residues are scattered on a concave β-sheet of the CARP domain, suggesting that a wide area of the β-sheet is involved in binding to actin. These observations suggest that the CARP domain of CAP binds to actin in a distinct manner from other known actin-binding proteins.

Overexpression of CAP1 and its significance in tumor cell proliferation, migration and invasion in glioma

Adenylate cyclase-associated protein 1 (CAP1), a protein related to the regulation of actin filaments and the Ras/cAMP pathway, is associated with tumor progression. Nevertheless, the expression level and effects of CAP1 in regards to glioma have not been reported. In the present study, we examined the expression of CAP1 in glioma and tumor adjacent normal brain tissues by tissue microarray and immunohistochemistry. Our results showed that CAP1 was overexpressed in glioma tissues in comparison with that noted in the tumor adjacent normal brain tissues and increased staining of CAP1 was found to be correlated with WHO stage. In addition, we discovered that knockdown of CAP1 by specific RNA interference markedly inhibited cell growth and caused downregulation of the proliferation markers, PCNA and cyclin A. We further demonstrated that knockdown of CAP1 inhibited cell metastatic abilities by downregulating N-cadherin and vimentin and upregulating E-cadherin. These findings revealed that CAP1 expression is markedly increased in human glioma and that downregulation of CAP1 in tumors may serve as a treatment for glioma patients.

The role of cyclase-associated protein in regulating actin filament dynamics - more than a monomer-sequestration factor

Dynamic reorganization of the actin cytoskeleton is fundamental to a number of cell biological events. A variety of actin-regulatory proteins modulate polymerization and depolymerization of actin and contribute to actin cytoskeletal reorganization. Cyclase-associated protein (CAP) is a conserved actin-monomer-binding protein that has been studied for over 20 years. Early studies have shown that CAP sequesters actin monomers; recent studies, however, have revealed more active roles of CAP in actin filament dynamics. CAP enhances the recharging of actin monomers with ATP antagonistically to ADF/cofilin, and also promotes the severing of actin filaments in cooperation with ADF/cofilin. Self-oligomerization and binding to other proteins regulate activities and localization of CAP. CAP has crucial roles in cell signaling, development, vesicle trafficking, cell migration and muscle sarcomere assembly. This Commentary discusses the recent advances in our understanding of the functions of CAP and its implications as an important regulator of actin cytoskeletal dynamics, which are involved in various cellular activities.

Upregulated expression of CAP1 is associated with tumor migration and metastasis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers that exhibits high incidences of intrahepatic metastasis and tumor recurrence. Adenylate cyclase-associated protein 1 (CAP1), a protein involved in the regulation of actin filaments, was recently reported to play a role in cell motility and the pathology of pancreatic cancer. In this study, we examined a potential role of CAP1 in HCC progression, and found that CAP1 was overexpressed in HCC specimens compared with adjacent noncancerous liver tissues by Western blot analysis and real-time PCR assay. Further, immunohistochemical analysis in 107 HCC specimens revealed that overexpression of CAP1 was closely correlated only with tumor metastasis, but not with other clinicopathologic parameters. Univariate and multivariate survival analyses showed that CAP1 could be an independent prognostic factor for patients' survival. In addition, immunofluorescent assay demonstrated that CAP1 was colocalized with actin in the leading edge of lamellipodium in HCC cells. Importantly, knocking-down the expression of CAP1 using small interfering RNA (siRNA) targeting CAP1 led to impaired migration of HCC cells. Collectively, our results indicated that upregulated expression of CAP1 might contribute heavily to the metastasis of HCC.

CAP1 was associated with actin and involved in Schwann cell differentiation and motility after sciatic nerve injury

Adenylate cyclase-associated protein 1 (CAP1), a member of cyclase-associated proteins that regulating actin dynamics, was shown to regulate actin filaments, localize to dynamic actin structures and mediate such processes as establishment of cell polarity, motility, morphogenesis, receptor-mediated endocytosis and mRNA location. But little is known about the role of CAP1 during peripheral nervous system injury. Here, we found the spatiotemporal protein expression of CAP1 after sciatic nerve crush. After crush, CAP1 had an increased protein expression level, reached a peak at about day 5 and then returned to the normal level at 4 weeks, similar to Oct-6. Besides, in 5-day injured tissue, using double immunofluorescent staining we found CAP1 had a colocalization with S100 and Oct-6. In vitro, during the process of cAMP-induced Schwann cells differentiation, we observed enhanced expression of CAP1 and P0. Specially, CAP1-specific siRNA-tranfected SCs did not show significant actin structure which form cellure surface tension and protrusion shape after cAMP treatment. And we observed the interaction of CAP1 with actin and that CAP1-specific siRNA-transfected SCs had a decreased motility and migration. Together, all these data indicated that the change of CAP1 protein expression was associated with Schwann cells motility and differentiation after the crush of sciatic nerve.

The genetic architecture of biofilm formation in a clinical isolate of Saccharomyces cerevisiae

Biofilms are microbial communities that form on surfaces. They are the primary form of microbial growth in nature and can have detrimental impacts on human health. Some strains of the budding yeast Saccharomyces cerevisiae form colony biofilms, and there is substantial variation in colony architecture between biofilm-forming strains. To identify the genetic basis of biofilm variation, we developed a novel version of quantitative trait locus mapping, which leverages cryptic variation in a clinical isolate of S. cerevisiae. We mapped 13 loci linked to heterogeneity in biofilm architecture and identified the gene most closely associated with each locus. Of these candidate genes, six are members of the cyclic AMP-protein kinase A pathway, an evolutionarily conserved cell signaling network. Principal among these is CYR1, which encodes the enzyme that catalyzes production of cAMP. Through a combination of gene expression measurements, cell signaling assays, and gene overexpression, we determined the functional effects of allelic variation at CYR1. We found that increased pathway activity resulting from protein coding and expression variation of CYR1 enhances the formation of colony biofilms. Four other candidate genes encode kinases and transcription factors that are targets of this pathway. The protein products of several of these genes together regulate expression of the sixth candidate, FLO11, which encodes a cell adhesion protein. Our results indicate that epistatic interactions between alleles with both positive and negative effects on cyclic AMP-protein kinase A signaling underlie much of the architectural variation we observe in colony biofilms. They are also among the first to demonstrate genetic variation acting at multiple levels of an integrated signaling and regulatory network. Based on these results, we propose a mechanistic model that relates genetic variation to gene network function and phenotypic outcomes.

The Cyclase-associated protein Cap1 is important for proper regulation of infection-related morphogenesis in Magnaporthe oryzae

Surface recognition and penetration are critical steps in the infection cycle of many plant pathogenic fungi. In Magnaporthe oryzae, cAMP signaling is involved in surface recognition and pathogenesis. Deletion of the MAC1 adenylate cyclase gene affected appressorium formation and plant infection. In this study, we used the affinity purification approach to identify proteins that are associated with Mac1 in vivo. One of the Mac1-interacting proteins is the adenylate cyclase-associated protein named Cap1. CAP genes are well-conserved in phytopathogenic fungi but none of them have been functionally characterized. Deletion of CAP1 blocked the effects of a dominant RAS2 allele and resulted in defects in invasive growth and a reduced intracellular cAMP level. The Δcap1 mutant was defective in germ tube growth, appressorium formation, and formation of typical blast lesions. Cap1-GFP had an actin-like localization pattern, localizing to the apical regions in vegetative hyphae, at the periphery of developing appressoria, and in circular structures at the base of mature appressoria. Interestingly, Cap1, similar to LifeAct, did not localize to the apical regions in invasive hyphae, suggesting that the apical actin cytoskeleton differs between vegetative and invasive hyphae. Domain deletion analysis indicated that the proline-rich region P2 but not the actin-binding domain (AB) of Cap1 was responsible for its subcellular localization. Nevertheless, the AB domain of Cap1 must be important for its function because CAP1^ΔAB only partially rescued the Δcap1 mutant. Furthermore, exogenous cAMP induced the formation of appressorium-like structures in non-germinated conidia in CAP1^ΔAB transformants. This novel observation suggested that AB domain deletion may result in overstimulation of appressorium formation by cAMP treatment. Overall, our results indicated that CAP1 is important for the activation of adenylate cyclase, appressorium morphogenesis, and plant infection in M. oryzae. CAP1 may also play a role in feedback inhibition of Ras2 signaling when Pmk1 is activated.

In Magnaporthe oryzae, cAMP signaling is known to play an important role in surface recognition and plant penetration. The Mac1 adenylate cyclase is essential for plant infection. To better understand Mac1 activation mechanisms, in this study we used the affinity purification approach to identify proteins that are associated with Mac1 in vivo. One of the Mac1-interacting protein is the adenylate cyclase associated protein (CAP) encoded by the CAP1 gene. Results from our study indicated that Cap1 is important for Mac1 activation and plant infection in M. oryzae. The Δcap1 mutant was defective in germ tube growth and appressorium formation and failed to cause typical blast lesions. Like LifeAct, Cap1 localized to apical patches in vegetative hyphae but not in invasive hyphae. The P2 proline-rich region was important for Cap1 localization but the actin-binding domain played a role in feedback inhibition of Ras signaling. To our knowledge, functional characterization of CAP genes has not been reported in filamentous fungi. Our results indicate that CAP1 is important for regulating adenylate cyclase activities, appressorium morphogenesis, and plant infection. Further characterization of CAP1 will be important to better understand the interaction between cAMP signaling and the PMK1 pathway in M. oryzae.

CAS-1, a C. elegans cyclase-associated protein, is required for sarcomeric actin assembly in striated muscle

Assembly of contractile apparatuses in striated muscle requires precisely regulated reorganization of the actin cytoskeletal proteins into sarcomeric organization. Regulation of actin filament dynamics is one of the essential processes of myofibril assembly, but the mechanism of actin regulation in striated muscle is not clearly understood. Actin depolymerizing factor (ADF)/cofilin is a key enhancer of actin filament dynamics in striated muscle in both vertebrates and nematodes. Here, we report that CAS-1, a cyclase-associated protein in Caenorhabditis elegans, promotes ADF/cofilin-dependent actin filament turnover in vitro and is required for sarcomeric actin organization in striated muscle. CAS-1 is predominantly expressed in striated muscle from embryos to adults. In vitro, CAS-1 binds to actin monomers and enhances exchange of actin-bound ATP/ADP even in the presence of UNC-60B, a muscle-specific ADF/cofilin that inhibits the nucleotide exchange. As a result, CAS-1 and UNC-60B cooperatively enhance actin filament turnover. The two proteins also cooperate to shorten actin filaments. A cas-1 mutation is homozygous lethal with defects in sarcomeric actin organization. cas-1-mutant embryos and worms have aggregates of actin in muscle cells, and UNC-60B is mislocalized to the aggregates. These results provide genetic and biochemical evidence that cyclase-associated protein is a critical regulator of sarcomeric actin organization in striated muscle.

Ectopic expression of cyclase associated protein CAP restores the streaming and aggregation defects of adenylyl cyclase a deficient Dictyostelium discoideum cells

Background

Cell adhesion, an integral part of D. discoideum development, is important for morphogenesis and regulated gene expression in the multicellular context and is required to trigger cell-differentiation. G-protein linked adenylyl cyclase pathways are crucially involved and a mutant lacking the aggregation specific adenylyl cyclase ACA does not undergo multicellular development.

Results

Here, we have investigated the role of cyclase-associated protein (CAP), an important regulator of cell polarity and F-actin/G-actin ratio in the aca^- mutant. We show that ectopic expression of GFP-CAP improves cell polarization, streaming and aggregation in aca^- cells, but it fails to completely restore development. Our studies indicate a requirement of CAP in the ACA dependent signal transduction for progression of the development of unicellular amoebae into multicellular structures. The reduced expression of the cell adhesion molecule DdCAD1 together with csA is responsible for the defects in aca^- cells to initiate multicellular development. Early development was restored by the expression of GFP-CAP that enhanced the DdCAD1 transcript levels and to a lesser extent the csA mRNA levels.

Conclusions

Collectively, our data shows a novel role of CAP in regulating cell adhesion mechanisms during development that might be envisioned to unravel the functions of mammalian CAP during animal embryogenesis.

Increased expression of endothelial iNOS accounts for hyporesponsiveness of pulmonary artery to vasoconstrictors after paraquat poisoning

Paraquat is a toxic herbicide that induces severe acute lung injury (ALI) and pulmonary hypertension in humans. Although vascular disorders are present and contribute to increased mortality in ALI patients, there is little data available on vascular responsiveness after toxic exposure to paraquat. We aimed to evaluate the vascular response of isolated pulmonary arteries from rats treated with a dose of paraquat that induces ALI. Paraquat treatment did not modify the relaxant response of pulmonary artery to acetylcholine, but greatly reduced phenylephrine-induced contraction. Removal of the endothelium, inhibition of nitric oxide synthase (NOS) with L-NAME or selective inhibition of inducible NOS (iNOS) with L-NIL, restored contraction of vessels from paraquat poisoned rats to the same level as those not exposed to paraquat. The basal production of NO and expression of iNOS were increased in endothelium-intact but not in endothelium-denuded vessels from paraquat-poisoned rats. Expression of endothelial NOS was not modified. Our findings suggest that paraquat poisoning increases endothelial iNOS expression and basal NO production decreasing responsiveness of pulmonary artery to vasoconstrictors. Thus, our results do not support the hypothesis that pulmonary hypertension in paraquat-induced ALI is mediated by a reduction in endothelial NO production or increased contractility of pulmonary artery.

Candida albicans Cyr1, Cap1 and G-actin form a sensor/effector apparatus for activating cAMP synthesis in hyphal growth

A key virulence trait of Candida albicans is its ability to undergo the yeast-to-hyphal growth transition in response to environmental signals. This transition critically requires a rapid activation of the adenylyl cyclase Cyr1 to generate a cAMP spike. However, the identity of the signal sensors and mechanisms of signal processing and integration remain largely unclear. Recent evidence suggests that some sensors are embedded in Cyr1 itself. To test this hypothesis, we asked whether purified Cyr1 can respond to hyphal induction. Here, we report that Cyr1 co-purifies with Cap1 and G-actin as a tripartite complex which can increase cAMP synthesis in response to hyphal inducing signals in an actin-dependent manner. Cap1 binds Cyr1 and G-actin through its N- and C-terminus respectively. Deleting the G-actin binding sites or treating the complex with the actin toxin latrunculin A or cytochalasin A inhibits the activation of cAMP synthesis. Strains expressing Cap1 mutants lacking the G-actin binding site are impaired in both cAMP synthesis and hyphal morphogenesis. Thus, our findings reveal an essentially intact sensor/effector apparatus composed of Cyr1, Cap1 and G-actin. Furthermore, G-actin's regulatory role in this apparatus may prove to be the missing link whereby cellular actin status knowingly influences cAMP-mediated cellular processes.

Reconstitution and dissection of the 600-kDa Srv2/CAP complex: roles for oligomerization and cofilin-actin binding in driving actin turnover

Srv2/cyclase-associated protein is expressed in virtually all plant, animal, and fungal organisms and has a conserved role in promoting actin depolymerizing factor/cofilin-mediated actin turnover. This is achieved by the abilities of Srv2 to recycle cofilin from ADP-actin monomers and to promote nucleotide exchange (ATP for ADP) on actin monomers. Despite this important and universal role in facilitating actin turnover, the mechanism underlying Srv2 function has remained elusive. Previous studies have demonstrated a critical functional role for the G-actin-binding C-terminal half of Srv2. Here we describe an equally important role in vivo for the N-terminal half of Srv2 in driving actin turnover. We pinpoint this activity to a conserved patch of surface residues on the N-terminal dimeric helical folded domain of Srv2, and we show that this functional site interacts with cofilin-actin complexes. Furthermore, we show that this site is essential for Srv2 acceleration of cofilin-mediated actin turnover in vitro. A cognate Srv2-binding site is identified on a conserved surface of cofilin, suggesting that this function likely extends to other organisms. In addition, our analyses reveal that higher order oligomerization of Srv2 depends on its N-terminal predicted coiled coil domain and that oligomerization optimizes Srv2 function in vitro and in vivo. Based on these data, we present a revised model for the mechanism by which Srv2 promotes actin turnover, in which coordinated activities of its N- and C-terminal halves catalyze sequential steps in recycling cofilin and actin monomers.

Mitochondrial shuttling of CAP1 promotes actin- and cofilin-dependent apoptosis

Mitochondria play a central role in regulating apoptosis by releasing proapoptotic contents such as cytochrome c, and generating reactive oxygen species (ROS). Early in apoptosis, proteins translocate to mitochondria to promote the release of their contents. Here, we show that the actin- and cofilin-interacting protein CAP1 has a role in apoptosis. When we induced apoptosis, CAP1 rapidly translocated to the mitochondria independently of caspase activation. Translocation was proapoptotic because CAP1-knockdown cells were resistant to apoptosis inducers. Overexpression of wild-type CAP1 did not stimulate apoptosis on its own, but stimulated cofilin-induced apoptosis. Apoptosis induction required a mitochondrial-targeting domain, localized in the N-terminus and also the actin-binding domain in the C-terminus. Taken together, these studies suggest that CAP1 provides a direct link from the actin cytoskeleton to the mitochondria by functioning as an actin shuttle.

Up-regulation of multiple proteins and biological processes during maxillary expansion in rats

Background

Maxillary expansion (ME) is a common practice in orthodontics that aims to increase the constricted maxillary arch width. Relapse often occurs, however, and better treatment strategies are needed. In order to develop a more effective method, this study was designed to further examine the process of tissue remodeling during ME, to identify the changes in expression of several proteins of interest, and to clarify the molecular mechanism responsible for tissue remodeling.

Methods

Male Wistar rats were randomly divided into control and ME groups. The rats were euthanized at various intervals over 11 days, and the dissected palates were prepared for histological examination. The structure of the midpalatal sutures changed little during the first three days. Proteins from samples in the ground midpalatal tissues obtained on the third day were subjected to two-dimensional polyacrylamide gel electrophoresis (2-DE) and matrix assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis. Validation of protein expression was performed by Western blot analyses.

Results

From day 5, chondrocytes in the inner layer of suture cartilage and osteoblasts at the end of the suture cartilage began to proliferate, and the skeletal matrix increased later adjacent to the cartilage in the ME group. Comparative proteomic analysis showed increases in 22 protein spots present in the ME group. The changes in three proteins closely related to osteogenesis (parathyroid hormone, osteoprotegerin and vimentin) were confirmed by Western blotting.

Conclusion

Many proteins are over-expressed during ME, and they may play an important role in the remodeling process.

Mechanism of oligomerisation of cyclase-associated protein from Dictyostelium discoideum in solution

Cyclase-associated protein (CAP) is a highly conserved modular protein implicated in the regulation of actin filament dynamics and a variety of developmental and morphological processes. The protein exists as a high molecular weight complex in cell extracts and purified protein possesses a high tendency to aggregate, a major obstacle for crystallisation. Using a mutagenesis approach, we show that two structural features underlie the mechanism of oligomerisation in Dictyostelium discoideum CAP. Positively charged clusters on the surface of the N-terminal helix-barrel domain are involved in inter-molecular interactions with the N or C-terminal domains. Abolishing these interactions mainly renders dimers due to a domain swap feature in the extreme C-terminal region of the protein that was previously described. Based on earlier studies with yeast CAP, we also generated constructs with mutations in the extreme N-terminal region of Dictyostelium CAP that did not show significantly altered oligomerisation behaviour. Constructs with mutations in the earlier identified protein-protein interaction interface on the N-terminal domain of CAP could not be expressed as soluble protein. Assessment of the soluble proteins indicates that the mutations did not affect their overall fold. Further studies point to the correlation between stability of full-length CAP with its multimerisation behaviour, where oligomer formation leads to a more stable protein.

Structural evidence for variable oligomerization of the N-terminal domain of cyclase-associated protein (CAP)

Cyclase-associated protein (CAP) is a highly conserved and widely distributed protein that links the nutritional response signaling to cytoskeleton remodeling. In yeast, CAP is a component of the adenylyl cyclase complex and helps to activate the Ras-mediated catalytic cycle of the cyclase. While the N-terminal domain of CAP (N-CAP) provides a binding site for adenylyl cyclase, the C-terminal domain (C-CAP) possesses actin binding activity. Our attempts to crystallize full-length recombinant CAP from Dictyostelium discoideum resulted in growth of orthorhombic crystals containing only the N-terminal domain (residues 42-227) due to auto-proteolytic cleavage. The structure was solved by molecular replacement with data at 2.2 A resolution. The present crystal structure allows the characterization of a head-to-tail N-CAP dimer in the asymmetric unit and a crystallographic side-to-side dimer. Comparison with previously published structures of N-CAP reveals variable modes of dimerization of this domain, but the presence of a common interface for the side-to-side dimer.

Glucose signaling in Saccharomyces cerevisiae

Eukaryotic cells possess an exquisitely interwoven and fine-tuned series of signal transduction mechanisms with which to sense and respond to the ubiquitous fermentable carbon source glucose. The budding yeast Saccharomyces cerevisiae has proven to be a fertile model system with which to identify glucose signaling factors, determine the relevant functional and physical interrelationships, and characterize the corresponding metabolic, transcriptomic, and proteomic readouts. The early events in glucose signaling appear to require both extracellular sensing by transmembrane proteins and intracellular sensing by G proteins. Intermediate steps involve cAMP-dependent stimulation of protein kinase A (PKA) as well as one or more redundant PKA-independent pathways. The final steps are mediated by a relatively small collection of transcriptional regulators that collaborate closely to maximize the cellular rates of energy generation and growth. Understanding the nuclear events in this process may necessitate the further elaboration of a new model for eukaryotic gene regulation, called "reverse recruitment." An essential feature of this idea is that fine-structure mapping of nuclear architecture will be required to understand the reception of regulatory signals that emanate from the plasma membrane and cytoplasm. Completion of this task should result in a much improved understanding of eukaryotic growth, differentiation, and carcinogenesis.

Column chromatographic prefractionation leads to the detection of 543 different gene products in human fetal brain

In a previous publication a large series of proteins were identified in fetal human brain by the use of two-dimensional electrophoresis (2-DE) with subsequent matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) and MALDI-tandem time-of-flight (TOF/TOF) analysis. Further identification of many more different spots by traditional 2-DE without additional step such as narrow immobilized ph gradient (IPG) strips or prefractionation seems unlikely and we therefore decided to separate extracted brain proteins by ion-exchange chromatography using a TSK gel DEAE-5PW column followed by 2-DE of individual fractions and analysis by MALDI-TOF/TOF with LIFT technology in fetal brain of the early second trimester. About 1880 protein spots corresponding to 543 different gene products were identified. These proteins included housekeeping, signaling, cytoskeletal, metabolic, antioxidant, and neuron/synaptosomal specific proteins. Among these, 314 gene products (314/543, 57.8%), which have never been detected in traditional 2-DE of human fetal brain, were observed by this method. This updated map of fetal brain proteins may serve as data base and reference map for fetal brain proteins, and the methodology applied may be used as a valuable analytical tool for the basis of protein expressional studies in health and disease.

Adenylyl cyclase-associated protein Aca1 regulates virulence and differentiation of Cryptococcus neoformans via the cyclic AMP-protein kinase A cascade

The evolutionarily conserved cyclic AMP (cAMP) signaling pathway controls cell functions in response to environmental cues in organisms as diverse as yeast and mammals. In the basidiomycetous human pathogenic fungus Cryptococcus neoformans, the cAMP pathway governs virulence and morphological differentiation. Here we identified and characterized adenylyl cyclase-associated protein, Aca1, which functions in parallel with the Galpha subunit Gpa1 to control the adenylyl cyclase (Cac1). Aca1 interacted with the C terminus of Cac1 in the yeast two-hybrid system. By molecular and genetic approaches, Aca1 was shown to play a critical role in mating by regulating cell fusion and filamentous growth in a cAMP-dependent manner. Aca1 also regulates melanin and capsule production via the Cac1-cAMP-protein kinase A pathway. Genetic epistasis studies support models in which Aca1 and Gpa1 are necessary and sufficient components that cooperate to activate adenylyl cyclase. Taken together, these studies further define the cAMP signaling cascade controlling virulence of this ubiquitous human fungal pathogen.

Identification of proteins that interact with two regulators of appressorium development, adenylate cyclase and cAMP-dependent protein kinase A, in the rice blast fungus Magnaporthe grisea

Adenylate cyclase (MAC1) and the catalytic subunit of cAMP-dependent protein kinase A (CPKA) are required for appressorium development and pathogenesis in the rice blast pathogen Magnaporthe grisea. To identify new components in the cAMP signal transduction pathway, we used the yeast two-hybrid system to screen MAC1 and CPKA against an appressorium cDNA library. The cDNA library was constructed by GATEWAY recombinational cloning, enabling transfer of the library to various alternative vectors. The protein phosphatase domain in MAC1, which is unique to fungal adenylate cyclases, interacted with a MAP kinase kinase and a Ser/Thr kinase. Interactions of MAC1 with the kinases may prove to be part of feedback loops between the corresponding signaling pathways. A predicted membrane protein, ACI1, which is highly expressed under conditions that are conducive to appressorium formation, also interacted with MAC1. ACI1 has an extracellular domain containing eight-cysteines, which is also present in other fungal proteins implicated in pathogenesis. The N-terminal half of CPKA, which includes a glutamine-rich sequence unique to a group of fungal sequences, interacted with a putative transcriptional regulator and two different glycosyl hydrolases. Phosphorylation motifs in these sequences suggest that they could be CPKA substrates. The protein interaction assay employed here can now be scaled up to identify interactions between a larger set of proteins in the M. grisea interactome.

The cyclase-associated protein CAP as regulator of cell polarity and cAMP signaling in Dictyostelium

Cyclase-associated protein (CAP) is an evolutionarily conserved regulator of the G-actin/F-actin ratio and, in yeast, is involved in regulating the adenylyl cyclase activity. We show that cell polarization, F-actin organization, and phototaxis are altered in a Dictyostelium CAP knockout mutant. Furthermore, in complementation assays we determined the roles of the individual domains in signaling and regulation of the actin cytoskeleton. We studied in detail the adenylyl cyclase activity and found that the mutant cells have normal levels of the aggregation phase-specific adenylyl cyclase and that receptor-mediated activation is intact. However, cAMP relay that is responsible for the generation of propagating cAMP waves that control the chemotactic aggregation of starving Dictyostelium cells was altered, and the cAMP-induced cGMP production was significantly reduced. The data suggest an interaction of CAP with adenylyl cyclase in Dictyostelium and an influence on signaling pathways directly as well as through its function as a regulatory component of the cytoskeleton.

Structure of the N-terminal domain of the adenylyl cyclase-associated protein (CAP) from Dictyostelium discoideum

Cyclase-associated proteins (CAPs) are widely distributed and highly conserved proteins that regulate actin remodeling in response to cellular signals. The N termini of CAPs play a role in Ras signaling and bind adenylyl cyclase; the C termini bind to G-actin and thereby alter the dynamic rearrangements of the microfilament system. We report here the X-ray structure of the core of the N-terminal domain of the CAP from Dictyostelium discoideum, which comprises residues 51-226, determined by a combination of single isomorphous replacement with anomalous scattering (SIRAS). The overall structure of this fragment is an alpha helix bundle composed of six antiparallel helices. Results from gel filtration and crosslinking experiments for CAP(1-226), CAP(255-464), and the full-length protein, together with the CAP N-terminal domain structure and the recently determined CAP C-terminal domain structure, provide evidence that the functional structure of CAP is multimeric.

Sgt1p contributes to cyclic AMP pathway activity and physically interacts with the adenylyl cyclase Cyr1p/Cdc35p in budding yeast

Sgt1p is a highly conserved eucaryotic protein that is required for both SCF (Skp1p/Cdc53p-Cullin-F-box)-mediated ubiquitination and kinetochore function in yeast. We show here that Sgtlp is also involved in the cyclic AMP (cAMP) pathway in Saccharomyces cerevisiae. SGT1 is an allele-specific suppressor of cdc35-1, a thermosensitive mutation in the leucine-rich repeat domain of the adenylyl cyclase Cyrlp/Cdc35p. We demonstrate that Sgt1p and Cyrlp/Cdc35p physically interact and that the activity of the cAMP pathway is affected in an sgt1 conditional mutant. Sequence analysis suggests that Sgtlp has features of a cochaperone. Thus, Sgt1p is a novel activator of adenylyl cyclase in S. cerevisiae and may function in the assembly or the conformational activation of specific multiprotein complexes.

Cyclase-associated proteins: CAPacity for linking signal transduction and actin polymerization

Many extracellular signals elicit changes in the actin cytoskeleton, which are mediated through an array of signaling proteins and pathways. One family of proteins that plays a role in regulating actin remodeling in response to cellular signals are the cyclase-associated proteins (CAPs). CAPs are highly conserved monomeric actin binding proteins present in a wide range of organisms including yeast, fly, plants, and mammals. The original CAP was isolated as a component of the Saccharomyces cerevisiae adenylyl cyclase complex that serves as an effector of Ras during nutritional signaling. CAPs are multifunctional molecules that contain domains involved in actin binding, adenylyl cyclase association in yeast, SH3 binding, and oligomerization. Genetic studies in yeast have implicated CAPs in vesicle trafficking and endocytosis. CAPs play a developmental role in multicellular organisms, and studies of Drosophila have illuminated the importance of the actin cytoskeleton during eye development and in establishing oocyte polarity. This review will highlight the critical structural and functional domains of CAPs, describe recent studies that have implied important roles for these proteins in linking cell signaling with actin polymerization, and highlight their roles in vesicle trafficking and development.

Critical function of the Ras-associating domain as a primary Ras-binding site for regulation of Saccharomyces cerevisiae adenylyl cyclase

Mammalian candidate effectors of the small GTPase Ras, such as RalGDS, afadin/AF-6, Rin1, and phospholipase Cepsilon, have been shown to share structurally conserved modules termed Ras-associating (RA) domains at their Ras-binding sites. The Ras-binding domains of Raf-1 and phosphoinositide 3-kinase gamma (other Ras effectors) also share a similar tertiary structure with the RA domains. On the other hand, the primary Ras-binding site of Saccharomyces cerevisiae adenylyl cyclase, the best characterized Ras effector, has been mapped by mutational studies to the leucine-rich repeats (LRR) domain (amino acids 674-1300), whose structure apparently bears no resemblance to the RA domains. By a computer algorithm-based search we have unexpectedly found an RA domain in the N-terminal 81 amino acid residues (676) of the LRR domain. The purified RA-domain polypeptide exhibits an ability to bind directly to Ras in a GTP-dependent manner and to competitively inhibit Ras-dependent activation of adenylyl cyclase in vitro, with an affinity comparable with that of the whole LRR domain. The specificity of binding of the RA domain to various Ras effector region mutants is indistinguishable from that of the full-length adenylyl cyclase. The activated RAS2 (RAS2(Val-19))-dependent heat shock sensitivity of yeast cells is suppressed by overexpression of the RA domain polypeptide. Further, mutations of the RA domain abolish its Ras binding activity, and adenylyl cyclase molecules carrying these mutations are rendered unactivatable by Ras in vitro. This RA domain bears highest similarity to the Ras-binding domain of Raf-1 based on comparison of its primary and predicted secondary structures with those of other Ras effectors. These results indicate that the RA domain is a primary Ras-binding site for activation of adenylyl cyclase, implicating RA domains as universal modules for interaction of effectors with Ras, conserved from yeast to mammals.

Association of yeast adenylyl cyclase with cyclase-associated protein CAP forms a second Ras-binding site which mediates its Ras-dependent activation

Posttranslational modification, in particular farnesylation, of Ras is crucial for activation of Saccharomyces cerevisiae adenylyl cyclase (CYR1). Based on the previous observation that association of CYR1 with cyclase-associated protein (CAP) is essential for its activation by posttranslationally modified Ras, we postulated that the associated CAP might contribute to the formation of a Ras-binding site of CYR1, which mediates CYR1 activation, other than the primary Ras-binding site, the leucine-rich repeat domain. Here, we observed a posttranslational modification-dependent association of Ras with a complex between CAP and CYR1 C-terminal region. When CAP mutants defective in Ras signaling but retaining the CYR1-binding activity were isolated by screening of a pool of randomly mutagenized CAP, CYR1 complexed with two of the obtained three mutants failed to be activated efficiently by modified Ras and exhibited a severely impaired ability to bind Ras, providing a genetic evidence for the importance of the physical association with Ras at the second Ras-binding site. On the other hand, CYR1, complexed with the other CAP mutant, failed to be activated by Ras but exhibited a greatly enhanced binding to Ras. Conversely, a Ras mutant E31K, which exhibits a greatly enhanced binding to the CYR1-CAP complex, failed to activate CYR1 efficiently. Thus, the strength of interaction at the second Ras-binding site appears to be a critical determinant of CYR1 regulation by Ras: too-weak and too-strong interactions are both detrimental to CYR1 activation. These results, taken together with those obtained with mammalian Raf, suggest the importance of the second Ras-binding site in effector regulation.

Assessing the role of the ASP56/CAP homologue of Dictyostelium discoideum and the requirements for subcellular localization

The CAP (cyclase-associated protein) homologue of Dictyostelium discoideum is a phosphatidylinositol 4,5-bisphosphate (PIP(2)) regulated G-actin sequestering protein which is present in the cytosol and shows enrichment at plasma membrane regions. It is composed of two domains separated by a proline rich stretch. The sequestering activity has been localized to the C-terminal domain of the protein, whereas the presence of the N-terminal domain seems to be required for PIP(2)-regulation of the sequestering activity. Here we have constructed GFP-fusions of N- and C-domain and found that the N-terminal domain showed CAP-specific enrichment at the anterior and posterior ends of cells like endogenous CAP irrespective of the presence of the proline rich region. Mutant cells expressing strongly reduced levels of CAP were generated by homologous recombination. They had an altered cell morphology with very heterogeneous cell sizes and exhibited a cytokinesis defect. Growth on bacteria was normal both in suspension and on agar plates as was phagocytosis of yeast and bacteria. In suspension in axenic medium mutant cells grew more slowly and did not reach saturation densities observed for wild-type cells. This was paralleled by a reduction in fluid phase endocytosis. Development was delayed by several hours under all conditions assayed, furthermore, motile behaviour was affected.

A cytoskeletal localizing domain in the cyclase-associated protein, CAP/Srv2p, regulates access to a distant SH3-binding site

In the yeast, Saccharomyces cerevisiae, adenylyl cyclase consists of a 200-kDa catalytic subunit (CYR1) and a 70-kDa subunit (CAP/SRV2). CAP/Srv2p assists the small G protein Ras to activate adenylyl cyclase. CAP also regulates the cytoskeleton through an actin sequestering activity and is directed to cortical actin patches by a proline-rich SH3-binding site (P2). In this report we analyze the role of the actin cytoskeleton in Ras/cAMP signaling. Two alleles of CAP, L16P(Srv2) and R19T (SupC), first isolated in genetic screens for mutants that attenuate cAMP levels, reduced adenylyl cyclase binding, and cortical actin patch localization. A third mutation, L27F, also failed to localize but showed no loss of either cAMP signaling or adenylyl cyclase binding. However, all three N-terminal mutations reduced CAP-CAP multimer formation and SH3 domain binding, although the SH3-binding site is about 350 amino acids away. Finally, disruption of the actin cytoskeleton with latrunculin-A did not affect the cAMP phenotypes of the hyperactive Ras2(Val19) allele. These data identify a novel region of CAP that controls access to the SH3-binding site and demonstrate that cytoskeletal localization of CAP or an intact cytoskeleton per se is not necessary for cAMP signaling.