Cardiac defects and altered ryanodine receptor function in mice lacking FKBP12

Left ventricular noncompaction: A rarity or something else

<zakljucak> Nedovoljno formiran miokard je atipicna forma kardiomiopatije koju treba poznavati i na koju treba misliti pri rutinskim ehokardiografskim pregledima. Novija istrazivanja ukazuju da LVNC ima vecu prevalenciju zahvaljujuci poboljsanju imaging tehnika. Kako su kriterijumi za dijagnozu LVNC prvenstveno ehokardiografski, potrebno je upoznati lekare koji se bave ultrazvucnim pregledima srca sa osnovnim karkteristikama ovog oboljenja, kako bi ga u buducnosti lakse prepoznali. Nedovoljno formiran miokard je udruzen sa drugim nesrcanim oboljenjima, kao sto su neuromuskularna oboljenja. Predlaze se skrining bolesnika, narocito u porodicama sa neuromuskularnim oboljenjima da bi se pronasli bolesnici sa LVNC, kao i skrining bolesnika sa LVNC kako bi se otkrila neuromuskularna oboljenja. Kod familijarnog javljanja bolesti utvrdjena je genetska osnova nasledjivanja. Zbog pretpostavke da postoji dug preklinicki period, potrebno je da se otkriju bolesnici u asimptomatskoj ili oligosimptomatskoj fazi, kako bi se pratili i pravilno tretirali. Iako postoje kontroverze koje se odnose na etiologiju, patogenezu, dijagnosticke kriterijume i prognozu, vecina istrazivaca izrazava stav da i ovu kardiomiopatiju SZO treba da svrsta u poseban entitet.

Familial occurrence of isolated non-compaction cardiomyopathy

BACKGROUND AND AIMS

Isolated left ventricular non-compaction cardiomyopathy (LVNC) may have an autosomal dominant or X-linked recessive inheritance. We focus on the familial occurrence of LVNC after misdiagnosing this disorder in symptomatic patients in two families. After identification of the index patient we studied the families more intensively in order to unmask affected family members.

METHODS AND RESULTS

LVNC was defined as an end-systolic non-compacted subendocardial layer of the left ventricular wall of at least twice the thickness of the subepicardial compacted layer (2D echocardiogram and MRI). This was studied in 13 patients in 2 families (A and B). LVNC was found in 3 out of 11 patients in family A. The grandmother was asymptomatic. Her daughter suffered from recurrent syncope and heart failure. Her daughter received a cardiac transplant because of progressive heart failure at the age of 14years. In family B, LVNC was found in 2 patients, a father and his son and presumed in a brother and a sister of the father who died suddenly at the age of 17 and 21years, respectively.

CONCLUSIONS

In all symptomatic patients, proven LVNC was previously misdiagnosed as hypertrophic or dilated cardiomyopathy. Misdiagnosis may lead to insufficient treatment and will misdirect targeted molecular genetic analysis. LVNC was identified in seven patients in two families. Family screening may unmask affected family members for primary prevention including anti-coagulation and ICD-therapy.

Isolated ventricular non-compaction: clinical study and genetic review

Isolated non-compaction of the ventricular myocardium (INVM), sometimes referred to as 'spongy myocardium', is a congenital and exceedingly rare cardiomyopathy. Isolated ventricular non-compaction occurs in the absence of other structural heart diseases and, hypothetically, it is due to the arrest of myocardial morphogenesis. Isolated non-compaction of the ventricular myocardium may manifest itself from infancy to young adulthood with a high mortality rate. Both sexes are affected. In our study, we present a case of INVM (left and right ventricles) in a 3-year-old girl, diagnosed by two-dimensional echocardiography. The anomaly presented as a restrictive cardiomyopathy. The girl was admitted to our hospital with heart failure, when she was 10 months old. She was treated with dopamine, digoxin, furosemide, spironolactone, and acenocoumarol and her condition improved. Presently, the girl remains asymptomatic and for 3 years of follow-up, her development has been almost normal. We here describe the genetic background of this disorder (based on a literature review).

Identification and comparative analysis of sixteen fungal peptidyl-prolyl cis/trans isomerase repertoires

BACKGROUND

The peptidyl-prolyl cis/trans isomerase (PPIase) class of proteins is present in all known eukaryotes, prokaryotes, and archaea, and it is comprised of three member families that share the ability to catalyze the cis/trans isomerisation of a prolyl bond. Some fungi have been used as model systems to investigate the role of PPIases within the cell, however how representative these repertoires are of other fungi or humans has not been fully investigated.

RESULTS

PPIase numbers within these fungal repertoires appears associated with genome size and orthology between repertoires was found to be low. Phylogenetic analysis showed the single-domain FKBPs to evolve prior to the multi-domain FKBPs, whereas the multi-domain cyclophilins appear to evolve throughout cyclophilin evolution. A comparison of their known functions has identified, besides a common role within protein folding, multiple roles for the cyclophilins within pre-mRNA splicing and cellular signalling, and within transcription and cell cycle regulation for the parvulins. However, no such commonality was found with the FKBPs. Twelve of the 17 human cyclophilins and both human parvulins, but only one of the 13 human FKBPs, identified orthologues within these fungi. hPar14 orthologues were restricted to the Pezizomycotina fungi, and R. oryzae is unique in the known fungi in possessing an hCyp33 orthologue and a TPR-containing FKBP. The repertoires of Cryptococcus neoformans, Aspergillus fumigatus, and Aspergillus nidulans were found to exhibit the highest orthology to the human repertoire, and Saccharomyces cerevisiae one of the lowest.

CONCLUSION

Given this data, we would hypothesize that: (i) the evolution of the fungal PPIases is driven, at least in part, by the size of the proteome, (ii) evolutionary pressures differ both between the different PPIase families and the different fungi, and (iii) whilst the cyclophilins and parvulins have evolved to perform conserved functions, the FKBPs have evolved to perform more variable roles. Also, the repertoire of Cryptococcus neoformans may represent a better model fungal system within which to study the functions of the PPIases as its genome size and genetic tractability are equal to those of Saccharomyces cerevisiae, whilst its repertoires exhibits greater orthology to that of humans. However, further experimental investigations are required to confirm this.

Reversed Pulmonary Artery Flow in Isolated Noncompaction of the Ventricular Myocardium

OBJECTIVE

To investigate the morphology and genetics of a fetus at 22 weeks. This fetus demonstrated progressive fetal hydrops and cardiomegaly with retrograde flow in the pulmonary artery and progressive myocardial deterioration and heart failure.

METHODS

Postmortem examination, light and electron microscopy of the myocardium, karyotyping, fetal DNA analysis, screening for mutations in the G4.5 gene, alpha-dystrobrevin gene, FKBP 12 gene, Desmin, Syntrophin and Cypher/ZASP genes, which have been described as being associated with noncompaction ventricular myocardium, using single-strand DNA conformation polymorphism analysis and DNA sequencing.

RESULTS

The morphological diagnosis was compatible with noncompaction ventricular myocardium or spongyforme myopathy. The karyotype was normal. Mutation analysis in exons and introns of all six genes did not show any known mutation.

CONCLUSION

Noncompaction ventricular myocardium or spongyforme myopathy may be associated with mutations in genes which have previously not been thought to be associated with this phenotype. Alternatively, this disease could be the result of abnormal cardiac hemodynamics.

Roles of cardiac ryanodine receptor in heart failure and sudden cardiac death

Calcium (Ca2+) plays an important role as a messenger in the excitation-contraction coupling process of the myocardium. It is stored in the sarcoplasmic reticulum (SR) and released via a calcium release channel called the ryanodine receptor. Cardiac ryanodine receptor (RyR2) controls Ca2+ release, which is essential for cardiac contractility. There are several molecules which bind and regulate the function of RyR2 including calstabin2, calmodulin, protein kinase A (PKA), phosphatase, sorcin and calsequestrin. Alteration of RyR2 and associated molecules can cause functional and/or structural changes of the heart, leading to heart failure and sudden cardiac death. In this review, the alteration of RyR2 and its regulatory proteins, and its roles in heart failure and sudden cardiac death, are discussed. Evidence of a possible novel therapy targeting RyR2 and its associated regulatory proteins, currently proposed by investigators, is also included in this article.

The C terminus of the immunophilin PASTICCINO1 is required for plant development and for interaction with a NAC-like transcription factor

PASTICCINO1 (PAS1) is a high molecular weight FK506-binding protein (FKBP) involved in the control of cell proliferation and differentiation during plant development. Mutations in the C-terminal region of PAS1 result in severe developmental defects. We show here that the C-terminal domain of PAS1 controls the subcellular distribution of this protein. We also demonstrated in vitro and in vivo, by Forster resonance energy transfer, that this C-terminal region is required for interaction with FAN (FKBP-associated NAC), a new member of the plant-specific family of NAC transcription factors. PAS1 and FAN are translocated into the nucleus upon auxin treatment in plant seedlings. The nuclear translocation of PAS1 is dependent on the presence of the C terminus of the protein. Finally, we showed that FAN is involved in PAS1-regulated processes because FAN overproduction partly complemented the pas1 phenotype. We suggest that PAS1 regulates the function of this NAC-like transcription factor by controlling its targeting to the nucleus upon plant cell division.

Molecular mechanisms controlling the coupled development of myocardium and coronary vasculature

Cardiac failure affects 1.5% of the adult population and is predominantly caused by myocardial dysfunction secondary to coronary vascular insufficiency. Current therapeutic strategies improve prognosis only modestly, as the primary cause -- loss of normally functioning cardiac myocytes -- is not being corrected. Adult cardiac myocytes are unable to divide and regenerate to any significant extent following injury. New cardiac myocytes are, however, created during embryogenesis from progenitor cells and then by cell division from existing cardiac myocytes. This process is intimately linked to the development of coronary vasculature from progenitors originating in the endothelium, the proepicardial organ and neural crest. In this review, we systematically evaluate approx. 90 mouse mutations that impair heart muscle growth during development. These studies provide genetic evidence for interactions between myocytes, endothelium and cells derived from the proepicardial organ and the neural crest that co-ordinate myocardial and coronary vascular development. Conditional knockout and transgenic rescue experiments indicate that Vegfa, Bmpr1a (ALK3), Fgfr1/2, Mapk14 (p38), Hand1, Hand2, Gata4, Zfpm2 (FOG2), Srf and Txnrd2 in cardiac myocytes, Rxra and Wt1 in the proepicardial organ, EfnB2, Tek, Mapk7, Pten, Nf1 and Casp8 in the endothelium, and Bmpr1a and Pax3 in neural crest cells are key molecules controlling myocardial development. Coupling of myocardial and coronary development is mediated by BMP (bone morphogenetic protein), FGF (fibroblast growth factor) and VEGFA (vascular endothelial growth factor A) signalling, and also probably involves hypoxia. Pharmacological targeting of these molecules and pathways could, in principle, be used to recreate the embryonic state and achieve coupled myocardial and coronary vascular regeneration in failing hearts.

Interstitial 1q43-q43 deletion with left ventricular noncompaction myocardium

We describe a newborn infant with del(1)(q) syndrome, presenting with rare congenital cardiomyopathy and left ventricular noncompaction myocardium (LVNC), as well as typical clinical features such as facial dysmorphism and psychomotor retardation. Although conventional chromosome banding at 850 bands per haploid set indicated a karyotype of 46,XX,add(1)(q42.3), FISH analysis confirmed that the deleted portion was limited to within q43, and q44 was preserved. Therefore, the chromosome constitution is 46,XX,del(1)(q43q43), which has not previously been reported in the literature. Screening for the mutations in the candidate genes for LVNC, i.e. G4.5, CSX, Dystrobrevin, FKBP12, and Desmin, produced negative results. Interestingly, the deleted portion includes the locus for the cardiac ryanodine receptor type 2 gene (RyR2), that selectively binds to the FKBP12 homolog, FKBP12.6. The relationship between this rare myocardial abnormality and deletion of q43 is currently unknown and awaits further accumulation of cases with the same chromosomal aberration.

Genetic analysis in patients with left ventricular noncompaction and evidence for genetic heterogeneity

Left ventricular noncompaction (LVNC) is a cardiomyopathy characterized by numerous excessively trabeculations and deep intertrabecular recesses. This study was performed to investigate Japanese LVNC patients for disease-causing mutations in a series of selected candidate genes. DNA was isolated from the peripheral blood of 79 cases including 20 familial cases and 59 sporadic cases. DNA samples were screened for mutations in the genes encoding G4.5 (TAZ), alpha-dystrobrevin (DTNA), alpha1-syntrophin (SNTA1), FK506 Binding protein 1A (FKBP1A or FKPB12: FKBP1A), and LIM Domain Binding protein 3 (Cypher/ZASP: LDB3), using single-strand conformational polymorphism analysis and DNA sequencing. DNA variants were identified in 6 of the 79 cases, including four familial cases and two sporadic cases. A splice acceptor mutation of intron 8 in TAZ (IVS8-1G>C) was identified in one family with isolated LVNC, resulting in deletion of exon 9 from mRNA. In a sporadic case of isolated LVNC and Barth syndrome (BTHS), a 158insC in exon 2 of TAZ resulting in a frame-shift mutation was identified. A 1876G>A substitution changing an aspartic acid to asparagine (D626N) was identified in LDB3 in four members of two families with LVNC. A 163G>A polymorphism was identified in LDB3, which changed a valine to isoleucine (V55I) in one patient with isolated LVNC. In addition, in a family with nonisolated LVNC, a 362C>T mutation was identified in DTNA. LVNC, like other forms of inherited cardiomyopathy, is a genetically heterogeneous disease, associated with variable clinical symptoms and can be inherited as an autosomal or X-linked recessive disorder.

Inhibition of target of rapamycin signaling by rapamycin in the unicellular green alga Chlamydomonas reinhardtii

The macrolide rapamycin specifically binds the 12-kD FK506-binding protein (FKBP12), and this complex potently inhibits the target of rapamycin (TOR) kinase. The identification of TOR in Arabidopsis (Arabidopsis thaliana) revealed that TOR is conserved in photosynthetic eukaryotes. However, research on TOR signaling in plants has been hampered by the natural resistance of plants to rapamycin. Here, we report TOR inactivation by rapamycin treatment in a photosynthetic organism. We identified and characterized TOR and FKBP12 homologs in the unicellular green alga Chlamydomonas reinhardtii. Whereas growth of wild-type Chlamydomonas cells is sensitive to rapamycin, cells lacking FKBP12 are fully resistant to the drug, indicating that this protein mediates rapamycin action to inhibit cell growth. Unlike its plant homolog, Chlamydomonas FKBP12 exhibits high affinity to rapamycin in vivo, which was increased by mutation of conserved residues in the drug-binding pocket. Furthermore, pull-down assays demonstrated that TOR binds FKBP12 in the presence of rapamycin. Finally, rapamycin treatment resulted in a pronounced increase of vacuole size that resembled autophagic-like processes. Thus, our findings suggest that Chlamydomonas cell growth is positively controlled by a conserved TOR kinase and establish this unicellular alga as a useful model system for studying TOR signaling in photosynthetic eukaryotes.

Would modulation of intracellular Ca2+ be antiarrhythmic?

Under several types of conditions, reversal of steps of excitation-contraction coupling (RECC) can give rise to nondriven electrical activity. In this review we explore those conditions for several cardiac cell types (SA, atrial, Purkinje, ventricular cells). We find that abnormal spontaneous Ca2+ release from intracellular Ca2+ stores, aberrant Ca2+ influx from sarcolemmal channels or abnormal Ca2+ surges in nonuniform muscle can be the initiators of the RECC. Often, with such increases in Ca2+, spontaneous Ca2+ waves occur and lead to membrane depolarizations. Because the change in membrane voltage is produced by Ca2+-dependent changes in ion channel function, we also review here what is known about the molecular interaction of Ca2+ and several Ca2+-dependent processes, including the intracellular Ca2+ release channels implicated in the genetic basis of some forms of human arrhythmias. Finally, we review what is known about the effectiveness of several agents in modifying such Ca2+-dependent arrhythmias.

Pathogenic roles of cardiac autoantibodies in dilated cardiomyopathy

Whether autoimmunity could cause dilated cardiomyopathy (DCM) was disputed for more than half a century. Autoantibodies against various cardiac antigens have been found in the sera of patients with DCM but none of these autoantibodies has been shown to have a substantial role in the development of DCM. It was recently reported that the injection of autoantibodies against cardiac troponin I (cTnI) can induce DCM in normal mice. This observation showed that autoantibodies can cause DCM and put an end to the controversy. Clinical trials of immunoglobulin-adsorption therapy for DCM have already started in Germany and the results seem promising. Here, we discuss the recent findings and possibilities of immunoglobulin-adsorption therapy for this deadly disease.

Plant immunophilins: functional versatility beyond protein maturation

Originally identified as the cellular targets of immunosuppressant drugs, the immunophilins encompass two ubiquitous protein families: the FK-506 binding proteins or FKBPs, and the cyclosporin-binding proteins or cyclophilins. Present in organisms ranging from bacteria to animals and plants, these proteins are characterized by their enzymatic activity; the peptidyl-prolyl cis-trans isomerization of polypeptides. Whilst this function is important for protein folding, it has formed the functional basis for more complex interactions between immunophilins and their target proteins. Beginning with a brief historical overview of the immunophilin family, and a representative illustration of the current state of knowledge that has accumulated for these proteins in diverse organisms, a detailed description is presented of the recent advances in the elucidation of the role of this ubiquitous protein family in plant biology. Though still in its infancy, investigation into the function of plant immunophilins has so far yielded interesting results--as a significant component of the chloroplast proteome, the abundance of immunophilins located in the thylakoid lumen suggests that these proteins may play important roles in this relatively uncharacterized subcellular compartment. Moreover, the importance of the complex multidomain immunophilins in functions pertaining to development is underscored by the strong phenotypes displayed by their corresponding mutants.

Non-FK506-binding protein-12 neuroimmunophilin ligands increase neurite elongation and accelerate nerve regeneration

Neurotrophic activity of neuroimmunophilin ligands (FK506 and its nonimmunosuppressant derivatives) has been assumed to be mediated by the FK506-binding protein-12 (FKBP-12). We recently showed that activity is retained in hippocampal neurons from FKBP-12 knockout mice, indicating that binding to FKBP-12 is not necessary. Here we show that three nonimmunosuppressant FK506 derivatives (V-13,450, V-13,629, and V-13,670) that do not bind FKBP-12 (>12.5 mM affinity) are equipotent to FKBP-12 ligands (FK506, V-10,367, and V-13,449) for increasing neurite elongation in SH-SY5Y cells. One non-FKBP-12 ligand (V-13,670) is also shown to accelerate functional recovery and nerve regeneration in the rat sciatic nerve crush model. Surprisingly, it exhibited an unusual dose-response effect upon oral administration, showing a novel bimodal dose-response for behavioral functional recovery and myelination, but not for axonal size, suggesting both Schwann cell and neuronal targets. Orally active non-FKBP-12 neuroimmunophilin ligands may be useful for the treatment of human neurological disorders without any potential side effects resulting from FKBP-12 binding.

Rapamycin stimulates apoptosis of childhood acute lymphoblastic leukemia cells

The phosphatidyl-inositol 3 kinase (PI3k)/Akt pathway has been implicated in childhood acute lymphoblastic leukemia (ALL). Because rapamycin suppresses the oncogenic processes sustained by PI3k/Akt, we investigated whether rapamycin affects blast survival. We found that rapamycin induces apoptosis of blasts in 56% of the bone marrow samples analyzed. Using the PI3k inhibitor wortmannin, we show that the PI3k/Akt pathway is involved in blast survival. Moreover, rapamycin increased doxorubicin-induced apoptosis even in nonresponder samples. Anthracyclines activate nuclear factor kappaB (NF-kappaB), and disruption of this signaling pathway increases the efficacy of apoptogenic stimuli. Rapamycin inhibited doxorubicin-induced NF-kappaB in ALL samples. Using a short interfering (si) RNA approach, we demonstrate that FKBP51, a large immunophilin inhibited by rapamycin, is essential for drug-induced NF-kappaB activation in human leukemia. Furthermore, rapamycin did not increase doxorubicin-induced apoptosis when NF-kappaB was overexpressed. In conclusion, rapamycin targets 2 pathways that are crucial for cell survival and chemoresistance of malignant lymphoblasts--PI3k/Akt through the mammalian target of rapamycin and NF-kappaB through FKBP51--suggesting that the drug could be beneficial in the treatment of childhood ALL.

Negative regulation of TGF-beta signaling in development

The TGF-beta superfamily members have important roles in controlling patterning and tissue formation in both invertebrates and vertebrates. Two types of signal transducers, receptors and Smads, mediate the signaling to regulate expression of their target genes. Despite of the relatively simple signal transduction pathway, many modulators have been found to contribute to a tight regulation of this pathway in a variety of mechanisms. This article reviews the negative regulation of TGF-beta signaling with focus on its roles in vertebrate development.

Paradoxical SR Ca2+ release in guinea-pig cardiac myocytes after beta-adrenergic stimulation revealed by two-photon photolysis of caged Ca2+

In heart muscle the amplification and shaping of Ca(2+) signals governing contraction are orchestrated by recruiting a variable number of Ca(2+) sparks. Sparks reflect Ca(2+) release from the sarcoplasmic reticulum (SR) via Ca(2+) release channels (ryanodine receptors, RyRs). RyRs are activated by Ca(2+) influx via L-type Ca(2+) channels with a specific probability that may depend on regulatory mechanisms (e.g. beta-adrenergic stimulation) or diseased states (e.g. heart failure). Changes of RyR phosphorylation may be critical for both regulation and impaired function in disease. Using UV flash photolysis of caged Ca(2+) and short applications of caffeine in guinea-pig ventricular myocytes, we found that Ca(2+) release signals on the cellular level were largely governed by global SR content. During beta-adrenergic stimulation resting myocytes exhibited smaller SR Ca(2+) release signals when activated by photolysis (62.3% of control), resulting from reduced SR Ca(2+) content under these conditions (58.6% of control). In contrast, local signals triggered with diffraction limited two-photon photolysis displayed the opposite behaviour, exhibiting a larger Ca(2+) release (164% of control) despite reduced global and local SR Ca(2+) content. This apparent paradox implies changes of RyR open probabilities after beta-adrenergic stimulation, enhancing local regenerativity and reliability of Ca(2+) signalling. Thus, our results underscore the importance of phosphorylation of RyRs (or of a related protein), as a regulatory physiological mechanism that may also provide new therapeutic avenues to recover impaired Ca(2+) signalling during cardiac disease.

Regulation of ryanodine receptors by FK506 binding proteins

Ryanodine receptors (RyRs) are the major sarcoplasmic reticulum calcium-release channels required for excitation-contraction coupling in skeletal and cardiac muscle. Mutations in RyRs have been linked to several human diseases. Mutations in the cardiac isoform of RyR2 are associated with catecholaminergic polymorphic ventricular arrhythmias (CPVT), and arrhythmogenic right ventricular dysplasia type 2 (ARVD2), whereas mutations in the skeletal muscle isoform (RyR1) are linked to malignant hyperthermia (MH) and central core disease (CCD). RyRs are modulated by several other proteins, including the FK506 binding proteins (FKBPs), FKBP12 and FKBP12.6. These immunophilins appear to stabilize a closed state of the channel and are important for cooperative interactions among the subunits of RyRs. This review discusses the regulation of RyRs by FKBPs and the possibility that defective modulation of RyR2 by FKBP12.6 could play a role in heart failure, CPVT, and ARVD2. Also discussed are the consequences of FKBP12 depletion to skeletal muscle and the possibility of FKBP12 involvement in certain forms of MH or CCD.

Identification of cardiac malformations in mice lacking Ptdsr using a novel high-throughput magnetic resonance imaging technique

BACKGROUND

Congenital heart defects are the leading non-infectious cause of death in children. Genetic studies in the mouse have been crucial to uncover new genes and signaling pathways associated with heart development and congenital heart disease. The identification of murine models of congenital cardiac malformations in high-throughput mutagenesis screens and in gene-targeted models is hindered by the opacity of the mouse embryo.

RESULTS

We developed and optimized a novel method for high-throughput multi-embryo magnetic resonance imaging (MRI). Using this approach we identified cardiac malformations in phosphatidylserine receptor (Ptdsr) deficient embryos. These included ventricular septal defects, double-outlet right ventricle, and hypoplasia of the pulmonary artery and thymus. These results indicate that Ptdsr plays a key role in cardiac development.

CONCLUSIONS

Our novel multi-embryo MRI technique enables high-throughput identification of murine models for human congenital cardiopulmonary malformations at high spatial resolution. The technique can be easily adapted for mouse mutagenesis screens and, thus provides an important new tool for identifying new mouse models for human congenital heart diseases.

Interaction of FKBP12.6 with the cardiac ryanodine receptor C-terminal domain

The ryanodine receptor-calcium release channel complex (RyR) plays a pivotal role in excitation-contraction coupling in skeletal and cardiac muscle. RyR channel activity is modulated by interaction with FK506-binding protein (FKBP), and disruption of the RyR-FKBP association has been implicated in cardiomyopathy, cardiac hypertrophy, and heart failure. Evidence for an interaction between RyR and FKBP is well documented, both in skeletal muscle (RyR1-FKBP12) and in cardiac muscle (RyR2-FKBP12.6), however definition of the FKBP-binding site remains elusive. Early reports proposed interaction of a short RyR central domain with FKBP12/12.6, however this site has been questioned, and recently an alternative FKBP12.6 interaction site has been identified within the N-terminal half of RyR2. In this study, we report evidence for the human RyR2 C-terminal domain as a novel FKBP12.6-binding site. Using competition binding assays, we find that short C-terminal RyR2 fragments can displace bound FKBP12.6 from the native RyR2, although they are unable to exclusively support interaction with FKBP12.6. However, expression of a large RyR2 C-terminal construct in mammalian cells encompassing the pore-forming transmembrane domains exhibits rapamycin-sensitive binding specifically to FKBP12.6 but not to FKBP12. We also obtained some evidence for involvement of the RyR2 N-terminal, but not the central domain, in FKBP12.6 interaction. Our studies suggest that a novel interaction site for FKBP12.6 may be present at the RyR2 C terminus, proximal to the channel pore, a sterically appropriate location that would enable this protein to play a central role in the modulation of this critical ion channel.

A role for SlyD in the Escherichia coli hydrogenase biosynthetic pathway

The [NiFe] centers at the active sites of the Escherichia coli hydrogenase enzymes are assembled by a team of accessory proteins that includes the products of the hyp genes. To determine whether any other proteins are involved in this process, the sequential peptide affinity system was used. The analysis of the proteins in a complex with HypB revealed the peptidyl-prolyl cis/trans-isomerase SlyD, a metal-binding protein that has not been previously linked to the hydrogenase biosynthetic pathway. The association between HypB and SlyD was confirmed by chemical cross-linking of purified proteins. Deletion of the slyD gene resulted in a marked reduction of the hydrogenase activity in cell extracts prepared from anaerobic cultures, and an in-gel assay was used to demonstrate diminished activities of both hydrogenase 1 and 2. Western analysis revealed a decrease in the final proteolytic processing of the hydrogenase 3 HycE protein, indicating that the metal center was not assembled properly. These deficiencies were all rescued by growth in medium containing excess nickel, but zinc did not have any phenotypic effect. Experiments with radioactive nickel demonstrated that less nickel accumulated in DeltaslyD cells compared with wild type, and overexpression of SlyD from an inducible promoter doubled the level of cellular nickel. These experiments demonstrate that SlyD has a role in the nickel insertion step of the hydrogenase maturation pathway, and the possible functions of SlyD are discussed.

Ryanodine receptor defects in muscle genetic diseases

Ryanodine receptor (RyR), a homotetrameric Ca2+ release channel, is one of the main actors in the generation of Ca2+ signals that trigger muscle contraction. Three genes encode three isoforms of RyRs, which have tissue-restricted distribution. RyR1 and RyR2 are typical of muscle cells, with RyR1 originally considered the skeletal muscle type and RyR2 the cardiac type. However, RyR1 and RyR2 have recently been found in numerous other cell types, including, for instance, peripheral B and T lymphocytes. In contrast, RyR3 is widely distributed among cells. RyR1 and RyR2 are localized in a specialized portion of the sarcoplasmic reticulum (SR), the terminal cisternae, which is the portion of the SR Ca2+ store that releases Ca2+ to control the process of muscle contraction. A specific role for RyR3 has not yet been established: probably, its co-expression with the other RyR isoforms contributes to qualitatively modulate Ca2+-dependent processes in muscle cells and in neurons. Several mutations in the genes encoding RyR1 and RyR2 have been identified in autosomal dominant diseases of skeletal and cardiac muscle, such as malignant hyperthermia (MH), central core disease (CCD), catecholaminergic polymorphic ventricular tachycardia (CPVT), and arrhythmogenic right ventricular dysplasia type 2 (ARVD2). More recently, CCD cases with recessive inheritance have also been described. MH is a pharmacogenetic disease, but the others manifest as congenital myopathies. Even if their clinical phenotypes are well established, particularly in skeletal muscle, the molecular mechanisms that generate the conditions are not clear. A number of studies on cellular models have attempted to elucidate the molecular defects associated with the different mutations, but the problem of understanding how mutations in the same gene generate such an array of diverse pathological traits and diseases of widely different degrees of severity is still open. This review will consider the molecular and cellular effects of RyR mutations, summarizing recent data in the literature on Ca2+ dysregulation, which may lead to a better understanding of the functioning of RyRs.

Genetic models for transforming growth factor beta superfamily signaling in ovarian follicle development

The transforming growth factor beta (TGFbeta) superfamily has wide-ranging and profound effects on many aspects of cellular growth and development. Many TGFbeta-related ligands, receptors, and intracellular signaling proteins are expressed in the ovary and are critical for normal follicle development. Our laboratory and others have analyzed the in vivo function of the TGFbeta superfamily signal transduction pathways by using gene knockout and knockin approaches. Two TGFbeta superfamily ligands, growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), are expressed in developing oocytes. Based on in vivo data using knockout models, GDF9 is critical at both the primary and preovulatory stages of follicle development, and physiologically interacts with BMP15 during the latter stages of folliculogenesis. A knockin model of activin betaB expressed from the activin betaA locus, revealed that activin betaB can act as a hypomorphic protein and rescue some but not all of activin betaAs functions. Questions of functional redundancy of signaling components and multiple receptor utilization by different ligands still need to be addressed for these pathways. Answers will likely come from using existing single null mouse models to generate combinatorial ligand and receptor null mice. These new models may reveal the in vivo genetic interactions of TGFbeta superfamily ligands, receptors, binding proteins, and downstream signaling pathways.

Calcineurin signaling in avian cardiovascular development

Experiments were initiated in avian embryos to determine the embryonic expression of calcineurin protein phosphatase isoforms as well as to identify developmental processes affected by inhibition of calcineurin signal transduction. Chicken calcineurin A alpha (CnAalpha) and calcineurin A beta (CnAbeta) are differentially expressed in the developing cardiovascular system, including primitive heart tube and valve primordia. Inhibition of calcineurin signaling by cyclosporin A (CsA) treatment in ovo resulted in distinct cardiovascular malformations, depending on the timing and localization of treatment. Initial formation of the heart tube was apparently normal in embryos treated with CsA from embryonic day (E)1 to E2, but hallmarks of heart failure were apparent with treatment from E2 to E3. Vascular defects were apparent in whole embryos treated on either day, but local administration of CsA directly to the forming vessels on E2 did not inhibit blood vessel formation. This observation supports an indirect effect of calcineurin inhibition on angiogenic remodeling as a result of compromised heart development. Together these studies are consistent with multiple roles for calcineurin signaling in the developing cardiovascular system.

Altered excitation-contraction coupling with skeletal muscle specific FKBP12 deficiency

The immunophilin FKBP12 binds the skeletal muscle Ca2+ release channel or ryanodine receptor (RyR1), but the functional consequences of this interaction are not known. In this study, we have generated skeletal muscle specific FKBP12-deficient mice to investigate the role of FKBP12 in skeletal muscle. Primary myotubes from these mice show no obvious change in either Ca2+ stores or resting Ca2+ levels but display decreased voltage-gated intracellular Ca2+ release and increased L-type Ca2+ currents. Consistent with the decreased voltage-gated Ca2+ release, maximal tetanic force production is decreased and the force frequency curves are shifted to the right in extensor digitorum longus (EDL) muscles of the mutant mice. In contrast, there is no decrease in maximal tetanic force production in the mutant diaphragm or soleus muscle. The force frequency curve is shifted to the left in the FKBP12-deficient diaphragm muscle compared with controls. No changes in myosin heavy chain (MHC) phenotype are observed in EDL or soleus muscle of the FKBP12-deficient mice, but diaphragm muscle displays an increased ratio of slow to fast MHC isoforms. Also, calcineurin levels are increased in the diaphragm of the mutant mice but not in the soleus or EDL. In summary, FKBP12 deficiency alters both orthograde and retrograde coupling between the L-type Ca2+ channel and RyR1 and the consequences of these changes depend on muscle type and activity. In highly used muscles such as the diaphragm, adaptation to the loss of FKBP12 occurs, possibly due to the increased Ca2+ influx.

Arabidopsis immunophilin-like TWD1 functionally interacts with vacuolar ABC transporters

Previously, the immunophilin-like protein TWD1 from Arabidopsis has been demonstrated to interact with the ABC transporters AtPGP1 and its closest homologue, AtPGP19. Physiological and biochemical investigation of pgp1/pgp19 and of twd1 plants suggested a regulatory role of TWD1 on AtPGP1/AtPGP19 transport activities. To further understand the dramatic pleiotropic phenotype that is caused by loss-of-function mutation of the TWD1 gene, we were interested in other TWD1 interacting proteins. AtMRP1, a multidrug resistance-associated (MRP/ABCC)-like ABC transporter, has been isolated in a yeast two-hybrid screen. We demonstrate molecular interaction between TWD1 and ABC transporters AtMRP1 and its closest homologue, AtMRP2. Unlike AtPGP1, AtMRP1 binds to the C-terminal tetratricopeptide repeat domain of TWD1, which is well known to mediate protein-protein interactions. Domain mapping proved that TWD1 binds to a motif of AtMRP1 that resembles calmodulin-binding motifs; and calmodulin binding to the C-terminus of MRP1 was verified. By membrane fractionation and GFP-tagging, we localized AtMRP1 to the central vacuolar membrane and the TWD1-AtMRP1 complex was verified in vivo by coimmunoprecipitation. We were able to demonstrate that TWD1 binds to isolated vacuoles and has a significant impact on the uptake of metolachlor-GS and estradiol-beta-glucuronide, well-known substrates of vacuolar transporters AtMRP1 and AtMRP2.

Isolated left ventricular noncompaction is rarely caused by mutations in G4.5, alpha-dystrobrevin and FK Binding Protein-12

Isolated left ventricular noncompaction (LVNC) is a form of cardiomyopathy that most commonly presents in infancy with a hypertrophic and dilated left ventricle characterized by deep trabeculations and intertrabecular recesses. Our goal was to determine the frequency of mutations in G4.5, alpha-dystrobrevin, and FK Binding protein-12 in isolated LVNC patients. No mutations were identified in 47 of the 48 patients studied, while a splice site acceptor site mutation of intron 10 of G4.5 was identified in one patient, resulting in the deletion of exon 10 from the mRNA.

Modulation of the Cardiomyocyte Cell Cycle in Genetically Altered Animals

Many forms of cardiovascular disease are associated with cardiomyocyte loss via apoptosis and/or necrosis. Although there is currently debate regarding the level at which adult cardiomyocytes can reenter the cell cycle and proliferate, it is clear that the intrinsic regenerative growth capacity is insufficient to reverse the progression to failure in badly injured hearts. The ability to reactivate cardiomyocyte proliferation in damaged hearts might permit regenerative growth, provided that the nascent cells are able to participate in a functional syncytium with the surviving myocardium. In this review, techniques commonly used to monitor cardiomyocyte cell cycle activity in normal and injured hearts are discussed. In addition, several genetic models are described wherein the expression of fundamental cell cycle regulatory proteins has been altered in cardiomyocytes.

Models of Dilated Cardiomyopathy in Small Animals and Novel Positive Inotropic Therapies

Several randomized clinical trials of vesnarinone and milrinone in patients with heart failure left disappointing results in the 1990s. Thereafter, use of positive inotropic agents has been avoided. Exceptions are the use of digitalis glycosides to treat mild-moderate heart failure and the intravenous administration of catecholamines and phosphodiesterase inhibitors in patients with acute and/or refractory heart failure. It is not, however, exactly known whether chronic enhancement of cardiac contractility indeed has harmful effects, besides increased risk of arrhythmia and mortality. We investigated the potential chronic benefit of positive inotropic modification to treat progressive cardiomyopathy and associated heart failure using a genetic complementation strategy of muscle lim-protein and phospholamban (PLN) double mutagenesis in the mouse and found clear evidence of positive effects. Subsequent somatic modification of PLN function via gene transfer with recombinant adeno-associated virus vectors in small animal models of dilated cardiomyopathy further supported the chronic benefit of enhanced cardiac function achieved in an beta-adrenergic stimulus-independent manner. This study examines current small animal models of dilated cardiomyopathy and recent multiple attempts to use these models as novel gene-based inotropic therapies.

BMP10 is essential for maintaining cardiac growth during murine cardiogenesis

During cardiogenesis, perturbation of a key transition at mid-gestation from cardiac patterning to cardiac growth and chamber maturation often leads to diverse types of congenital heart disease, such as ventricular septal defect (VSD), myocardium noncompaction, and ventricular hypertrabeculation. This transition, which occurs at embryonic day (E) 9.0-9.5 in murine embryos and E24-28 in human embryos, is crucial for the developing heart to maintain normal cardiac growth and function in response to an increasing hemodynamic load. Although, ventricular trabeculation and compaction are key morphogenetic events associated with this transition, the molecular and cellular mechanisms are currently unclear. Initially, cardiac restricted cytokine bone morphogenetic protein 10 (BMP10) was identified as being upregulated in hypertrabeculated hearts from mutant embryos deficient in FK506 binding protein 12 (FKBP12). To determine the biological function of BMP10 during cardiac development, we generated BMP10-deficient mice. Here we describe an essential role of BMP10 in regulating cardiac growth and chamber maturation. BMP10 null mice display ectopic and elevated expression of p57(kip2) and a dramatic reduction in proliferative activity in cardiomyocytes at E9.0-E9.5. BMP10 is also required for maintaining normal expression levels of several key cardiogenic factors (e.g. NKX2.5 and MEF2C) in the developing myocardium at mid-gestation. Furthermore, BMP10-conditioned medium is able to rescue BMP10-deficient hearts in culture. Our data suggest an important pathway that involves a genetic interaction between BMP10, cell cycle regulatory proteins and several major cardiac transcription factors in orchestrating this transition in cardiogenesis at mid-gestation. This may provide an underlying mechanism for understanding the pathogenesis of both structural and functional congenital heart defects.

The immunophilin-interacting protein AtFIP37 from Arabidopsis is essential for plant development and is involved in trichome endoreduplication

The FKBP12 (FK506-binding protein 12 kD) immunophilin interacts with several protein partners in mammals and is a physiological regulator of the cell cycle. In Arabidopsis, only one specific partner of AtFKBP12, namely AtFIP37 (FKBP12 interacting protein 37 kD), has been identified but its function in plant development is not known. We present here the functional analysis of AtFIP37 in Arabidopsis. Knockout mutants of AtFIP37 show an embryo-lethal phenotype that is caused by a strong delay in endosperm development and embryo arrest. AtFIP37 promoter::beta-glucuronidase reporter gene constructs show that the gene is expressed during embryogenesis and throughout plant development, in undifferentiating cells such as meristem or embryonic cells as well as highly differentiating cells such as trichomes. A translational fusion with the enhanced yellow fluorescent protein indicates that AtFIP37 is a nuclear protein localized in multiple subnuclear foci that show a speckled distribution pattern. Overexpression of AtFIP37 in transgenic lines induces the formation of large trichome cells with up to six branches. These large trichomes have a DNA content up to 256C, implying that these cells have undergone extra rounds of endoreduplication. Altogether, these data show that AtFIP37 is critical for life in Arabidopsis and implies a role for AtFIP37 in the regulation of the cell cycle as shown for FKBP12 and TOR (target of rapamycin) in mammals.

Calcineurin inhibitors block dorsal-side signaling that affect late-stage development of the heart, kidney, liver, gut and somitic tissue during Xenopus embryogenesis

Calcineurin, a calcium/calmodulin-dependent serine/threonine protein phosphatase, is a key constituent of signaling pathways involved in antigen-dependent T-cell activation and development of the mammalian heart. In addition, calcineurin constitutes a part of the Wnt/calcium-signaling pathway that regulates early stages of dorsoventral axis formation in Xenopus embryos. Although some of the Wnt family members are involved in organ formation at relatively late stages of Xenopus development, the involvement of calcineurin in the development of those organs remains unclear. In the present study, we demonstrate that calcineurin inhibitors (cyclosporine A, FK506, and FK520), but not non-calcineurin inhibitors (rapamycin and GPI1046) that bind the same intracellular receptor as that for FK506, induce edema and gut coiling disruption and exhibit teratogenesis in the kidney, heart, gut, liver, and somitic tissue during Xenopus development. The same effects were observed by injecting the calcineurin inhibitors into the dorsal side, but not ventral side, of blastomeres at the 4-cell stage, although the inhibitors did not affect dorsoventral axis formation. These results suggest that calcineurin is involved in dorsal-side signaling that leads to the formation of the heart, kidney, liver, gut and somitic tissue during Xenopus embryogenesis.

Immunophilins and parvulins. Superfamily of peptidyl prolyl isomerases in Arabidopsis

Immunophilins are defined as receptors for immunosuppressive drugs including cyclosporin A, FK506, and rapamycin. The cyclosporin A receptors are referred to as cyclophilins (CYPs) and FK506- and rapamycin-binding proteins are abbreviated as FKBPs. These two groups of proteins (collectively called immunophilins) share little sequence homology, but both have peptidyl prolyl cis/trans isomerase (PPIase) activity that is involved in protein folding processes. Studies have identified immunophilins in all organisms examined including bacteria, fungi, animals, and plants. Nevertheless, the physiological function of immunophilins is poorly understood in any organism. In this study, we have surveyed the genes encoding immunophilins in Arabidopsis genome. A total of 52 genes have been found to encode putative immunophilins, among which 23 are putative FKBPs and 29 are putative CYPs. This is by far the largest immunophilin family identified in any organism. Both FKBPs and CYPs can be classified into single domain and multiple domain members. The single domain members contain a basic catalytic domain and some of them have signal sequences for targeting to a specific organelle. The multiple domain members contain not only the catalytic domain but also defined modules that are involved in protein-protein interaction or other functions. A striking feature of immunophilins in Arabidopsis is that a large fraction of FKBPs and CYPs are localized in the chloroplast, a possible explanation for why plants have a larger immunophilin family than animals. Parvulins represent another family of PPIases that are unrelated to immunophilins in protein sequences and drug binding properties. Three parvulin genes were found in Arabidopsis genome. The expression of many immunophilin and parvulin genes is ubiquitous except for those encoding chloroplast members that are often detected only in the green tissues. The large number of genes and diversity of structure domains and cellular localization make PPIases a versatile superfamily of proteins that clearly function in many cellular processes in plants.

The 12 kDa FK506-binding protein, FKBP12, modulates the Ca(2+)-flux properties of the type-3 ryanodine receptor

We have characterised the functional regulation of the type-3 ryanodine receptor by the 12 kDa FK506-binding protein. Wild-type type-3 ryanodine receptor and mutant type-3 ryanodine receptor in which the critical valine at position 2322 in the central 12 kDa FK506-binding protein binding site was substituted by aspartate, were stably expressed in human embryonic kidney cells. In contrast to the wild-type receptor, the mutant receptor was strongly impaired in binding to immobilised glutathione S-transferase 12 kDa FK506-binding protein. Caffeine-induced 45Ca(2+)-efflux was markedly increased in cells expressing mutant type-3 ryanodine receptor whereas the maximal-releasable Ca2+ was not affected. Confocal Ca2+ imaging provided clear evidence for a much higher sensitivity of the mutant receptor, which showed global Ca2+ release at about 20-fold lower caffeine concentrations than the wild-type receptor. Spontaneous Ca2+ sparks were observed in both wild-type- and mutant-expressing cells but the number of sparking cells was about 1.5-fold higher in the mutant group, suggesting that the degree of FK506 binding controls the stability of the closed state of ryanodine receptor channels. Furthermore, overexpression of 12 kDa FK506-binding protein decreased the number of sparking cells in the wild-type-expressing cells whereas it did not affect the number of sparking cells in cells expressing the mutant receptor. Concerning spark properties, the amplitude and duration of Ca2+ sparks mediated by mutant channels were significantly reduced in comparison to wild-type channels. This suggests that functional coupling between different mutant type-3 ryanodine receptor channels in a cluster is impaired. Our findings show for the first time that the central binding site for the 12 kDa FK506-binding protein of type-3 ryanodine receptor, encompassing the critical valine proline motif, plays a crucial role in the modulation of the Ca2+ release properties of the type-3 ryanodine receptor channel, including the regulation of both global Ca2+ responses and spontaneous Ca2+ sparks.

Calcineurin and intracellular Ca2+-release channels: regulation or association?

The Ca(2+)- and calmodulin-dependent phosphatase calcineurin was reported to interact with the inositol 1,4,5-trisphosphate receptor (IP(3)R) and the ryanodine receptor (RyR) and to modulate their phosphorylation status and activity. However, controversial data on the molecular mechanisms involved and on the functional relevance of calcineurin for these channel-complexes have been described. Hence, we will focus on the functional importance of calcineurin for IP(3)R and RyR function and on the different mechanisms by which Ca(2+)-dependent dephosphorylation can affect the gating of those intracellular Ca(2+)-release channels. Since many studies made use of immunosuppressive drugs that are inhibiting calcineurin activity, we will also have to take the different side effects of these drugs into account for the proper interpretation of the effects of calcineurin on intracellular Ca(2+)-release channels. In addition, it became recently known that various other phosphatases and kinases can associate with these channels, thereby forming macromolecular complexes. The relevance of these enzymes for IP(3)R and RyR functioning will be reviewed since in some cases they could interfere with the effects ascribed to calcineurin. Finally, we will discuss the downstream effects of calcineurin on the regulation of the expression levels of intracellular Ca(2+)-release channels as well as the relation between IP(3)R- and RyR-mediated Ca(2+) release and calcineurin-dependent gene expression.

Regulation of peptide bond cis/trans isomerization by enzyme catalysis and its implication in physiological processes

In some cases, the slow rotational movement underlying peptide bond cis/trans isomerizations is found to control the biological activity of proteins. Peptide bond cis/trans isomerases as cyclophilins, Fk506-binding proteins, parvulins, and bacterial hsp70 generally assist in the interconversion of the polypeptide substrate cis/trans isomers, and rate acceleration is the dominating mechanism of action in cells. We present evidence disputing the hypothesis that some of the molecular properties of these proteins play an auxiliary role in enzyme function.

Fkbp8: novel isoforms, genomic organization, and characterization of a forebrain promoter in transgenic mice

The immunophilin homolog FKBP8 has been implicated in the regulation of apoptosis. Here we show that the 38-kDa form of FKBP8 (FKBP38) derives from a truncated ORF. The extended FKBP8 ORFs are 46 and 44 kDa in mouse and 45 kDa in human. Although the genomic organization of mouse and human FKBP8 is evolutionarily conserved, additional first exons are encoded by the murine locus. A 4.4-kb murine Fkbp8 gene fragment, containing a GC-rich potential promoter, directed expression of a LacZ reporter gene to forebrain neurons in transgenic mice. Expression of the transgene was observed in CA1 pyramidal neurons of the hippocampus in transgenic mice from three lines. One transgenic founder mouse exhibited widespread forebrain expression of the LacZ transgene that resembles the pattern for the endogenous Fkbp8 gene. Thus promoter/enhancer elements for forebrain expression are located around the first exons of the mouse Fkbp8 gene.

Left ventricular hypertrabeculation/noncompaction

In normal human hearts the left ventricle (LV) has up to 3 prominent trabeculations and is, thus, less trabeculated than the right ventricle. Rarely, more than 3 prominent trabeculations can be found at autopsy and by various imaging techniques in the LV. For this abnormality, different synonyms are used such as spongy myocardium, LV noncompaction, and LV hypertrabeculation (LVHT). In this review it is stated that: (1) LVHT has a higher prevalence than previously thought and the prevalence of LVHT seems to increase with the improvement of cardiac imaging; (2) because LVHT is most frequently diagnosed primarily by echocardiography, echocardiographers should be aware and trained to recognize this abnormality; (3) LVHT is frequently associated with other cardiac and extracardiac, particularly neuromuscular, disorders; (4) there are indications that the cause of LVHT is usually a genetic one and quite heterogeneous; and (5) controversies exist about diagnostic criteria, nomenclature, prognosis, origin, pathogenesis, and the necessity to classify LVHT as a distinct entity and cardiomyopathy by the World Health Organization.

Functional identification of distinct sets of antitumor activities mediated by the FKBP gene family

Assigning biologic function to the many sequenced but still uncharacterized genes remains the greatest obstacle confronting the human genome project. Differential gene expression profiling routinely detects uncharacterized genes aberrantly expressed in conditions such as cancer but cannot determine which genes are functionally involved in such complex phenotypes. Integrating gene expression profiling with specific modulation of gene expression in relevant disease models can identify complex biologic functions controlled by currently uncharacterized genes. Here, we used systemic gene transfer in tumor-bearing mice to identify novel antiinvasive and antimetastatic functions for Fkbp8, and subsequently for Fkbp1a. Fkbp8 is a previously uncharacterized member of the FK-506-binding protein (FKBP) gene family down-regulated in aggressive tumors. Antitumor effects produced by Fkbp1a gene expression are mediated by cellular pathways entirely distinct from those responsible for antitumor effects produced by Fkbp1a binding to its bacterially derived ligand, rapamycin. We then used gene expression profiling to identify syndecan 1 (Sdc1) and matrix metalloproteinase 9 (MMP9) as genes directly regulated by Fkbp1a and Fkbp8. FKBP gene expression coordinately induces the expression of the antiinvasive Sdc1 gene and suppresses the proinvasive MMP9 gene. Conversely, short interfering RNA-mediated suppression of Fkbp1a increases tumor cell invasion and MMP9 levels, while down-regulating Sdc1. Thus, syndecan 1 and MMP9 appear to mediate the antiinvasive and antimetastatic effects produced by FKBP gene expression. These studies show that uncharacterized genes differentially expressed in metastatic cancers can play important functional roles in the metastatic phenotype. Furthermore, identifying gene regulatory networks that function to control tumor progression may permit more accurate modeling of the complex molecular mechanisms of this disease.

Distinct pathways involving the FK506-binding proteins 12 and 12.6 underlie IL-2-versus IL-15-mediated proliferation of T cells

The molecular basis for the different roles of IL-2 and IL-15 in lymphocyte function has been poorly defined. Searching for differences that underlie the distinct T cell responses to the two cytokines, we observed a marked susceptibility of the IL-15-induced but not of the IL-2-induced proliferation to rapamycin despite a decrease of p70S6 kinase (p70S6K) activation by the drug in response to both cytokines. Activated splenic T lymphocytes deficient in the FK506-binding protein (FKBP) 12, a target of rapamycin activity, had reduced proliferation in response to IL-15 but not to IL-2. This decreased proliferation was accompanied by reduced activation of p70S6K and of the extracellular signal-regulated kinases (ERK) after IL-15 treatment. In contrast to FKBP12-/- cells, splenic FKBP12.6-/- T cells exhibited a decreased proliferative response to IL-2 in the presence of rapamycin without affecting p70S6K or ERK activation. Thus, IL-15 induces T cell proliferation mainly via FKBP12-mediated p70S6K activation. In contrast, IL-2 signaling involves multiple pathways that include at least one additional pathway that depends on FKBP12.6.

Autoantibodies against cardiac troponin I are responsible for dilated cardiomyopathy in PD-1-deficient mice

We recently reported that mice deficient in the programmed cell death-1 (PD-1) immunoinhibitory coreceptor develop autoimmune dilated cardiomyopathy (DCM), with production of high-titer autoantibodies against a heart-specific, 30-kDa protein. In this study, we purified the 30-kDa protein from heart extract and identified it as cardiac troponin I (cTnI), encoded by a gene in which mutations can cause familial hypertrophic cardiomyopathy (HCM). Administration of monoclonal antibodies to cTnI induced dilatation and dysfunction of hearts in wild-type mice. Monoclonal antibodies to cTnI stained the surface of cardiomyocytes and augmented the voltage-dependent L-type Ca2+ current of normal cardiomyocytes. These findings suggest that antibodies to cTnI induce heart dysfunction and dilatation by chronic stimulation of Ca2+ influx in cardiomyocytes.

TACE is required for fetal murine cardiac development and modeling

Tumor necrosis factor-alpha converting enzyme (TACE) is a membrane-anchored, Zn-dependent metalloprotease, which belongs to the ADAM (a disintegrin and metalloprotease) family. TACE functions as a membrane sheddase to release the ectodomain portions of many transmembrane proteins, including the precursors of TNFalpha, TGFalpha, several other cytokines, as well as the receptors for TNFalpha, and neuregulin (ErbB4). Mice with TACE(DeltaZn/DeltaZn) null mutation die at birth with phenotypic changes, including failure of eyelid fusion, hair and skin defects, and abnormalities of lung development. Abnormal fetal heart development was not previously described. Herein, we report that TACE(DeltaZn/DeltaZn) null mutant mice by late gestation exhibit markedly enlarged fetal hearts with increased myocardial trabeculation and reduced cell compaction, mimicking the pathological changes of noncompaction of ventricular myocardium. In addition, larger cardiomyocyte cell size and increased cell proliferation were observed in ventricles of TACE(DeltaZn/DeltaZn) knockout mouse hearts. At the molecular level, reduced expression of epidermal growth factor receptor, attenuated protein cleavage of ErbB4, and changes in MAPK activation were also detected in TACE(DeltaZn/DeltaZn) knockout heart tissues. The data suggest that TACE-mediated cell surface protein ectodomain shedding plays an essential and a novel regulatory role during cardiac development and modeling.

Gene expression of FK506-binding proteins 12.6 and 12 during chicken development

FKBPs are cytosolic receptors for the immunosuppressive drug FK506. FKBP12.6 and FKBP12 associate with cardiac and skeletal muscle isoforms of ryanodine receptors and thereby regulate intracellular Ca(2+) release. The amino acid sequences of FKBP12.6 and FKBP12 are highly conserved among mammals and chicken. The expression profiles of FKBP12.6 and FKBP12 genes during chicken development were compared by Northern blot and in situ hybridization analyses. Transcripts of the FKBP12 gene were abundant throughout the embryo at early stages of development but subsequently underwent gradual down-regulation. Expression of the FKBP12.6 gene was mostly restricted to the heart during early embryogenesis and also underwent subsequent down-regulation, becoming localized to the atrium after hatching. Treatment of early embryos with FK506 had no apparent effect on embryogenesis. Retinoic acid induced marked abnormalities in cardiogenesis, but it did not affect FKBP gene expression. These results suggest that, even though FKBP12.6 and FKBP12 genes are expressed in chick embryos, FK506-sensitive functions of the encoded proteins do not appear to contribute to early embryogenesis or cardiogenesis.

Transforming growth factor beta in cardiovascular development and function

Transforming growth factor betas (TGFbetas) are pleiotropic cytokines involved in many biological processes. Genetic engineering and tissue explanation studies have revealed specific non-overlapping roles for TGFbeta ligands and their signaling molecules in development and in normal function of the cardiovascular system in the adult. In the embryo, TGFbetas appear to be involved in epithelial-mesenchymal transformations (EMT) during endocardial cushion formation, and in epicardial epithelial-mesenchymal transformations essential for coronary vasculature, ventricular myocardial development and compaction. In the adult, TGFbetas are involved in cardiac hypertrophy, vascular remodeling and regulation of the renal renin-angiotensin system. The evidence for TGFbeta activities during cardiovascular development and physiologic function will be given and areas which need further investigation will be discussed.

Dysregulated ryanodine receptors mediate cellular toxicity: restoration of normal phenotype by FKBP12.6

Ca2+ homeostasis is a vital cellular control mechanism in which Ca2+ release from intracellular stores plays a central role. Ryanodine receptor (RyR)-mediated Ca2+ release is a key modulator of Ca2+ homeostasis, and the defective regulation of RyR is pathogenic. However, the molecular events underlying RyR-mediated pathology remain undefined. Cells stably expressing recombinant human RyR2 (Chinese hamster ovary cells, CHOhRyR2) had similar resting cytoplasmic Ca2+ levels ([Ca2+]c) to wild-type CHO cells (CHOWT) but exhibited increased cytoplasmic Ca2+ flux associated with decreased cell viability and proliferation. Intracellular Ca2+ flux increased with human RyR2 (hRyR2) expression levels and determined the extent of phenotypic modulation. Co-expression of FKBP12.6, but not FKBP12, or incubation of cells with ryanodine suppressed intracellular Ca2+ flux and restored normal cell viability and proliferation. Restoration of normal phenotype was independent of the status of resting [Ca2+]c or ER Ca2+ load. Heparin inhibition of endogenous inositol trisphosphate receptors (IP3R) had little effect on intracellular Ca2+ handling or viability. However, purinergic stimulation of endogenous IP3R resulted in apoptotic cell death mediated by hRyR2 suggesting functional interaction occurred between IP3R and hRyR2 Ca2+ release channels. These data demonstrate that defective regulation of RyR causes altered cellular phenotype via profound perturbations in intracellular Ca2+ signaling and highlight a key modulatory role of FKBP12.6 in hRyR2 Ca2+ channel function.