Spontaneous Fusion Research Articles

Comparison of hybrid clones derived from human breast epithelial cells and three different cancer cell lines regarding in vitro cancer stem/ initiating cell properties

BackgroundSeveral physiological (fertilization, placentation, wound healing) and pathophysiological processes (infection with enveloped viruses, cancer) depend on cell fusion. In cancer it was postulated that the fusion of cancer cells with normal cells such as macrophages or stem cells may not only give rise to hybrid cells exhibiting novel properties, such as an increased metastatic capacity and drug resistance, but possibly also cancer stem/ initiating cell properties. Hence, hybrid clone cells (M13HS, M13MDA435 and M13MDA231) that were derived from spontaneous fusion events of human M13SV1-EGFP-Neo breast epithelial cells and HS578T-Hyg, MDA-MB-435-Hyg and MDA-MB-231-Hyg cancer cells were investigated regarding potential in vitro cancer stem/ initiating cell properties.MethodsCD44/CD24 expression pattern and ALDH1 activity of parental cells and hybrid clones was determined by flow cytometry. A colony formation and mammosphere formation assay was applied to determine the cells’ capability to form colonies and mammospheres. Sox9, Slug and Snail expression levels were determined by Western blot analysis.ResultsFlow cytometry revealed that all hybrid clone cells were CD44+/CD24−/low, but differed markedly among each other regarding ALDH1 activity. Likewise, each hybrid clone possessed a unique colony formation and mammosphere capacity as well as unique Snail, Slug and Sox9 expression patterns. Nonetheless, comparison of hybrid clones revealed that M13HS hybrids exhibited more in vitro cancer stem/ initiating cell properties than M13MDA231 and M13MDA435 hybrids, such as more ALDH1 positive cells or an increased capacity to form colonies and mammospheres.ConclusionThe fate whether cancer stem/ initiating cells may originate from cell fusion events likely depends on the specific characteristics of the parental cells.

Loss of Doc2b does not influence transmission at Purkinje cell to deep nuclei synapses under physiological conditions.

Doc2a and Doc2b are high-affinity calcium-binding proteins that interact with SNARE proteins and phospholipids. Experiments performed on cultured cells indicated that Doc2 proteins promote spontaneous vesicle fusion and asynchronous neurotransmitter release, regulate vesicle priming, mediate augmentation, and regulate transmission during sustained activity. Here, we assess the role of Doc2 proteins in synaptic transmission under physiological conditions at mature synapses made by Purkinje cells onto neurons in the deep cerebellar nuclei (PC to DCN synapses). PCs express Doc2b but not Doc2a. Surprisingly, spontaneous neurotransmitter release, synaptic strength, the time course of evoked release, responses evoked by sustained high-frequency stimulation, and short-term plasticity were normal in Doc2b KO mice. Thus, in stark contrast to numerous functions previously proposed for Doc2, here we find that Doc2b removal does not influence transmission at PC-to-DCN synapses, indicating that conclusions based on studies of Doc2b in cultured cells do not necessarily generalize to mature synapses under physiological conditions.

Genome remodeling upon mesenchymal tumor cell fusion contributes to tumor progression and metastatic spread.

Cell fusion in tumor progression mostly refers to the merging of a cancer cell with a cell that has migration and immune escape capabilities such as macrophages. Here we show that spontaneous hybrids made from the fusion of transformed mesenchymal cells with partners from the same lineage undergo nonrecurrent large-scale genomic rearrangements, leading to the creation of highly aneuploid cells with novel phenotypic traits, including metastatic spreading capabilities. Moreover, in contrast to their parents, hybrids were the only cells able to recapitulate in vivo all features of human pleomorphic sarcomas, a rare and genetically complex mesenchymal tumor. Hybrid tumors not only displayed specific mesenchymal markers, but also combined a complex genetic profile with a highly metastatic behavior, like their human counterparts. Finally, we provide evidence that patient-derived pleomorphic sarcoma cells are inclined to spontaneous cell fusion. The resulting hybrids also gain in aggressiveness, exhibiting superior growth capacity in mouse models. Altogether, these results indicate that cell fusion has the potential to promote cancer progression by increasing growth and/or metastatic capacities, regardless of the nature of the companion cell. Moreover, such events likely occur upon sarcoma development, paving the way for better understanding of the biology, and aggressiveness of these tumors.

Genetic inactivation of mTORC1 or mTORC2 in neurons reveals distinct functions in glutamatergic synaptic transmission.

Although mTOR signaling is known as a broad regulator of cell growth and proliferation, in neurons it regulates synaptic transmission, which is thought to be a major mechanism through which altered mTOR signaling leads to neurological disease. Although previous studies have delineated postsynaptic roles for mTOR, whether it regulates presynaptic function is largely unknown. Moreover, the mTOR kinase operates in two complexes, mTORC1 and mTORC2, suggesting that mTOR's role in synaptic transmission may be complex-specific. To better understand their roles in synaptic transmission, we genetically inactivated mTORC1 or mTORC2 in cultured mouse glutamatergic hippocampal neurons. Inactivation of either complex reduced neuron growth and evoked EPSCs (eEPSCs), however, the effects of mTORC1 on eEPSCs were postsynaptic and the effects of mTORC2 were presynaptic. Despite postsynaptic inhibition of evoked release, mTORC1 inactivation enhanced spontaneous vesicle fusion and replenishment, suggesting that mTORC1 and mTORC2 differentially modulate postsynaptic responsiveness and presynaptic release to optimize glutamatergic synaptic transmission.

Prefused Lysosomes Cluster on Autophagosome Regulated by VAMP8

Lysosome-autophagosome fusion is critical to autophagosome maturation [1]. Although several proteins that regulate their fusion have been identified, the prefusion state and its regulatory mechanism remain unclear. Herein, we show that, upon stimulation, a prefusion architecture involving multiple lysosomes could form clusters around individual autophagosomes and thus facilitated fusion. The soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein on lysosomes—vesicle-associated membrane protein 8 (VAMP8)—played an important role in forming the prefusion state of lysosomal clusters. To hinder spontaneous fusion, several C-terminal residues of VAMP8 were phosphorylated for the partial zippering of the SNARE complex, which caused the accumulation of unfused lysosomes upon autophagosomes. The phosphorylation not only reduces spontaneous fusion for minimizing autophgic flux under normal conditions, but also preassembles multiple lysosomes to increase fusion possibility for fast resuming autophagy upon stimulation. 1. Tian, Z. et al. 2019 Prog. Lipid. Res. 73,:92-100.

Past, present, and future in pediatric spinal surgery.

According the almost 55 years of experience in Pediatric Spinal surgery it was easy for me to describe the evolution during the past of the surgical techniques as well as the indications for spinal deformities done first without any instrumentation (still useful from time to time nowadays), as from the back as on the front, post-operative immobilization achieved thanks to casting. The real instrumentation appeared successively with Harrington, Luque, and simultaneously the introduction of pedicle screw thanks Raymond Roy Camille. It was necessary to wait another 20 years to get the segmental 3D strategy of the CD instrumentation still the basis of modern spinal surgeries techniques whatever using Hooks Screws, Universal clamps or Hybrid constructs. For present & future, Early surgery is still indicated for localized lesion generally secondary to congenital malformations with or without spinal cord decompression. But for extended lesions especially involving the thoracic area cast and brace is still the good choice whatever the etiology with or without pelvic obliquity. When this treatment fails many attempts with various techniques were used with some success for spinal growth without disturbances about the respiratory function. But it was also demonstrated that the number of complications were still high, with in many cases the necessity to perform a final surgical fusion. It is why the development of the bipolar minimal invasive technique appeared, with very promising results, including the fact that a substantial number of patients get a spontaneous fusion, excluding final surgery. For the older or adolescent patients, the evolution toward a race to obtain the maximum correction of the Cobb angle become more and more disputable as is was demonstrated that the most important for the future regarding the spinal function is the 3D dynamic balance of the discs spaces left free below and above the fused area.

Interfacial water at synthetic and natural lipid bilayers probed by vibrational sum-frequency generation spectroscopy

Background: At lipid interfaces, water plays a crucial role in carrying biological processes, so that there is a huge interest in unravelling the behaviour of water close to membranes. At charged bio-interfaces, water dipoles form an organized layer. Probing such an interfacial thin layer buried between macroscopic bulk environments is a real challenge. Vibrational sum frequency generation (SFG) spectroscopy is intrinsically specific to interfaces, and has already proven to be an ideal tool to investigate model membranes and their surrounding water. Objectives: The goal of this work is to measure the vibrational SFG response of interfacial water around different model membranes — from easiest synthetic lipids to more complex natural lipids, — in order to use it as diagnostic signal able to distinguish the lipid bilayer interface by its charge properties. Materials and methods: Lipid bilayers made either of synthetic or natural lipids (Avanti Polar Lipids) were physisorbed on CaF2 prisms (Crystran), by using the method of the spontaneous fusion of lipid vesicles, to form so called solid-supported lipid bilayers (SSLBs). The model membranes were investigated by SFG spectroscopy at the solid/water interface. Results: The SFG response was measured between 3600 cm-1 and 2800 cm-1, where OH stretching vibrations of water molecules show-up. The SFG intensity of the OH peak maximum at 3125 cm-1 was recorded during the adsorption of lipid vesicles on the surface, and provided knowledge of the changes of the charge properties of the interface due to the adsorption of the model membranes. The SFG signal indicated that the organization of water was larger at negatively charged than at positively lipid interfaces, and reached the highest value with natural E. сoli сardiolipin layers. Moreover, when the full composition of natural lipids was unknown, the behaviour of the SFG response enabled establishing the charge characteristics of the corresponding lipid interfaces. Conclusion: The SFG response of water enabled estimating average charge behaviour of synthetic and natural lipid bilayers in pure water, thus paving the way to use the SFG signal of water as new diagnostic tool to identify lipid interfaces.

A comprehensive review of the treatment and management of Charcot spine.

Charcot spine arthropathy (CSA), a result of reduced afferent innervation, is an occurrence of Charcot joint, a progressive, degenerative disorder in vertebral joints, related mostly to spinal cord injury. The repeated microtrauma is a result of a lack of muscle protection and destroys cartilage, ligaments, and disc spaces, leading to vertebrae destruction, joint instability, subluxation, and dislocation. Joint destruction compresses nerve roots, resulting in pain, paresthesia, sensory loss, dysautonomia, and spasticity. CSA presents with back pain, spinal deformity and instability, and audible spine noises during movement. Autonomic dysfunction includes bowel and bladder dysfunction. It is slowly progressive and usually diagnosed at a late stage, usually, on average, 20 years after the first initial insult. Diagnosis is rarely clinical related to the nature of nonspecific symptoms and requires imaging with computed tomography (CT) and magnetic resonance imaging (MRI). Conservative management focuses on the prevention of fractures and the progression of deformities. This includes bed rest, orthoses, and braces. These could be useful in elderly or frail patients who are not candidates for surgical treatment, or in minimally symptomatic patients, such as patients with spontaneous fusion leading to a stable spine. Symptomatic treatment is offered for autonomic dysfunction, such as anticholinergics for bladder control. Most patients require surgical treatment. Spinal fusion is achieved with open, minimally-open (MOA) or minimally-invasive (MIS) approaches. The gold standard is open circumferential fusion; data is lacking to determine the superiority of open or MIS approaches. Patients usually improve after surgery; however, the rarity of the condition makes it difficult to estimate outcomes. This is a review of the latest and seminal literature about the treatment and chronic management of Charcot spine. The review includes the background of the syndrome, clinical presentation, and diagnosis, and compares the different treatment options that are currently available.

Interferon-induced transmembrane proteins inhibit cell fusion mediated by trophoblast syncytins

Type I interferon (IFN) induced by virus infections during pregnancy can cause placental damage, but the mechanisms and identities of IFN-stimulated genes that are involved in this damage remain under investigation. The IFN-induced transmembrane proteins (IFITMs) inhibit virus infections by preventing virus membrane fusion with cells and by inhibiting fusion of infected cells (syncytialization). Fusion of placental trophoblasts via expression of endogenous retroviral fusogens known as syncytins forms the syncytiotrophoblast, a multinucleated cell structure essential for fetal development. We found here that IFN blocks fusion of BeWo human placental trophoblasts. Stably expressed IFITM1, -2, and -3 also blocked fusion of these trophoblasts while making them more resistant to virus infections. Conversely, stable IFITM knockdowns in BeWo trophoblasts increased their spontaneous fusion and allowed fusion in the presence of IFN while also making the cells more susceptible to virus infection. We additionally found that exogenous expression of IFITMs in HEK293T cells blocked fusion with cells expressing syncytin-1 or syncytin-2, confirming the ability of IFITMs to block individual syncytin-mediated fusion. Overall, our data indicate that IFITMs inhibit trophoblast fusion and suggest that there may be a critical balance between these antifusogenic effects and the beneficial antiviral effects of IFITMs in virus infections during pregnancy.

Alternative polyadenylation of Pax3 controls muscle stem cell fate and muscle function.

Adult stem cells are essential for tissue homeostasis. In skeletal muscle, muscle stem cells (MuSCs) reside in a quiescent state, but little is known about the mechanisms that control homeostatic turnover. Here we show that, in mice, the variation in MuSC activation rate among different muscles (for example, limb versus diaphragm muscles) is determined by the levels of the transcription factor Pax3. We further show that Pax3 levels are controlled by alternative polyadenylation of its transcript, which is regulated by the small nucleolar RNA U1. Isoforms of the Pax3 messenger RNA that differ in their 3' untranslated regions are differentially susceptible to regulation by microRNA miR206, which results in varying levels of the Pax3 protein in vivo. These findings highlight a previously unrecognized mechanism of the homeostatic regulation of stem cell fate by multiple RNA species.

Skeletal muscle during homeostasis

Stem Cells Muscle stem cells function in the regeneration of skeletal muscle after injury, but their role in homeostasis is unclear. De Morree et al. show that, in the absence of injury, stem cells in different muscles have different rates of spontaneous activation and fusion, which depend on the level of Pax3 protein (see the Perspective by Xi and Pyle). Regulation of Pax3 protein occurs posttranscriptionally through the small nucleolar RNA U1 and microRNA miR206. This work explains how muscle stem cells are maintained under normal conditions and shows that homeostatic muscle stem cell activation varies in different muscle groups. Science , this issue p. [734][1]; see also p. [684][2] [1]: /lookup/doi/10.1126/science.aax1694 [2]: /lookup/doi/10.1126/science.aaz4859

1719P - Fusion of immortalized myoblasts induces genomic instability that drives tumour development and progression

BackgroundSarcoma are a heterogeneous group of tumor which can be split into two subgroups with distinct genetics. Half of sarcoma presents an important genomic reorganization correlated to tumor aggressiveness. At this stage, the origin of this instability is still unknown. Cell fusion is a physiological mechanism involved in several processes including myoblast differentiation and already described to be involved in aneuploidy generation and genomic instability. We thus hypothesized that cell fusion could participate to sarcoma oncogenesis by generating genomic instability. MethodsWe established cell line of hybrids from spontaneous fusion of immortalized myoblasts. Tumor and metastasis development were evaluated upon grafting and whole genome and transcriptome sequencing with in-vitro mechanistic studies were performed to decipher phenotypes acquired by hybrids upon fusion. ResultsIn vitro hybrid cell lines show a more aggressive phenotype than parental cell lines by increasing proliferation and clonogenic capacities. Only hybrids form tumors upon grafting and may develop also metastasis. Aneuploidy triggered by cell fusion induces genome reorganization and in vivo tumor genome show alterations corresponding to those observed in human rhabdomyosarcoma. Indeed, 85% of hybrid tumors harbor DMD deletions as observed in sarcoma with myogenic origin. The study of this protein reveals that tumors lose the expression of Dp427 isoform which is the one reported as a tumor suppressor. This malignant transformation of hybrids is associated to transcriptomic remodeling toward a decrease of the expression of genes involved in muscle differentiation. ConclusionsTo our knowledge, this is the first model able to reproduce the complex genomic of sarcoma. The detection of those hybrid cells in sarcoma tumor allowed us to push forward they are involved in sarcoma development and progression and their quantification in tumors or in circulating cells could thus establish an early prognostic marker. Finally, specific therapeutic targeting of this hybrids could represent new approach. Legal entity responsible for the studyFrederic Chibon. FundingAssociation pour la Recherche contre le Cancer (ARC) Fondation pour la Recherche Médicale (FRM). DisclosureAll authors have declared no conflicts of interest.

Percutaneous facet joints arthrodesis technology in surgical treatment of degenerative diseases of lumbar spine

Background. Minimally invasive technology of fusion broadly introduced in clinical practice represent one of modern trends in spinal surgery on the other hand those technical solutions lack to provide posterior fusion. As a consequence, patients treated with minimally invasive techniques are vulnerable in terms of pseudarthrosis and implant instability therefore measures focused on those complications’ prevention are still actual.The study objective is to evaluate efficacy and safety of suggested percutaneous facet joints arthrodesis technique as an auxiliary option to interbody fusion.Materials and methods. This is a prospective non-randomized study of 80 patients with degenerative diseases of the lumbar spine who were treated applying minimally invasive transforaminal lumbar interbody fusion, lateral lumbar interbody fusion and anterior lumbar interbody fusion. In 20 cases out of those enrolled interbody fusion was supplemented with percutaneous posterior facet joints arthrodesis. Computed tomography was administered at the period of 6 and 12 months after surgery to assess anterior and posterior fusion. The minimal follow-up period accounted for 12 months.Results. The suggested percutaneous facet joints arthrodesis fifty-fold increased the probability of posterior fusion formation compared to the rate of spontaneous spinal fusion (p <0.0001, logistic regression was applied). In three cases posterior fusion formed prior to interbody fusion providing stability of segment operated on. No adverse events and no complications associated with percutaneous arthrodesis were detected.Conclusion. The suggested percutaneous facet joints arthrodesis is safe and effective minimally invasive technique that facilitates additional posterior spinal fusion formation in a short-term period herewith decreasing symptomatic pseudarthrosis development in patients operated on using minimally invasive spinal fixation and fusion.

Incidence of Fusion Across Total Disc Replacement With Heterotopic Ossification: Are Ball and Socket Disk Replacements Fusing With and Without Radiographic Evidence.

This is a level III retrospective study. The authors aim to review the outcomes and complications of ball and socket total disk replacements (TDRs). TDR is a motion-preserving technique that closely reproduces physiologic kinematics of the cervical spine. However, heterotopic ossification and spontaneous fusion after implantation of the total cervical disk have been reported in several studies to decrease the range of motion postulated by in vitro and in vivo biomechanical studies. The medical records of 117 consecutive patients undergoing cervical TDR over a 5-year period with Mobi-C, Prodisc-C, Prestige LP, and Secure-C implants were followed. Outcomes assessed included Visual Analogue Scale neck and arm and Neck Disability Index scores. The radiographic assessment looked at heterotopic ossification leading to fusion and complication rates. Of the 117 patients that underwent TDR, 56% were male with the group's mean age being 46.2±10.3 years and body mass index of 18.9±13.6 kg/m. The longest follow-up was 5 years with Prodisc-C group, with overall fusion noted in 16% of patients. One patient was also noted to have fusion which was not seen radiographically but noted intraoperatively for adjacent segment disease. There has been no demonstrable radiographic fusion seen in the Prestige LP group, however, the follow-up has only been 12-24 months for this group. In this study, we have demonstrated radiographic fusion anterior to the ball and socket TDR as well as the uncovertebral joint. We postulate that with the use of a mobile core disk there is an increased potential for fusion leading to a nonfunctional disk replacement.

Effects of bacterial endotoxin on regulation of the heart, a sensory-CNS-motor nerve circuit and neuromuscular junctions: Crustacean model

Eatable crustaceans are susceptible to bacterial septicemia from injury or a compromised immune defense, which can possibly have detrimental effects in mammals that consume them. Since many crustaceans (i.e., crabs, lobsters and crayfish) are used for animal food and human consumption, it is of interest to understand the effects potential bacterial infections can have on their health as well as ours, including effects on cardiovascular and neuromuscular activities. The Red Swamp crayfish (Procambarus clarkii) was used as a model crustacean to investigate the effect of direct exposure to isolated endotoxin lipopolysaccharide (LPS) and the associated peptidoglycans from gram-negative bacteria (Serratia marcescens). S. marcescens is a common strain identified to cause septicemia in mammals and is prevalently found in nature. LPS injection into the hemolymph of crayfish revealed acute changes in heart rate and effects on survival. Direct LPS exposure on an in situ sensory-CNS-motor circuit produces a decrease in recruiting of the motor nerve at 500 μg/ml but has no significant effect at 100 μg/ml. At the isolated neuromuscular junction, the direct action of the LPS endotoxin (500 μg/ml) enhances evoked synaptic transmission, while not altering facilitation. Also, the amplitude and the frequency of spontaneous vesicle fusion events was not altered by LPS exposure. However, the resting membrane potential of the muscle transiently hyperpolarizes. These direct actions on tissues appear to be independent of innate immune responses and suggest the LPS targets on these tissues have a role in excitability of cellular function. {242 words}.

Activity-evoked and spontaneous opening of synaptic fusion pores

Synaptic release of neuropeptides packaged in dense-core vesicles (DCVs) regulates synapses, circuits, and behaviors including feeding, sleeping, and pain perception. Here, synaptic DCV fusion pore openings are imaged without interference from cotransmitting small synaptic vesicles (SSVs) with the use of a fluorogen-activating protein (FAP). Activity-evoked kiss and run exocytosis opens synaptic DCV fusion pores away from active zones that readily conduct molecules larger than most native neuropeptides (i.e., molecular weight [MW] up to, at least, 4.5 kDa). Remarkably, these synaptic fusion pores also open spontaneously in the absence of stimulation and extracellular Ca2+ SNARE perturbations demonstrate different mechanisms for activity-evoked and spontaneous fusion pore openings with the latter sharing features of spontaneous small molecule transmitter release by active zone-associated SSVs. Fusion pore opening at resting synapses provides a mechanism for activity-independent peptidergic transmission.

Minocycline impairs TNF-\u03b1-induced cell fusion of M13SV1-Cre cells with MDA-MB-435-pFDR1 cells by suppressing NF-\u03baB transcriptional activity and its induction of target-gene expression of fusion-relevant factors

BackgroundTo date, several studies have confirmed that driving forces of the inflammatory tumour microenvironment trigger spontaneous cancer cell fusion. However, less is known about the underlying factors and mechanisms that facilitate inflammation-induced cell fusion of a cancer cell with a normal cell. Recently, we demonstrated that minocycline, a tetracycline antibiotic, successfully inhibited the TNF-α-induced fusion of MDA-MB-435 cancer cells with M13SV1 breast epithelial cells. Here, we investigated how minocycline interferes with the TNF-α induced signal transduction pathway.MethodsA Cre-LoxP recombination system was used to quantify the fusion of MDA-MB-435-pFDR1 cancer cells and M13SV1-Cre breast epithelial cells. The impact of minocycline on the TNF-α signalling pathway was determined by western blotting. The transcriptional activity of NF-κB was characterised by immunocytochemistry, western blot and ChIP analyses. An NF-κB-luciferase reporter assay was indicative of NF-κB activity.ResultsMinocycline treatment successfully inhibited the TNFR1-TRAF2 interaction in both cell types, while minocycline abrogated the phosphorylation of IκBα and NF-κB-p65 to suppress nuclear NF-κB and its promotor activity only in M13SV1-Cre cells, which attenuated the expression of MMP9 and ICAM1. In MDA-MB-435-pFDR1 cells, minocycline increased the activity of NF-κB, leading to greater nuclear accumulation of NF-κB-p65, thus increasing promoter activity to stimulate the expression of ICAM1. Even though TNF-α also activated all MAPKs (ERK1/2, p38 and JNK), minocycline differentially affected these kinases to either inhibit or stimulate their activation. Moreover, SRC activation was analysed as an upstream activator of MAPKs, but no activation by TNF-α was revealed. The addition of several specific inhibitors that block the activation of SRC, MAPKs, AP-1 and NF-κB confirmed that only NF-κB inhibition was successful in inhibiting the TNF-α-induced cell fusion process.ConclusionMinocycline is a potent inhibitor in the TNF-α-induced cell fusion process by targeting the NF-κB pathway. Thus, minocycline prevented NF-κB activation and nuclear translocation to abolish the target-gene expression of MMP9 and ICAM1 in M13SV1-Cre cells, resulting in reduced cell fusion frequency.

Phosphatidylinositol 4,5-bisphosphate drives Ca2+-independent membrane penetration by the tandem C2 domain proteins synaptotagmin-1 and Doc2β

Exocytosis mediates the release of neurotransmitters and hormones from neurons and neuroendocrine cells. Tandem C2 domain proteins in the synaptotagmin (syt) and double C2 domain (Doc2) families regulate exocytotic membrane fusion via direct interactions with Ca2+ and phospholipid bilayers. Syt1 is a fast-acting, low-affinity Ca2+ sensor that penetrates membranes upon binding Ca2+ to trigger synchronous vesicle fusion. The closely related Doc2β is a slow-acting, high-affinity Ca2+ sensor that triggers spontaneous and asynchronous vesicle fusion, but whether it also penetrates membranes is unknown. Both syt1 and Doc2β bind the dynamically regulated plasma membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2), but it is unclear whether PIP2 serves only as a membrane contact or enables specialized membrane-binding modes by these Ca2+ sensors. Furthermore, it has been shown that PIP2 uncaging can trigger rapid, syt1-dependent exocytosis in the absence of Ca2+ influx, suggesting that current models for the action of these Ca2+ sensors are incomplete. Here, using a series of steady-state and time-resolved fluorescence measurements, we show that Doc2β, like syt1, penetrates membranes in a Ca2+-dependent manner. Unexpectedly, we observed that PIP2 can drive membrane penetration by both syt1 and Doc2β in the absence of Ca2+, providing a plausible mechanism for Ca2+-independent, PIP2-dependent exocytosis. Quantitative measurements of penetration depth revealed that, in the presence of Ca2+, PIP2 drives Doc2β, but not syt1, substantially deeper into the membrane, defining a biophysical regulatory mechanism specific to this high-affinity Ca2+ sensor. Our results provide evidence of a novel role for PIP2 in regulating, and under some circumstances triggering, exocytosis.

Similarities and differences between mesenchymal stem/progenitor cells derived from various human tissues.

BACKGROUNDMesenchymal stromal/stem cells (MSCs) constitute a promising tool in regenerative medicine and can be isolated from different human tissues. However, their biological properties are still not fully characterized. Whereas MSCs from different tissue exhibit many common characteristics, their biological activity and some markers are different and depend on their tissue of origin. Understanding the factors that underlie MSC biology should constitute important points for consideration for researchers interested in clinical MSC application.AIMTo characterize the biological activity of MSCs during longterm culture isolated from: bone marrow (BM-MSCs), adipose tissue (AT-MSCs), skeletal muscles (SM-MSCs), and skin (SK-MSCs).METHODSMSCs were isolated from the tissues, cultured for 10 passages, and assessed for: phenotype with immunofluorescence and flow cytometry, multipotency with differentiation capacity for osteo-, chondro-, and adipogenesis, stemness markers with qPCR for mRNA for Sox2 and Oct4, and genetic stability for p53 and c-Myc; 27 bioactive factors were screened using the multiplex ELISA array, and spontaneous fusion involving a co-culture of SM-MSCs with BM-MSCs or AT-MSCs stained with PKH26 (red) or PKH67 (green) was performed.RESULTSAll MSCs showed the basic MSC phenotype; however, their expression decreased during the follow-up period, as confirmed by fluorescence intensity. The examined MSCs express CD146 marker associated with proangiogenic properties; however their expression decreased in AT-MSCs and SM-MSCs, but was maintained in BM-MSCs. In contrast, in SK-MSCs CD146 expression increased in late passages. All MSCs, except BM-MSCs, expressed PW1, a marker associated with differentiation capacity and apoptosis. BM-MSCs and AT-MSCs expressed stemness markers Sox2 and Oct4 in long-term culture. All MSCs showed a stable p53 and c-Myc expression. BM-MSCs and AT-MSCs maintained their differentiation capacity during the follow-up period. In contrast, SK-MSCs and SM-MSCs had a limited ability to differentiate into adipocytes. BM-MSCs and AT-MSCs revealed similarities in phenotype maintenance, capacity for multilineage differentiation, and secretion of bioactive factors. Because AT-MSCs fused with SM-MSCs as effectively as BM-MSCs, AT-MSCs may constitute an alternative source for BM-MSCs.CONCLUSIONLong-term culture affects the biological activity of MSCs obtained from various tissues. The source of MSCs and number of passages are important considerations in regenerative medicine.

Cell Fusion in Malignancy: A Cause or Consequence? A Provocateur or Cure?

Cell fusion has been observed in malignancy, and cancer cells have been found especially apt to fuse with other cells. Investigation of human and experimental malignancies suggests spontaneous fusion of normal cells can induce manifold genetic changes and manifestations of malignant transformation. Fusion of transformed cells with other cells can promote the progression of cancer to more malignant forms. However, observations in various fields suggest cell fusion also potentially contributes to natural defenses against cancer. Thus, cell fusion potentially corrects genetic and/or phenotypic changes underlying malignant transformation. Cell fusion also might help nonmalignant cells in tumors thwart tumor growth. Perhaps most importantly, cell fusion may generate genetic changes that lead to the expression of neoantigens, provide the mass of neoantigen expression needed to elicit immunity, and promote the function of antigen-presenting cells in a way that favors protective immunity as a defense against malignancy. To the extent that cell fusion promotes cellular, tissue, and/or systemic resistance to malignancy, the propensity of tumor cells to fuse with other cells might constitute a natural defense against malignancy.