The protein kinase Akt/PKB regulates both prelamin A degradation and Lmna gene expression

Nuclear lamin A/C phosphorylation by loss of Androgen Receptor is a global determinant of cancer-associated fibroblast activation

Alterations of nuclear structure and function, and associated impact on gene transcription, are a hallmark of cancer cells. Little is known of these alterations in Cancer-Associated Fibroblasts (CAFs), a key component of the tumor stroma. Here we show that loss of androgen receptor (AR), which triggers early steps of CAF activation in human dermal fibroblasts (HDFs), leads to nuclear membrane alterations and increased micronuclei formation, which are unlinked from induction of cellular senescence. Similar alterations occur in fully established CAFs, which are overcome by restored AR function. AR associates with nuclear lamin A/C and loss of AR results in a substantially increased lamin A/C nucleoplasmic redistribution. Mechanistically, AR functions as a bridge between lamin A/C with the protein phosphatase PPP1. In parallel with a decreased lamin-PPP1 association, AR loss results in a marked increase of lamin A/C phosphorylation at Ser 301, which is also a feature of CAFs. Phosphorylated lamin A/C at Ser 301 binds to the transcription promoter regulatory region of several CAF effector genes, which are upregulated due to the loss of AR. More directly, expression of a lamin A/C Ser301 phosphomimetic mutant alone is sufficient to convert normal fibroblasts into tumor-promoting CAFs of the myofibroblast subtype, without an impact on senescence. These findings highlight the pivotal role of the AR-lamin A/C-PPP1 axis and lamin A/C phosphorylation at Ser 301 in driving CAF activation.

Overview of cellular homeostasis-associated nuclear envelope lamins and associated input signals

With the discovery of the role of the nuclear envelope protein lamin in human genetic diseases, further diverse roles of lamins have been elucidated. The roles of lamins have been addressed in cellular homeostasis including gene regulation, cell cycle, cellular senescence, adipogenesis, bone remodeling as well as modulation of cancer biology. Features of laminopathies line with oxidative stress-associated cellular senescence, differentiation, and longevity and share with downstream of aging-oxidative stress. Thus, in this review, we highlighted various roles of lamin as key molecule of nuclear maintenance, specially lamin-A/C, and mutated LMNA gene clearly reveal aging-related genetic phenotypes, such as enhanced differentiation, adipogenesis, and osteoporosis. The modulatory roles of lamin-A/C in stem cell differentiation, skin, cardiac regulation, and oncology have also been elucidated. In addition to recent advances in laminopathies, we highlighted for the first kinase-dependent nuclear lamin biology and recently developed modulatory mechanisms or effector signals of lamin regulation. Advanced knowledge of the lamin-A/C proteins as diverse signaling modulators might be biological key to unlocking the complex signaling of aging-related human diseases and homeostasis in cellular process.

Plasticity of cancer invasion and energy metabolism

Energy deprivation is a frequent adverse event in tumors that is caused by mutations, malperfusion, hypoxia, and nutrition deficit. The resulting bioenergetic stress leads to signaling and metabolic adaptation responses in tumor cells, secures survival, and adjusts migration activity. The kinetic responses of cancer cells to energy deficit were recently identified, including a switch of invasive cancer cells to energy-conservative amoeboid migration and an enhanced capability for distant metastasis. We review the energy programs employed by different cancer invasion modes including collective, mesenchymal, and amoeboid migration, as well as their interconversion in response to energy deprivation, and we discuss the consequences for metastatic escape. Understanding the energy requirements of amoeboid and other dissemination strategies offers rationales for improving therapeutic targeting of metastatic cancer progression.

Role of C-Terminal Phosphorylation of Lamin A in DNA Damage and Cellular Senescence

The nuclear matrix protein lamin A is a multifunctional protein with roles in DNA replication and repair, gene activation, transcriptional regulation, and maintenance of higher-order chromatin structure. Phosphorylation is the main determinant of lamin A mobility in the nucleus and nuclear membrane dissolution during mitosis. However, little is known about the regulation of lamin A phosphorylation during interphase. Interestingly, C-terminal lamin A mutations trigger cellular senescence. Recently, we showed that the C-terminal region of lamin A interacts with casein kinase II (CK2). In the present study, we have expanded on our previous research to further investigate lamin A phosphorylation and elucidate the mechanisms underlying the effect of C-terminal mutations on cellular senescence. Our results indicate that glycogen synthase kinase 3β (GSK3β) and CK2 jointly mediate the phosphorylation of lamin A at C-terminal Ser628 and Ser636 residues. Furthermore, a loss of phosphorylation at either of these two sites affects the nuclear distribution of lamin A, leading to an impaired DNA damage response as well as cellular senescence. Thus, phosphorylation at C-terminal sites in lamin A appears to be important for maintaining genomic stability and preventing cellular senescence. These findings provide insight into how loss of the C-terminal region of lamin A may induce premature aging. Furthermore, enhancement of GSK3β and CK2 activity may represent a possible therapeutic approach for the treatment of aging-related diseases.

Serum Mass Spectrometry Proteomics and Protein Set Identification in Response to FOLFOX-4 in Drug-Resistant Ovarian Carcinoma

Ovarian cancer is a highly lethal gynecological malignancy. Drug resistance rapidly occurs, and different therapeutic approaches are needed. So far, no biomarkers have been discovered to predict early response to therapies in the case of multi-treated ovarian cancer patients. The aim of our investigation was to identify a protein panel and the molecular pathways involved in chemotherapy response through a combination of studying proteomics and network enrichment analysis by considering a subset of samples from a clinical setting. Differential mass spectrometry studies were performed on 14 serum samples from patients with heavily pretreated platinum-resistant ovarian cancer who received the FOLFOX-4 regimen as a salvage therapy. The serum was analyzed at baseline time (T0) before FOLFOX-4 treatment, and before the second cycle of treatment (T1), with the aim of understanding if it was possible, after a first treatment cycle, to detect significant proteome changes that could be associated with patients responses to therapy. A total of 291 shared expressed proteins was identified and 12 proteins were finally selected between patients who attained partial response or no-response to chemotherapy when both response to therapy and time dependence (T0, T1) were considered in the statistical analysis. The protein panel included APOL1, GSN, GFI1, LCATL, MNA, LYVE1, ROR1, SHBG, SOD3, TEC, VPS18, and ZNF573. Using a bioinformatics network enrichment approach and metanalysis study, relationships between serum and cellular proteins were identified. An analysis of protein networks was conducted and identified at least three biological processes with functional and therapeutic significance in ovarian cancer, including lipoproteins metabolic process, structural component modulation in relation to cellular apoptosis and autophagy, and cellular oxidative stress response. Five proteins were almost independent from the network (LYVE1, ROR1, TEC, GFI1, and ZNF573). All proteins were associated with response to drug-resistant ovarian cancer resistant and were mechanistically connected to the pathways associated with cancer arrest. These results can be the basis for extending a biomarker discovery process to a clinical trial, as an early predictive tool of chemo-response to FOLFOX-4 of heavily treated ovarian cancer patients and for supporting the oncologist to continue or to interrupt the therapy.

Low lamin A levels enhance confined cell migration and metastatic capacity in breast cancer

Aberrations in nuclear size and shape are commonly used to identify cancerous tissue. However, it remains unclear whether the disturbed nuclear structure directly contributes to the cancer pathology or is merely a consequence of other events occurring during tumorigenesis. Here, we show that highly invasive and proliferative breast cancer cells frequently exhibit Akt-driven lower expression of the nuclear envelope proteins lamin A/C, leading to increased nuclear deformability that permits enhanced cell migration through confined environments that mimic interstitial spaces encountered during metastasis. Importantly, increasing lamin A/C expression in highly invasive breast cancer cells reflected gene expression changes characteristic of human breast tumors with higher LMNA expression, and specifically affected pathways related to cell-ECM interactions, cell metabolism, and PI3K/Akt signaling. Further supporting an important role of lamins in breast cancer metastasis, analysis of lamin levels in human breast tumors revealed a significant association between lower lamin A levels, Akt signaling, and decreased disease-free survival. These findings suggest that downregulation of lamin A/C in breast cancer cells may influence both cellular physical properties and biochemical signaling to promote metastatic progression.

The Nuclear Envelope as a Regulator of Immune Cell Function

The traditional view of the nuclear envelope (NE) was that it represented a relatively inert physical barrier within the cell, whose main purpose was to separate the nucleoplasm from the cytoplasm. However, recent research suggests that this is far from the case, with new and important cellular functions being attributed to this organelle. In this review we describe research suggesting an important contribution of the NE and its constituents in regulating the functions of cells of the innate and adaptive immune system. One of the standout properties of immune cells is their ability to migrate around the body, allowing them to carry out their physiological/pathophysiology cellular role at the appropriate location. This together with the physiological role of the tissue, changes in tissue matrix composition due to disease and aging, and the activation status of the immune cell, all result in immune cells being subjected to different mechanical forces. We report research which suggests that the NE may be an important sensor/transducer of these mechanical signals and propose that the NE is an integrator of both mechanical and chemical signals, allowing the cells of the innate immune system to precisely regulate gene transcription and functionality. By presenting this overview we hope to stimulate the interests of researchers into this often-overlooked organelle and propose it should join the ranks of mitochondria and phagosome, which are important organelles contributing to immune cell function.

ATM Modulates Nuclear Mechanics by Regulating Lamin A Levels

Ataxia-telangiectasia mutated (ATM) is one of the three main apical kinases at the crux of DNA damage response and repair in mammalian cells. ATM activates a cascade of downstream effector proteins to regulate DNA repair and cell cycle checkpoints in response to DNA double-strand breaks. While ATM is predominantly known for its role in DNA damage response and repair, new roles of ATM have recently begun to emerge, such as in regulating oxidative stress or metabolic pathways. Here, we report the surprising discovery that ATM inhibition and deletion lead to reduced expression of the nuclear envelope protein lamin A. Lamins are nuclear intermediate filaments that modulate nuclear shape, structure, and stiffness. Accordingly, inhibition or deletion of ATM resulted in increased nuclear deformability and enhanced cell migration through confined spaces, which requires substantial nuclear deformation. These findings point to a novel connection between ATM and lamin A and may have broad implications for cells with ATM mutations—as found in patients suffering from Ataxia Telangiectasia and many human cancers—which could lead to enhanced cell migration and increased metastatic potential.

Mechanisms Involved in the Promoting Activity of Fibroblasts in HTLV-1-Mediated Lymphomagenesis: Insights into the Plasticity of Lymphomatous Cells

Among the mechanisms leading to progression to Adult T-cell Leukaemia/Lymphoma in Human T-cell Leukaemia Virus type 1 (HTLV-1)-infected subjects, the contribution of stromal components remains poorly understood. To dissect the role of fibroblasts in HTLV-1-mediated lymphomagenesis, transcriptome studies, cytofluorimetric and qRT-PCR analyses of surface and intracellular markers linked to plasticity and stemness in coculture, and in vivo experiments were performed. A transcriptomic comparison between a more lymphomagenic (C91/III) and the parental (C91/PL) cell line evidenced hyperactivation of the PI3K/Akt pathway, confirmed by phospho-ELISA and 2-DE and WB analyses. C91/III cells also showed higher expression of mesenchymal and stemness genes. Short-term coculture with human foreskin fibroblasts (HFF) induced these features in C91/PL cells, and significantly increased not only the cancer stem cells (CSCs)-supporting CD10+GPR77+ HFF subpopulation, but also the percentage of ALDH1bright C91/PL cells. A non-cytotoxic acetylsalicylic acid treatment decreased HFF-induced ALDH1bright C91/PL cells, downregulated mesenchymal and stemness genes in cocultured cells, and delayed lymphoma growth in immunosuppressed mice, thus hindering the supportive activity of HFF on CSCs. These data suggest that crosstalk with HFF significantly intensifies the aggressiveness and plasticity of C91/PL cells, leading to the enrichment in lymphoma-initiating cells. Additional research is needed to better characterize these preliminary findings.

Lamin post-translational modifications: emerging toggles of nuclear organization and function

Nuclear lamins are ancient type V intermediate filaments with diverse functions that include maintaining nuclear shape, mechanosignaling, tethering and stabilizing chromatin, regulating gene expression, and contributing to cell cycle progression. Despite these numerous roles, an outstanding question has been how lamins are regulated. Accumulating work indicates that a range of lamin post-translational modifications (PTMs) control their functions both in homeostatic cells and in disease states such as progeria, muscular dystrophy, and viral infection. Here, we review the current knowledge of the diverse types of PTMs that regulate lamins in a site-specific manner. We highlight methods that can be used to characterize lamin PTMs whose functions are currently unknown and provide a perspective on the future of the lamin PTM field.

An Unbiased Approach to Mapping the Signaling Network of the Pseudorabies Virus US3 Protein

The US3 serine/threonine protein kinase is conserved among the alphaherpesvirus family and represents an important virulence factor. US3 plays a role in viral nuclear egress, induces dramatic alterations of the cytoskeleton, represses apoptosis, enhances gene expression and modulates the immune response. Although several substrates of US3 have been identified, an unbiased screen to identify US3 phosphorylation targets has not yet been described. Here, we perform a shotgun and phosphoproteomics analysis of cells expressing the US3 protein of pseudorabies virus (PRV) to identify US3 phosphorylation targets in an unbiased way. We identified several cellular proteins that are differentially phosphorylated upon US3 expression and validated the phosphorylation of lamin A/C at serine 404, both in US3-transfected and PRV-infected cells. These results provide new insights into the signaling network of the US3 protein kinase and may serve as a basis for future research into the role of the US3 protein in the viral replication cycle.

The adenoviral protein E4orf4: a probing tool to decipher mechanical stress-induced nuclear envelope remodeling in tumor cells

The human adenovirus (Ad) type 2/5 early region 4 (E4) ORF4 protein (E4orf4) exerts a remarkable tumor cell-selective killing activity in mammalian cells. This indicates that E4orf4 can target tumor cell-defining features and is a unique tool to probe cancer cell vulnerabilities. Recently, we found that E4orf4, through an interaction with the polarity protein PAR3, subverts nuclear envelope (NE) remodeling processes in a tumor cell-selective manner. In this Perspective, we outline mechanical signals that modify nuclear dynamics and tumor cell behavior to highlight potential mechanisms for E4orf4's tumoricidal activity. Through an analysis of E4orf4's cellular targets, we define a protein subnetwork that comprises phosphatase systems interconnected to polarity protein hubs, which could contribute to enhanced NE plasticity. We infer that elucidating E4orf4's protein network at a functional level could uncover key mechanisms of NE remodeling that define the tumor cell phenotype.

Lamin A involvement in ageing processes

Lamin A, a main constituent of the nuclear lamina, is the major splicing product of the LMNA gene, which also encodes lamin C, lamin A delta 10 and lamin C2. Involvement of lamin A in the ageing process became clear after the discovery that a group of progeroid syndromes, currently referred to as progeroid laminopathies, are caused by mutations in LMNA gene. Progeroid laminopathies include Hutchinson-Gilford Progeria, Mandibuloacral Dysplasia, Atypical Progeria and atypical-Werner syndrome, disabling and life-threatening diseases with accelerated ageing, bone resorption, lipodystrophy, skin abnormalities and cardiovascular disorders. Defects in lamin A post-translational maturation occur in progeroid syndromes and accumulated prelamin A affects ageing-related processes, such as mTOR signaling, epigenetic modifications, stress response, inflammation, microRNA activation and mechanosignaling. In this review, we briefly describe the role of these pathways in physiological ageing and go in deep into lamin A-dependent mechanisms that accelerate the ageing process. Finally, we propose that lamin A acts as a sensor of cell intrinsic and environmental stress through transient prelamin A accumulation, which triggers stress response mechanisms. Exacerbation of lamin A sensor activity due to stably elevated prelamin A levels contributes to the onset of a permanent stress response condition, which triggers accelerated ageing.

Lamin A/C and the Immune System: One Intermediate Filament, Many Faces

Nuclear envelope lamin A/C proteins are a major component of the mammalian nuclear lamina, a dense fibrous protein meshwork located in the nuclear interior. Lamin A/C proteins regulate nuclear mechanics and structure and control cellular signaling, gene transcription, epigenetic regulation, cell cycle progression, cell differentiation, and cell migration. The immune system is composed of the innate and adaptive branches. Innate immunity is mediated by myeloid cells such as neutrophils, macrophages, and dendritic cells. These cells produce a rapid and nonspecific response through phagocytosis, cytokine production, and complement activation, as well as activating adaptive immunity. Specific adaptive immunity is activated by antigen presentation by antigen presenting cells (APCs) and the cytokine microenvironment, and is mainly mediated by the cellular functions of T cells and the production of antibodies by B cells. Unlike most cell types, immune cells regulate their lamin A/C protein expression relatively rapidly to exert their functions, with expression increasing in macrophages, reducing in neutrophils, and increasing transiently in T cells. In this review, we discuss and summarize studies that have addressed the role played by lamin A/C in the functions of innate and adaptive immune cells in the context of human inflammatory and autoimmune diseases, pathogen infections, and cancer.

Targeting RAS-converting enzyme 1 overcomes senescence and improves progeria-like phenotypes of ZMPSTE24 deficiency

Several progeroid disorders are caused by deficiency in the endoprotease ZMPSTE24 which leads to accumulation of prelamin A at the nuclear envelope. ZMPSTE24 cleaves prelamin A twice: at the third carboxyl-terminal amino acid following farnesylation of a -CSIM motif; and 15 residues upstream to produce mature lamin A. The carboxyl-terminal cleavage can also be performed by RAS-converting enzyme 1 (RCE1) but little is known about the importance of this cleavage for the ability of prelamin A to cause disease. Here, we found that knockout of RCE1 delayed senescence and increased proliferation of ZMPSTE24-deficient fibroblasts from a patient with non-classical Hutchinson-Gilford progeria syndrome (HGPS), but did not influence proliferation of classical LMNA-mutant HGPS cells. Knockout of Rce1 in Zmpste24-deficient mice at postnatal week 4-5 increased body weight and doubled the median survival time. The absence of Rce1 in Zmpste24-deficient fibroblasts did not influence nuclear shape but reduced an interaction between prelamin A and AKT which activated AKT-mTOR signaling and was required for the increased proliferation. Prelamin A levels increased in Rce1-deficient cells due to a slower turnover rate but its localization at the nuclear rim was unaffected. These results strengthen the idea that the presence of misshapen nuclei does not prevent phenotype improvement and suggest that targeting RCE1 might be useful for treating the rare progeroid disorders associated with ZMPSTE24 deficiency.

Deregulated PTEN/PI3K/AKT/mTOR signaling in prostate cancer: Still a potential druggable target?

Although the prognosis of patients with localized prostate cancer is good after surgery, with a favorable response to androgen deprivation therapy, about one third of them invariably relapse, and progress to castration-resistant prostate cancer. Overall, prostate cancer therapies remain scarcely effective, thus it is mandatory to devise alternative treatments enhancing the efficacy of surgical castration and hormone administration. Dysregulation of the phosphoinositide 3-kinase pathway has attracted growing attention in prostate cancer due to the highly frequent association of epigenetic and post-translational modifications as well as to genetic alterations of both phosphoinositide 3-kinase and PTEN to onset and/or progression of this malignancy, and to resistance to canonical androgen-deprivation therapy. Here we provide a summary of the biological functions of the major players of this cascade and their deregulation in prostate cancer, summarizing the results of preclinical and clinical studies with PI3K signaling inhibitors and the reasons of failure independent from genomic changes.

Lamin A/C negatively regulated by miR-124-3p modulates apoptosis of vascular smooth muscle cells during cyclic stretch application in rats

AIM

Apoptosis of vascular smooth muscle cells (VSMCs) influenced by abnormal cyclic stretch is crucial for vascular remodelling during hypertension. Lamin A/C, a nuclear envelope protein, is mechano-responsive, but the role of lamin A/C in VSMC apoptosis is still unclear.

METHODS

FX-5000T Strain Unit provided cyclic stretch (CS) in vitro. AnnexinV/PI and cleaved Caspase 3 ELISA detected apoptosis. qPCR was used to investigate the expression of miR-124-3p and a luciferase reporter assay was used to evaluate the ability of miR-124-3p binding to the Lmna 3'UTR. Protein changes of lamin A/C and relevant molecules were detected using western blot. Ingenuity Pathway Analysis and Protein/DNA array detected the potential transcription factors. Renal hypertensive rats verified these changes.

RESULTS

High cyclic stretch (15%-CS) induced VSMC apoptosis and repressed lamin A/C expressions compared with normal (5%-CS) control. Downregulation of lamin A/C enhanced VSMC apoptosis. In addition, 15%-CS had no significant effect on mRNA expression of Lmna, and lamin A/C degradation was not induced by autophagy. 15%-CS elevated miR-124-3p bound to the 3'UTR of Lmna and negatively regulated protein expression of lamin A/C. Similar changes occurred in renal hypertensive rats compared with sham controls. Lamin A/C repression affected activity of TP53, CREB1, MYC, STAT1/5/6 and JUN, which may in turn affect apoptosis.

CONCLUSION

Our data suggested that the decreased expression of lamin A/C upon abnormal cyclic stretch and hypertension may induce VSMC apoptosis. These mechano-responsive factors play important roles in VSMC apoptosis and might be novel therapeutic targets for vascular remodelling in hypertension.

Forced Unfolding of Proteins Directs Biochemical Cascades

Many proteins in cells and in the extracellular matrix assemble into force-bearing networks, and some proteins clearly transduce mechanical stimuli into biochemical signals. Although structural mechanisms remain poorly understood, the designs of such proteins enable mechanical forces to either inhibit or facilitate interactions of protein domains with other proteins, including small molecules and enzymes, including proteases and kinases. Here, we review some of the structural proteins and processes that exhibit distinct modes of force-dependent signal conversion.

Elevated TGF β2 serum levels in Emery-Dreifuss Muscular Dystrophy: Implications for myocyte and tenocyte differentiation and fibrogenic processes

Among rare diseases caused by mutations in LMNA gene, Emery-Dreifuss Muscular Dystrophy type 2 and Limb-Girdle muscular Dystrophy 1B are characterized by muscle weakness and wasting, joint contractures, cardiomyopathy with conduction system disorders. Circulating biomarkers for these pathologies have not been identified. Here, we analyzed the secretome of a cohort of patients affected by these muscular laminopathies in the attempt to identify a common signature. Multiplex cytokine assay showed that transforming growth factor beta 2 (TGF β2) and interleukin 17 serum levels are consistently elevated in the vast majority of examined patients, while interleukin 6 and basic fibroblast growth factor are altered in subgroups of patients. Levels of TGF β2 are also increased in fibroblast and myoblast cultures established from patient biopsies as well as in serum from mice bearing the H222P Lmna mutation causing Emery-Dreifuss Muscular Dystrophy in humans. Both patient serum and fibroblast conditioned media activated a TGF β2-dependent fibrogenic program in normal human myoblasts and tenocytes and inhibited myoblast differentiation. Consistent with these results, a TGF β2 neutralizing antibody avoided fibrogenic marker activation and myogenesis impairment. Cell intrinsic TGF β2-dependent mechanisms were also determined in laminopathic cells, where TGF β2 activated AKT/mTOR phosphorylation. These data show that TGF β2 contributes to the pathogenesis of Emery-Dreifuss Muscular Dystrophy type 2 and Limb-Girdle muscular Dystrophy 1B and can be considered a potential biomarker of those diseases. Further, the evidence of TGF β2 pathogenetic effects in tenocytes provides the first mechanistic insight into occurrence of joint contractures in muscular laminopathies.

Ankrd2 in Mechanotransduction and Oxidative Stress Response in Skeletal Muscle: New Cues for the Pathogenesis of Muscular Laminopathies

Ankrd2 (ankyrin repeats containing domain 2) or Arpp (ankyrin repeat, PEST sequence, and proline-rich region) is a member of the muscle ankyrin repeat protein family. Ankrd2 is mostly expressed in skeletal muscle, where it plays an intriguing role in the transcriptional response to stress induced by mechanical stimulation as well as by cellular reactive oxygen species. Our studies in myoblasts from Emery-Dreifuss muscular dystrophy 2, a LMNA-linked disease affecting skeletal and cardiac muscles, demonstrated that Ankrd2 is a lamin A-binding protein and that mutated lamins found in Emery-Dreifuss muscular dystrophy change the dynamics of Ankrd2 nuclear import, thus affecting oxidative stress response. In this review, besides describing the latest advances related to Ankrd2 studies, including novel discoveries on Ankrd2 isoform-specific functions, we report the main findings on the relationship of Ankrd2 with A-type lamins and discuss known and potential mechanisms involving defective Ankrd2-lamin A interplay in the pathogenesis of muscular laminopathies.

Protein kinases involved in epidermal barrier formation: The AKT family and other animals

Formation of a stratified epidermis is required for the performance of the essential functions of the skin; to act as an outside-in barrier against the access of microorganisms and other external factors, to prevent loss of water and solutes via inside-out barrier functions and to withstand mechanical stresses. Epidermal barrier function is initiated during embryonic development and is then maintained throughout life and restored after injury. A variety of interrelated processes are required for the formation of a stratified epidermis, and how these processes are both temporally and spatially regulated has long been an aspect of dermatological research. In this review, we describe the roles of multiple protein kinases in the regulation of processes required for epidermal barrier formation.

Mechanosensing by the Lamina Protects against Nuclear Rupture, DNA Damage, and Cell-Cycle Arrest

Whether cell forces or extracellular matrix (ECM) can impact genome integrity is largely unclear. Here, acute perturbations (∼1 h) to actomyosin stress or ECM elasticity cause rapid and reversible changes in lamin-A, DNA damage, and cell cycle. The findings are especially relevant to organs such as the heart because DNA damage permanently arrests cardiomyocyte proliferation shortly after birth and thereby eliminates regeneration after injury including heart attack. Embryonic hearts, cardiac-differentiated iPS cells (induced pluripotent stem cells), and various nonmuscle cell types all show that actomyosin-driven nuclear rupture causes cytoplasmic mis-localization of DNA repair factors and excess DNA damage. Binucleation and micronuclei increase as telomeres shorten, which all favor cell-cycle arrest. Deficiencies in lamin-A and repair factors exacerbate these effects, but lamin-A-associated defects are rescued by repair factor overexpression and also by contractility modulators in clinical trials. Contractile cells on stiff ECM normally exhibit low phosphorylation and slow degradation of lamin-A by matrix-metalloprotease-2 (MMP2), and inhibition of this lamin-A turnover and also actomyosin contractility are seen to minimize DNA damage. Lamin-A is thus stress stabilized to mechano-protect the genome.

The Biology of the Nuclear Envelope and Its Implications in Cancer Biology

The formation of the nuclear envelope and the subsequent compartmentalization of the genome is a defining feature of eukaryotes. Traditionally, the nuclear envelope was purely viewed as a physical barrier to preserve genetic material in eukaryotic cells. However, in the last few decades, it has been revealed to be a critical cellular component in controlling gene expression and has been implicated in several human diseases. In cancer, the relevance of the cell nucleus was first reported in the mid-1800s when an altered nuclear morphology was observed in tumor cells. This review aims to give a current and comprehensive view of the role of the nuclear envelope on cancer first by recapitulating the changes of the nuclear envelope during cell division, second, by reviewing the role of the nuclear envelope in cell cycle regulation, signaling, and the regulation of the genome, and finally, by addressing the nuclear envelope link to cell migration and metastasis and its use in cancer prognosis.

The Cutting Edge: The Role of mTOR Signaling in Laminopathies

The mechanistic target of rapamycin (mTOR) is a ubiquitous serine/threonine kinase that regulates anabolic and catabolic processes, in response to environmental inputs. The existence of mTOR in numerous cell compartments explains its specific ability to sense stress, execute growth signals, and regulate autophagy. mTOR signaling deregulation is closely related to aging and age-related disorders, among which progeroid laminopathies represent genetically characterized clinical entities with well-defined phenotypes. These diseases are caused by LMNA mutations and feature altered bone turnover, metabolic dysregulation, and mild to severe segmental progeria. Different LMNA mutations cause muscular, adipose tissue and nerve pathologies in the absence of major systemic involvement. This review explores recent advances on mTOR involvement in progeroid and tissue-specific laminopathies. Indeed, hyper-activation of protein kinase B (AKT)/mTOR signaling has been demonstrated in muscular laminopathies, and rescue of mTOR-regulated pathways increases lifespan in animal models of Emery-Dreifuss muscular dystrophy. Further, rapamycin, the best known mTOR inhibitor, has been used to elicit autophagy and degradation of mutated lamin A or progerin in progeroid cells. This review focuses on mTOR-dependent pathogenetic events identified in Emery-Dreifuss muscular dystrophy, LMNA-related cardiomyopathies, Hutchinson-Gilford Progeria, mandibuloacral dysplasia, and type 2 familial partial lipodystrophy. Pharmacological application of mTOR inhibitors in view of therapeutic strategies is also discussed.

Defective Nuclear Lamina in Aneuploidy and Carcinogenesis

Aneuploidy, loss or gain of whole chromosomes, is a prominent feature of carcinomas, and is generally considered to play an important role in the initiation and progression of cancer. In high-grade serous ovarian cancer, the only common gene aberration is the p53 point mutation, though extensive genomic perturbation is common due to severe aneuploidy, which presents as a deviant karyotype. Several mechanisms for the development of aneuploidy in cancer cells have been recognized, including chromosomal non-disjunction during mitosis, centrosome amplification, and more recently, nuclear envelope rupture at interphase. Many cancer types including ovarian cancer have lost or reduced expression of Lamin A/C, a structural component of the lamina matrix that underlies the nuclear envelope in differentiated cells. Several recent studies suggest that a nuclear lamina defect caused by the loss or reduction of Lamin A/C leads to failure in cytokinesis and formation of tetraploid cells, transient nuclear envelope rupture, and formation of nuclear protrusions and micronuclei during the cell cycle gap phase. Thus, loss and reduction of Lamin A/C underlies the two common features of cancer—aberrations in nuclear morphology and aneuploidy. We discuss here and emphasize the newly recognized mechanism of chromosomal instability due to the rupture of a defective nuclear lamina, which may account for the rapid genomic changes in carcinogenesis.

Nuclear Nestin deficiency drives tumor senescence via lamin A/C-dependent nuclear deformation

Emerging evidence has revealed that Nestin not only serves as a biomarker for multipotent stem cells, but also regulates cell proliferation and invasion in various tumors. However, the mechanistic contributions of Nestin to cancer pathogenesis are still unknown. In the present study, previously thought to reside exclusively in the cytoplasm, Nestin can also be found in the nucleus and participate in protecting tumor cells against cellular senescence. Specifically, we reveal that Nestin has a nuclear localization signal (aa318–aa347) at the downstream of rod domain. We then find nuclear Nestin could interact with lamin A/C. Mechanistic investigations demonstrate that Nestin depletion results in the activation of cyclin-dependent kinase 5 (Cdk5), which causes the phosphorylation of lamin A/C (mainly at S392 site) and its subsequent translocation to the cytoplasm for degradation. The findings establish a role for nuclear Nestin in tumor senescence, which involves its nucleus-localized form and interaction with lamin A/C.

Nestin can be localised in the nucleus of cancer cells, but its nuclear role in tumorigenesis is unclear. Here, the authors show that nuclear Nestin prevents senescence in tumor cells by stabilising lamin A/C from proteasomal degradation to maintain nuclear integrity.

New biological research and understanding of Papanicolaou's test

The development of the Papanicolaou smear test by Dr. George Nicholas Papanicolaou (1883-1962) is one of the most significant achievements in screening for disease and cancer prevention in history. The Papanicolaou smear has been used for screening of cervical cancer since the 1950s. The test is technically straightforward and practical and based on a simple scientific observation: malignant cells have an aberrant nuclear morphology that can be distinguished from benign cells. Here, we review the scientific understanding that has been achieved and continues to be made on the causes and consequences of abnormal nuclear morphology, the basis of Dr. Papanicolaou's invention. The deformed nuclear shape is caused by the loss of lamina and nuclear envelope structural proteins. The consequences of a nuclear envelope defect include chromosomal numerical instability, altered chromatin organization and gene expression, and increased cell mobility because of a malleable nuclear envelope. HPV (Human Papilloma Virus) infection is recognized as the key etiology in the development of cervical cancer. Persistent HPV infection causes disruption of the nuclear lamina, which presents as a change in nuclear morphology detectable by a Papanicolaou smear. Thus, the causes and consequences of nuclear deformation are now linked to the mechanisms of viral carcinogenesis, and are still undergoing active investigation to reveal the details. Recently a statue was installed in front of the Papanicolaou's Cancer Research Building to honor the inventor. Remarkably, the invention nearly 60 years ago by Dr. Papanicolaou still exerts clinical impacts and inspires scientific inquiries.

Progerin phosphorylation in interphase is lower and less mechanosensitive than lamin-A,C in iPS-derived mesenchymal stem cells

Interphase phosphorylation of lamin-A,C depends dynamically on a cell's microenvironment, including the stiffness of extracellular matrix. However, phosphorylation dynamics is poorly understood for diseased forms such as progerin, a permanently farnesylated mutant of LMNA that accelerates aging of stiff and mechanically stressed tissues. Here, fine-excision alignment mass spectrometry (FEA-MS) is developed to quantify progerin and its phosphorylation levels in patient iPS cells differentiated to mesenchymal stem cells (MSCs). The stoichiometry of total A-type lamins (including progerin) versus B-type lamins measured for Progeria iPS-MSCs prove similar to that of normal MSCs, with total A-type lamins more abundant than B-type lamins. However, progerin behaves more like farnesylated B-type lamins in mechanically-induced segregation from nuclear blebs. Phosphorylation of progerin at multiple sites in iPS-MSCs cultured on rigid plastic is also lower than that of normal lamin-A and C. Reduction of nuclear tension upon i) cell rounding/detachment from plastic, ii) culture on soft gels, and iii) inhibition of actomyosin stress increases phosphorylation and degradation of lamin-C > lamin-A > progerin. Such mechano-sensitivity diminishes, however, with passage as progerin and DNA damage accumulate. Lastly, transcription-regulating retinoids exert equal effects on both diseased and normal A-type lamins, suggesting a differential mechano-responsiveness might best explain the stiff tissue defects in Progeria.

New Insights into Protein Kinase B/Akt Signaling: Role of Localized Akt Activation and Compartment-Specific Target Proteins for the Cellular Radiation Response

Genetic alterations driving aberrant activation of the survival kinase Protein Kinase B (Akt) are observed with high frequency during malignant transformation and cancer progression. Oncogenic gene mutations coding for the upstream regulators or Akt, e.g., growth factor receptors, RAS and phosphatidylinositol-3-kinase (PI3K), or for one of the three Akt isoforms as well as loss of the tumor suppressor Phosphatase and Tensin Homolog on Chromosome Ten (PTEN) lead to constitutive activation of Akt. By activating Akt, these genetic alterations not only promote growth, proliferation and malignant behavior of cancer cells by phosphorylation of various downstream signaling molecules and signaling nodes but can also contribute to chemo- and radioresistance in many types of tumors. Here we review current knowledge on the mechanisms dictating Akt’s activation and target selection including the involvement of miRNAs and with focus on compartmentalization of the signaling network. Moreover, we discuss recent advances in the cross-talk with DNA damage response highlighting nuclear Akt target proteins with potential involvement in the regulation of DNA double strand break repair.

Mandibuloacral dysplasia: A premature ageing disease with aspects of physiological ageing

Mandibuloacral dysplasia (MAD) is a rare genetic condition characterized by bone abnormalities including localized osteolysis and generalized osteoporosis, skin pigmentation, lipodystrophic signs and mildly accelerated ageing. The molecular defects associated with MAD are mutations in LMNA or ZMPSTE24 (FACE1) gene, causing type A or type B MAD, respectively. Downstream of LMNA or ZMPSTE24 mutations, the lamin A precursor, prelamin A, is accumulated in cells and affects chromatin dynamics and stress response. A new form of mandibuloacral dysplasia has been recently associated with mutations in POLD1 gene, encoding DNA polymerase delta, a major player in DNA replication. Of note, involvement of prelamin A in chromatin dynamics and recruitment of DNA repair factors has been also determined under physiological conditions, at the border between stress response and cellular senescence. Here, we review current knowledge on MAD clinical and pathogenetic aspects and highlight aspects typical of physiological ageing.

Cardiolaminopathies from bench to bedside: challenges in clinical decision-making with focus on arrhythmia-related outcomes

Lamin A/C gene mutations can be associated with cardiac diseases, usually referred to as 'cardiolaminopathies' characterized by arrhythmic disorders and/or left ventricular or biventricular dysfunction up to an overt picture of heart failure. The phenotypic cardiac manifestations of laminopathies are frequently mixed in complex clinical patterns and specifically may include bradyarrhythmias (sinus node disease or atrioventricular blocks), atrial arrhythmias (atrial fibrillation, atrial flutter, atrial standstill), ventricular tachyarrhythmias and heart failure of variable degrees of severity. Family history, physical examination, laboratory findings (specifically serum creatine phosphokinase values) and ECG findings are often important 'red flags' in diagnosing a 'cardiolaminopathy'. Sudden arrhythmic death, thromboembolic events or stroke and severe heart failure requiring heart transplantation are the most dramatic complications of the evolution of cardiolaminopathies and appropriate risk stratification is clinically needed combined with clinical follow-up. Treatment with cardiac electrical implantable devices is indicated in case of bradyarrhythmias (implant of a device with pacemaker functions), risk of life-threatening ventricular tachyarrhythmias (implant of an ICD) or in case of heart failure with wide QRS interval (implant of a device for cardiac resynchronization). New technologies introduced in the last 5 years can help physicians to reduce device-related complications, thanks to the extension of device longevity and availability of leadless pacemakers or defibrillators, to be implanted in appropriately selected patients. An improved knowledge of the complex pathophysiological pathways involved in cardiolaminopathies and in the determinants of their progression to more severe forms will help to improve clinical management and to better target pharmacological and non-pharmacological treatments.

Barrier-to-autointegration factor (BAF) involvement in prelamin A-related chromatin organization changes

Chromatin disorganization is one of the major alterations linked to prelamin A processing impairment. In this study we demonstrate that BAF is necessary to modulate prelamin A effects on chromatin structure. We show that when prelamin A and BAF cannot properly interact no prelamin A-dependent effects on chromatin occur; similar to what is observed in human Nestor Guillermo Progeria Syndrome cells harboring a BAF mutation, in HEK293 cells expressing a BAF mutant unable to bind prelamin A, or in siRNA mediated BAF-depleted HEK293 cells expressing prelamin A. BAF is necessary to induce histone trimethyl-H3K9 as well as HP1-alpha and LAP2-alpha nuclear relocalization in response to prelamin A accumulation. These findings are enforced by electron microscopy evaluations showing how the prelamin A-BAF interaction governs overall chromatin organization. Finally, we demonstrate that the LAP2-alpha nuclear localization defect observed in HGPS cells involves the progerin-BAF interaction, thus establishing a functional link between BAF and prelamin A pathological forms.

Are mechanically sensitive regulators involved in the function and (patho)physiology of cerebral palsy-related contractures?

Skeletal muscle tissue is mechanosensitive, as it is able to sense mechanical impacts and to translate these into biochemical signals making the tissue adapt. Among its mechanosensitive nature, skeletal muscle tissue is the largest metabolic organ of the human body. Disturbances in skeletal muscle mechanosensing and metabolism cause and contribute to many diseases, i.e. muscular dystrophies/myopathies, cardiovascular diseases, COPD or diabetes mellitus type 2. A less commonly focused muscle-related disorder is clinically known as muscle contractures that derive from cerebral palsy (CP) conditions in young and adults. Muscle contractures are characterized by gradually increasing passive muscle stiffness resulting in complete fixation of joints. Different mechanisms have been identified in CP-related contractures, i.e. altered calcium handling, altered metabolism or altered titin regulation. The muscle-related extracellular matrix (ECM), specifically collagens, plays a role in CP-related contractures. Herein, we focus on mechanically sensitive complexes, known as costameres (Cstms), and discuss their potential role in CP-related contractures. We extend our discussion to the ECM due to the limited knowledge of its role in CP-related contractures. The aims of this review are (1) to summarize CP-related contracture mechanisms, (2) to raise novel hypotheses on the genesis of contractures with a focus on Cstms, and (3) to stimulate novel approaches to study CP-related contractures.

The telomeric protein AKTIP interacts with A- and B-type lamins and is involved in regulation of cellular senescence

AKTIP is a shelterin-interacting protein required for replication of telomeric DNA. Here, we show that AKTIP biochemically interacts with A- and B-type lamins and affects lamin A, but not lamin C or B, expression. In interphase cells, AKTIP localizes at the nuclear rim and in discrete regions of the nucleoplasm just like lamins. Double immunostaining revealed that AKTIP partially co-localizes with lamin B1 and lamin A/C in interphase cells, and that proper AKTIP localization requires functional lamin A. In mitotic cells, AKTIP is enriched at the spindle poles and at the midbody of late telophase cells similar to lamin B1. AKTIP-depleted cells show senescence-associated markers and recapitulate several aspects of the progeroid phenotype. Collectively, our results indicate that AKTIP is a new player in lamin-related processes, including those that govern nuclear architecture, telomere homeostasis and cellular senescence.

Expression and functional proteomic analyses of osteocytes from Xenopus laevis tested under mechanical stress conditions: preliminary observations on an appropriate new animal model

Hitherto, the role of the osteocyte as transducer of mechanical stimuli into biological signals is far from settled. In this study, we used an appropriate model represented by the cortex of Xenopus laevis long bone diaphysis lacking (unlike the mammalian one) of vascular structures and containing only osteocytes inside the bone matrix. These structural features allow any change of protein profile that might be observed upon different experimental conditions, such as bone adaptation to stress/mechanical loading, to be ascribed specifically to osteocytes. The study was conducted by combining ultrastructural observations and two-dimensional electrophoresis for proteomic analysis. The osteocyte population was extracted from long bones of lower limbs of amphibian skeletons after different protocols (free and forced swimming). The experiments were performed on 210 frogs subdivided into five trials, each including free swimming frogs (controls) and frogs submitted to forced swimming (stressed). The stressed groups were obliged to swim (on movable spheres covering the bottom of a pool on a vibrating plate) continuously for 8 h, and killed 24 h later along with the control groups. Long bones free of soft tissues (periosteum, endosteum and bone marrow), as well as muscles of posterior limbs, were processed and analyzed for proteins differentially expressed or phosphorylated between the two sample groups. The comparative analysis showed that protein phosphorylation profiles differ between control and stressed groups. In particular, we found in long bones of stressed samples that both Erk1/2 and Akt are hyperphosphorylated; moreover, the different phosphorylation of putative Akt substrates (recognized by specific Akt phosphosubstrates-antibody) in stressed vs. control samples clearly demonstrated that Akt signaling is boosted by forced swimming (leading to an increase of mechanical stress) of amphibian long bones. In parallel, we found in posterior limb muscles that the expression of heat shock protein HSP27 and HSP70 stress markers increased upon the forced swimming condition. Because the cortexes of frog long bones are characterized by the presence of only osteocytes, all our results establish the suitability of the X. laevis animal model to study the bone response to stress conditions mediated by this cell type and pave the way for further analysis of the signaling pathways involved in these signal transduction mechanisms.

Suspension state increases reattachment of breast cancer cells by up-regulating lamin A/C

Extravasation is a rate-limiting step of tumor metastasis, for which adhesion to endothelium of circulating tumor cells (CTCs) is the prerequisite. The suspension state of CTCs undergoing detachment from primary tumor is a persistent biomechanical cue, which potentially regulates the biophysical characteristics and cellular behaviors of tumor cells. In this study, breast tumor cells MDA-MB-231 in suspension culture condition were used to investigate the effect of suspension state on reattachment of CTCs. Our study demonstrated that suspension state significantly increased the adhesion ability of breast tumor cells. In addition, suspension state markedly promoted the formation of stress fibers and focal adhesions and reduced the motility in reattached breast cancer cells. Moreover, lamin A/C was reversibly accumulated at posttranscriptional level under suspension state, improving the cell stiffness of reattached breast cancer cells. Disruption of actin cytoskeleton by cytochalasin D caused lamin A/C accumulation. Conversely, decreasing actomyosin contraction by ROCK inhibitor Y27632 reduced lamin A/C level. Knocking down lamin A/C weakened the suspension-induced increase of adhesion, and also abolished the suspension-induced decrease of motility and increase of stress fibers and focal adhesion in reattaching tumor cells, suggesting a crucial role of lamin A/C. In conclusion, it was demonstrated that suspension state promoted the reattachment of breast tumor cells by up-regulating lamin A/C via cytoskeleton disruption. These findings highlight the important role of suspension state for tumor cells in tumor metastasis.

Lamins and metabolism

Lamins are nuclear intermediate filaments (IFs) with important roles in most nuclear activities, including nuclear organization and cell-cycle progression. Mutations in human lamins cause over 17 different diseases, termed laminopathies. Most of these diseases are autosomal dominant and can be roughly divided into four major groups: muscle diseases, peripheral neuronal diseases, accelerated aging disorders and metabolic diseases including Dunnigan type familial partial lipodystrophy (FLPD), acquired partial lipodystrophy (APL) and autosomal dominant leucodystrophy. Mutations in lamins are also associated with the metabolic syndrome (MS). Cells derived from patients suffering from metabolic laminopathies, as well as cells derived from the corresponding animal models, show a disruption of the mechanistic target of rapamycin (mTOR) pathway, abnormal autophagy, altered proliferative rate and down-regulation of genes that regulate adipogenesis. In addition, treating Hutchinson-Gilford progeria syndrome (HGPS) cells with the mTOR inhibitor rapamycin improves their fate. In this review, we will discuss the ways by which lamin genes are involved in the regulation of cell metabolism.

Comparing lamin proteins post-translational relative stability using a 2A peptide-based system reveals elevated resistance of progerin to cellular degradation

Nuclear lamins are the major components of the nuclear lamina at the periphery of the nucleus, supporting the nuclear envelope and participating in many nuclear processes, including DNA replication, transcription and chromatin organization. A group of diseases, the laminopathies, is associated with mutations in lamin genes. One of the most striking cases is Hutchinson-Gilford progeria syndrome (HGPS) which is the consequence of a lamin A dominant negative mutant named progerin. Due to the abnormal presence of a permanent C-terminal farnesyl tail, progerin gradually accumulates on the nuclear membrane, perturbing a diversity of signalings and transcriptional events. The accumulation of progerin has led to the speculation that progerin possesses higher stability than the wild type lamin A protein. However, the low solubility of lamin proteins renders traditional immunoprecipitation-dependent methods such as pulse-chase analysis ineffective for comparing the relative stabilities of mutant and wild type lamins. Here, we employ a novel platform for inferring differences in lamin stability, which is based on normalization to a co-translated reporter protein following porcine teschovirus-1 2A peptide-mediated co-translational cleavage. The results obtained using this method support the notion that progerin is more stable than lamin A. Moreover, treatment of FTI reduces progerin relative stability to the level of wild type lamin A.

Cross-talk between the CK2 and AKT signaling pathways in cancer

CK2 and AKT display a high degree of cross-regulation of their respective functions, both directly, through physical interaction and phosphorylation, and indirectly, through an intense cross-talk of key downstream effectors, ultimately leading to sustained AKT activation. Being CK2 and AKT attractive targets for therapeutic intervention, here we would like to emphasize how AKT and CK2 might influence cell fate through their complex isoform-specific and contextual-dependent cross-talk, to the extent that such functional interplay should be considered when devising therapies that target one or both these key signaling kinases.

Mechanosensing by the nucleus: From pathways to scaling relationships

Cho, Irianto, and Discher review emerging mechanisms of nuclear mechanosensing and propose through meta-analyses of published data the universality of mechanosensing pathways.

The nucleus is linked mechanically to the extracellular matrix via multiple polymers that transmit forces to the nuclear envelope and into the nuclear interior. Here, we review some of the emerging mechanisms of nuclear mechanosensing, which range from changes in protein conformation and transcription factor localization to chromosome reorganization and membrane dilation up to rupture. Nuclear mechanosensing encompasses biophysically complex pathways that often converge on the main structural proteins of the nucleus, the lamins. We also perform meta-analyses of public transcriptomics and proteomics data, which indicate that some of the mechanosensing pathways relaying signals from the collagen matrix to the nucleus apply to a broad range of species, tissues, and diseases.

Reversal of the glycolytic phenotype of primary effusion lymphoma cells by combined targeting of cellular metabolism and PI3K/Akt/ mTOR signaling

PEL is a B-cell non-Hodgkin lymphoma, occurring predominantly as a lymphomatous effusion in body cavities, characterized by aggressive clinical course, with no standard therapy. Based on previous reports that PEL cells display a Warburg phenotype, we hypothesized that the highly hypoxic environment in which they grow in vivo makes them more reliant on glycolysis, and more vulnerable to drugs targeting this pathway. We established here that indeed PEL cells in hypoxia are more sensitive to glycolysis inhibition. Furthermore, since PI3K/Akt/mTOR has been proposed as a drug target in PEL, we ascertained that pathway-specific inhibitors, namely the dual PI3K and mTOR inhibitor, PF-04691502, and the Akt inhibitor, Akti 1/2, display improved cytotoxicity to PEL cells in hypoxic conditions. Unexpectedly, we found that these drugs reduce lactate production/extracellular acidification rate, and, in combination with the glycolysis inhibitor 2-deoxyglucose (2-DG), they shift PEL cells metabolism from aerobic glycolysis towards oxidative respiration. Moreover, the associations possess strong synergistic cytotoxicity towards PEL cells, and thus may reduce adverse reaction in vivo, while displaying very low toxicity to normal lymphocytes. Finally, we showed that the association of 2-DG and PF-04691502 maintains its cytotoxic and proapoptotic effect also in PEL cells co-cultured with human primary mesothelial cells, a condition known to mimic the in vivo environment and to exert a protective and pro-survival action. All together, these results provide a compelling rationale for the clinical development of new therapies for the treatment of PEL, based on combined targeting of glycolytic metabolism and constitutively activated signaling pathways.

Nuclear envelope structural defect underlies the main cause of aneuploidy in ovarian carcinogenesis

BACKGROUND

The Cancer Atlas project has shown that p53 is the only commonly (96 %) mutated gene found in high-grade serous epithelial ovarian cancer, the major histological subtype. Another general genetic change is extensive aneuploidy caused by chromosomal numerical instability, which is thought to promote malignant transformation. Conventionally, aneuploidy is thought to be the result of mitotic errors and chromosomal nondisjunction during mitosis. Previously, we found that ovarian cancer cells often lost or reduced nuclear lamina proteins lamin A/C, and suppression of lamin A/C in cultured ovarian epithelial cells leads to aneuploidy. Following up, we investigated the mechanisms of lamin A/C-suppression in promoting aneuploidy and synergy with p53 inactivation.

RESULTS

We found that suppression of lamin A/C by siRNA in human ovarian surface epithelial cells led to frequent nuclear protrusions and formation of micronuclei. Lamin A/C-suppressed cells also often underwent mitotic failure and furrow regression to form tetraploid cells, which frequently underwent aberrant multiple polar mitosis to form aneuploid cells. In ovarian surface epithelial cells isolated from p53 null mice, transient suppression of lamin A/C produced massive aneuploidy with complex karyotypes, and the cells formed malignant tumors when implanted in mice.

CONCLUSIONS

Based on the results, we conclude that a nuclear envelope structural defect, such as the loss or reduction of lamin A/C proteins, leads to aneuploidy by both the formation of tetraploid intermediates following mitotic failure, and the reduction of chromosome (s) following nuclear budding and subsequent loss of micronuclei. We suggest that the nuclear envelope defect, rather than chromosomal unequal distribution during cytokinesis, is the main cause of aneuploidy in ovarian cancer development.

Regulation of lamin properties and functions: does phosphorylation do it all?

The main functions of lamins are their mechanical and structural roles as major building blocks of the karyoskeleton. They are also involved in chromatin structure regulation, gene expression, intracellular signalling pathway modulation and development. All essential lamin functions seem to depend on their capacity for assembly or disassembly after the receipt of specific signals, and after specific, selective and precisely regulated interactions through their various domains. Reversible phosphorylation of lamins is crucial for their functions, so it is important to understand how lamin polymerization and interactions are modulated, and which sequences may undergo such modifications. This review combines experimental data with results of our in silico analyses focused on lamin phosphorylation in model organisms to show the presence of evolutionarily conserved sequences and to indicate specific in vivo phosphorylations that affect particular functions.

The effect of the lamin A and its mutants on nuclear structure, cell proliferation, protein stability, and mobility in embryonic cells

LMNA gene encodes for nuclear intermediate filament proteins lamin A/C. Mutations in this gene lead to a spectrum of genetic disorders, collectively referred to as laminopathies. Lamin A/C are widely expressed in most differentiated somatic cells but not in early embryos and some undifferentiated cells. To investigate the role of lamin A/C in cell phenotype maintenance and differentiation, which could be a determinant of the pathogenesis of laminopathies, we examined the role played by exogenous lamin A and its mutants in differentiated cell lines (HeLa, NHDF) and less-differentiated HEK 293 cells. We introduced exogenous wild-type and mutated (H222P, L263P, E358K D446V, and ∆50) lamin A into different cell types and analyzed proteins’ impact on proliferation, protein mobility, and endogenous nuclear envelope protein distribution. The mutants give rise to a broad spectrum of nuclear phenotypes and relocate lamin C. The mutations ∆50 and D446V enhance proliferation in comparison to wild-type lamin A and control cells, but no changes in exogenous protein mobility measured by FRAP were observed. Interestingly, although transcripts for lamins A and C are at similar level in HEK 293 cells, only lamin C protein is detected in western blots. Also, exogenous lamin A and its mutants, when expressed in HEK 293 cells underwent posttranscriptional processing. Overall, our results provide new insight into the maintenance of lamin A in less-differentiated cells. Embryonic cells are very sensitive to lamin A imbalance, and its upregulation disturbs lamin C, which may influence gene expression and many regulatory pathways.

Causes and consequences of nuclear envelope alterations in tumour progression

Morphological changes in the size and shape of the nucleus are highly prevalent in cancer, but the underlying molecular mechanisms and the functional relevance remain poorly understood. Nuclear envelope proteins, which can modulate nuclear shape and organization, have emerged as key components in a variety of signalling pathways long implicated in tumourigenesis and metastasis. The expression of nuclear envelope proteins is altered in many cancers, and changes in levels of nuclear envelope proteins lamins A and C are associated with poor prognosis in multiple human cancers. In this review we highlight the role of the nuclear envelope in different processes important for tumour initiation and cancer progression, with a focus on lamins A and C. Lamin A/C controls many cellular processes with key roles in cancer, including cell invasion, stemness, genomic stability, signal transduction, transcriptional regulation, and resistance to mechanical stress. In addition, we discuss potential mechanisms mediating the changes in lamin levels observed in many cancers. A better understanding of cause-and-effect relationships between lamin expression and tumour progression could reveal important mechanisms for coordinated regulation of oncogenic processes, and indicate therapeutic vulnerabilities that could be exploited for improved patient outcome.

Potential therapeutic effects of the MTOR inhibitors for preventing ageing and progeria-related disorders

The mammalian target of rapamycin (mTOR) pathway is an highly conserved signal transduction axis involved in many cellular processes, such as cell growth, survival, transcription, translation, apoptosis, metabolism, motility and autophagy. Recently, this signalling pathway has come to the attention of the scientific community owing to the unexpected finding that inhibition of mTOR by rapamycin, an antibiotic with immunosuppressant and chemotherapeutic properties, extends lifespan in diverse animal models. Moreover, rapamycin has been reported to rescue the cellular phenotype in a progeroid syndrome [Hutchinson–Gilford Progeria syndrome (HGPS)] that recapitulates most of the traits of physiological ageing. The promising perspectives raised by these results warrant a better understanding of mTOR signalling and the potential applications of mTOR inhibitors to counteract ageing‐associated diseases and increase longevity. This review is focused on these issues.

Modulation of TGFbeta 2 levels by lamin A in U2-OS osteoblast-like cells: understanding the osteolytic process triggered by altered lamins

Transforming growth factor beta (TGFbeta) plays an essential role in bone homeostasis and deregulation of TGFbeta occurs in bone pathologies. Patients affected by Mandibuloacral Dysplasia (MADA), a progeroid disease linked to LMNA mutations, suffer from an osteolytic process. Our previous work showed that MADA osteoblasts secrete excess amount of TGFbeta 2, which in turn elicits differentiation of human blood precursors into osteoclasts. Here, we sought to determine how altered lamin A affects TGFbeta signaling. Our results show that wild-type lamin A negatively modulates TGFbeta 2 levels in osteoblast-like U2-OS cells, while the R527H mutated prelamin A as well as farnesylated prelamin A do not, ultimately leading to increased secretion of TGFbeta 2. TGFbeta 2 in turn, triggers the Akt/mTOR pathway and upregulates osteoprotegerin and cathepsin K. TGFbeta 2 neutralization rescues Akt/mTOR activation and the downstream transcriptional effects, an effect also obtained by statins or RAD001 treatment. Our results unravel an unexpected role of lamin A in TGFbeta 2 regulation and indicate rapamycin analogs and neutralizing antibodies to TGFbeta 2 as new potential therapeutic tools for MADA.

Lamin A is involved in the development of vascular calcification induced by chronic kidney failure and phosphorus load

Vascular calcification remains one of the main factors associated to morbidity and mortality in both ageing and chronic kidney disease. Both hyperphosphataemia, a well-known promoter of vascular calcification, and abnormal processing defects of lamin A/C have been associated to ageing. The main aim of this study was to analyse the effect of phosphorus load in the differential expression pattern of genes and proteins, particularly of lamin A/C, which are involved in phenotypic change of the vascular smooth muscle cells to osteoblast-like cells. The in vivo study of the calcified abdominal aortas from nephrectomized rats receiving a high phosphorus diet showed among others, a repression of muscle related proteins and overexpression of lamin A/C. Similar results were observed in vitro, where primary vascular smooth muscle cells cultured in calcifying medium showed increased expression of prelamin A and lamin A and abnormalities in the nuclear morphology. Co-immunoprecipitation assays showed novel and important physical interactions between lamin A and RUNX2 during the process of calcification. In fact, the knockdown of prelamin A and lamin A inhibited the increase of Runx2, osteocalcin and osteopontin gene expression, calcium deposition, nuclear abnormalities and the RUNX2 protein translocation into the nucleus of the cell. These in vivo and in vitro results highlight the important role played by lamin A in the process of vascular calcification.