Targeting the glutamine-arginine-proline metabolism axis in cancer.

Metabolic abnormalities are an important feature of tumours. The glutamine-arginine-proline axis is an important node of cancer metabolism and plays a major role in amino acid metabolism. This axis also acts as a scaffold for the synthesis of other nonessential amino acids and essential metabolites. In this paper, we briefly review (1) the glutamine addiction exhibited by tumour cells with accelerated glutamine transport and metabolism; (2) the methods regulating extracellular glutamine entry, intracellular glutamine synthesis and the fate of intracellular glutamine; (3) the glutamine, proline and arginine metabolic pathways and their interaction; and (4) the research progress in tumour therapy targeting the glutamine-arginine-proline metabolic system, with a focus on summarising the therapeutic research progress of strategies targeting of one of the key enzymes of this metabolic system, P5CS (ALDH18A1). This review provides a new basis for treatments targeting the metabolic characteristics of tumours.

Two novel homozygous variants of ATP6V0A2 and ALDH18A1 lead to autosomal recessive cutis laxa type 2 and 3 in two Pakistani families.

BACKGROUND: Autosomal recessive cutis laxa type 2A (ARCL2A; OMIM: 219200) is characterized by neurovegetative, developmental and progeroid elastic skin anomalies. It is caused by biallelic variation in ATPase, H+ transporting V0 subunit A2 (ATP6V0A2; OMIM: 611716) located on chromosome 12q24.31. Autosomal recessive cutis laxa type 3A (ARCL3A; OMIM: 219150) is another subclinical type characterized by short stature, ophthalmological abnormalities and a progeria-like appearance. The ARCL3A is caused by loss of function alterations in the aldehyde dehydrogenase 18 family member A1 (ALDH18A1; OMIM: 138250) gene located at chromosome 10q24.1. METHODS: Whole-exome sequencing (WES), and Sanger sequencing were performed for molecular diagnosis. 3D protein modeling was performed to investigate the deleterious effect of the variant on protein structure. RESULTS: In this study, clinical and molecular diagnosis were performed for two families, ED-01 and DWF-41, which displayed hallmark features of ARCL2A and ARCL3A, respectively. Three affected individuals in the ED-01 family (IV-4, IV-5 and V-3) displayed sagging loose skin, down-slanting palpebral fissures, excessive wrinkles on the abdomen, hands and feet, and prominent veins on the trunk. Meanwhile the affected individuals in the DWF-41 family (V-2 and V-3) had progeroid skin, short stature, dysmorphology, low muscle tone, epilepsy, lordosis, scoliosis, delayed puberty and internal genitalia. WES in the index patient (ED-01: IV-4) identified a novel homozygous deletion (NM_012463.3: c.1977_1980del; p.[Val660LeufsTer23]) in exon 16 of the ATP6V0A2 while in DWF-41 a novel homozygous missense variant (NM_001323413.1:c.1867G>A; p.[Asp623Asn]) in exon 15 of the ALDH18A1 was identified. Sanger validation in all available family members confirmed the autosomal recessive modes of inheritances in each family. Three dimensional in-silico protein modeling suggested deleterious impact of the identified variants. Furthermore, these variants were assigned class 1 or "pathogenic" as per guidelines of American College of Medical Genetics 2015. Screening of ethnically matched healthy controls (n = 200 chromosomes), excluded the presence of these variations in general population. CONCLUSIONS: To the best of our knowledge, this is the first report of ATP6V0A2 and ALDH18A1 variations in the Pakhtun ethnicity of Pakistani population. The study confirms that WES can be used as a first-line diagnostic test in patients with cutis laxa, and provides basis for population screening and premarital testing to reduce the diseases burden in future generations.

Proline metabolism in cancer.

Cancer cells often change their metabolism to support uncontrolled proliferation. Proline is the only proteogenic secondary amino acid that is abundant in the body. Recent studies have shown that proline metabolism plays an important role in metabolic reprogramming and affects the occurrence and development of cancer. Proline metabolism is related to ATP production, protein and nucleotide synthesis, and redox homeostasis in tumor cells. Proline can be synthesized by aldehyde dehydrogenase family 18 member A1 (ALDH18A1) and delta1-pyrroline-5-carboxylate reductase (PYCR), up-regulating ALDH18A1 and PYCR can promote the proliferation and invasion of cancer cells. As the main storage of proline, collagen can influence cancer cells proliferation, invasion, and metastasis. Its synthesis depends on the hydroxylation of proline catalyzed by prolyl 4-hydroxylases (P4Hs), which will affect the plasticity and metastasis of cancer cells. The degradation of proline occurs in the mitochondria and involves an oxidation step catalyzed by proline dehydrogenase/proline oxidase (PRODH/POX). Proline catabolism has a dual role in cancer, linking apoptosis with the survival and metastasis of cancer cells. In addition, it has been demonstrated that the regulation of proline metabolic enzymes at the genetic and post-translational levels is related to cancer. This article reviews the role of proline metabolic enzymes in cancer proliferation, apoptosis, metastasis, and development. Research on proline metabolism may provide a new strategy for cancer treatment.

SPG9A with the new occurrence of an ALDH18A1 mutation in a CMT1A family with PMP22 duplication: case report.

BACKGROUND: ALDH18A1 mutations lead to delta-1-pyrroline-5-carboxylate-synthetase (P5CS) deficiency, which is a urea cycle-related disorder including SPG9A, SPG9B, autosomal dominant cutis laxa-3 (ADCL3), and autosomal recessive cutis laxa type 3A (ARCL3A). These diseases exhibit a broad clinical spectrum, which makes the diagnosis of P5CS deficiency difficult. We report here a rare Japanese family including both patients with an ALDH18A1 mutation (SPG9A) and ones with CMT1A. CASE PRESENTATION: A Japanese family included five patients with the CMT phenotype and five with the HSP phenotype in four generations. The patients with the HSP phenotype showed a pure or complicated form, and intrafamilial clinical variability was noted. Genetically, FISH analysis revealed that two CMT patients had a PMP22 duplication (CMT1A). Exome analysis and Sanger sequencing revealed five HSP patients had an ALDH18A1 heterozygous mutation of c.755G > A, which led to SPG9A. Haplotype analysis revealed that the ALDH18A1 mutation must have newly occurred. To date, although de novo mutations of ALDH18A1 have been described in ADCL3A, they were not mentioned in SPG9A in earlier reports. Thus, this is the first SPG9A family with a de novo mutation or the new occurrence of gonadal mosaicism of ALDH18A1. Analysis of serum amino acid levels revealed that two SPG9A patients and two unaffected family members had low citrulline levels and one had a low level of ornithine. CONCLUSIONS: Since the newly occurring ALDH18A1 mutation, c.755G > A, is the same as that in two ADHSP families and one sporadic patient with SPG9A reported previously, this genomic site might easily undergo mutation. The patients with the c.755G > A mutation in our family showed clinical variability of symptoms like in the earlier reported two families and one sporadic patient with this mutation. Further studies are required to clarify the relationship between the amino acid levels and clinical manifestations, which will reveal how P5CS deficiency influences disease phenotypes including ARCL3A, ADCL3, SPG9B, and SPG9A.

Clinical and Molecular Delineation of Cutis Laxa Syndromes: Paradigms for Homeostasis.

Cutis laxa (CL) syndromes are a large and heterogeneous group of rare connective tissue disorders that share loose redundant skin as a hallmark clinical feature, which reflects dermal elastic fiber fragmentation. Both acquired and congenital-Mendelian- forms exist. Acquired forms are progressive and often preceded by inflammatory triggers in the skin, but may show systemic elastolysis. Mendelian forms are often pleiotropic in nature and classified upon systemic manifestations and mode of inheritance. Though impaired elastogenesis is a common denominator in all Mendelian forms of CL, the underlying gene defects are diverse and affect structural components of the elastic fiber or impair metabolic pathways interfering with cellular trafficking, proline synthesis, or mitochondrial functioning. In this chapter we provide a detailed overview of the clinical and molecular characteristics of the different cutis laxa types and review the latest insights on elastic fiber assembly and homeostasis from both human and animal studies.

Δ1 -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder.

The bifunctional homooligomeric enzyme Δ1 -pyrroline-5-carboxylate synthetase (P5CS) and its encoding gene ALDH18A1 were associated with disease in 1998. Two siblings who presented paradoxical hyperammonemia (alleviated by protein), mental disability, short stature, cataracts, cutis laxa, and joint laxity, were found to carry biallelic ALDH18A1 mutations. They showed biochemical indications of decreased ornithine/proline synthesis, agreeing with the role of P5CS in the biosynthesis of these amino acids. Of 32 patients reported with this neurocutaneous syndrome, 21 familial ones hosted homozygous or compound heterozygous ALDH18A1 mutations, while 11 sporadic ones carried de novo heterozygous ALDH18A1 mutations. In 2015 to 2016, an upper motor neuron syndrome (spastic paraparesis/paraplegia SPG9) complicated with some traits of the neurocutaneous syndrome, although without report of cutis laxa, joint laxity, or herniae, was associated with monoallelic or biallelic ALDH18A1 mutations with, respectively, dominant and recessive inheritance. Of 50 SPG9 patients reported, 14 and 36 (34/2 familial/sporadic) carried, respectively, biallelic and monoallelic mutations. Thus, two neurocutaneous syndromes (recessive and dominant cutis laxa 3, abbreviated ARCL3A and ADCL3, respectively) and two SPG9 syndromes (recessive SPG9B and dominant SPG9A) are caused by essentially different spectra of ALDH18A1 mutations. On the bases of the clinical data (including our own prior patients' reports), the ALDH18A1 mutations spectra, and our knowledge on the P5CS protein, we conclude that the four syndromes share the same pathogenic mechanisms based on decreased P5CS function. Thus, these syndromes represent a continuum of increasing severity (SPG9A < SPG9B < ADCL3 ≤ ARCL3A) of the same disease, P5CS deficiency, in which the dominant mutations cause loss-of-function by dominant-negative mechanisms.

Glutamine to proline conversion is associated with response to glutaminase inhibition in breast cancer.

INTRODUCTION: Glutaminase inhibitors target cancer cells by blocking the conversion of glutamine to glutamate, thereby potentially interfering with anaplerosis and synthesis of amino acids and glutathione. The drug CB-839 has shown promising effects in preclinical experiments and is currently undergoing clinical trials in several human malignancies, including triple-negative breast cancer (TNBC). However, response to glutaminase inhibitors is variable and there is a need for identification of predictive response biomarkers. The aim of this study was to determine how glutamine is utilized in two patient-derived xenograft (PDX) models of breast cancer representing luminal-like/ER+ (MAS98.06) and basal-like/triple-negative (MAS98.12) breast cancer and to explore the metabolic effects of CB-839 treatment. EXPERIMENTAL: MAS98.06 and MAS98.12 PDX mice received CB-839 (200 mg/kg) or drug vehicle two times daily p.o. for up to 28 days (n = 5 per group), and the effect on tumor growth was evaluated. Expression of 60 genes and seven glutaminolysis key enzymes were determined using gene expression microarray analysis and immunohistochemistry (IHC), respectively, in untreated tumors. Uptake and conversion of glutamine were determined in the PDX models using HR MAS MRS after i.v. infusion of [5-13C] glutamine when the models had received CB-839 (200 mg/kg) or vehicle for 2 days (n = 5 per group). RESULTS: Tumor growth measurements showed that CB-839 significantly inhibited tumor growth in MAS98.06 tumors, but not in MAS98.12 tumors. Gene expression and IHC analysis indicated a higher proline synthesis from glutamine in untreated MAS98.06 tumors. This was confirmed by HR MAS MRS of untreated tumors demonstrating that MAS98.06 used glutamine to produce proline, glutamate, and alanine, and MAS98.12 to produce glutamate and lactate. In both models, treatment with CB-839 resulted in accumulation of glutamine. In addition, CB-839 caused depletion of alanine, proline, and glutamate ([1-13C] glutamate) in the MAS98.06 model. CONCLUSION: Our findings indicate that TNBCs may not be universally sensitive to glutaminase inhibitors. The major difference in the metabolic fate of glutamine between responding MAS98.06 xenografts and non-responding MAS98.12 xenografts is the utilization of glutamine for production of proline. We therefore suggest that addiction to proline synthesis from glutamine is associated with response to CB-839 in breast cancer. The effect of glutaminase inhibition in two breast cancer patient-derived xenograft (PDX) models. 13C HR MAS MRS analysis of tumor tissue from CB-839-treated and untreated models receiving 13C-labeled glutamine ([5-13C] Gln) shows that the glutaminase inhibitor CB-839 is causing an accumulation of glutamine (arrow up) in two PDX models representing luminal-like breast cancer (MAS98.06) and basal-like breast cancer (MAS98.12). In MAS98.06 tumors, CB-839 is in addition causing depletion of proline ([5-13C] Pro), alanine ([1-13C] Ala), and glutamate ([1-13C] Glu), which could explain why CB-839 causes tumor growth inhibition in MAS98.06 tumors, but not in MAS98.12 tumors.

Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia.

Mutations in ALDH18A1 can cause autosomal recessive and dominant hereditary spastic paraplegia and autosomal recessive and dominant cutis laxa. ALDH18A1 encodes delta-1-pyrroline-5-carboxylate synthetase (P5CS), which consists of two domains, the glutamate 5-kinase (G5K) and the gamma-glutamyl phosphate reductase (GR5P) domain. The location of the mutations in the gene has influence on whether the amino acid levels are affected. Mutations affecting the G5K domain have previously been found to cause reduced plasma levels of proline, citrulline and arginine, whereas such effect is not seen with mutations affecting the GR5P domain. We present a 19-year old male patient with autosomal recessive spastic paraplegia and compound heterozygosity for two ALDH18A1 mutations, one in each of the P5CS domains. This young man has spastic paraplegia with onset in childhood and temporal lobe epilepsy, but normal levels of proline, ornithine and arginine. To our knowledge, this is the first case with compound heterozygous mutations affecting both P5CS domains, where levels of plasma amino acids have been reported.

Recurrent De Novo Mutations Affecting Residue Arg138 of Pyrroline-5-Carboxylate Synthase Cause a Progeroid Form of Autosomal-Dominant Cutis Laxa.

Progeroid disorders overlapping with De Barsy syndrome (DBS) are collectively denoted as autosomal-recessive cutis laxa type 3 (ARCL3). They are caused by biallelic mutations in PYCR1 or ALDH18A1, encoding pyrroline-5-carboxylate reductase 1 and pyrroline-5-carboxylate synthase (P5CS), respectively, which both operate in the mitochondrial proline cycle. We report here on eight unrelated individuals born to non-consanguineous families clinically diagnosed with DBS or wrinkly skin syndrome. We found three heterozygous mutations in ALDH18A1 leading to amino acid substitutions of the same highly conserved residue, Arg138 in P5CS. A de novo origin was confirmed in all six probands for whom parental DNA was available. Using fibroblasts from affected individuals and heterologous overexpression, we found that the P5CS-p.Arg138Trp protein was stable and able to interact with wild-type P5CS but showed an altered sub-mitochondrial distribution. A reduced size upon native gel electrophoresis indicated an alteration of the structure or composition of P5CS mutant complex. Furthermore, we found that the mutant cells had a reduced P5CS enzymatic activity leading to a delayed proline accumulation. In summary, recurrent de novo mutations, affecting the highly conserved residue Arg138 of P5CS, cause an autosomal-dominant form of cutis laxa with progeroid features. Our data provide insights into the etiology of cutis laxa diseases and will have immediate impact on diagnostics and genetic counseling.

Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia.

Hereditary spastic paraplegias are heterogeneous neurological disorders characterized by a pyramidal syndrome with symptoms predominantly affecting the lower limbs. Some limited pyramidal involvement also occurs in patients with an autosomal recessive neurocutaneous syndrome due to ALDH18A1 mutations. ALDH18A1 encodes delta-1-pyrroline-5-carboxylate synthase (P5CS), an enzyme that catalyses the first and common step of proline and ornithine biosynthesis from glutamate. Through exome sequencing and candidate gene screening, we report two families with autosomal recessive transmission of ALDH18A1 mutations, and predominant complex hereditary spastic paraplegia with marked cognitive impairment, without any cutaneous abnormality. More interestingly, we also identified monoallelic ALDH18A1 mutations segregating in three independent families with autosomal dominant pure or complex hereditary spastic paraplegia, as well as in two sporadic patients. Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency. Glutamine loading tests in two fibroblast cultures from two related affected subjects confirmed a metabolic block at the level of P5CS in vivo. Besides expanding the clinical spectrum of ALDH18A1-related pathology, we describe mutations segregating in an autosomal dominant pattern. The latter are associated with a potential trait biomarker; we therefore suggest including amino acid chromatography in the clinico-genetic work-up of hereditary spastic paraplegia, particularly in dominant cases, as the associated phenotype is not distinct from other causative genes.

Severe congenital cutis laxa with cardiovascular manifestations due to homozygous deletions in ALDH18A1.

Autosomal recessive cutis laxa (ARCL) type 2 constitutes a heterogeneous group of diseases mainly characterized by lax and wrinkled skin, skeletal anomalies, and a variable degree of intellectual disability. ALDH18A1-related ARCL is the most severe form within this disease spectrum. Here we report on the clinical and molecular findings of two affected individuals from two unrelated families. The patients presented with typical features of de Barsy syndrome and an overall progeroid appearance. However, the phenotype was highly variable including cardiovascular involvement in the more severe case. Investigation of a skin biopsy of one patient revealed not only the typical alterations of elastic fibers, but also an altered structure of mitochondria in cutaneous fibroblasts. Using conventional sequencing and copy number analysis we identified a frameshift deletion of one nucleotide and a microdeletion affecting the ALDH18A1 gene, respectively, in a homozygous state in both patients. Expression analysis in dermal fibroblasts from the patient carrying the microdeletion showed an almost complete absence of the ALDH18A1 mRNA resulting in an absence of the ALDH18A1 protein. So far, only 13 affected individuals from seven unrelated families suffering from ALDH18A1-related cutis laxa have been described in literature. Our findings provide new insights into the clinical spectrum and show that beside point mutations microdeletions are a possible cause of ALDH18A1-ARCL.

Deciphering glutamine metabolism patterns for malignancy and tumor microenvironment in clear cell renal cell carcinoma.

Clear cell renal cell carcinoma (ccRCC) is the most common subtype of kidney cancer characterized by metabolic reprogramming. Glutamine metabolism is pivotal in metabolic reprogramming, contributing to the significant heterogeneity observed in ccRCC. Consequently, developing prognostic markers associated with glutamine metabolism could enhance personalized treatment strategies for ccRCC patients. This study obtained RNA sequencing and clinical data from 763 ccRCC cases sourced from multiple databases. Consensus clustering of 74 glutamine metabolism related genes (GMRGs)- profiles stratified the patients into three clusters, each of which exhibited distinct prognosis, tumor microenvironment, and biological characteristics. Then, six genes (SMTNL2, MIOX, TMEM27, SLC16A12, HRH2, and SAA1) were identified by machine-learning algorithms to develop a predictive signature related to glutamine metabolism, termed as GMRScore. The GMRScore showed significant differences in clinical prognosis, expression profile of immune checkpoints, abundance of immune cells, and immunotherapy response of ccRCC patients. Besides, the nomogram incorporating the GMRScore and clinical features showed strong predictive performance in prognosis of ccRCC patients. ALDH18A1, one of the GRMGs, exhibited elevated expression level in ccRCC and was related to markedly poorer prognosis in the integrated cohort, validated by proteomic profiling of 232 ccRCC samples from Fudan University Shanghai Cancer Center (FUSCC). Conducting western blotting, CCK-8, transwell, and flow cytometry assays, we found the knockdown of ALDH18A1 in ccRCC significantly promoted apoptosis and inhibited proliferation, invasion, and epithelial-mesenchymal transition (EMT) in two human ccRCC cell lines (786-O and 769-P). In conclusion, we developed a glutamine metabolism-related prognostic signature in ccRCC, which is tightly linked to the tumor immune microenvironment and immunotherapy response, potentially facilitating precision therapy for ccRCC patients. Additionally, this study revealed the key role of ALDH18A1 in promoting ccRCC progression for the first time.

Autosomal recessive cutis laxa type IIIA: Report of a patient with severe phenotype and review of the literature.

Autosomal recessive cutis laxa type IIIA is a very rare genetic condition, caused by pathogenic variants in ALDH18A1, encoding delta-1-pyrroline-5-carboxylate synthase (P5CS). This enzyme catalyzes the reduction of glutamic acid to delta1-pyrroline-5-carboxylate, playing a key role in the de novo biosynthesis of proline, ornithine, and arginine. Autosomal recessive cutis laxa type IIIA is characterized by abundant and wrinkled skin, skeletal anomalies, cataract or corneal clouding and neuro-developmental disorders of variable degree. We report on a patient with autosomal recessive cutis laxa type IIIA, due to a homozygous missense c.1273C > T; p. (Arg425Cys) pathogenic variant in ALDH18A1. The patient presented a severe phenotype with serious urological involvement, peculiar cerebro-vascular abnormalities and neurodevelopmental compromise. This description contributes to better characterize the phenotypic spectrum associated with ALDH18A1 pathogenic variants, confirming the systemic involvement as a typical feature of autosomal recessive cutis laxa type IIIA.

Novel Compound Missense and Intronic Splicing Mutation in ALDH18A1 Causes Autosomal Recessive Spastic Paraplegia.

Background: Hereditary spastic paraplegia (HSP) caused by mutations in ALDH18A1 have been reported as spastic paraplegia 9 (SPG9), with autosomal dominant and autosomal recessive transmission (SPG9A and SPG9B). SPG9 is rare and has shown phenotypic and genotypic heterogeneity in previous reports. Methods: This study screened ALDH18A1 mutations in autosomal recessive HSP patients using combined whole exome sequencing and RNA splicing analysis. We conducted in silico investigations, co-segregation analysis, and ELISA-based analysis of P5CS (Δ1-pyrroline-5-carboxylate synthetase; encoded by ALDH18A1) concentration to validate the pathogenicity of the detected ALDH18A1 variants. All previously reported bi-allelic ALDH18A1 mutations and cases were reviewed to summarize the genetic and clinical features of ALDH18A1-related HSP. Results: A novel missense mutation c.880T>C, p.S294P and an intronic splicing mutation c.-28-13A>G were both detected in ALDH18A1 in an autosomal recessive family presenting with a complicated form HSP. ELISA assays revealed significantly decreased P5CS concentration in the proband's plasma compared with that in the healthy controls. Moreover, review of previously reported recessive cases showed that SPG9B patients in our cohort presented with milder symptoms, i.e., later age at onset and without cognitive impairment. Conclusion: The present study expands the genetic and clinical spectrum of SPG9B caused by ALDH18A1 mutation. Our work defines new genetic variants to facilitate future diagnoses, in addition to demonstrating the highly informative value of splicing mutation prediction in the characterization of disease-related intronic variants.

Tremor as an early sign of hereditary spastic paraplegia due to mutations in ALDH18A1.

BACKGROUND: The ALDH18A1 gene is located at 10q24.1 and encodes delta-1-pyrroline-5-carboxylate synthetase (P5CS), a mitochondrial bifunctional enzyme that catalyzes the first two steps in de novo biosynthesis of proline, ornithine, citrulline, and arginine. ALDH18A1-related disorders have been classified into four groups, such as autosomal dominant and recessive hereditary spastic paraplegia (SPG9A and SPG9B, respectively), as well as autosomal dominant and recessive cutis laxa (ADCL3 and ARCL3A, respectively). Neurodegeneration is a characteristic feature of all groups. CASE REPORT: Here, we report a girl with compound heterozygous disease-causing variants (c.-28-2A>G and c.383G>A, p.Arg128His) in the ALDH18A1 gene, revealed by whole exome sequencing. The c.-28-2A>G variant in intron 1, inherited from the mother, is a novel mutation, while the c.383G>A variant in exon 4, inherited from the father, has already been reported. The patient presented with vigorous infantile tremor preceding progressive spastic paraplegia. Dysmorphic features included elongated face, deep-set ears, upturned nose, long philtrum and pointed chin. Intrauterine and postnatal growth retardation, microcephaly, global developmental delay and profound intellectual disability were also noticed. Blood fasting ammonia level, plasma proline, ornithine and arginine levels were normal, while citrulline level was slightly decreased. Brain MRI revealed moderate hypoplasia of the corpus callosum and reduction of white matter volume. CONCLUSIONS: The patient represents SPG9B, a rare form of autosomal recessive hereditary spastic paraplegias. The early onset tremor, preceding lower limb spasticity appears to be a unique early manifestation of neurodegeneration in this case.

Salubrinal in Combination With 4E1RCat Synergistically Impairs Melanoma Development by Disrupting the Protein Synthetic Machinery.

Increased protein synthesis is a key process in melanoma, which is regulated by the ALDH18A1 gene encoding pyrroline-5-carboxylate synthase (P5CS). P5CS is involved in proline biosynthesis and targeting ALDH18A1 has previously been shown to inhibit melanoma development by decreasing intracellular proline levels to increase the phosphorylation of eIF2α mediated by GCN2, which then impairs mRNA translation. Since there are no current inhibitors of P5CS, decreased eIF2α phosphorylation in melanoma was targeted using salubrinal (a specific inhibitor of eIF2α phosphatase enzymes). While salubrinal alone was ineffective, the combined use of salubrinal and 4E1RCat (a dual inhibitor of eIF4E:4E-BP1 and eIF4E:eIF4G interaction to prevent assembly of the eIF4F complex and inhibit cap-dependent translation) was found to be effective at decreasing protein synthesis, protein translation, and cell cycle progression to synergistically decrease melanoma cell viability and inhibited xenograft melanoma tumor development. The combination of these agents synergistically decreased melanoma cell viability while having minimal effect on normal cells. This is the first report demonstrating that it is possible to inhibit melanoma viability by targeting eIF2α signaling using salubrinal and 4E1RCat to disrupt assembly of the eIF4F complex.

The Role of MYCN in Symmetric vs. Asymmetric Cell Division of Human Neuroblastoma Cells.

Asymmetric cell division (ACD) is an important physiological event in the development of various organisms and maintenance of tissue homeostasis. ACD produces two different cells in a single cell division: a stem/progenitor cell and differentiated cell. Although the balance between self-renewal and differentiation is precisely controlled, disruptions to ACD and/or enhancements in the self-renewal division (symmetric cell division: SCD) of stem cells resulted in the formation of tumors in Drosophila neuroblasts. ACD is now regarded as one of the characteristics of human cancer stem cells, and is a driving force for cancer cell heterogeneity. We recently reported that MYCN controls the balance between SCD and ACD in human neuroblastoma cells. In this mini-review, we discuss the mechanisms underlying MYCN-mediated cell division fate.

Proline Metabolism in Tumor Growth and Metastatic Progression.

Cancer cells show a formidable capacity to survive under stringent conditions, to elude mechanisms of control, such as apoptosis, and to resist therapy. Cancer cells reprogram their metabolism to support uncontrolled proliferation and metastatic progression. Phenotypic and functional heterogeneity are hallmarks of cancer cells, which endow them with aggressiveness, metastatic capacity, and resistance to therapy. This heterogeneity is regulated by a variety of intrinsic and extrinsic stimuli including those from the tumor microenvironment. Increasing evidence points to a key role for the metabolism of non-essential amino acids in this complex scenario. Here we discuss the impact of proline metabolism in cancer development and progression, with particular emphasis on the enzymes involved in proline synthesis and catabolism, which are linked to pathways of energy, redox, and anaplerosis. In particular, we emphasize how proline availability influences collagen synthesis and maturation and the acquisition of cancer cell plasticity and heterogeneity. Specifically, we propose a model whereby proline availability generates a cycle based on collagen synthesis and degradation, which, in turn, influences the epigenetic landscape and tumor heterogeneity. Therapeutic strategies targeting this metabolic-epigenetic axis hold great promise for the treatment of metastatic cancers.

Hereditary Spastic Paraplegia Is a Common Phenotypic Finding in ARG1 Deficiency, P5CS Deficiency and HHH Syndrome: Three Inborn Errors of Metabolism Caused by Alteration of an Interconnected Pathway of Glutamate and Urea Cycle Metabolism.

Hereditary Spastic Paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative disorders characterized by a progressive rigidity and weakness of the lower limbs, caused by pyramidal tract lesions. As of today, 80 different forms of HSP have been mapped, 64 genes have been cloned, and new forms are constantly being described. HSPs represent an intensively studied field, and the functional understanding of the biochemical and molecular pathogenetic pathways are starting to be elucidated. Recently, dominant and recessive mutations in the ALDH18A1 gene resulting in the deficiency of the encoded enzyme (delta-1-pyrroline-5-carboxylate synthase, P5CS) have been pathogenetically linked to HSP. P5CS is a critical enzyme in the conversion of glutamate to pyrroline-5-carboxylate, an intermediate that enters in the proline biosynthesis and that is connected with the urea cycle. Interestingly, two urea cycle disorders, Argininemia and Hyperornithinemia-Hyperammonemia-Homocitrullinuria syndrome, are clinically characterized by highly penetrant spastic paraplegia. These three diseases represent a peculiar group of HSPs caused by Inborn Errors of Metabolism. Here we comment on these forms, on the common features among them and on the hypotheses for possible shared pathogenetic mechanisms causing the HSP phenotype.

Imaging in cutis laxa syndrome caused by a dominant negative ALDH18A1 mutation, with hypotheses for intracranial vascular tortuosity and wide perivascular spaces.

The autosomal dominant progeroid form of cutis laxa is a recently identified multiple congenital anomaly disorder characterized by thin, wrinkled skin, a progeroid appearance, intra-uterine growth retardation, postnatal growth restriction, psychomotor developmental delay, microcephaly, cataract, hypotonia and contractures. De novo heterozygous mutations in ALDH18A1 have been described in this condition. We present neuroimaging abnormalities in three patients. One patient had intracranial arterial and venous tortuosity, widened ventricular and extra-axial cerebrospinal fluid (CSF) spaces, wide perivascular spaces and increased T2 signal intensity in the cerebral white matter over time. The second patient had vascular tortuosity. The third patient had prominent ventricular and extra-axial cerebrospinal fluid (CSF) spaces on CT. We propose an embryological mechanism for the development of intracranial vascular tortuosity and discuss the anatomical basis of wide perivascular spaces in relation to this syndrome. Although we do not know the clinical implications of these cerebral vascular anomalies, we suggest inclusion of neuroimaging in the baseline evaluation of these patients.