Acylglycerol Kinase Research Articles

Sengers syndrome: six novel AGK mutations in seven new families and review of the phenotypic and mutational spectrum of 29 patients.

BackgroundSengers syndrome is an autosomal recessive condition characterized by congenital cataract, hypertrophic cardiomyopathy, skeletal myopathy and lactic acidosis. Mutations in the acylglycerol kinase (AGK) gene have been recently described as the cause of Sengers syndrome in nine families.MethodsWe investigated the clinical and molecular features of Sengers syndrome in seven new families; five families with the severe and two with the milder form.ResultsSequence analysis of AGK revealed compound heterozygous or homozygous predicted loss-of-function mutations in all affected individuals. A total of eight different disease alleles were identified, of which six were novel, homozygous c.523_524delAT (p.Ile175Tyrfs*2), c.424-1G > A (splice site), c.409C > T (p.Arg137*) and c.877 + 3G > T (splice site), and compound heterozygous c.871C > T (p.Gln291*) and c.1035dup (p.Ile346Tyrfs*39). All patients displayed perinatal or early-onset cardiomyopathy and cataract, clinical features pathognomonic for Sengers syndrome. Other common findings included blood lactic acidosis and tachydyspnoea while nystagmus, eosinophilia and cervical meningocele were documented in only either one or two cases. Deficiency of the adenine nucleotide translocator was found in heart and skeletal muscle biopsies from two patients associated with respiratory chain complex I deficiency. In contrast to previous findings, mitochondrial DNA content was normal in both tissues.ConclusionWe compare our findings to those in 21 previously reported AGK mutation-positive Sengers patients, confirming that Sengers syndrome is a clinically recognisable disorder of mitochondrial energy metabolism.

Acylglycerol kinase promotes cell proliferation and tumorigenicity in breast cancer via suppression of the FOXO1 transcription factor.

BackgroundAcylglycerol kinase (AGK) is reported to be overexpressed in multiple cancers. The clinical significance and biological role of AGK in breast cancer, however, remain to be established.MethodsAGK expression in breast cancer cell lines, paired patient tissues were determined using immunoblotting and Real-time PCR. 203 human breast cancer tissue samples were analyzed by immunochemistry (IHC) to investigate the relationship between AGK expression and the clinicopathological features of breast cancer. Functional assays, such as colony formation, anchorage-independent growth and BrdU assay, and a xenograft tumor model were used to determine the oncogenic role of AGK in human breast cancer progression. The effect of AGK on FOXO1 transactivity was further investigated using the luciferase reporter assays, and by detection of the FOXO1 downstream genes.ResultsHerein, we report that AGK was markedly overexpressed in breast cancer cells and clinical tissues. Immunohistochemical analysis showed that the expression of AGK significantly correlated with patients’ clinicopathologic characteristics, including clinical stage and tumor-nodule-metastasis (TNM) classification. Breast cancer patients with higher levels of AGK expression had shorter overall survival compared to patients with lower AGK levels. We gained valuable insights into the mechanism of AGK expression in breast cancer cells by demonstrating that overexpressing AGK significantly enhanced, whereas silencing endogenous AGK inhibited, the proliferation and tumorigenicity of breast cancer cells both in vitro and in vivo. Furthermore, overexpression of AGK enhanced G1-S phase transition in breast cancer cells, which was associated with activation of AKT, suppression of FOXO1 transactivity, downregulation of cyclin-dependent kinase inhibitors p21 Cip1 and p27 Kip1 and upregulation of the cell cycle regulator cyclin D1.ConclusionsTaken together, these findings provide new evidence that AGK plays an important role in promoting proliferation and tumorigenesis in human breast cancer and may serve as a novel prognostic biomarker and therapeutic target in this disease.

Sengers syndrome is caused by a deficiency of the acylglycerol kinase

Sengers syndrome is caused by a deficiency of the acylglycerol kinase

Identification of kinase fusion oncogenes in post-Chernobyl radiation-induced thyroid cancers

Exposure to ionizing radiation during childhood markedly increases the risk of developing papillary thyroid cancer. We examined tissues from 26 Ukrainian patients with thyroid cancer who were younger than 10 years of age and living in contaminated areas during the time of the Chernobyl nuclear reactor accident. We identified nonoverlapping somatic driver mutations in all 26 cases through candidate gene assays and next-generation RNA sequencing. We found that 22 tumors harbored fusion oncogenes that arose primarily through intrachromosomal rearrangements. Altogether, 23 of the oncogenic drivers identified in this cohort aberrantly activate MAPK signaling, including the 2 somatic rearrangements resulting in fusion of transcription factor ETS variant 6 (ETV6) with neurotrophic tyrosine kinase receptor, type 3 (NTRK3) and fusion of acylglycerol kinase (AGK) with BRAF. Two other tumors harbored distinct fusions leading to overexpression of the nuclear receptor PPARγ. Fusion oncogenes were less prevalent in tumors from a cohort of children with pediatric thyroid cancers that had not been exposed to radiation but were from the same geographical regions. Radiation-induced thyroid cancers provide a paradigm of tumorigenesis driven by fusion oncogenes that activate MAPK signaling or, less frequently, a PPARγ-driven transcriptional program.

Mitochondrial citrate synthase crystals: Novel finding in Sengers syndrome caused by acylglycerol kinase (AGK) mutations

We report on two families with Sengers syndrome and mutations in the acylglycerol kinase gene (AGK). In the first family, two brothers presented with vascular strokes, lactic acidosis, cardiomyopathy and cataracts, abnormal muscle cell histopathology and mitochondrial function. One proband had very abnormal mitochondria with citrate synthase crystals visible in electron micrographs, associated with markedly high citrate synthase activity. Exome sequencing was used to identify mutations in the AGK gene in the index patient. Targeted sequencing confirmed the same homozygous mutation (c.3G>A, p.M1I) in the brother. The second family had four affected members, of which we examined two. They also presented with similar clinical symptoms, but no strokes. Postmortem heart and skeletal muscle tissues showed low complex I, III and IV activities in the heart, but normal in the muscle. Skin fibroblasts showed elevated lactate/pyruvate ratios and low complex I+III activity. Targeted sequencing led to identification of a homozygous c.979A>T, p.K327* mutation.AGK is located in the mitochondria and phosphorylates monoacylglycerol and diacylglycerol to lysophosphatidic acid and phosphatidic acid. Disruption of these signaling molecules affects the mitochondria's response to superoxide radicals, resulting in oxidative damage to mitochondrial DNA, lipids and proteins, and stimulation of cellular detoxification pathways. High levels of manganese superoxide dismutase protein were detected in all four affected individuals, consistent with increased free radical damage. Phosphatidic acid is also involved in the synthesis of phospholipids and its loss will result in changes to the lipid composition of the inner mitochondrial membrane. These effects manifest as cataract formation in the eye, respiratory chain dysfunction and cardiac hypertrophy in heart tissue.These two pedigrees confirm that mutation of AGK is responsible for the severe neonatal presentation of Sengers syndrome. The identification of citrate synthase precipitates by electron microscopy and the presence of vascular strokes in two siblings may expand the cellular and clinical phenotype of this disease.

Expression of lysophosphatidic acid, autotaxin and acylglycerol kinase

AbstractPurpose To measure the levels of LPA and LPA‐producing enzymes, autotaxin (ATX) and acylglycerol kinase (AGK) in the vitreous fluid from patients with proliferative diabetic retinopathy (PDR) and to correlate their levels with clinical disease activity and the level of vascular endothelial growth factor (VEGF). In addition, we examined the expression of ATX, AGK and VEGFR‐2 in the retinas of diabetic rats.Methods Vitreous samples from 42 PDR and 35 nondiabetic patients were studied by enzyme‐linked immunosorbent assay. Vitreous samples and retinas of rats were examined by Western blot analysis.Results VEGF, LPA and AGK levels in vitreous samples from PDR patients were significantly higher than those in control patients without diabetes (p<0.001 for all comparisons). ATX levels in PDR with active neovascularization and inactive PDR were significantly lower than those in nondiabetic patients (p=0.045). Mean VEGF and AGK levels in PDR with active neovascularization were significantly higher than those in inactive PDR and nondiabetic patients (p<0.001 for both comparisons). A significant correlation was observed between levels of VEGF and levels of AGK in PDR patients (r=0.954, p<0.001). Western blot analysis revealed a significant increase in the expression of AGK and VEGFR‐2 in vitreous samples and the retinas of diabetic rats compared to nondiabetic controls, whereas ATX was significantly downregulated.Conclusion ATX‐AGK‐LPA signaling axis might be an important player in the development and progression of diabetic retinopathy.

Expression of lysophosphatidic acid, autotaxin and acylglycerol kinase as biomarkers in diabetic retinopathy

The proinflammatory lysophosphatidic acid (LPA) is a potent activator of several transcriptional factors and signaling pathways and a potent modulator of genes involved in inflammation, angiogenesis and fibrosis. This study was conducted to measure the levels of LPA and LPA-producing enzymes, autotaxin (ATX) and acylglycerol kinase (AGK) in the vitreous fluid from patients with proliferative diabetic retinopathy (PDR) and to correlate their levels with clinical disease activity and the level of vascular endothelial growth factor (VEGF). In addition, we examined the expression of ATX, AGK and VEGF receptor-2 (VEGFR-2) in the retinas of diabetic rats. Vitreous samples from 42 PDR and 35 nondiabetic patients were studied by enzyme-linked immunosorbent assay. Vitreous samples and retinas of rats were examined by Western blot analysis. VEGF, LPA and AGK levels in vitreous samples from PDR patients were significantly higher than those in control patients without diabetes (p < 0.001 for all comparisons). ATX levels in PDR with active neovascularization and inactive PDR were significantly lower than those in nondiabetic patients (p = 0.045). Mean VEGF and AGK levels in PDR with active neovascularization were significantly higher than those in inactive PDR and nondiabetic patients (p < 0.001 for both comparisons). A significant correlation was observed between levels of VEGF and levels of AGK in PDR patients (r = 0.954; p < 0.001). Western blot analysis revealed a significant increase in the expression of AGK and VEGFR-2 in vitreous samples and the retinas of diabetic rats compared to nondiabetic controls, whereas ATX was significantly downregulated. Our findings suggest that ATX-AGK-LPA signaling axis might be an important player in the development and progression of diabetic retinopathy.

Disorders of phospholipids, sphingolipids and fatty acids biosynthesis: toward a new category of inherited metabolic diseases

We wish to delineate a novel, and rapidly expanding, group of inborn errors of metabolism with neurological/muscular presentations: the defects in phospholipids, sphingolipids and long chain fatty acids biosynthesis. At least 14 disorders have been described so far. Clinical presentations are diverse but can be divided into (1) diseases of the central nervous system; (2) peripheral neuropathies; and (3) muscular/cardiac presentations. (1) Leukodystrophy and/or iron deposits in basal ganglia is a common feature of phospholipase A2 deficiency, fatty acid hydroxylase deficiency, and pantothenate kinase-associated neurodegeneration. Infantile epilepsy has been reported in GM3 synthetase deficiency. Spastic quadriplegia with ichthyosis and intellectual disability are the presenting signs of the elongase 4 deficiency and the Sjogren-Larsson syndrome caused by fatty aldehyde dehydrogenase deficiency. Spastic paraplegia and muscle wasting are also seen in patients with mutations in the neuropathy target esterase gene. (2) Peripheral neuropathy is a prominent feature in PHARC syndrome due to α/β-hydrolase 12 deficiency, and in hereditary sensory autonomic neuropathy type I due to serine palmitoyl-CoA transferase deficiency. (3) Muscular/cardiac presentations include recurrent myoglobinuria in phosphatidate phosphatase 1 (Lipin1) deficiency; cardiomyopathy and multivisceral involvement in Barth syndrome secondary to tafazzin mutations; congenital muscular dystrophy due to choline kinase deficiency, Sengers syndrome due to acylglycerol kinase deficiency and Chanarin Dorfman syndrome due to α/β- hydrolase 5 deficiency. These synthesis defects of complex lipid molecules stand at the frontier between classical inborn errors of metabolism and other genetic diseases involving the metabolism of structural proteins.

Mutations of the Mitochondrial-tRNA Modifier MTO1 Cause Hypertrophic Cardiomyopathy and Lactic Acidosis

Dysfunction of mitochondrial respiration is an increasingly recognized cause of isolated hypertrophic cardiomyopathy. To gain insight into the genetic origin of this condition, we used next-generation exome sequencing to identify mutations in MTO1, which encodes mitochondrial translation optimization 1. Two affected siblings carried a maternal c.1858dup (p.Arg620Lysfs(∗)8) frameshift and a paternal c.1282G>A (p.Ala428Thr) missense mutation. A third unrelated individual was homozygous for the latter change. In both humans and yeast, MTO1 increases the accuracy and efficiency of mtDNA translation by catalyzing the 5-carboxymethylaminomethylation of the wobble uridine base in three mitochondrial tRNAs (mt-tRNAs). Accordingly, mutant muscle and fibroblasts showed variably combined reduction in mtDNA-dependent respiratory chain activities. Reduced respiration in mutant cells was corrected by expressing a wild-type MTO1 cDNA. Conversely, defective respiration of a yeast mto1Δ strain failed to be corrected by an Mto1(Pro622∗) variant, equivalent to human MTO1(Arg620Lysfs∗8), whereas incomplete correction was achieved by an Mto1(Ala431Thr) variant, corresponding to human MTO1(Ala428Thr). The respiratory yeast phenotype was dramatically worsened in stress conditions and in the presence of a paromomycin-resistant (P(R)) mitochondrial rRNA mutation. Lastly, in vivo mtDNA translation was impaired in the mutant yeast strains.

Identification of a truncation mutation of acylglycerol kinase (AGK) gene in a novel autosomal recessive cataract locus

Hereditary forms of cataract are genetically heterogeneous. Mutations in crystallin genes account for most Mendelian forms, but identification of other cataract genes has provided insights into additional molecular mechanisms that control lens transparency. In a multiplex consanguineous family with isolated congenital cataract, we identified a novel autosomal recessive cataract locus on 7q33-q36.1. Exome sequencing revealed a splice-site mutation in AGK, encoding acylglycerol kinase, which we confirm led to aberrant splicing and predicted premature truncation. This is the first mutation in this lipid metabolism gene to be implicated in the development of isolated cataract, although it remains to be seen if the mechanism involves perturbation of lenticular lipid composition or aberrant signaling during lens morphogenesis.

Lack of the Mitochondrial Protein Acylglycerol Kinase Causes Sengers Syndrome

Exome sequencing of an individual with congenital cataracts, hypertrophic cardiomyopathy, skeletal myopathy, and lactic acidosis, all typical symptoms of Sengers syndrome, discovered two nonsense mutations in the gene encoding mitochondrial acylglycerol kinase (AGK). Mutation screening of AGK in further individuals with congenital cataracts and cardiomyopathy identified numerous loss-of-function mutations in an additional eight families, confirming the causal nature of AGK deficiency in Sengers syndrome. The loss of AGK led to a decrease of the adenine nucleotide translocator in the inner mitochondrial membrane in muscle, consistent with a role of AGK in driving the assembly of the translocator as a result of its effects on phospholipid metabolism in mitochondria.

Expression of autotaxin and acylglycerol kinase in proliferative vitreoretinal epiretinal membranes

Lysophosphatidic acid (LPA)/LPA(1) receptor pathway is involved in inflammation, angiogenesis and fibrosis. This study was conducted to analyse the expression of LPA-producing enzymes, autotaxin (ATX) and acylglycerol kinase (AGK) and LPA(1) receptor, in proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR) epiretinal membranes. Nine active and 13 inactive membranes from patients with PDR and 21 membranes from patients with PVR were studied by immunohistochemistry. In PDR membranes, vascular endothelial cells expressed ATX and AGK in 16 and 19 membranes, respectively. Stromal cells expressed ATX and AGK in 19 and 22 membranes, respectively. Immunoreactivity for LPA(1) receptor was noted in vascular endothelial cells and stromal cells in the five membranes stained for LPA(1) receptor. Numbers of blood vessels and stromal cells expressing CD34, ATX and AGK were significantly higher in active membranes than in inactive membranes. Significant correlations were detected between number of blood vessels expressing the panendothelial cell marker CD34 and number of blood vessels and stromal cells expressing ATX and AGK. In PVR membranes, spindle-shaped myofibroblasts expressing α-smooth muscle actin co-expressed ATX, AGK and LPA(1) receptor. The LPA/LPA(1) receptor pathway may be involved in inflammatory, angiogenic and fibrotic responses in proliferative vitreoretinal disorders.

Expression of Autotaxin and Acylglycerol kinase in prostate cancer: Association with cancer development and progression

Lysophosphatidic acid (LPA) may enhance diverse biologic activities in prostate cancer. This study was conducted to analyze expression levels of LPA-producing enzymes, autotaxin (ATX) and acylglycerol kinase (AGK), in prostate cancer with relevance to clinicopathological parameters. Real-time RT-PCR and western blotting were performed for ATX and AGK in non-neoplastic prostate cells (PrECs and PrSCs) and prostate cancer cell-lines (DU-145, PC-3, LNCaP, and AILNCaP). Immunohistochemical analyses were conducted in tissue specimens of 132 localized prostate cancer patients who underwent radical prostatectomy between 2001 and 2007 (median observation period, 22 months). Both enzymes were negatively expressed in PrECs and PrSCs at mRNA and protein levels. ATX expression was higher than AGK in AILNCaP, DU-145, and PC-3 cell-lines, while AGK was mainly expressed in LNCaP cells. Immunohistochemically, ATX and AGK expressions were negative in non-neoplastic epithelia, while both were weakly expressed in the majority of high-grade intra-epithelial neoplasia (HG-PIN). In cancer foci, ATX and AGK expressions were strong in 49% and 62%, weak in 40% and 32%, and negative in 11% and 6%, respectively. Expressions of both enzymes were significantly correlated with primary Gleason grade of cancer foci (P < 0.0001) and capsular invasion (P = 0.03 and 0.003 respectively). ATX expression was significantly correlated with probability of prostate specific antigen (PSA)-failure after surgery (P < 0.0001). In conclusion, LPA-producing enzymes (ATX and AGK) were frequently expressed in prostate cancer cells and precancerous HG-PIN. In particular, high expression levels of ATX were associated with both malignant potentials and poor outcomes.

Role of acylglycerol kinase in LPA-induced IL-8 secretion and transactivation of epidermal growth factor-receptor in human bronchial epithelial cells

LPA (lysophosphatidic acid) is a potent bioactive phospholipid, which regulates a number of diverse cellular responses through G protein-coupled LPA receptors. Intracellular LPA is generated by the phosphorylation of monoacylglycerol by acylglycerol kinase (AGK); however, the role of intracellular LPA in signaling and cellular responses remains to be elucidated. Here, we investigated signaling pathways of IL-8 secretion mediated by AGK and intracellular LPA in human bronchial epithelial cells (HBEpCs). Expression of AGK in HBEpCs was detected by real-time PCR, and overexpressed AGK was mainly localized in mitochondria as determined by immunofluorescence and confocal microscopy. Overexpression of lentiviral AGK wild type increased intracellular LPA production ( approximately 1.8-fold), enhanced LPA-mediated IL-8 secretion, and stimulated tyrosine phosphorylation epidermal growth factor-receptor (EGF-R). Furthermore, downregulation of native AGK by AGK small interfering RNA decreased intracellular LPA levels ( approximately 2-fold) and attenuated LPA-induced p38 MAPK, JNK, and NF-kappaB activation, tyrosine phosphorylation of EGF-R, and IL-8 secretion. These results suggest that native AGK regulates LPA-mediated IL-8 secretion involving MAPKs, NF-kappaB, and transactivation of EGF-R. Thus AGK may play an important role in innate immunity and airway remodeling during inflammation.

Gene expression profiles of lysophosphatidic acid‐related molecules in the prostate: Relevance to prostate cancer and benign hyperplasia

To elucidate gene expression profiles of lysophosphatidic acid (LPA)-related molecules in cancer, pre-cancerous lesion, and benign hyperplasia of the prostate. Prostate tissue samples were surgically obtained from 10 patients with localized prostate cancer and seven patients with invasive bladder cancer. Cancer cells and the corresponding stromal cells from normal prostate, high grade intraepithelial neoplasia (HGPIN), benign hyperplastic glands were isolated by laser capture microdissection. mRNA levels of three LPA receptors, LPA1, LPA2, LPA3, two LPA-synthesizing enzymes, autotaxin (ATX), acylglycerol kinase (AGK), and a LPA-degradation enzyme, prostatic acid phosphatase (PAP), were quantitatively assessed. The expression levels of the same genes were also determined in three human prostate cancer cell lines LNCaP, PC-3, and DU-145. LPA1 mRNA level was significantly decreased in HGPIN and cancer epithelia when compared to the benign glands. LPA3 mRNA level was elevated in cancer epithelia compared to benign glands. LPA3, AGK, and PAP were predominantly expressed in LNCaP cells while LPA1 and ATX gene expressions were found in PC-3 and Du-145 cells. In BPH, AGK was abundantly expressed in the stroma while PAP was predominant in epithelial cells. By acting via LPA3, LPA may play an important role in the development of prostate cancer. Switching of LPA receptor expression from LPA3 to LPA1, may be involved in prostate cancer progression and/or androgen independence. LPA may also play a key role in the development of benign prostatic hyperplasia.

Role of Acylglycerol Kinase in Lysophosphatidic Acid–Induced Transactivation of Epidermal Growth Factor Receptor and Expression of Cyclooxygenase 2 and Interleukin-8 in Primary Human Bronchial Epithelial Cells

Restricted accessAbstractFirst published March 2007Role of Acylglycerol Kinase in Lysophosphatidic Acid–Induced Transactivation of Epidermal Growth Factor Receptor and Expression of Cyclooxygenase 2 and Interleukin-8 in Primary Human Bronchial Epithelial CellsS. Kalari, Y. Zhao, […], E. Berdyshev, P.V. Usatyuk, D. He, and V. Natarajan+3-3View all authors and affiliationsVolume 55, Issue 2https://doi.org/10.1177/108155890705500247

Pathways Involved in EGF‐Stimulated LPA Production by Ovarian Carcinoma Cells

Lysophosphatidic acid (LPA) refers to a family of small lipid mediators involved in diverse cellular processes. LPA binds to G-protein coupled receptors to induce cellular effects that include proliferation, angiogenesis, and migration and metastasis of tumor cells. Levels of LPA have been shown to be increased in the acites fluid surrounding ovarian tumors. Several enzymes are potentially involved in the production and metabolism of LPA, including phospholipase D (PLD), autotaxin (ATX), and acylglycerol kinase (AGK). However, the pathways and mechanisms that regulate LPA production are poorly understood. We have shown that epidermal growth factor (EGF) can stimulate LPA production. We hypothesize that EGF stimulates one or more phospholipase activities to increase LPA production. In this study, LPA levels in the medium increased within 30 minutes after addition of EGF to ovarian cancer cell lines, OVCAR3 and SKOV3. LPA receptor antagonist Ki16425 inhibits both LPA and EGF-induced LPA production in SKOV3 cells. Over-expression of PLD2 increases PLD activity, as does EGF, in OVCAR3 cells and membrane preparations. This over-expression also increases basal levels of LPA production. Levels of mRNA for ATX are reduced in OVCAR3 cells incubated with siRNA for ATX. However, ATX siRNA did not significantly inhibit basal or EGF-stimulated LPA production measured at 30 minutes. Both ovarian cancer cell lines express acylglycerol kinase, another enzyme potentially involved in LPA production. Together, these results suggest that multiple enzymes can participate in LPA production (Supported by DAMD17-01-1-0730).

Critical role of acylglycerol kinase in epidermal growth factor-induced mitogenesis of prostate cancer cells

The bioactive phospholipids, LPA (lysophosphatidic acid) and PA (phosphatidic acid), regulate pivotal processes related to the pathogenesis of cancer. Recently, we cloned a novel type of lipid kinase that phosphorylates monoacylglycerols (such as 2-arachidonoylglycerol, an endogenous cannabinoid receptor ligand) and diacylglycerols, to form LPA and PA, respectively. This AGK (acylglycerol kinase) is highly expressed in prostate cancer cell lines and the results reviewed here suggest that AGK might be a critical player in the initiation and progression of prostate cancer. Intriguingly, down-regulation of endogenous AGK inhibited EGF (epidermal growth factor), but not LPA-induced ERK1/2 (extracellular-signal-regulated kinase 1/2) activation and progression through the S-phase of the cell cycle. In this review, we will summarize the evidence demonstrating that AGK amplifies EGF growth signalling pathways that play an important role in the pathophysiology of prostate cancer. Because LPA has long been implicated as an autocrine and paracrine growth stimulatory factor for prostate cancer cells, the identification of this novel lipid kinase that regulates its production could provide new and useful targets for preventive or therapeutic measures.

Critical role of acylglycerol kinase in epidermal growth factor-induced mitogenesis of prostate cancer cells.

The bioactive phospholipids, LPA (lysophosphatidic acid) and PA (phosphatidic acid), regulate pivotal processes related to the pathogenesis of cancer. Recently, we cloned a novel type of lipid kinase that phosphorylates monoacylglycerols (such as 2-arachidonoylglycerol, an endogenous cannabinoid receptor ligand) and diacylglycerols, to form LPA and PA, respectively. This AGK (acylglycerol kinase) is highly expressed in prostate cancer cell lines and the results reviewed here suggest that AGK might be a critical player in the initiation and progression of prostate cancer. Intriguingly, down-regulation of endogenous AGK inhibited EGF (epidermal growth factor), but not LPA-induced ERK1/2 (extracellular-signal-regulated kinase 1/2) activation and progression through the S-phase of the cell cycle. In this review, we will summarize the evidence demonstrating that AGK amplifies EGF growth signalling pathways that play an important role in the pathophysiology of prostate cancer. Because LPA has long been implicated as an autocrine and paracrine growth stimulatory factor for prostate cancer cells, the identification of this novel lipid kinase that regulates its production could provide new and useful targets for preventive or therapeutic measures.

A novel acylglycerol kinase that produces lysophosphatidic acid modulates cross talk with EGFR in prostate cancer cells

The bioactive phospholipids, lysophosphatidic acid (LPA) and phosphatidic acid (PA), regulate pivotal processes related to the pathogenesis of cancer. Here, we report characterization of a novel lipid kinase, designated acylglycerol kinase (AGK), that phosphorylates monoacylglycerol and diacylglycerol to form LPA and PA, respectively. Confocal microscopy and subcellular fractionation suggest that AGK is localized to the mitochondria. AGK expression was up-regulated in prostate cancers compared with normal prostate tissues from the same patient. Expression of AGK in PC-3 prostate cancer cells markedly increased formation and secretion of LPA. This increase resulted in concomitant transactivation of the EGF receptor and sustained activation of extracellular signal related kinase (ERK) 1/2, culminating in enhanced cell proliferation. AGK expression also increased migratory responses. Conversely, down-regulating expression of endogenous AGK inhibited EGF- but not LPA-induced ERK1/2 activation and progression through the S phase of the cell cycle. Hence, AGK can amplify EGF signaling pathways and may play an important role in the pathophysiology of prostate cancer.