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

Multifaceted role of NF-κB in hepatocellular carcinoma therapy: Molecular landscape, therapeutic compounds and nanomaterial approaches

The predominant kind of liver cancer is hepatocellular carcinoma (HCC) that its treatment have been troublesome difficulties for physicians due to aggressive behavior of tumor cells in proliferation and metastasis. Moreover, stemness of HCC cells can result in tumor recurrence and angiogenesis occurs. Another problem is development of resistance to chemotherapy and radiotherapy in HCC cells. Genomic mutations participate in malignant behavior of HCC and nuclear factor-kappaB (NF-κB) has been one of the oncogenic factors in different human cancers that after nuclear translocation, it binds to promoter of genes in regulating their expression. Overexpression of NF-κB has been well-documented in increasing proliferation and invasion of tumor cells and notably, when its expression enhances, it induces chemoresistance and radio-resistance. Highlighting function of NF-κB in HCC can shed some light on the pathways regulating progression of tumor cells. The first aspect is proliferation acceleration and apoptosis inhibition in HCC cells mediated by enhancement in expression level of NF-κB. Moreover, NF-κB is able to enhance invasion of HCC cells via upregulation of MMPs and EMT, and it triggers angiogenesis as another step for increasing spread of tumor cells in tissues and organs. When NF-κB expression enhances, it stimulates chemoresistance and radio-resistance in HCC cells and by increasing stemness and population of cancer-stem cells, it can provide the way for recurrence of tumor. Overexpression of NF-κB mediates therapy resistance in HCC cells and it can be regulated by non-coding RNAs in HCC. Moreover, inhibition of NF-κB by anti-cancer and epigenetic drugs suppresses HCC tumorigenesis. More importantly, nanoparticles are considered for suppressing NF-κB axis in cancer and their prospectives and results can also be utilized for treatment of HCC. Nanomaterials are promising factors in treatment of HCC and by delivery of genes and drugs, they suppress HCC progression. Furthermore, nanomaterials provide phototherapy in HCC ablation.

Acylglycerol kinase promotes paclitaxel resistance in nasopharyngeal carcinoma cells by regulating FOXM1 via the JAK2/STAT3 pathway

OBJECTIVE

Drug resistance is an important factor that impedes the treatment of nasopharyngeal cancer (NPC). Acylglycerol kinase (AGK) has been found to be overexpressed in NPC and correlates with poor prognosis. Our objective was to demonstrate the effect of AGK on paclitaxel resistance in NPC and determine the underlying mechanisms.

METHODS

MTT assay was employed to determine the IC50 of paclitaxel in NPC cells after different treatments. Flow cytometry assays were employed to evaluate cell apoptosis. RT-qPCR and Western blot assays were used to detect alterations in mRNA and protein expression, respectively. Luciferase assays and chromatin immunoprecipitation (ChIP) assays were used to determine the relationship between and the regulatory effect of STAT3 on the promoter of FOXM1.

RESULTS

AGK was elevated in paclitaxel-resistant NPC cells, and knockdown of AGK suppressed the resistance of CNE1-TR and CNE2-TR cells to paclitaxel. Moreover, upregulation of FOXM1 rescued the effects of AGK knockdown. Furthermore, the JAK2/STAT3 signalling pathway was overactivated in CNE1-TR and CNE2-TR cells, and knockdown of AGK suppressed JAK2/STAT3 signalling. STAT3 was verified to bind to and activate the promoter region of FOXM1. An in vivo tumour xenograft assay also verified that AGK knockdown inhibited tumour growth and mitigated paclitaxel resistance by regulating the JAK2/STAT3/FOXM1 axis.

CONCLUSION

AGK levels were increased in paclitaxel-resistant NPC cells. AGK activates JAK2/STAT3 signalling, thus promoting FOXM1 transcription and eventually enhancing the drug resistance of NPC cells.

Lysophosphatidic acid represses autophagy in prostate carcinoma cells

Lysophosphatidic acid (LPA) is a small signaling phospholipid that mediates diverse functions including cell proliferation, migration, and survival by engaging LPA-agonized G-protein coupled receptors. Autophagy is a survival mechanism in response to nutrient depletion or organellar damage that encloses idle or damaged organelles within autophagosomes that are then delivered to lysosomes for degradation. However, the relationship between LPA and autophagy is largely unknown. The purpose of this study is to elucidate whether LPA affects autophagy through the ERK1/2 and (or) the Akt-mTOR signaling pathways. In this study, we investigated the effect of LPA on autophagy-regulating pathways in various prostate-derived cancer cells including PC3, LNCaP, and Du145 cells grown in complete medium and exposed to serum-free medium. Using Western blotting and ELISA, we determined that LPA stimulates the ERK and mTOR pathways in complete and serum-free medium. The mTOR pathway led to phosphorylation of S6K and ULK, which respectively stimulates protein synthesis and arrests autophagy. Consistent with this, LPA exposure suppressed autophagy as measured by LC3 maturation and formation of GFP-LC3 puncta. Altogether, these results suggest that LPA suffices to activate mTORC1 and suppress autophagy in prostate cancer cells.

Modulation of Nav1.8 by Lysophosphatidic Acid in the Induction of Bone Cancer Pain

Given that lysophosphatidic acid (LPA) and the tetrodotoxin-resistant sodium channel Nav1.8 are both involved in bone cancer pain, the present study was designed to investigate whether crosstalk between the LPA receptor LPA1 (also known as EDG2) and Nav1.8 in the dorsal root ganglion (DRG) contributes to the induction of bone cancer pain. We showed that the EDG2 antagonist Ki16198 blocked the mechanical allodynia induced by intrathecal LPA in naïve rats and attenuated mechanical allodynia in a rat model of bone cancer. EDG2 and Nav1.8 expression in L4-6 DRGs was upregulated following intrathecal or hindpaw injection of LPA. EDG2 and Nav1.8 expression in ipsilateral L4-6 DRGs increased with the development of bone cancer. Furthermore, we showed that EDG2 co-localized with Nav1.8 and LPA remarkably enhanced Nav1.8 currents in DRG neurons, and this was blocked by either a protein kinase C (PKC) inhibitor or a PKCε inhibitor. Overall, we demonstrated the modulation of Nav1.8 by LPA in DRG neurons, and that this probably underlies the peripheral mechanism by which bone cancer pain is induced.

Acylglycerol kinase promotes the proliferation and cell cycle progression of oral squamous cell carcinoma

Cell proliferation is a major underlying cause of mortality amongst patients with oral squamous cell carcinoma (OSCC); however, the underlying mechanisms have remained to be elucidated. Acylglycerol kinase (AGK) is a multisubstrate lipid kinase, which is known to be associated with the progression of various types of human cancer. The present study aimed to investigate the role of AGK in cell proliferation and cell cycle progression in OSCC. The expression levels of AGK were detected in cancerous and adjacent normal tissue samples from four patients with OSCC undergoing surgical resection, and in OSCC cell lines, using the polymerase chain reaction (PCR) and western blot analysis. The effects of AGK on the proliferation and cell cycle progression of OSCC cells were assessed using a short hairpin RNA lentivirus or expressed-plasmid transfection. In addition, the expression levels of cyclin D1 and p21, as well as cell proliferation- and cell cycle-associated proteins were detected by PCR and western blotting. The results of the present study demonstrated that the expression levels of AGK were significantly higher in the cancerous tissues and OSCC cell lines, compared with the adjacent normal tissues and control cells, respectively. Furthermore, MTT and colony formation assays, in addition to flow cytometric analysis were conducted, in order to assess the role of AGK in cell proliferation and cell cycle progression. The cell proliferation and cell cycle progression of an established OSCC cell line were demonstrated to be decreased following AGK knockdown, and enhanced by AGK overexpression in vitro. Aberrant AGK expression in OSCC was shown to be associated with cell proliferation and cell cycle progression. The results of the present study provide evidence that AGK may promote cell proliferation and cell cycle progression in OSCC.

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.

Lysophosphatidic acid signaling in airway epithelium: role in airway inflammation and remodeling

Lysophosphatidic acid (LPA), a potent bioactive phospholipid, induces diverse cellular responses, including cell proliferation, migration, and cytokine release. LPA can be generated intracellularly and extracellularly through multiple synthetic pathways by action of various enzymes, such as phospholipase A(1/2) (PLA(1/2)), phospholipase D (PLD), acylglycerol kinase (AGK), and lysophospholipase D (lysoPLD). Metabolism of LPA is regulated by a family of lipid phosphate phosphatases (LPPs). Significant amounts of LPA have been detected in various biological fluids, including serum, saliva, and bronchoalveolar lavage fluid (BALF). The most significant effects of LPA appear to be through activation of the G-protein-coupled receptors (GPCRs), termed LPA(1-6). LPA regulates gene expression through activation of several transcriptional factors, such as nuclear factor-kappaB (NF-kappaB), AP-1, and C/EBPbeta. In addition to GPCRs, cross-talk between LPA receptors and receptor tyrosine kinases (RTKs) partly regulates LPA-induced intracellular signaling and cellular responses. Airway epithelial cells participate in innate immunity through the release of cytokines, chemokines, lipid mediators, other inflammatory mediators and an increase in barrier function in response to a variety of inhaled stimuli. Expression of LPA receptors has been demonstrated in airway epithelial cells. This review summarizes our recent observations of the role of LPA/LPA-Rs in regulation of airway epithelium, especially in relation to the secretion of pro- and anti-inflammatory mediators and regulation of airway barrier function.

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.

A qualitative proteome investigation of the sediment portion of human urine: Implications in the biomarker discovery process

Inherent to the biomarker discovery process is a comparative analysis of physiological states. It is therefore critical that the proteome detection protocol does not bias the analysis. With urine, the sediment portion, obtained upon thawing frozen urine, is routinely discarded prior to proteome analysis. However, our results demonstrate that such a practice inadvertently induces bias, having significant implications in the biomarker discovery process. We present the first proteome investigation of human urinary sediments, identifying 60 proteins in this phase by MS. Many sediment proteins were also detected in the urinary supernatant, indicating that several proteins partition between the two phases. This partitioning is dependant on the pH of the sample, as well as the degree of sample agitation. As a consequence of discarding the sediment portion of urine, the concentration of potential candidate biomarkers in the supernatant phase will be altered or, in other instances, may be completely removed from the sample. To minimize this, the pH of all samples should first be normalized, and the samples vigorously vortexed prior to discarding the sediments. For more comprehensive biomarker investigations, we suggest that urinary sediments be analyzed along with the supernatant proteins.

Involvement of Cyr61 in growth, migration, and metastasis of prostate cancer cells

Cyr61 has been reported to participate in the development and progression of various cancers; however, its role in prostate cancer (PCa) still remains poorly understood. In this study, we explored the function of Cyr61 in a series of malignant PCa cell lines, including LnCap, Du145, and PC3. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and crystal violet assays demonstrated that Cyr61 was essential for the proliferation of PCa cells. Soft agar assay and xenograft analysis showed that downregulation of Cyr61 suppressed the tumorigenicity of Du145 cells both in vitro and in vivo. Either silencing the cellular Cyr61 by RNA interference or neutralising the endogenous Cyr61 by antibody inhibited the migration of Du145 cells. In contrast, purified protein of Cyr61 promoted the migration of LnCap cells in a dose-dependent manner. These results suggested that Cyr61 was involved in the migration of PCa cells. We also observed the accumulation of mature focal adhesion complexes associated with the impaired migration through Cyr61 downregulation. Also, further studies showed that Cyr61 regulated the level of activated Rac1 as well as its downstream targets, including phosphorylated JNK, E-cadherin, and p27^kip1, which are key molecules involved in cell growth, migration, and invasion. The in vivo mouse tail vein injection experiment revealed that Cyr61 affected the metastatic capacity of Du145 cells, suggesting that Cyr61 was required for prostate tumour metastasis. Altogether, our results demonstrated that Cyr61 played an important role in the tumorigenicity and metastasis of PCa cells, which will benefit the development of therapeutic strategy for PCas.

Glycerolipid metabolism and signaling in health and disease

Maintenance of body temperature is achieved partly by modulating lipolysis by a network of complex regulatory mechanisms. Lipolysis is an integral part of the glycerolipid/free fatty acid (GL/FFA) cycle, which is the focus of this review, and we discuss the significance of this pathway in the regulation of many physiological processes besides thermogenesis. GL/FFA cycle is referred to as a "futile" cycle because it involves continuous formation and hydrolysis of GL with the release of heat, at the expense of ATP. However, we present evidence underscoring the "vital" cellular signaling roles of the GL/FFA cycle for many biological processes. Probably because of its importance in many cellular functions, GL/FFA cycling is under stringent control and is organized as several composite short substrate/product cycles where forward and backward reactions are catalyzed by separate enzymes. We believe that the renaissance of the GL/FFA cycle is timely, considering the emerging view that many of the neutral lipids are in fact key signaling molecules whose production is closely linked to GL/FFA cycling processes. The evidence supporting the view that alterations in GL/FFA cycling are involved in the pathogenesis of "fatal" conditions such as obesity, type 2 diabetes, and cancer is discussed. We also review the different enzymatic and transport steps that encompass the GL/FFA cycle leading to the generation of several metabolic signals possibly implicated in the regulation of biological processes ranging from energy homeostasis, insulin secretion and appetite control to aging and longevity. Finally, we present a perspective of the possible therapeutic implications of targeting this cycling.