High glucose suppresses expression of equilibrative nucleoside transporter 1 (ENT1) in rat cardiac fibroblasts through a mechanism dependent on PKC-zeta and MAP kinases

hENT1 reverses chemoresistance by regulating glycolysis in pancreatic cancer

Gemcitabine (GEM) chemotherapy, as the first-line regimen for pancreatic cancer, tends to induce drug resistance, which ultimately worsens the prognosis of patients with pancreatic cancer. Our previous study indicated a close correlation between pancreatic cancer progression and glucose metabolism, especially at the chemoresistant stage, highlighting the importance of the application of 18F-FDG PET dual-phase imaging in the early detection of pancreatic cancer. We speculate that glycolysis, participates in the development of chemoresistance in pancreatic cancer. In this article, we wanted to determine whether manipulating hENT1 expression in pancreatic cancer cells can reverse GEM chemoresistance and whether glucose transport and glycolysis are involved during this process. We found that hENT1 reversed GEM-induced drug resistance by inhibiting glycolysis and altering glucose transport mediated by HIF-1α in pancreatic cancer. Our findings also suggest that 18F-FDG PET dual-phase imaging after the 4th chemotherapy treatment can accurately identify drug-resistant pancreatic tumors and improve hENT1 reversal therapy. Our findings highlight that the dynamic observation of (retention index) RI changes from the beginning of treatment can also be helpful for evaluating the therapeutic effect.

Expression of Concentrative Nucleoside Transporters ( SLC28A) in the Human Placenta: Effects of Gestation Age and Prototype Differentiation-Affecting Agents

Equilibrative ( SLC29A) and concentrative ( SLC28A) nucleoside transporters contribute to proper placental development and mediate uptake of nucleosides/nucleoside-derived drugs. We analyzed placental expression of SLC28A mRNA during gestation. Moreover, we studied in choriocarcinoma-derived BeWo cells whether SLC29A and SLC28A mRNA levels can be modulated by activity of adenylyl cyclase, retinoic acid receptor activation, CpG islands methylation, or histone acetylation, using forskolin, all- trans-retinoic acid, 5-azacytidine, and sodium butyrate/sodium valproate, respectively. We found that expression of SLC28A1, SLC28A2, and SLC28A3 increases during gestation and reveals considerable interindividual variability. SLC28A2 was shown to be a dominant subtype in the first-trimester and term human placenta, while SLC28A1 exhibited negligible expression in the term placenta only. In BeWo cells, we detected mRNA of SLC28A2 and SLC28A3. Levels of the latter were affected by 5-azacytidine and all- trans-retinoic acid, while the former was modulated by sodium valproate (but not sodium butyrate), all- trans-retinoic acid, 5-azacytidine, and forskolin that caused 25-fold increase in SLC28A2 mRNA; we documented by analysis of syncytin-1 that the observed changes in SLC28A expression do not correlate with the morphological differentiation state of BeWo cells. Upregulated SLC28A2 mRNA was reflected in elevated uptake of [³H]-adenosine, high-affinity substrate of concentrative nucleoside transporter 2. Using KT-5720 and inhibitors of phosphodiesterases, we subsequently confirmed importance of cAMP/protein kinase A pathway in SLC28A2 regulation. On the other hand, SLC29A genes exhibited constitutive expression and none of the tested compounds increased SLC28A1 expression to detectable levels. In conclusion, we provide the first evidence that methylation status and activation of retinoic acid receptor affect placental SLC28A2 and SLC28A3 transcription and substrates of concentrative nucleoside transporter 2 might be taken up in higher extent in placentas with overactivated cAMP/protein kinase A pathway and likely in the term placenta.

The Level of TWIST1 expression determines the response of colon cancer cells to mitogen-activated protein kinases inhibitors

BACKGROUND/AIM

Currently, it has been proposed that combination of 5-fluorouracil (5FU) with inhibitors of the mitogen-activated protein kinases (MAPKs) signaling pathway might enhance the efficacy of 5FU-based chemotherapy in colon cancer. Our study aimed to investigate an impact of TWIST1 silencing on the sensitivity of cancer cells to 5FU and selected MAPK inhibitors.

MATERIALS AND METHODS

The suppression of TWIST1 expression in human colon cancer HT29 and HCT116 cell lines was achieved by transduction with lentiviral vector carrying the TWIST1 silencing sequence (pLL3.7-sh TWIST1). The statistical calculation was performed with analysis of variance or Dunnett's test for comparison to control group. Paired Student's t-test was performed when two groups were analyzed.

RESULTS

Suppression of TWIST1 reduced the proliferation rate of colon cancer cells and enhanced their sensitivity to 5FU and MAPKs inhibitors. The sensitivity of HT29 cells to examined compounds was more dependent on TWIST1 expression level compared to HCT116 cells. The most noticeable effect of TWIST1 suppression on sensitivity of both colon cancer cell lines to combined treatment of 5FU and the MAPKs inhibitors was observed for inhibitors of p38α/β and JNK1-3. We also noted that the suppression of TWIST1 significantly sensitized both cell lines to combined treatment of 5FU and Rac inhibitor.

CONCLUSIONS

Our observations point to TWIST1 expression level as a marker of colon cancer sensitivity to combined treatment of 5FU and MAPKs inhibitors.

Protein Kinases C-Mediated Regulations of Drug Transporter Activity, Localization and Expression

Drug transporters are now recognized as major actors in pharmacokinetics, involved notably in drug–drug interactions and drug adverse effects. Factors that govern their activity, localization and expression are therefore important to consider. In the present review, the implications of protein kinases C (PKCs) in transporter regulations are summarized and discussed. Both solute carrier (SLC) and ATP-binding cassette (ABC) drug transporters can be regulated by PKCs-related signaling pathways. PKCs thus target activity, membrane localization and/or expression level of major influx and efflux drug transporters, in various normal and pathological types of cells and tissues, often in a PKC isoform-specific manner. PKCs are notably implicated in membrane insertion of bile acid transporters in liver and, in this way, are thought to contribute to cholestatic or choleretic effects of endogenous compounds or drugs. The exact clinical relevance of PKCs-related regulation of drug transporters in terms of drug resistance, pharmacokinetics, drug–drug interactions and drug toxicity remains however to be precisely determined. This issue is likely important to consider in the context of the development of new drugs targeting PKCs-mediated signaling pathways, for treating notably cancers, diabetes or psychiatric disorders.

Adenosine transporters and receptors: key elements for retinal function and neuroprotection

Adenosine is an important neuroactive substance in the central nervous system, including in the retina where subclasses of adenosine receptors and transporters are expressed since early stages of development. Here, we review some evidence showing that adenosine plays important functions in the mature as well as in the developing tissue. Adenosine transporters are divided into equilibrative and concentrative, and the major transporter subtype present in the retina is the ENT1. This transporter is responsible for a bidirectional transport of adenosine and the uptake or release of this nucleoside appears to be regulated by different signaling pathways that are also controlled by activation of adenosine receptors. Adenosine receptors are also key players in retina physiology regulating a variety of functions in the mature and developing tissue. Regulation of excitatory neurotransmitter release and neuroprotection are the main functions played be adenosine in the mature tissue, while regulation of cell survival and neurogenesis are some of the functions played by adenosine in developing retina. Since adenosine is neuroprotective against excitotoxic and metabolic dysfunctions observed in neurological and ocular diseases, the search for adenosine-related drugs regulating adenosine transporters and receptors can be important for advancement of therapeutic strategies against these diseases.

PKC δ and βII regulate angiotensin II-mediated fibrosis through p38: a mechanism of RV fibrosis in pulmonary hypertension

Pulmonary hypertension (PH) eventually leads to right ventricular (RV) fibrosis and dysfunction that is associated with increased morbidity and mortality. Although angiotensin II plays an important role in RV remodeling associated with hypoxic PH, the molecular mechanisms underlying RV fibrosis in PH largely remain unresolved. We hypothesized that PKC-p38 signaling is involved in RV collagen accumulation in PH and in response to angiotensin II stimulation. Adult male Sprague-Dawley rats were exposed to 3 wk of normoxia or hypoxia (10% FiO2 ) as a model of PH. Hypoxic rats developed RV hypertrophy and fibrosis associated with an increase in PKC βII and δ protein expression and p38 dephosphorylation in freshly isolated RV cardiac fibroblasts. Further mechanistic studies were performed in cultured primary cardiac fibroblasts stimulated with angiotensin II, a key activator of ventricular fibrosis in PH. Angiotensin II induced a reduction in p38 phosphorylation that was attenuated following chemical inhibition of PKC βII and δ. Molecular and chemical inhibition of PKC βII and δ abrogated angiotensin II-induced cardiac fibroblast proliferation and collagen deposition in vitro. The effects of PKC inhibition on proliferation and fibrosis were reversed by chemical inhibition of p38. Conversely, constitutive activation of p38 attenuated angiotensin II-induced increase of cardiac fibroblast proliferation and collagen accumulation. PKC βII- and δ-dependent inactivation of p38 regulates cardiac fibroblast proliferation and collagen deposition in response to angiotensin II, which suggests that the PKC-p38 signaling in cardiac fibroblasts may be involved and important in the pathophysiology of RV fibrosis in PH.

Nucleoside transporters in the purinome

The purinome is a rich complex of proteins and cofactors that are involved in fundamental aspects of cellular homeostasis and cellular responses. The purinome is evolutionarily ancient and is made up of thousands of members. Our understanding of the mechanisms linking some parts of this complex network and the physiological relevance of the various connections is well advanced. However, our understanding of other parts of the purinome is less well developed. Our research focuses on the adenosine or nucleoside transporters (NTs), which are members of the membrane purinome. Nucleoside transporters are integral membrane proteins that are responsible for the flux of nucleosides, such as adenosine, and nucleoside analog drugs, used in a variety of anti-cancer, anti-viral and anti-parasite therapies, across cell membranes. Nucleoside transporters form the SLC28 and SLC29 families of solute carriers and the protein members of these families are widely distributed in human tissues including the central nervous system (CNS). NTs modulate purinergic signaling in the CNS primarily through their effects on modulating prevailing adenosine levels inside and outside the cell. By clearing the extracellular milieu of adenosine, NTs can terminate adenosine receptor-dependent signaling and this raises the possibility of regulatory feedback loops that tie together receptor signaling with transporter function. Despite the important role of NTs as modulators of purinergic signaling in the human body, very little is known about the nature or underlying mechanisms of regulation of either the SLC28 or SLC29 families, particularly within the context of the CNS purinome. Here we provide a brief overview of our current understanding of the regulation of members of the SLC29 family and highlight some interesting avenues for future research.

Advanced oxidation protein products activate intrarenal renin-angiotensin system via a CD36-mediated, redox-dependent pathway

AIMS

Activation of intrarenal renin-angiotensin system (RAS) has a detrimental effect on the progression of chronic kidney diseases (CKDs), although the regulation of intrarenal RAS remains unclear. The aim of the present study was to evaluate the role of advanced oxidation protein products (AOPPs) in intrarenal RAS activation.

RESULTS

AOPPs upregulated the expression of almost all components of RAS and increased activity of angiotensin-converting enzyme in cultured proximal tubular epithelial cells. The triggering effect of AOPP-albumin was 100-times stronger than that of unmodified albumin. The effect of AOPP-albumin was mainly mediated by a CD36-dependent, redox-sensitive signaling involving activation of protein kinase Cα, NADPH oxidase, and nuclear factor-κB/activation protein-1. Chronic AOPP-albumin loading in unilateral nephrectomy rats resulted in deposition of AOPPs in renal tubular cells accompanied with local RAS activation and functional perturbations such as increase in urinary albumin excretion. Accumulation of AOPPs was also detected in human renal tubular cells and correlated with expression of angiotensin II in renal biopsies from 19 patients with IgA nephropathy.

INNOVATION AND CONCLUSION

This study demonstrated for the first time that AOPPs modified albumin functions as a strong trigger of intrarenal RAS via a CD36-mediated, redox-dependent pathway. Given the fact that accumulation of AOPPs is prevalent in diabetes and CKD, targeting AOPPs could be a strategy for the therapeutic intervention of CKD. Antioxid. Redox Signal. 18, 19-35.