Dopamine D1 receptor activation induces dehydroepiandrosterone sulfotransferase (SULT2A1) in HepG2 cells.

AIM: Dopamine receptors are present in the nervous system and also widely distributed in the periphery. The aim of this study was to investigate the role of D1 subtype dopamine receptors (DRD1) in the regulation of dehydroepiandrosterone sulfotransferase (SULT2A1) in HepG2 cells. METHODS: HepG2 cells were treated with DRD1 agonists with or without DRD1 antagonist for 9 d. DRD1 and SULT2A1 mRNA expression, protein expression, and SULT2A1 activity were detected using RT-PCR, Western blotting and HPLC, respectively. The level of cAMP was measured using a commercial kit. RESULTS: All the 5 DR subtypes (DRD1-DRD5) were found to be expressed in HepG2 cells. Treatment of HepG2 cells with the specific DRD1 agonists SKF82958 (2.5 µmol/L) or SKF38393 (5 and 50 µmol/L) significantly increased the mRNA and protein expression of both DRD1 and SULT2A1, and increased SULT2A1 activity and cAMP levels. These effects were partially blocked by co-treatment with the specific DRD1 antagonist SCH23390 (2.5 µmol/L). In addition, transfection of HepG2 cells with DRD1-specific siRNAs decreased DRD1 mRNA expression by 40%, which resulted in the reduction of SULT2A1 mRNA expression by 60%, protein expression by 40%, and enzyme activity by 20%. CONCLUSION: DRD1 activation upregulates DRD1 and SULT2A1 expression and SULT2A1 activity in HepG2 cells, suggesting that the DRD1 subtype may be involved in the metabolism of drugs and xenobiotics through regulating SULT2A1.

Inhibition of EGFR autophosphorylation plays an important role in the anti-breast cancer efficacy of the dithiocarbamate derivative TM208.

AIM: To investigate the effects of a novel dithiocarbamate derivative TM208 on human breast cancer cells as well as the pharmacokinetic characteristics of TM208 in human breast cancer xenograft mice. METHODS: Human breast cancer MCF-7 and MDA-MB-231 cells were treated with TM208 or a positive control drug tamoxifen. Cell proliferation was examined using SRB and colony formation assays. Cell apoptosis was analyzed with Annexin V-FITC/PI staining assay. Protein expression was examined with Western blot, ELISA and immunohistochemical analyses. MCF-7 breast cancer xenograft nude mice were orally administered TM208 (50 or 150 mg·kg(-1)·d(-1)) or tamoxifen (50 mg·kg(-1)·d(-1)) for 18 d. On d 19, the tumors were collected for analyses. Blood samples were collected from the mice treated with the high dose of TM208, and plasma concentrations of TM208 were measured using LC-MS/MS. RESULTS: Treatment of MCF-7 and MDA-MB-231 cells with TM208 dose-dependently inhibited the cell proliferation and colony formation in vitro (the IC50 values were 36.38 ± 3.77 and 18.13 ± 0.76 µmol/L, respectively). TM208 (20-150 µmol/L) dose-dependently induced apoptosis of both the breast cancer cells in vitro. In MCF-7 breast cancer xenograft nude mice, TM208 administration dose-dependently reduced the tumor growth, but did not result in the accumulation of TM208 or weight loss. TM208 dose-dependently inhibited the phosphorylation of EGFR and ERK1/2 in both the breast cancer cells in vitro as well as in the MCF-7 xenograft tumor. CONCLUSION: Inhibition of EGFR autophosphorylation plays an important role in the anticancer effect of TM208 against human breast cancer.

GRP78 mediates radiation resistance of a stem cell-like subpopulation within the MCF-7 breast cancer cell line.

Emerging evidence indicates that breast cancer-initiating cells (CICs) are relatively resistant to radiotherapy; however, the critical mechanisms determining breast CIC resistance to radiation remain elusive. In the present study, a subpopulation of cells displaying characteristics generally attributed to stem cells was identified within the breast cancer cell line MCF-7. This subpopulation displays cancer stem cell features characterized by overexpression of embryonic stem cell markers, high tumorigenic potential following transplantation into BALB/c-nu mice, self-renewal capacity and resistance to ionizing radiation (IR). Moreover, glucose­regulated protein 78KD (GRP78), which was found to play a crucial role in stem cell oncogenesis, was also shown to be overexpressed in this subpopulation. GRP78 is required for the cancer stem-like subpopulation cell resistance to IR, as knockdown of this gene augments the effects of IR, while overexpression of GRP78 increases the radiation resistance of the subpopulation to IR. These findings indicate that GRP78 acts as a potential therapeutic target aimed at tumor-generating subsets of breast cancer cells.

Methotrexate and 5-aminoimidazole-4-carboxamide riboside exert synergistic anticancer action against human breast cancer and hepatocellular carcinoma.

AIM: To investigate the influences of methotrexate (MTX) on the anticancer actions and pharmacokinetics of 5-aminoimidazole-4-carboxamide riboside (AICA riboside) in human breast cancer and hepatocellular carcinoma. METHODS: Human breast cancer cell line MCF-7 and human hepatocellular carcinoma cell line HepG2 were examined. The cell proliferation was assessed using a sulforhodamine B assay. Western blotting and radioactivity assays were used to analyze the phosphorylation of AMPK. The DNA synthesis was analyzed with BrdU incorporation. Nude mice bearing MCF-7 cell xenografts were used to for in vivo study. MTX (50 mg/kg, ip, per week) and AICA riboside (200 mg/kg, ip, every other day) were administered the animals for 2 weeks. The concentrations of AICA riboside and its active metabolite AICA ribotide in the plasma and tumors were measured with HPLC. RESULTS: Synergistic cytotoxicity in vitro was observed with MTX (0.1, 0.5, and 1 µmol/L) combined with AICA riboside (0.25-1 mmol/L) in MCF-7 cells, and with MTX (0.5 and 1 µmol/L) combined with AICA riboside (0.5 and 1 mmol/L) in HepG2 cells. MTX (1 µmol/L) significantly enhanced the AICA riboside-induced AMPK activation and BrdU incorporation in both MCF-7 and HepG2 cells. Co-treatment with MTX and AICA riboside exerted more potent inhibition on the tumor growth in nude mice than either drug alone. After injection of AICA riboside (200 mg/kg, iv) in nude mice bearing MCF-7 xenografts, MTX (50 mg/kg, iv) significantly increased the concentrations of AICA riboside and its active metabolite AICA ribotide in tumors. CONCLUSION: MTX and AICA riboside exert synergistic anticancer action against MCF-7 and HepG2 cells in vitro and in vivo. MTX increases the concentration of AICA riboside and its active metabolite AICA ribotide in tumors in vivo.

A mechanism-based pharmacokinetic/pharmacodynamic model for CYP3A1/2 induction by dexamethasone in rats.

AIM: To develop a pharmacokinetic/pharmacodynamic (PK/PD) model describing the receptor/gene-mediated induction of CYP3A1/2 by dexamethasone (DEX) in rats. METHODS: A group of male Sprague-Dawley rats receiving DEX (100 mg/kg, ip) were sacrificed at various time points up to 60 h post-treatment. Their blood sample and liver were collected. The plasma concentration of DEX was determined with a reverse phase HPLC method. CYP3A1/2 mRNA, protein levels and enzyme activity were measured using RT-PCR, ELISA and the testosterone substrate assay, respectively. Data analyses were performed using a first-order conditional estimate (FOCE) with INTERACTION method in NONMEM version 7.1.2. RESULTS: A two-compartment model with zero-order absorption was applied to describe the pharmacokinetic characteristics of DEX. Systemic clearance, the apparent volume of distribution and the duration of zero-order absorption were calculated to be 172.7 mL·kg(-1)·h(-1), 657.4 mL/kg and 10.47 h, respectively. An indirect response model with a series of transit compartments was developed to describe the induction of CYP3A1/2 via PXR transactivation by DEX. The maximum induction of CYP3A1 and CYP3A2 mRNA levels was achieved, showing nearly 21.29- and 8.67-fold increases relative to the basal levels, respectively. The CYP3A1 and CYP3A2 protein levels were increased by 8.02-fold and 2.49-fold, respectively. The total enzyme activities of CYP3A1/2 were shown to increase by up to 2.79-fold, with a lag time of 40 h from the Tmax of the DEX plasma concentration. The final PK/PD model was able to recapitulate the delayed induction of CYP3A1/2 mRNA, protein and enzyme activity by DEX. CONCLUSION: A mechanism-based PK/PD model was developed to characterize the complex concentration-induction response relationship between DEX and CYP3A1/2 and to resolve the drug- and system-specific PK/PD parameters for the course of induction.

Mechanism underlying carbon tetrachloride-inhibited protein synthesis in liver.

AIM: To study the mechanism underlying carbon tetrachloride (CCl(4)) -induced alterations of protein synthesis in liver. METHODS: Male Sprague-Dawley rats were given CCl(4) (1 mL/100 g body weight) and (3)H-leucine incorporation. Malondialdehyde (MDA) level in the liver, in vitro response of hepatocyte nuclei nucleotide triphosphatase (NTPase) to free radicals, and nuclear export of total mRNA with 3'-poly A(+) were measured respectively. Survival response of HepG2 cells to CCl(4) treatment was assessed by methyl thiazolyl tetrazolium. Km and Vmax values of nuclear envelope NTPase activity in liver of rats treated with CCl(4) were assayed by a double-reciprocal plot. RESULTS: The protein synthesis was inhibited while the MDA level was significantly increased in liver of rats treated with CCl(4). In addition, CCl(4) decreased the NTPase binding capacity of nuclear envelope (Km value) in cultured HepG2 cells. Moreover, in vitro ferrous radicals from Fenton's system suppressed the NTPase activity of liver nuclear envelope in a dose-dependent manner. Down-regulation of the nuclear envelope NTPase activity indicated a lower energy provision for nucleocytoplasmic transport of mRNA molecules, an evidence in CCl(4)-treated HepG2 cells correspondingly supported by the nuclear sequestration of poly (A)(+) mRNA molecules in morphological hybridization research. CONCLUSION: Inhibition of mRNA transport, suggestive of decreased NTPase activity of the nuclear envelope, may be involved in carbon tetrachloride-inhibited protein synthesis in liver.

[Glucose regulated protein 78 kD].

One of the most important chaperones located on endoplasmic reticulum, GRP78, referred as BiP (immunoglobulin heavy chain binding protein), belongs to heat shock protein 70 family. GRP78 exists conservatively among a wide variety of biological species, and acts as a central regulator of endoplasmic reticulum (ER) functions, participating in ER protein folding and assembly process, and maintaining ER Ca2+ homeostasis, unfolded protein response and specific anti-apoptotic actions. Specific regulatory cis-elements such as ER stress response element (ERSE) and cAMP response element (CRE) were identified on the promoter of GRP78. Dynamic epigenetic interactions between specific transcription factors such as AFT6 and regulatory elements in GRP78 gene promoter might contribute to human GRP78 constitutive or inducible transcription, resulting from some physiological and pathological stresses. Recently, cellular relationship between GRP78 expression and hepatic steatosis, cancer and nervous system diseases in human was underwent further clinical and biochemical research, which will benefit to human beings.

Tunicamycin suppresses cisplatin-induced HepG2 cell apoptosis via enhancing p53 protein nuclear export.

Cisplatin is a widely used anticancer drug; however, resistance to cisplatin-based chemotherapy is a major cause of treatment failure in patients with tumors. The present study was undertaken to investigate whether and how endoplasmic reticulum (ER) stress initiated by tunicamycin, which inhibits glycosylation, influences cisplatin-induced apoptosis in HepG2 cells. Pretreatment of HepG2 cells with ER stress inducers brought about a decrease in both cisplatin-induced cytotoxic effects and apoptosis. In order to further explore the mechanism underlying tumor resistance to cisplatin, we observed that increased nuclear export of endogenous p53 protein by pharmacological inducers of ER stress, such as tunicamycin, was associated with the suppression of cisplatin-induced apoptosis. These results suggested that tumor suppressor p53 protein may play a key role in cisplatin-induced HepG2 cells apoptosis. It is therefore suggested that the treatment of some tumor patients with cisplatin be combined with the down-regulation of endogenous ER stress to improve the clinical results of cisplatin-based chemotherapy.

Protective effect of taurine on hypochlorous acid toxicity to nuclear nucleoside triphosphatase in isolated nuclei from rat liver.

AIM: Taurine has been shown to be an effective scavenger of hypochlorous acid (HOCl). The role of HOCl is well established in tissue damage associated with inflammation and injury. In the present study, the effect of HOCl on nuclear nucleoside triphosphatase of hepatocytes and the ability of taurine to prevent this effect were investigated. METHODS: Isolated hepatic nuclei from rat liver were exposed to HOCl with or without taurine. The NTPase activity on nuclear envelope was assayed using ATP and GTP as substrates, respectively. RESULTS: The first series of experiments evaluated the toxicity of HOCl and the efficacy of taurine to protect NTPase. HOCl at 10(-9)-5 x 10(-6) mol/L reduced nuclear NTPase activities in a concentration dependent manner (ATP and GTP as substrates) (P<0.01). HOCl at 10(-6) mol/L reduced the NTPase activity by 65% (ATP as substrate) and 76% (GTP as substrate). Taurine (10(-7) to 10(-4) mol/L) was tested for protection against HOCl at 10(-6) mol/L and the nuclei treated with 5 x 10(-4) mol/L taurine exhibited only 20% and 12% reduction in NTPase activities compared to untreated controls. A second study was performed comparing taurine to glutathione (GSH). GSH and HOCl at 10(-6) mol/L exhibited 46% and 67.4% reduction in NTPase activities compared with control. GSH (10(-4) mol/L) which was incubated with the nuclei and HOCl still exhibited 44.2% and 44.8% reduction in NTPase activities of untreated control. Taurine with HOCl only exhibited 15.2% and 17.1% reduction in NTPase activities, which provided more powerful protection against HOCl than GSH. The third experiment was undertaken to evaluate the specificity of taurine against HOCl. Incubation of rat hepatic nuclei with Fe(3+)/H(2)O(2) (1 m mol/L vs 5 micromol/L) resulted in a decrease in nuclear NTPase activities (P<0.01). When hepatic nuclei were incubated with Tau (10(-4) mol/L) and Fe(3+)/H(2)O(2) (1m mol/L vs 5 micromol/L), nuclear NTPase activities were only slightly increased as compared with that of incubation with Fe(3+)/H(2)O(2) alone. However, GSH failed to alter the NTPase activities induced by Fe(3+)/H(2)O(2). CONCLUSION: The present findings indicate that HOCl can act as an inhibitor of nuclear NTPase. Taurine can antagonistically reduce the toxicity of HOCl to NTPase.

Phospholipase A2 inhibits nuclear nucleoside triphosphatase activity and mRNA export in isolated nuclei from rat liver.

The present study is undertaken to investigate whether the phospholipase A(2) (PLA(2)) influences mRNA nucleocytoplasmic transport evaluated by nucleoside triphosphatase (NTPase) activity and mRNA export in isolated hepatic nuclear envelope. Isolated hepatic nuclei from rat liver were exposed to PLA(2) (10(-5) approximately 10(-2)/ml) with or without incorporation of nuclei with phosphatidylcholine (PC) liposome. Messenger RNA exports and NTPase activities of nuclear membrane were assayed using ATP and GTP as substrates. We found that the RNA efflux, evaluated by [3H] uridine, was potently decreased in a concentration-dependent manner, by incubation of hepatic nuclei with PLA(2), regardless using ATP or GTP as substrates. The PC content in nuclear membrane was also decreased by PLA(2)-treatment. The PC was incorporated into the nuclear membrane by addition of phospholipid liposomes into the incubation mixture. PC incorporation into the nuclear membrane did not alter mRNA export. However this resulted in a significant increase in mRNA export rate in PLA(2)-treated group. Messenger RNA export rate in PLA(2) (10(-3) unit/mL)- treated nuclear membrane was positively correlated with level of PC incorporation, both using ATP and GTP as substrates. The activity of nucleoside triphosphatase, a nuclear membrane-associated enzyme, showed parallel variations with mRNA transport. It is concluded that nuclear PLA(2) plays a regulatory role in RNA transport, which can be antagonized by exogenous PC. These might be pathophysiologically significance, although the mechanisms by which this effect takes place remain to be clarified.