Retraction Notice to: LINC00472 Acts as a Tumor Suppressor in NSCLC through KLLN-Mediated p53-Signaling Pathway via MicroRNA-149-3p and MicroRNA-4270

[This retracts the article DOI: 10.1016/j.omtn.2019.06.003.].

SHCBP1 promotes cisplatin induced apoptosis resistance, migration and invasion through activating Wnt pathway

Lung cancer is the leading cause for cancer death due to refractory nature to current treatment strategies, understanding the regulatory mechanism of therapy resistance of lung cancer is important for lung cancer therapy. Here, we aimed to study the role of SHCBP1 in lung cancer cisplatin resistance, we found SHCBP1 was upregulated in lung cancer tissues and cells, patients with high SHCBP1 had poor prognosis. SHC binding and spindle associated 1 (SHCBP1) overexpression promoted cisplatin induced apoptosis resistance, migration and invasion determined by apoptosis assay and transwell assay with or without Matrigel, while SHCBP1 knockdown inhibited cisplatin induced apoptosis resistance, migration and invasion. Wnt pathway promoted lung cancer progression, we found SHCBP1 activated Wnt pathway, characterized by promoting β-catenin nuclear translocation. Inhibition of Wnt pathway in SHCBP1 overexpression cells reversed the effect of SHCBP1 overexpression, confirming SHCBP1 promoted lung cancer progression through activating Wnt pathway. We also found SHCBP1 expression was positively corrected with Wnt pathway activity in lung cancer samples. In summary, we found SHCBP1 promoted cisplatin induced apoptosis resistance, migration and invasion through activating Wnt pathway, providing a potential target for lung cancer therapy.

LINC00472 Acts as a Tumor Suppressor in NSCLC through KLLN-Mediated p53-Signaling Pathway via MicroRNA-149-3p and MicroRNA-4270

Long non-coding RNAs and microRNAs (miRNAs) have been reported to participate in the progression of non-small-cell lung cancer (NSCLC). Long intergenic non-protein-coding RNA 472 (LINC00472), miR-149-3p, and miR-4270 were found to be involved in tumor activities, suggesting potential roles in NSCLC. Thus, this study aimed to examine the ability of LINC00472 to influence the progression of NSCLC with the involvement of miR-149-3p and miR-4270. Initially, differentially expressed long non-coding RNAs (lncRNAs), downstream regulatory miRNAs, and genes related to NSCLC were identified. Next, the interaction among LINC00472, miR-149-3p and miR-4270, and KLLN and the p53-signaling pathway was determined. The effect of LINC00472 on the expression of E-cadherin, N-cadherin, and Vimentin was examined through gain-of-function and loss-of-function experiments. Lastly, the effects of LINC00472 on NSCLC tumor growth were assessed in vivo. LINC00472 and KLLN were found to exhibit low levels, while miR-149-3p and miR-4270 were highly expressed in NSCLC. In addition, the overexpression of LINC00472 was observed to upregulate KLLN and activate the p53-signaling pathway, which ultimately inhibited the invasion, migration, and EMT of NSCLC cells via miR-149-3p and miR-4270, corresponding to decreased N-cadherin and Vimentin and increased E-cadherin. The overexpression of LINC00472 exerted an inhibitory effect on tumor growth in vivo. Taken together, the key evidence suggests that the overexpression of LINC00472 can downregulate miR-149-3p and miR-4270 to upregulate KLLN and activate the p53-signaling pathway, thus inhibiting the development of NSCLC. This study highlights the potential of LINC00472 as a promising therapeutic target for NSCLC treatment.

Long non-coding RNA MALAT1 is up-regulated in ovarian cancer tissue and promotes SK-OV-3 cell proliferation and invasion

Ovarian cancer is a gynecological malignancy worldwide. Long non-coding RNAs (lncRNAs) research is an emerging area in cancer studies, but little is known about lncRNA metastasis associated lung adenocarcinoma transcript 1 (MALAT1) in ovarian cancer. This study aims to investigate expression and roles of MALAT1 in ovarian cancer. MALAT1 level was detected in 20 ovarian cancer patients. MALAT1 expression was promoted by transforming growth factor β1 (TGFB1) treatment and inhibited by siRNA transfection in human ovarian cancer cell line SK-OV-3, after which changes in cell viability, proliferation, migration and invasion were analyzed by MTT, colony formation and Transwell assays. Protein levels of mitogen-activated protein kinase factors, including MAPK kinase 1 (MEK1), extracellular signal-regulated kinase (ERK1), p38 and c-Jun N-terminal kinase 1 (JNK1), were detected by western blot. Results showed that MALAT1 was significantly up-regulated in ovarian cancer tissues compared to adjacent normal tissues (P < 0.001), and its expression was correlated to tumor size (r2 = 0.7770, P < 0.0001) and metastasis. TGFB1 and siRNA successfully altered MALAT1 levels in SK-OV-3 cells. Knockdown of MALAT1 suppressed SK-OV-3 cell viability, proliferation, migration and invasion (P < 0.05), and inhibited phosphorylation of MEK1, ERK1, p38 and JNK1, which suggested that MALAT1 promoted ovarian cancer cell proliferation, migration and invasion, and that MAPK pathways might be one of the regulatory mechanisms of MALAT1. This study reveals that MALAT1 is a potential biomarker for tumor growth and metastasis, as well as a promising therapeutic target in ovarian cancer, facilitating further ovarian cancer research.

miR-455 inhibits breast cancer cell proliferation through targeting CDK14

Breast cancer is the most frequently occurring cancer in women worldwide, microRNAs (miRNAs) play critical role in the initiation and progression of breast cancer. Here, we studied the effect of miR-455 on cell proliferation of breast cancer, and found that miR-455 was downregulated in breast cancer tissues and cells. Its overexpression inhibited cell proliferation, whereas its knockdown promoted cell proliferation of breast cancer. We found a Cdc2-related protein kinase CDK14 was the target of miR-455, when the 3^'UTR of CDK14 was cloned into luciferase reporter vector and transfected into cells, miR-455 mimic could inhibit the luciferase activity in a dose-dependent manner, miR-455 inhibitor increased the luciferase activity, but the mutant miR-455 mimic couldn't change the luciferase activity, suggesting miR-455 directly bound to the 3^'UTR of CDK14. Meanwhile, we also found miR-455 inhibited Cyclin D1 expression and promoted p21 expression, confirming miR-455 inhibited cell proliferation. Double knockdown of miR-455 and CDK14 inhibited the proliferation of breast cancer cell, confirming miR-455 inhibiting cell proliferation by targeting CDK14. Moreover, miR-455 levels were negatively correlated with CDK14 levels in breast cancer tissues. Our finding revealed miR-455 inhibits breast cancer cell proliferation through targeting CDK14, it might be a target for breast cancer therapy.

[Relationships between electrophysiological characteristic of speech evoked auditory brainstem response and Mandarin monosyllable discriminative ability at different hearing impairment]

OBJECTIVE

To investigate the relationships between electrophysiological characteristic of speech evoked auditory brainstem response(s-ABR) and Mandarin phonetically balanced maximum(PBmax) at different hearing impairment, so as to provide more clues for the mechanism of speech cognitive behavior.

METHOD

Forty-one ears in 41 normal hearing adults(NH), thirty ears in 30 conductive hearing loss patients(CHL) and twenty-seven ears in 27 sensorineural hearing loss patients(SNHL) were included in present study. The speech discrimination scores were obtained by Mandarin phonemic-balanced monosyllable lists via speech audiometric software. Their s-ABRs were recorded with speech syllables /da/ with the intensity of phonetically balanced maximum(PBmax). The electrophysiological characteristic of s-ABR, as well as the relationships between PBmax and s-ABR parameters including latency in time domain, fundamental frequency(F0) and first formant(F1) in frequency domain were analyzed statistically.

RESULTS

All subjects completed good speech perception tests and PBmax of CHL and SNHL had no significant difference (P>0.05), but both significantly less than that of NH (P<0.05). While divided the subjects into three groups by 90%<PBmax≤100%, 80%<PBmax≤90% and PBmax≤80%, the results showed that all subjects decreased amplitudes of F0 and F1, and increased latency of feature peaks as PBmax reduced. In the same PBmax group, latency of feature peaks increased and amplitudes of F0 and F1 decreased from SNHL, CHL to NH. All subjects showed strongest significant positive correlation between amplitudes of F0 and F1with PBmax respectively, as well as significant negative correlation between latencies of all the feature peaks with PBmax. A stepwise regression analysis equation displayed that the sum of latencies of peak A and F, and amplitudes of F0 and F1 attributed to PBmax reached 76%, and their beta coefficient decreased from amplitudes of F0 and amplitudes of F1, latencies of peak F to latencies of peak A.

CONCLUSIONS

These electrophysiological characteristics of s-ABR showed closely and stably associated with Mandarin monosyllable discriminative abilities at different hearing impairment. Some electrophysiological characteristics such as amplitudes of F0 and F1, latencies of peak F and A may play more important roles in speech recognition assess, which may be applied combined or separately to further investigation of speech perception and temporal processing abilities.

LeERF-1, a novel AP2/ERF family gene within the B3 subcluster, is down-regulated by light signals in Lithospermum erythrorhizon

We previously showed that ethylene might be involved in the process of shikonin biosynthesis regulated by light signals. Here, we cloned a full-length cDNA of LeERF-1, a putative ethylene response factor gene, from Lithospermum erythrorhizon using the RACE (rapid amplification of cDNA ends) method. Phylogenetic analysis revealed that LeERF-1 was classified in the B3 subfamily, together with ERF1 and ORA59 of Arabidopsis. Heterologous expression of LeERF-1 in Arabidopsis showed that LeERF-1:eGFP fusion protein was precisely localised to the nucleus, implying that it might function as a transcription factor. Detailed expression analysis with real-time PCR showed that LeERF-1 was significantly down-regulated by white, blue and red light, although the inhibitory effect of red light was relatively weak compared to other light conditions. Tissue-specific expression analysis also indicated that LeERF-1 was dominantly expressed in the roots, which grow in soil in darkness. These patterns are all consistent with the effects of different light signals on regulating formation of shikonin and its derivatives, indicating that LeERF-1 might be a crucial positive regulator, like other B3 subfamily proteins (such as ORCA3 and ORA59), in regulating biosynthesis of secondary metabolites.

Novel nonsecosteroidal vitamin D receptor modulator inhibits the growth of LNCaP xenograft tumors in athymic mice without increased serum calcium

BACKGROUND

We recently reported on novel vitamin D receptor (VDR) modulators that are structurally distinct from the secosteroid 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), the endogenous activator of VDR. One of these compounds, LG190119, was tested for the ability to inhibit the growth of LNCaP human prostate cancer cell-derived tumors in athymic mice.

METHODS

In one study, athymic mice with established LNCaP xenograft tumors were dosed orally every day with LG190119 (3 or 10 mg/kg) or with a synthetic analog of 1,25(OH)(2)D(3), EB1089 (1 microg/kg), for 15 days. In another study ("prevention mode"), oral administration (every other day) of 10 mg/kg LG190119 or a non-hypercalcemic dose of 1,25(OH)(2)D(3) (0.5 microg/kg) was initiated prior to tumor development and continued for 84 days. In both studies, tumor volumes, mouse weights, and serum calcium levels were measured.

RESULTS

In the established tumor study, LG190119 at each dose resulted in significant tumor growth inhibition without hypercalcemia at both 10 and 15 days. EB1089 treatment resulted in significant tumor growth inhibition only at Day 10 and resulted in hypercalcemia at Day 15. In the prevention-mode study, LG190119 markedly slowed tumor growth without increased serum calcium in comparison with either vehicle or 1,25(OH)(2)D(3) treatment (P < 0.001).

CONCLUSIONS

LG190119 effectively inhibited LNCaP xenograft tumor growth without increased serum calcium levels or any other apparent side effects. Compounds of this class may represent promising new therapeutics for treatment of prostate cancer and other cancers with fewer undesirable side effects than currently used drugs.

Re-engineering adenovirus regulatory pathways to enhance oncolytic specificity and efficacy

Replicating adenoviruses may prove to be effective anticancer agents if they can be engineered to selectively destroy tumor cells. We have constructed a virus (01/PEME) containing a novel regulatory circuit in which p53-dependent expression of an antagonist of the E2F transcription factor inhibits viral replication in normal cells. In tumor cells, however, the combination of p53 pathway defects and deregulated E2F allows replication of 01/PEME at near wild-type levels. The re-engineered virus also showed significantly enhanced efficacy compared with extensively studied E1b-deleted viruses such as dl1520 in human xenograft tumor models.

Characterization of KCNQ5/Q3 potassium channels expressed in mammalian cells

Heteromeric KCNQ5/Q3 channels were stably expressed in Chinese Hamster ovary cells and characterized using the whole cell voltage-clamp technique. KCNQ5/Q3 channels were activated by the novel anticonvulsant, retigabine (EC(50) 1.4 microM) by a mechanism that involved drug-induced, leftward shifts in the voltage-dependence of channel activation (-31.8 mV by 30 microM retigabine). KCNQ5/Q3 channels were inhibited by linopirdine (IC(50) 7.7 microM) and barium (IC(50) 0.46 mM), at concentrations similar to those required to inhibit native M-currents. These findings identify KCNQ5/Q3 channels as a molecular target for retigabine and raise the possibility that activation of KCNQ5/Q3 channels may be responsible for some of the anti-convulsant activity of this agent. Furthermore, the sensitivity of KCNQ5/Q3 channels to linopirdine supports the possibility that potassium channels comprised of KCNQ5 and KCNQ3 may make a contribution to native M-currents.

Determination of pharmacokinetics of 8-chloroadenosine and its two major metabolites in dogs by high-performance liquid chromatography

High-performance liquid chromatography was used to measure concentration of 8-chloroadenosine (8-Cl-A) and its two major metabolites 8-chloroadenine (8-Cl-Ad) and 8-chloroinosine (8-Cl-I), and their pharmacokinetics in dogs. 8-Cl-A and its metabolites in serum were treated by deproteinization with acetonitrile, then organic impurities were extracted with dichloromethane, followed by centrifuged and direct injection of the supernatant into the liquid chromatograph. After intravenous injection of 8-Cl-A (30 mg/kg), the parent drug and 8-Cl-I were not detected, but the other metabolite, 8-Cl-Ad, was found at a high concentration for 240 min in dog serum. The main pharmacokinetic parameters of 8-Cl-Ad, t1/2beta and AUC, were 69.30 min and 580 microg min/ml. Our finding indicates that in dogs 8-Cl-A is rapidly metabolized and forms its major metabolites, 8-Cl-Ad and 8-Cl-I. 8-Cl-Ad appeared in many tissues, but 8-Cl-A and 8-Cl-I did not. The concentration of 8-Cl-Ad in dog tissues was highest in the liver and spleen, intermediate in the kidney, intestine, and lowest in the bone marrow, heart, and lungs. However, it was not detected in some liposoluble tissues such as the testes, brain, or uterus. Our study provides useful information for clinical experiment.

Retigabine, a novel anti-convulsant, enhances activation of KCNQ2/Q3 potassium channels

Retigabine [N-(2-amino-4-[fluorobenzylamino]-phenyl) carbamic acid; D-23129] is a novel anticonvulsant, unrelated to currently available antiepileptic agents, with activity in a broad range of seizure models. In the present study, we sought to determine whether retigabine could enhance current through M-like currents in PC12 cells and KCNQ2/Q3 K(+) channels expressed in Chinese hamster ovary cells (CHO-KCNQ2/Q3). In differentiated PC12 cells, retigabine enhanced a linopirdine-sensitive current. The effect of retigabine was associated with a slowing of M-like tail current deactivation in these cells. Retigabine (0.1 to 10 microM) induced a potassium current and hyperpolarized CHO cells expressing KCNQ2/Q3 cells but not in wild-type cells. Retigabine-induced currents in CHO-KCNQ2/Q3 cells were inhibited by 60.6 +/- 11% (n = 4) by the KCNQ2/Q3 blocker, linopirdine (10 microM), and 82.7 +/- 5.4% (n = 4) by BaCl(2) (10 mM). The mechanism by which retigabine enhanced KCNQ2/Q3 currents involved large, drug-induced, leftward shifts in the voltage dependence of channel activation (-33.1 +/- 2.6 mV, n = 4, by 10 microM retigabine). Retigabine shifted the voltage dependence of channel activation with an EC(50) value of 1.6 +/- 0.3 microM (slope factor was 1.2 +/- 0.1, n = 4 to 5 cells per concentration). Retigabine (0.1 to 10 microM) also slowed the rate of channel deactivation, predominantly by increasing the contribution of a slowly deactivating tail current component. Our findings identify KCNQ2/Q3 channels as a molecular target for retigabine and suggest that activation of KCNQ2/Q3 channels may be responsible for at least some of the anticonvulsant activity of this agent.

Novel nonsecosteroidal vitamin D mimics exert VDR-modulating activities with less calcium mobilization than 1,25-dihydroxyvitamin D3

BACKGROUND

The secosteroid 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) acts through the vitamin D receptor (VDR) to elicit many activities that make it a promising drug candidate for the treatment of a number of diseases, including cancer and psoriasis. Clinical use of 1,25(OH)2D3 has been limited by hypercalcemia elicited by pharmacologically effective doses. We hypothesized that structurally distinct, nonsecosteroidal mimics of 1,25(OH)2D3 might have different activity profiles from vitamin D analogs, and set out to discover such compounds by screening small-molecule libraries.

RESULTS

A bis-phenyl derivative was found to activate VDR in a transactivation screening assay. Additional related compounds were synthesized that mimicked various activities of 1,25(OH)2D3, including growth inhibition of cancer cells and keratinocytes, as well as induction of leukemic cell differentiation. In contrast to 1, 25(OH)2D3, these synthetic compounds did not demonstrate appreciable binding to serum vitamin D binding protein, a property that is correlated with fewer calcium effects in vivo. Two mimics tested in mice showed greater induction of a VDR target gene with less elevation of serum calcium than 1,25(OH)2D3.

CONCLUSIONS

These novel VDR modulators may have potential as therapeutics for cancer, leukemia and psoriasis with less calcium mobilization side effects than are associated with secosteroidal 1,25(OH)2D3 analogs.

Long QT syndrome-associated mutations in the Per-Arnt-Sim (PAS) domain of HERG potassium channels accelerate channel deactivation

Mutations in the human ether-a-go-go-related gene (HERG) cause long QT syndrome, an inherited disorder of cardiac repolarization that predisposes affected individuals to life-threatening arrhythmias. HERG encodes the cardiac rapid delayed rectifier potassium channel that mediates repolarization of ventricular action potentials. In this study, we used the oocyte expression system and voltage clamp techniques to determine the functional consequences of eight long QT syndrome-associated mutations located in the amino-terminal region of HERG (F29L, N33T, G53R, R56Q, C66G, H70R, A78P, and L86R). Mutant subunits formed functional channels with altered gating properties when expressed alone in oocytes. Deactivation was accelerated by all mutations. Some mutants shifted the voltage dependence of channel availability to more positive potentials. Voltage ramps indicated that fast deactivation of mutant channels would reduce outward current during the repolarization phase of the cardiac action potential and cause prolongation of the corrected QT interval, QTc. The amino-terminal region of HERG was recently crystallized and shown to possess a Per-Arnt-Sim (PAS) domain. The location of these mutations suggests they may disrupt the PAS domain and interfere with its interaction with the S4-S5 linker of the HERG channel.

Estrogen receptor beta activates the human retinoic acid receptor alpha-1 promoter in response to tamoxifen and other estrogen receptor antagonists, but not in response to estrogen

Human estrogen receptor-alpha (hERalpha) or -beta (hERbeta) transfected into Hep G2 or COS1 cells each responded to estrogen to increase transcription from an estrogen-responsive element (ERE)-driven reporter vector with similar fold induction through a classical mechanism involving direct receptor binding to DNA. ER antagonists inhibited this estrogen induction through both hERalpha and hERbeta, although raloxifene was more potent through ERalpha than ERbeta, and tamoxifen was more potent via ERbeta than ERalpha. We have shown previously that estrogen stimulated the human retinoic acid receptor-alpha-1 (hRARalpha-1) promoter through nonclassical EREs by a mechanism that was ERalpha dependent, but that did not involve direct receptor binding to DNA. We show here that in contrast to hERalpha, hERbeta did not induce reporter activity driven by the hRARalpha-1 promoter in the presence of estrogen. While hERbeta did not confer estrogen responsiveness on this promoter, it did elicit transcriptional activation in the presence of 4-hydroxytamoxifen (4-OH-Tam). Additionally, this 4-OH-Tam agonist activity via ERbeta was completely blocked by estrogen. Like ERalpha, transcriptional activation of this promoter by ERbeta was not mediated by direct receptor binding to DNA. While hERalpha was shown to act through two estrogen-responsive sequences within the promoter, hERbeta acted only at the 3'-region, through two Sp1 sites, in response to 4-OH-Tam. Other ER antagonists including raloxifene, ICI-164,384 and ICI-182,780 also acted as agonists through ERbeta via the hRARalpha-1 promoter. Through the use of mutant and chimeric receptors, it was shown that the 4-OH-Tam activity via ERbeta from the hRARalpha-1 promoter in Hep G2 cells required the amino-terminal region of ERbeta, a region that was not necessary for estrogen-induced ERbeta activity from an ERE in Hep G2 cells. Additionally, the progesterone receptor (PR) antagonist RU486 acted as a weak (IC50 >1 microM) antagonist via hERalpha and as a fairly potent (IC50 approximately 200 nM) antagonist via hERbeta from an ERE-driven reporter in cells that do not express PR. Although RU486 bound only weakly to ERalpha or ERbeta in vitro, it did bind to ERbeta in whole-cell binding assays, and therefore, it is likely metabolized to an ERbeta-interacting compound in the cell. Interestingly, RU486 acted as an agonist through ERbeta to stimulate the hRARalpha-1 promoter in Hep G2 cells. These findings may have ramifications in breast cancer treatment regimens utilizing tamoxifen or other ER antagonists and may explain some of the known estrogenic or antiestrogenic biological actions of RU486.

Influence of prior Na+ pump activity on pump and Na+/Ca2+ exchange currents in mouse ventricular myocytes

We examined the dependence of peak Na+ pump and Na+/Ca2+ exchanger currents on prior Na+ pump inhibition induced by exposure to zero extracellular K+ in voltage-clamped adult murine ventricular myocytes. Abrupt activation of the Na+ pump by reexposure of myocytes to extracellular K+ with a rapid solution switcher resulted in the development of a transient peak current at approximately 500 ms, followed by a decline over 1-2 min to a steady-state level. The magnitudes of both the peak Na+ pump current (Ip) and the peak outward Na+/Ca2+ exchange current, activated by rapidly reducing extracellular Na+ to zero with the solution switcher, were dependent on previous Na+ pump activity. [Na+] gradients (Na+-binding benzofuran isophthalate fluorescence) between the patch pipette and the bulk cytosol were relatively small and could not account for the large differences between peak and steady-state Ip and reverse Na+/Ca2+ exchanger currents. Our results are consistent with the presence of a subsarcolemmal Na+ concentration gradient, which is similar for the Na+ pump and the Na+/Ca2+ exchanger. These findings also support the hypothesis that the Na+ pump and the Na+/Ca2+ exchanger are colocalized in the sarcolemma.

A mutation in the pore region of HERG K+ channels expressed in Xenopus oocytes reduces rectification by shifting the voltage dependence of inactivation

1. The effects of a mutation in the human ether-a-go-go-related gene (HERG) (Ser631 to Ala, S631A) on the voltage- and extracellular [K+] dependence of inactivation were studied in Xenopus oocytes using two microelectrode and single channel voltage-clamp techniques. 2. The voltage required for half-inactivation of S631A HERG was 102 mV more positive than for wild-type (WT)-HERG, resulting in reduced rectification of the steady-state current-voltage relationship. In contrast, the voltage dependence of channel activation was not altered by the S631A mutation. These findings indicate that inactivation of HERG channels is not linked to activation. 3. Rectification of whole-cell S631A HERG current was caused by a voltage-dependent reduction in open probability, and inward rectification of the current-voltage relationship of single channels. 4. Elevation of extracellular [K+] from 2 to 20 mM shifted the half-point for inactivation by +20 mV for WT-HERG, and +25 mV for S631A HERG. Thus, elevated [K+]o and the S631A mutation affect HERG inactivation by different mechanisms. 5. The S631A mutation altered the ion translocation rate of HERG channels. The single channel conductance (gamma) of S631A HERG was 20 pS between -40 and-100 mV, and 6.0 pS between +40 and +100 mV (120 mM extracellular K+). This compares to a gamma of 12.1 and 5.1 pS for WT-HERG channels under the same conditions.

Effects of angiotensin II on intracellular calcium and contracture in metabolically inhibited cardiomyocytes

Angiotensin II (A-II) is known to potentiate ischemic dysfunction during ischemia, but the mechanisms involved are not completely established. We examined the effects of A-II on intracellular calcium concentration ([Ca++]i) and cell contracture caused by metabolic inhibition in isolated adult rabbit ventricular myocytes. [Ca++]i was assessed by flow cytometry, using the Ca(++)-sensitive fluorescent probe, fluo-3. After 90 min of exposure to 2 mM cyanide (CN) and 0 glucose, there was a significant increase in myocyte [Ca++]i. This increase was slightly augmented in the presence of 100 nM A-II. In the presence of partial Na+/K+ ATP pump inhibition ([K+]o = 0.8 mM), there was a more significant increase in [Ca++]i associated with exposure to CN + A-II vs. CN alone. Similar results were obtained with CN plus 2-deoxyglucose, and the effect of A-II was inhibited by 10 microM 5-(N-ethyl-N-isopropyl)amiloride. Myocytes exposed to 2 mM CN and 0 glucose gradually developed contracture over a 3-hr period. Addition of 100 nM A-II significantly (P < .01) enhanced loss of rod shape morphology during 3 hr of CN exposure. Partial inhibition of the Na+ pump by exposure to 0.8 mM K+ had no effect on myocyte survival in the absence of CN, but augmented the harmful effect of A-II on cell contracture caused by CN exposure. This effect of A-II was completely reversed by the addition of 1 mM amiloride, a Na+/H+ exchange inhibitor. We conclude that A-II directly enhances cell injury during CN exposure in isolated rabbit ventricular myocytes. We postulate that this effect of A-II is mediated by stimulation of Na+/H+ exchange with resultant increased [Na+]i and subsequent [Ca++]i loading, possibly via reverse Na+/Ca++ exchange.

Molecular physiology of cardiac delayed rectifier K+ channels

Delayed rectifier K+ current in cardiac myocytes is the sum of two distinct currents, IKr and IKs. The molecular basis of these channels has recently been defined. HERG subunits coassemble to form IKr channels. KvLQT1 and minK subunits coassemble to form IKs channels. Mutations in HERG or KVLQT1 genes predispose affected individuals to ventricular arrhythmias and sudden death.

Retinoid X receptor (RXR) ligands activate the human 25-hydroxyvitamin D3-24-hydroxylase promoter via RXR heterodimer binding to two vitamin D-responsive elements and elicit additive effects with 1,25-dihydroxyvitamin D3

We have previously shown that RNA levels of kidney 25-hydroxyvitamin D3-24-hydroxylase (24(OH)ase), a key metabolic enzyme for 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), is up-regulated by retinoids in mice within hours. Deletion analysis of approximately 5500 base pairs of the human 24(OH)ase promoter showed that the sequence between -316 and -142 contained the information necessary and sufficient for retinoid-induced activation of the promoter. This region contains two previously defined vitamin D-responsive elements (VDREs) at -294 to -274 and -174 to -151. Mutation of either VDRE diminished responsiveness of the -316 to -22 promoter sequence to retinoids or 1,25(OH)2D3, while mutation of both VDREs essentially abolished the activity of the ligands via the promoter. Heterologous promoter vectors driven by the VDREs were responsive to a retinoid X receptor (RXR)-selective ligand (LG100268), a retinoic acid receptor (RAR)-selective ligand (TTNPB), or 1,25(OH)2D3, while combinations of LG100268 with either TTNPB or 1,25(OH)2D3 resulted in additive increases in activity. Band shift analyses showed that vitamin D receptor, RAR, or RXR alone did not bind to the VDREs; however, the combination of either vitamin D receptor or RAR with RXR led to retardation of each of the labeled probes. Treatment of nontransfected CV-1 cells with retinoids or 1,25(OH)2D3 resulted in induction of 24(OH)ase RNA, and ligand combinations led to increased RNA levels. These data imply that either or both of the heterodimer partners can be occupied with ligand to induce this enzyme, with dual receptor occupation leading to increased activation.

Single HERG delayed rectifier K+ channels expressed in Xenopus oocytes

HERG is a K+ channel with properties similar to the rapidly activating component (I(Kr)) of delayed rectifier K+ current, which is important for repolarization of human cardiac myocytes. In this study, we have characterized the single-channel properties of HERG expressed in Xenopus oocytes. Currents were measured in cell-attached patches with an extracellular K concentration of 120 mM. The single HERG channel conductance, determined at test potentials between -50 and -110 mV, was 12.1 +/- 0.6 pS. At positive test potentials (+40 to +80 mV), the probability of channel opening was low and slope conductance was 5.1 +/- 0.6 pS. The mean channel open times at -90 mV were 2.9 +/- 0.5 and 11.8 +/- 1.0 ms, and the mean channel closed times were 0.54 +/- 0.02 and 14.5 +/- 5.3 ms. Single HERG channels were blocked by MK-499, a class III antiarrhythmic agent that blocks I(Kr) in cardiac myocytes. The development of block was more rapid in inside-out patches than in cell-attached patches or in whole cell recordings, indicating that block occurs from the cytoplasmic side of the membrane. The single-channel properties of HERG are similar to I(Kr) channels of isolated cardiac myocytes, which provides further evidence that HERG proteins coassemble to form I(Kr) channels.

Coassembly of K(V)LQT1 and minK (IsK) proteins to form cardiac I(Ks) potassium channel

The slowly activating delayed-rectifier K+ current, I(Ks), modulates the repolarization of cardiac action potentials. The molecular structure of the I(Ks) channel is not known, but physiological data indicate that one component of the I(Ks), channel is minK, a 130-amino-acid protein with a single putative transmembrane domain. The size and structure of this protein is such that it is unlikely that minK alone forms functional channels. We have previously used positional cloning techniques to define a new putative K+-channel gene, KVLQT1. Mutations in this gene cause long-QT syndrome, an inherited disorder that increases the risk of sudden death from cardiac arrhythmias. Here we show that KVLQT1 encodes a K+ channel with biophysical properties unlike other known cardiac currents. We considered that K(V)LQT1 might coassemble with another subunit to form functional channels in cardiac myocytes. Coexpression of K(V)LQT1 with minK induced a current that was almost identical to cardiac I(Ks). Therefore, K(V)LQT1 is the subunit that coassembles with minK to form I(Ks) channels and I(Ks) dysfunction is a cause of cardiac arrhythmia.

Fast inactivation causes rectification of the IKr channel

The mechanism of rectification of HERG, the human cardiac delayed rectifier K+ channel, was studied after heterologous expression in Xenopus oocytes. Currents were measured using two-microelectrode and macropatch voltage clamp techniques. The fully activated current-voltage (I-V) relationship for HERG inwardly rectified. Rectification was not altered by exposing the cytoplasmic side of a macropatch to a divalent-free solution, indicating this property was not caused by voltage-dependent block of outward current by Mg2+ or other soluble cytosolic molecules. The instantaneous I-V relationship for HERG was linear after removal of fast inactivation by a brief hyperpolarization. The time constants for the onset of and recovery from inactivation were a bell-shaped function of membrane potential. The time constants of inactivation varied from 1.8 ms at +50 mV to 16 ms at -20 mV; recovery from inactivation varied from 4.7 ms at -120 mV to 15 ms at -50 mV. Truncation of the NH2-terminal region of HERG shifted the voltage dependence of activation and inactivation by +20 to +30 mV. In addition, the rate of deactivation of the truncated channel was much faster than wild-type HERG. The mechanism of HERG rectification is voltage-gated fast inactivation. Inactivation of channels proceeds at a much faster rate than activation, such that no outward current is observed upon depolarization to very high membrane potentials. Fast inactivation of HERG and the resulting rectification are partly responsible for the prolonged plateau phase typical of ventricular action potentials.

Estrogen and estrogen receptor antagonists stimulate transcription from the human retinoic acid receptor-alpha 1 promoter via a novel sequence

We and others previously reported that up-regulation of retinoic acid receptor-alpha (RAR alpha) RNA and protein levels is elicited by estrogen in human breast cancer cells. We set out to determine the mechanism by which estrogen up-regulates RAR alpha. Cloning of 500 bp of the human (h) RAR alpha 1 promoter has been reported previously; we obtained this 500-bp DNA sequence by PCR techniques from human genomic DNA and tested its activity in the context of a luciferase-containing reporter vector in Hep G2 cell contransactivation assays. Estradiol elicited a 6- to 8-fold increase in luciferase activity from the reporter vector driven by hRAR alpha promoter sequence between -491 and +36 bp that was dependent on the presence of contransfected estrogen receptor (ER). Analysis of various truncated versions of this promoter sequence indicated that two regions of the sequence are sensitive to estrogen stimulation. The first resides in the region -49 to -79 bp upstream from the transcription start site and conferred approximately 2-fold activation by estrogen. This region does not contain a consensus estrogen response element, and ER binding to this DNA sequence was not observed. The second responsive sequence lies at -455 to -491 bp and conferred in additional 4- to 6-fold activation by estrogen. This upstream sequence contains two A/TGGTCA half-sites; however, direct binding of ER to this sequence was not observed. Additionally, ER DNA-binding domain mutants that are not capable of binding to DNA were just as effective as wild type ER in their ability to confer estrogen responsiveness to the RAR alpha promoter, implying that ER DNA-binding ability is not required for the estrogen-induced increase in transcriptional activity. Mutation of either half-site or of an additional immediate downstream sequence in the context of the -491 to +36 bp construct reduced the luciferase activity induction by estrogen from 6-fold to 1.5- to 2-fold. Placement of the region between -455 to -491 bp upstream of an SV40 promoter-driven luciferase vector conferred approximately 20- to 30-fold stimulation of luciferase activity by estrogen in an ER-dependent manner. The ER antagonists, 4-hydroxy-tamoxifen, keoxifene, and ICI 164384, each acted as weak agonist via the hRAR alpha promoter in contransactivation assays, exhibiting 20-30% of the efficacy that was demonstrated by estradiol. Interestingly, upon treatment of MCF7 cells with estradiol or the ER antagonists, increased levels of RAR alpha RNA and protein were observed with the antagonists as well as with estrogen.

cDNA cloning of a novel G protein-coupled receptor with a large extracellular loop structure

A cDNA designated as AZ3B has been isolated from a differentiated HL-6 0 cell cDNA library with a probe derived from the N-formyl peptide receptor gene. The 1.97-kb cDNA encodes a novel G protein-coupled receptor (GPCR) with 482 amino acids. In addition to the predicted 7 transmembrane domains common to all GPCRs, the protein encoded by AZ3B contains a large extracellular loop of approximately 172 amino acids between the fourth and the fifth transmembrane domains, a feature unique among the hundreds of GPCRs identified to date. High sequence homology exists between the AZ3B protein and a number of chemoattractant receptors in the amino-terminal 170 residues and the carboxyl-terminal 150 residues. Northern and flow cytometric analyses suggested that the AZ3B message and protein are widely expressed in several differentiated hematopoietic cell lines, in the lung, placenta, heart, and endothelial cells. We postulate that the AZ3B protein defines a distinct group of receptors within the GPCR superfamily.

Retinoid X receptor acts as a hormone receptor in vivo to induce a key metabolic enzyme for 1,25-dihydroxyvitamin D3

We demonstrate here that RNA levels of 25-hydroxy-vitamin D3-24-hydroxylase (24-(OH)ase), a key catabolic enzyme for 1,25-dihydroxyvitamin D3, are increased by a highly selective retinoid X receptor (RXR) ligand, LG100268, in mice within hours. Correspondingly, upon LG100268 treatment, kidney 24-(OH)ase enzymatic activity increases 5-10-fold. The endogenous retinoid hormones, all-trans-retinoic acid and 9-cis-retinoic acid, and the synthetic retinoic acid receptor-selective compound, TTNPB, also stimulate 24-(OH)ase. Additionally, we show that LG100268 stimulates transcription of a luciferase reporter plasmid driven by 24-(OH)ase promoter sequences in the presence of RXR in CV-1 cell cotransactivation assays. This first demonstration of a gene that is regulated in the intact animal through an RXR-mediated pathway confirms earlier hypotheses that RXR is a bona fide hormone receptor. Regulation of a key gene in the vitamin D signaling pathway by a retinoid transducer may provide a molecular basis for some of the documented biological effects of vitamin A on bone and vitamin D metabolism.

Post-translational processing of membrane-associated neu differentiation factor proisoforms expressed in mammalian cells

Expression vectors constructed from human and rat pro-neu differentiation factor (NDF) cDNAs were transfected in Chinese hamster ovary cells for expression of recombinant NDF molecules. Soluble NDF forms were released into culture medium after post-translational processing of the membrane-bound pro-NDF forms. Different human and rat NDF isoforms, after being purified from the culture medium, were subjected to structural and biochemical characterizations. The isolated human and rat NDF isoforms have been proteolytically processed at a specific site at the N terminus, which is different from that observed for the processing of rat or human NDF molecule prepared from natural origins. The processing of each recombinant NDF isoform at its C terminus was heterogeneous but consistently occurred at nearby peptide bonds. Specific N- and C-terminal processing by Chinese hamster ovary cells has resulted in the production of two types (alpha and beta) of recombinant NDFs containing 222-225 amino acid residues. Both human and rat NDF molecules are heavily glycosylated at two of the three potential Asn-linked glycosylation sites and contain O-linked sugars at 11 of the Thr/Ser sites. Glycosylation occurs at a short, Ser/Thr-rich spacer region that connects the N-terminal immunoglobulin homology unit to the epidermal growth factor domain. Cellular phosphorylation assay indicated that these secreted forms contain similar biological activity in receptor tyrosine autophosphorylation of mammary tumor cells.