Drug transporter regulation in tumors by DNA methylation

Epigenetic alterations, such as aberrant DNA methylation, are a hallmark of cancer. DNA hypermethylation of the promoter region affects, for example, the expression of tumor suppressor genes and is associated with their transcriptional silencing in tumors. A recent report has provided evidence for epigenetic silencing of the multispecific organic cation transporter SLC22A1 in hepatocellular carcinoma. Given the role of this transporter in the cellular uptake of several anticancer drugs, the study provided a novel mechanism to explain the substantial variability in treatment response, and it might provide a new strategy for optimization of pharmacotherapy of hepatocellular carcinoma

Plant hormone transporters: what we know and what we would like to know

Hormone transporters are crucial for plant hormone action, which is underlined by severe developmental and physiological impacts caused by their loss-of-function mutations. Here, we summarize recent knowledge on the individual roles of plant hormone transporters in local and long-distance transport. Our inventory reveals that many hormones are transported by members of distinct transporter classes, with an apparent dominance of the ATP-binding cassette (ABC) family and of the Nitrate transport1/Peptide transporter family (NPF). The current need to explore further hormone transporter regulation, their functional interaction, transport directionalities, and substrate specificities is briefly reviewed

Effects of MDPV on dopamine transporter regulation in male rats. Comparison with cocaine.

RATIONALE: MDPV (3,4-methylenedioxypyrovalerone) is a synthetic cathinone present in bath salts. It is a powerful psychostimulant and blocker of the dopamine transporter (DAT), like cocaine. It is known that acute exposure to psychostimulants induces rapid changes in DAT function. OBJECTIVES: To investigate the effects of MDPV on DAT function comparing with cocaine. METHODS: Binding of [3H]WIN 35428 was performed on PC 12 cells treated with MDPV and washed. Rat striatal synaptosomes were incubated with MDPV or cocaine (1 μM) for 1 h and [3H]dopamine (DA) uptake was performed. Also, different treatments with MDPV or cocaine were performed in Sprague-Dawley rats to assess locomotor activity and ex vivo [3H]DA uptake. RESULTS: MDPV increased surface [3H]WIN 35428 binding on PC 12 cells. In vitro incubation of synaptosomes with MDPV produced significant increases in Vmax and KM for [3H]DA uptake. In synaptosomes from MDPV- (1.5 mg/kg, s.c.) and cocaine- (30 mg/kg, i.p.) treated rats, there was a significantly higher and more persistent increase in [3H]DA uptake in the case of MDPV than cocaine. Repeated doses of MDPV developed tolerance to this DAT upregulation and 24 h after the 5-day treatment with MDPV, [3H]DA uptake was reduced. However, a challenge with the same drugs after withdrawal recovered the DAT upregulation by both drugs and showed an increased response to MDPV vs the first dose. At the same time, animals were sensitized to the stereotypies induced by both psychostimulants. CONCLUSIONS: MDPV induces a rapid and reversible functional upregulation of DAT more powerfully and lasting than cocaine

Achieving global perfect homeostasis through transporter regulation

Nutrient homeostasis—the maintenance of relatively constant internal nutrient concentrations in fluctuating external environments—is essential to the survival of most organisms. Transcriptional regulation of plasma membrane transporters by internal nutrient concentrations is typically assumed to be the main mechanism by which homeostasis is achieved. While this mechanism is homeostatic we show that it does not achieve global perfect homeostasis—a condition where internal nutrient concentrations are completely independent of external nutrient concentrations for all external nutrient concentrations. We show that the criterion for global perfect homeostasis is that transporter levels must be inversely proportional to net nutrient flux into the cell and that downregulation of active transporters (activity-dependent regulation) is a simple and biologically plausible mechanism that meets this criterion. Activity-dependent transporter regulation creates a trade-off between robustness and efficiency, i.e., the system's ability to withstand perturbation in external nutrients and the transporter production rate needed to maintain homeostasis. Additionally, we show that a system that utilizes both activity-dependent transporter downregulation and regulation of transporter synthesis by internal nutrient levels can create a system that mitigates the shortcomings of each of the individual mechanisms. This analysis highlights the utility of activity-dependent regulation in achieving homeostasis and calls for a re-examination of the mechanisms of regulation of other homeostatic systems

Learning from each other: ABC transporter regulation by protein phosphorylation in plant and mammalian systems

The ABC (ATP-binding cassette) transporter family in higher plants is highly expanded compared with those of mammalians. Moreover, some members of the plant ABCB subfamily display very high substrate specificity compared with their mammalian counterparts that are often associated with multidrug resistance (MDR) phenomena. In this review we highlight prominent functions of plant and mammalian ABC transporters and summarize our knowledge on their post-transcriptional regulation with a focus on protein phosphorylation. A deeper comparison of regulatory events of human cystic fibrosis transmembrane conductance regulator (CFTR) and ABCB1 from the model plant Arabidopsis reveals a surprisingly high degree of similarity. Both physically interact with orthologues of the FK506-binding proteins (FKBPs) that chaperon both transporters to the plasma membrane in an action that seems to involve Hsp90. Further both transporters are phosphorylated at regulatory domains that connect both nucleotide-binding folds. Taken together it appears that ABC transporters exhibit an evolutionary conserved but complex regulation by protein phosphorylation, which apparently is, at least in some cases, tightly connected with protein–protein interactions (PPI)

Dopamine transporter and transmission of psychopathological risk. A review of gene-environment interplay

Research underlines that intergenerational transmission of psychopathological risk results from a complex interplay of genetic and environmental risk factors which predispose child to develop emotionalbehavioral problems. Mechanisms of transmission are poorly understood, but few studies have focused on the role played by dopamine transporter (DAT) gene. This review aims to examine mediating mechanism of DAT genotype-environmental interaction (GxE), DAT genotype-environmental correlation (rGE), and methylation status involved in transmission of psychopathological risk. The review of literature was made through researches in university libraries on paper material, and telematics systems research. Studies have evidenced that DAT is implicated in intergenerational transmission of psychopathological risk. Results are mixed regarding its genetic variants, but mechanisms through which this gene can affect both quality of parenting and child development are partially established. Only few studies have examined methylation mechanisms that can be implicated. Findings suggest to involve an improved focus on DAT genotypes, methylation status associated, and their relationship with environment to better understanding child’s vulnerability and resilience following exposure to contextual risk factors associated with parental psychopathological symptoms

ABC TRANSPORTERS IN GLIOBLASTOMA: ANTICANCER DRUG TRANSPORT AND TRANSPORTER REGULATION AT THE BLOOD-BRAIN BARRIER

Glioblastoma is one of the deadliest cancers, with a median survival of only one year. Even after aggressive treatment consisting of surgical resection, radiation, and chemotherapy, most glioblastoma patients suffer from tumor recurrence within 6-9 months. One reason for treatment failure of anticancer drugs is the blood-brain barrier that protects the brain by impeding xenobiotic uptake from the blood. To this end, efflux transporters at the human blood-brain barrier, such as P-glycoprotein (ABCB1) and Breast Cancer Resistance Protein (ABCG2), prevent many compounds, including anticancer drugs, from entering the brain. Thus far, approaches to deliver anticancer drugs across the blood-brain barrier have been unsuccessful in clinical trials. Therefore, novel therapeutic strategies are needed to overcome the blood-brain barrier for improved glioblastoma treatment. Here, I address this need in 3 independent aims: Elucidate the involvement and cooperation of ABC transporters in anticancer drug transport at the blood-brain barrier Establish and characterize human glioblastoma models Evaluate the impact of dual PI3K/Akt inhibition on brain uptake of anticancer drugs Aim 1: While Abcb1/Abcg2 inhibition improved survival in mouse glioblastoma models, clinical trials had to be terminated due to a lack of efficacy, sparking a discussion that other ABC transporters might be involved in this process. To discern how multiple ABC transporters cooperate in restricting anticancer drug uptake at the blood-brain barrier, I evaluated the effect of several efflux transporters at the blood-brain barrier on the brain level of anticancer drugs using transporter inhibitors or knockout mice. The results from this study suggest that Abcc4 works in concert with Abcb1/Abcg2 in restricting brain access of the tested anticancer drugs in mice. Further experiments are necessary to confirm this cooperation at the human blood-brain barrier. In part, these findings might provide one possible explanation why therapeutic strategies that solely focus on ABCB1/ABCG2 failed to improve treatment outcomes for glioblastoma patients. Aim 2: Successful treatment of glioblastoma requires reliable preclinical animal models to evaluate novel approaches and assess their potential therapeutic benefit. While many different glioblastoma models exist, most are not well characterized and only recapitulate a subset of glioblastoma characteristics. Here, I describe and compare two human glioblastoma models, U87-luc2 and U251-FLuc. While both models behave similarly in vitro, they have different in vivo tumor characteristics, such as invasiveness and blood-brain barrier disruption. Together, the two glioblastoma models recapitulate the tumor characteristics of a majority of patients. Aim 3: Direct transporter inhibition is unsuccessful in improving glioblastoma patient survival due to the low efficacy of inhibitors and adverse effects associated with combination treatment. However, efflux transporter regulation could open a “window-in-time” to allow anticancer drug uptake into the brain. Here, I tested a novel molecular switch approach to overcome Abcb1/Abcg2-mediated efflux at the blood-brain barrier. My data indicate that PI3K/Akt could serve as a molecular switch to transiently turn off Abcb1/Abcg2 at the blood-brain barrier and increase brain levels of anticancer drugs

Inhibition of Food Intake by PACAP in the Hypothalamic Ventromedial Nuclei is Mediated by NMDA Receptors

Central injections of pituitary adenylate cyclase-activating polypeptide (PACAP) into the ventromedial nuclei (VMN) of the hypothalamus produce hypophagia that is dependent upon the PAC1 receptor; however, the signaling downstream of this receptor in the VMN is unknown. Though PACAP signaling has many targets, this neuropeptide has been shown to influence glutamate signaling in several brain regions through mechanisms involving NMDA receptor potentiation via activation of the Src family of protein tyrosine kinases. With this in mind, we examined the Src-NMDA receptor signaling pathway as a target for PACAP signaling in the VMN that may mediate its effects on feeding behavior. Under nocturnal feeding conditions, NMDA receptor antagonism prior to PACAP administration into the VMN attenuated PACAP-mediated decreases in feeding suggesting that glutamatergic signaling via NMDA receptors is necessary for PACAP-induced hypophagia. Furthermore, PACAP administration into the VMN resulted in increased tyrosine phosphorylation of the GluN2B subunit of the NMDA receptor, and inhibition of Src kinase activity also blocked the effects of PACAP administration into the VMN on feeding behavior. These results indicate that PACAP neurotransmission in the VMN likely augments glutamate signaling by potentiating NMDA receptors activity through the tyrosine phosphorylation events mediated by the Src kinase family, and modulation of NMDA receptor activity by PACAP in the hypothalamus may be a primary mechanism for its regulation of food intake

A prior history of binge-drinking increases sensitivity to the motivational valence of methamphetamine in female C57BL/6J mice.

Methamphetamine (MA) and alcohol use disorders exhibit a high degree of co-morbidity and sequential alcohol-MA mixing increases risk for co-abuse. Recently, we reported greater MA-conditioned reward in male C57BL/6J mice with a prior history of binge alcohol-drinking (14 days of 2-hour access to 5, 10, 20 and 40% alcohol). As female mice tend to binge-drink more alcohol than males and females tend to be more sensitive than males to the psychomotor-activating properties of MA, we first characterized the effects of binge-drinking upon MA-induced place-conditioning (four pairings of 0.25, 0.5, 1, 2, or 4 mg/kg IP) in females and then incorporated our prior data to analyze for sex differences in MA-conditioned reward. Prior binge-drinking history did not significantly affect locomotor hyperactivity or its sensitization in female mice. However, the dose-response function for place-conditioning was shifted to the left of water-drinking controls, indicating an increase in sensitivity to MA-conditioned reward. The examination of sex differences revealed no sex differences in alcohol intake, although females exhibited greater MA-induced locomotor stimulation than males, irrespective of their prior drinking history. No statistically significant sex difference was apparent for the potentiation of MA-conditioned reward produced by prior binge-drinking history. If relevant to humans, these data argue that both males and females with a prior binge-drinking history are similarly vulnerable to MA abuse and it remains to be determined whether or not the neural substrates underpinning this increased vulnerability reflect common or sex-specific adaptations in reward-related brain regions