The sodium dependent reduced folate carrier (Rfc1; Slc19a1) provides the major route for cellular uptake of antifolate chemotherapeutic drugs such as methotrexate (MTX) and reduced folates into liver, kidneys and other tissues. Despite its essential role in cancer treatment and for the body’s folate homeostasis, little is known about Rfc1 regulation. In rat hepatocytes, the 5´ untranslated region of this carrier exhibits, amongst other regulatory elements, a barbiturate recognition box which as yet has only been found in the promotor region of xenobiotic metabolizing enzymes, particularly those of the CYP450 enzyme family. We have therefore investigated the issue of Rfc1 regulation by phenobarbital (PB)-type CYP450 inducers on the functional, transcriptional and translational level using an adequate in vitro model for rat liver. A significant decrease in Rfc1 activity was observed following treatment (48 h) with 1-10 times therapeutic plasma concentrations of PB-type CYP450 inducers like PB, carbamazepine, chlorpromazine, clotrimazole and with the constitutive androstane receptor agonist TCPOBOP. This was not associated with reduced mRNA and protein levels. Further mechanistic investigations revealed that short-term treatment (2 h) of cells with protein phosphatase 2A inhibitor okadaic acid and proteinkinase C inductor PMA was related to a significant reduction of Rfc1 mediated MTX uptake. Finally, the reduction in Rfc1 activity caused by PB, TCPOBOP and PMA was almost completely reversed by simultaneous incubation with the specific PKC inhibitor bisindolylmaleimide. These results demonstrate, that clinical relevant concentrations of PB-type CYP450 inducers cause a significant PKC-dependent reduction in Rfc1 uptake activity on the posttranscriptional level.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:10647 |
| Date | 06 July 2004 |
| Creators | Halwachs, Sandra |
| Contributors | Universität Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | German |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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