Regulation of the Glutamate Transporters by JAK2

Abstract

The Janus-activated kinase-2 JAK2 is involved in the signaling of leptin and erythropoietin receptors and mediates neuroprotective effects of the hormones. In theory, JAK2 could be effective through modulation of the glutamate transporters, carriers accounting for the clearance of glutamate released during neurotransmission. The present study thus elucidated the effect of JAK2 on the glutamate transporters EAAT1, EAAT2, EAAT3 and EAAT4. To this end, cRNA encoding the carriers was injected into Xenopus oocytes with or without cRNA encoding JAK2 and glutamate transport was estimated from glutamate induced current (I_glu). I_glu was observed in Xenopus oocytes expressing EAAT1 or EAAT2 or EAAT3 or EAAT4, but not in water injected oocytes. Coexpression of JAK2 resulted in an increase of I_glu by 83% (EAAT1), 67% (EAAT2), 42% (EAAT3) and 126% (EAAT4). As shown for EAAT4 expressing Xenopus oocytes, the effect of JAK2 was mimicked by gain of function mutation ^V617FJAK2 but not by the inactive mutant ^K882EJAK2. Incubation with JAK2 inhibitor AG490 (40 µM) resulted in a gradual decrease of I_glu by 53%, 79% and 92% within 3, 6 and 24 hours. Confocal microscopy and chemiluminescence analysis revealed that JAK2 coexpression increased EAAT4 protein abundance in the cell membrane. Disruption of transcription did not appreciably modify the up-regulation of I_glu in EAAT4 expressing oocytes. The decay of I_glu following inhibition of carrier insertion with brefeldin A was similar in oocytes expressing EAAT4 + JAK2 and oocytes expressing EAAT4 alone, indicating that JAK2 did not appreciably affect carrier retrieval from the membrane. In conclusion, JAK2 is a novel powerful regulator of glutamate transporters and thus participates in the protection against excitotoxicity.

Upregulation of Peptide Transporters PEPT1 and PEPT2 by Janus Kinase JAK2

“…JAK2 has most recently been shown to be involved in the regulation of several transporters including the betaine/GABA transporter BGT1 [20], the creatine transporter CreaT [21], the glucose transporter SGLT1 [22] and several amino acid transporters [23,24]. Transporters contributing to intestinal nutrient uptake and expressed in tumor cells include the peptide transporters 1 (PEPT1) and 2 (PEPT2), carriers mediating the cellular uptake of di- and tripeptides [25,26,27].…”

Upregulation of the large conductance voltage- and Ca2+-activated K+ channels by Janus kinase 2

“…JAK2 has previously been shown to influence a variety of carriers, including facilitative glucose carriers (16,68), Na ϩ coupled glucose transport (21), Na ϩ coupled neutral amino acid transporter B(0)AT (SLC6A19) (5), Na ϩ coupled glutamate transport (22), Na ϩ and Cl Ϫ coupled transport of betaine and GABA (23), Na ϩ /H ϩ exchanger (7), and Na…”

“…For generating cRNA (18), the constructs encoding the mouse Ca 2ϩ -insensitive BK channel (BK M513Iϩ⌬899 -903 ) (45, 64) (kindly provided by J. Lingle), wild-type human JAK2, human inactive K882E JAK2 mutant, and human gain-of-function V617F JAK2 mutant (21,22) were used. The constructs were used for generation of cRNA as described previously (9,55).…”

Down-Regulation of Na+/K+ATPase Activity by Human Parvovirus B19 Capsid Protein VP1

“…Two-electrode voltage-clamp recordings were performed at a holding potential of -30 mV for determination of the endogeneous Na + /K + -ATPase activity. The data were filtered at 10 Hz and recorded with a GeneClamp 500 amplifier, a DigiData 1300 A/D-D/A converter and the pClamp 9.2 software packages for data acquisition and analysis (Axon Instruments, Foster City, CA, USA) [55]. The oocytes were maintained at 17°C in ND96 solution containing 88.5 mM NaCl, 2 mM KCl, 1 mM MgC1 2 , 1.8 mM CaC1 2 , 5 mM HEPES, tretracycline (Sigma, 0.11 mM), ciprofloxacin (Sigma, 4 μM), gentamycin (Refobacin© 0.2 mM), theophylline (Euphylong©, 0.5 mM) and sodium pyruvate (Sigma, 5 mM), pH was adjusted to 7.5 by addition of NaOH.…”