The rapid growth of tumor cells requires stimulation of uptake of nutrients including amino acids. The carriers accomplishing amino acid uptake include the Na⁺ coupled amino acid transporter ASCT2. Mechanisms up-regulating ASCT2 in tumor cells remained illdefined. Candidates include the Janus kinase-2 (JAK2), which is expressed in a variety of tumor cells and contributes to cell proliferation and cell survival. The gain of function mutant ^V617FJAK2 is found in and accounts for the majority of myeloproliferative diseases. The present study explored whether JAK2 modifies ASCT2 activity. ASCT2 was expressed in Xenopus oocytes with or without wild type JAK2, _V617FJAK2 or inactive _K882EJAK2 and electrogenic amino acid transport determined by dual electrode voltage clamp. Carrier protein abundance at the cell surface was determined by chemiluminescence. In ASCT2-expressing oocytes, but not in oocytes injected with water or JAK2 alone, extracellular addition of the amino acids alanine, serine, glutamine or cysteine (1 mM) each resulted in a current (I_aa), which was significantly increased following coexpression of JAK2 or _V617FJAK2, but not by coexpression of _K882EJAK2. _V617FJAK2 coexpression increased maximal transport rate without significantly modifying affinity of the carrier. The JAK2 inhibitor AG490 (40 mM) gradually decreased I_aa in ASCT2+_V617FJAK2 expressing oocytes. _V617FJAK2 increased carrier protein abundance in the cell membrane. In ASCT2 and _V617FJAK2 coexpressing oocytes the decline of Iaa following inhibition of carrier insertion by brefeldin A (5 mM) was similar in the absence and presence of JAK2 inhibitor AG490. In conclusion JAK2 is a powerful stimulator of ASCT2 carrier protein insertion and activity and thus presumably participates in the up-regulation of cellular amino acid uptake into _V617FJAK2 expressing tumor cells.