Beta-tubulin and P-glycoprotein: major determinants of vincristine accumulation in B-CLL cells.
Vincristine (VCR) accumulation in chronic lymphatic leukemia of B-cell origin (B-CLL) has recently been shown not to be inversely correlated to P-glycoprotein (PGP) levels. Therefore, we studied, in addition to PGP expression and accumulation of VCR, the cellular beta-tubulin content in quiescent and rhIL-2 activated B-CLL cells. VCR mediates cytotoxicity by binding to tubulin. Constitutive beta-tubulin levels in B-CLL cells varied considerably. Upon activation with rhIL-2, beta-tubulin expression increased significantly. Therefore, tubulin levels could be correlated over a wide range to VCR accumulation. When the PGP-mediated drug efflux was blocked by verapamil (VRP), tubulin levels correlated linearly to VCR accumulation. All B-CLL cases expressed PGP at different levels. There was no linear correlation between PGP expression and VCR accumulation. A modulation factor m was defined as a quotient of VCR accumulation in the presence and absence of VRP to define the extent by which VRP inhibited a steady-state accumulation of VCR. The factor allowed discrimination between B-CLLs expressing low versus high PGP, irrespective of the levels of tubulin. However, PGP and beta-tubulin levels together were predictive for VCR accumulation in steady state. There was no uniform-accumulation defect for VCR in B-cell CLL because beta-tubulin and PGP were expressed independently. Non PGP-mediated VCR transport seems to play a minor role in B-cell CLL. Leukemia-associated varying of cytoskeletal organization in B-cell CLL might be one reason for the diverse cellular responses to receptor-mediated signals.
Reichle
A
A
Klinik und Poliklinik der Medizinischen Klinik I, Universität Regensburg, Germany.
Diddens
H
H
Altmayr
F
F
Rastetter
J
J
Andreesen
R
R
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000368:Aged; D000369:Aged, 80 and over; D000972:Antineoplastic Agents, Phytogenic / Q000493:pharmacokinetics*; D015152:Blotting, Northern; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005260:Female; D006801:Humans; D016130:Immunophenotyping; D007376:Interleukin-2 / Q000494:pharmacology; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D011994:Recombinant Proteins / Q000494:pharmacology; D014404:Tubulin / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology; D014750:Vincristine / Q000493:pharmacokinetics*
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000972:Antineoplastic Agents, Phytogenic; D002121:Calcium Channel Blockers; D007376:Interleukin-2; D011994:Recombinant Proteins; D014404:Tubulin; D014750:Vincristine; D014700:Verapamil