Mitotic kinesin‐like protein 2 (MKLP‐2), a member of the kinesin‐6 family, is essential for cytokinesis. Paprotrain is a reversible inhibitor of MKLP‐2 uncompetitive with ATP (Ki = 3.4 ± 0.1 μM ) and noncompetitive with microtubules (MTs; Ki = 1.6 ± 0.1 μM ). It is specific for MKLP‐2 as it does not inhibit other members of the kinesin superfamily. IC50 values were (1.35 ± 0.2) μM in basal and (0.83 ± 0.1) μM in MT‐stimulated ATPase assays. After 24 h of treatment with paprotrain (10–50 μM ), a significant number of cells were in apoptosis, confirmed by immunodetection of cleaved poly(ADP‐ribose) polymerase (PARP) and activated caspase 3. Paprotrain (50 μM; 8 h) induced binucleated cells and impeded the relocation of the CPC (the chromosome passenger protein complex) from the inner centromeres to the central spindle during anaphase. In proliferation assays, paprotrain inhibited growth with EC50 values between 7.6 and 22 μM. Moreover, after treatment with paprotrain the majority of metaphase spindles (70 ± 10 % of total metaphase cells) had misaligned chromosomes. Higher concentrations of paprotrain (50 μM ) increased the percentage of multipolar spindles at the expense of normal bipolar spindles (14 ± 3 % of total metaphase cells at 50 μM versus 6 ± 1.6 % at 20 μM)[1]. Furthermore, the rate of polar body extrusion in oocytes treated with 50 µM Paprotrain was significantly reduced to 42.07 ± 7.41%[2].
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