Chen Lisa S, Redkar Sanjeev, Bearss David, Wierda William G, Gandhi Varsha
Department of Experimental Therapeutics, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Blood. 2009 Nov 5;114(19):4150-7. doi: 10.1182/blood-2009-03-212852. Epub 2009 Sep 4.
Pim kinases are involved in B-cell development and are overexpressed in B-cell chronic lymphocytic leukemia (CLL). We hypothesized that Pim kinase inhibition would affect B-cell survival. Identified from a screen of imidazo[1,2-b]pyridazine compounds, SGI-1776 inhibits Pim-1, Pim-2, and Pim-3. Treatment of CLL cells with SGI-1776 results in a concentration-dependent induction of apoptosis. To elucidate its mechanism of action, we evaluated the effect of SGI-1776 on Pim kinase function. Unlike in replicating cells, phosphorylation of traditional Pim-1 kinase targets, phospho-Bad (Ser112) and histone H3 (Ser10), and cell-cycle proteins were unaffected by SGI-1776, suggesting an alternative mechanism in CLL. Protein levels of total c-Myc as well as phospho-c-Myc(Ser62), a Pim-1 target site, were decreased after SGI-1776 treatment. Levels of antiapoptotic proteins Bcl-2, Bcl-X(L), XIAP, and proapoptotic Bak and Bax were unchanged; however, a significant reduction in Mcl-1 was observed that was not caused by caspase-mediated cleavage of Mcl-1 protein. The mechanism of decline in Mcl-1 was at the RNA level and was correlated with inhibition of global RNA synthesis. Consistent with a decline in new RNA synthesis, MCL-1 transcript levels were decreased after treatment with SGI-1776. These data suggest that SGI-1776 induces apoptosis in CLL and that the mechanism involves Mcl-1 reduction.
Pim激酶参与B细胞发育，且在B细胞慢性淋巴细胞白血病（CLL）中过表达。我们推测Pim激酶抑制会影响B细胞存活。从咪唑并[1,2 - b]哒嗪化合物筛选中鉴定出的SGI - 1776可抑制Pim - 1、Pim - 2和Pim - 3。用SGI - 1776处理CLL细胞会导致浓度依赖性的凋亡诱导。为阐明其作用机制，我们评估了SGI - 1776对Pim激酶功能的影响。与在增殖细胞中不同，传统Pim - 1激酶靶点磷酸化的Bad（Ser112）和组蛋白H3（Ser10）以及细胞周期蛋白不受SGI - 1776影响，提示在CLL中有另一种机制。SGI - 1776处理后，总c - Myc以及Pim - 1靶点位点磷酸化的c - Myc（Ser62）的蛋白水平降低。抗凋亡蛋白Bcl - 2、Bcl - X（L）、XIAP以及促凋亡蛋白Bak和Bax的水平未改变；然而，观察到Mcl - 1显著降低，这并非由半胱天冬酶介导的Mcl - 1蛋白裂解所致。Mcl - 1下降的机制在RNA水平，且与整体RNA合成的抑制相关。与新RNA合成下降一致，用SGI - 1776处理后MCL - 1转录水平降低。这些数据表明SGI - 1776在CLL中诱导凋亡，且其机制涉及Mcl - 1减少。
