A member of forkhead transcription factor FKHRL1 is a downstream effector of STI571-induced cell cycle arrest in BCR-ABL-expressing cells
A member of forkhead transcription factor FKHRL1 is a downstream effector of STI571-induced cell cycle arrest in BCR-ABL-expressing cells
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DOI：
10.1074/jbc.m211562200
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发表时间：
2003-02-21
影响因子：
4.8
通讯作者：
Ozawa, K
中科院分区：
文献类型：
--
作者：
Komatsu, N;Watanabe, T;Ozawa, K
Forkhead转录因子家族成员FKHRL 1位于细胞因子信号传导中磷脂酰肌醇3-激酶-Akt活化途径的下游。由于磷脂酰肌醇3-激酶-Akt活化途径是慢性粒细胞白血病（CML）中BCR-ABL介导的转化和存活信号传导所必需的，因此在本研究中，我们检测了FKHRL 1在BCR-ABL介导的信号传导途径中的参与。FKHRL 1在表达BCR-ABL的细胞系KCL 22和KU 812中被组成性磷酸化，其磷酸化被BCR-ABL酪氨酸激酶特异性抑制剂STI 571抑制。与此同时，ST 1571诱导细胞周期停滞在G（0）/G（1）期，伴随着上调细胞周期蛋白依赖性激酶抑制剂p27/Kip 1在KCL 22细胞。此外，FKHRL 1在异位表达BCR-ABL的TF-1/bcr-abl细胞系中组成型磷酸化，但在亲本TF-1细胞系中不存在。考虑到磷酸化FKHRL 1已失去转录活性且p27/Kip 1表达受去磷酸化“活性”FKHRL 1正调控的几条证据，BCR-ABL可能通过FKHRL 1作为转录因子功能的丧失下调p27/Kip 1表达。为了证明这一假设，我们在KCL 22细胞系中产生了他莫昔芬诱导的“活性FKHRL 1”FKHRL 1-TM（FKHRL 1的三重突变体，其中所有三个Akt磷酸化位点都已突变）雌激素受体系统。添加他莫昔芬抑制细胞生长，表明FKHRL 1在细胞核中的过表达拮抗CML细胞的失调增殖。总之，FKHRL 1调节CAM细胞中BCR-ABL信号传导的下游分子p27/Kip 1的表达。BCR-ABL诱导的FKHRL 1功能丧失可能部分通过下调p27/Kip 1蛋白参与CAM的致癌转化。
A member of the Forkhead transcription factor family, FKHRL1, lies downstream of the phosphatidylinositol 3-kinase-Akt activation pathway in cytokine signaling. Because the phosphatidylinositol 3-kinase-Akt activation pathway is required for BCR-ABL-mediated transformation and survival signaling in chronic myelogenous leukemia (CML), in this study we examined the involvement of FKHRL1 in the BCR-ABL-mediated signaling pathway. FKHRL1 was constitutively phosphorylated in BCR-ABL-expressing cell lines KCL22 and KU812, and its phosphorylation was inhibited by treatment with STI571, a specific inhibitor of BCR-ABL tyrosine kinase. Concomitantly, ST1571 induced cell cycle arrest at the G(0)/G(1) phase, accompanied by up-regulation of a cyclin-dependent kinase inhibitor p27/Kip1 in KCL22 cells. In addition, FKHRL1 was constitutively phosphorylated in the TF-1/bcr-abl cell line ectopically expressing BCR-ABL but not in the parent TF-1 cell line. Considering several lines of evidence that phosphorylated FKHRL1 has lost transcriptional activity and that p27/Kip1 expression is positively regulated by dephosphorylated "active" FKHRL1, BCR-ABL may down-regulate p27/Kip1 expression via the loss of FKHRL1 function as a transcription factor. To demonstrate this hypothesis, we generated a tamoxifen-inducible "active FKHRL1" FKHRL1-TM (a triple mutant of FKHRL1, in which all three Akt phosphorylation sites have been mutated), estrogen receptor system in the KCL22 cell line. The addition of tamoxifen inhibited the cell growth indicating that overexpression of FKHRL1 in the nucleus antagonized deregulated proliferation of CML cells. Collectively, FKHRL1 regulates the expression of p27/Kip1 as a downstream molecule of BCR-ABL signaling in CAM cells. BCR-ABL-induced loss of FKHRL1 function may be involved in oncogenic transformation of CAM partially via the down-regulation of p27/Kip1 proteins.