Hirakawa Yasuko, Nary Laura J, Medh Rheem D
Department of Biology, California State University Northridge, Northridge, CA 91330-8303, USA.
J Mol Signal. 2009 Sep 2;4:6. doi: 10.1186/1750-2187-4-6.
Glucocorticoid hormones (GCs) induce apoptosis of leukemic T-cells by transcriptional regulation via the GC receptor, GR. In the human leukemic CEM cell culture model, RCAN1 has been identified as one of the genes that is specifically upregulated only in the GC-sensitive CEM C7-14 cells, but not in the GC-resistant CEM-C1-15 sister cells in correlation with GC-evoked apoptosis. RCAN1 gene encodes two major protein isoforms of the regulator of calcineurin (RCAN1), RCAN1-1 and RCAN1-4 via alternative splicing of exons 1 and 4 respectively, to exons 5-7. Studies reported here evaluated the differential regulation and function of the two transcripts and protein products of RCAN1 by the synthetic GC dexamethasone (Dex), and by modulators of calcium signaling.
Dex selectively upregulates transcript specific for RCAN 1-1 in glucocorticoid (GC)-susceptible human leukemic CEM-C7-14 cells but not in GC-refractory CEM-C1-15 sister cells. Expression of the second major transcript, RCAN1-4, is upregulated by [Ca2+]i inducers, thapsigargin and A23187, but not by Dex, suggesting a mutually exclusive regulatory pathway for both RCAN1 transcripts. GC-mediated upregulation of RCAN1-1 transcript and RCAN1-1 protein was kinase dependent, and was blocked by staurosporine and the p38 MAP kinase inhibitor SB 202190. RCAN1-1 coimmunoprecipitates with calcineurin PP3C and Dex-mediated RCAN1-1 upregulation correlated with reduction in calcineurin PP3C activity.
Data presented here suggest that GCs specifically upregulate RCAN1-1 transcript and protein while inducers of [Ca2+]i selectively upregulate RCAN1-4. GC-mediated increase in RCAN1-1 abundance and binding possibly inhibits calcineurin activity and modulates apoptosis in CEM-C7-14 cells.
糖皮质激素（GCs）通过糖皮质激素受体（GR）进行转录调控，从而诱导白血病T细胞凋亡。在人白血病CEM细胞培养模型中，RCAN1被鉴定为仅在GC敏感的CEM C7 - 14细胞中特异性上调的基因之一，而在GC耐药的CEM - C1 - 15姐妹细胞中则不然，这与GC诱导的凋亡相关。RCAN1基因通过外显子1和4分别与外显子5 - 7的可变剪接，编码钙调神经磷酸酶调节剂（RCAN1）的两种主要蛋白质异构体，即RCAN1 - 1和RCAN1 - 4。本研究评估了合成糖皮质激素地塞米松（Dex）以及钙信号调节剂对RCAN1的两种转录本和蛋白质产物的差异调控及功能。
Dex在糖皮质激素（GC）敏感的人白血病CEM - C7 - 14细胞中选择性上调RCAN1 - 1特异性转录本，但在GC难治性CEM - C1 - 15姐妹细胞中则不然。第二种主要转录本RCAN1 - 4的表达受细胞内钙离子浓度（[Ca2+]i）诱导剂毒胡萝卜素和A23187上调，但不受Dex上调，这表明两种RCAN1转录本存在相互排斥的调控途径。GC介导的RCAN1 - 1转录本和RCAN1 - 1蛋白上调依赖于激酶，并且被星形孢菌素和p38丝裂原活化蛋白激酶抑制剂SB 202190阻断。RCAN1 - 1与钙调神经磷酸酶PP3C共免疫沉淀，并且Dex介导的RCAN1 - 1上调与钙调神经磷酸酶PP3C活性降低相关。
本研究数据表明，GC特异性上调RCAN1 - 1转录本和蛋白，而[Ca2+]i诱导剂选择性上调RCAN1 - 4。GC介导的RCAN1 - 1丰度增加和结合可能抑制钙调神经磷酸酶活性，并调节CEM - C7 - 14细胞中的凋亡。
