Georg-Speyer-Haus, Institute for Tumor Biology and Experimental Therapy, Frankfurt am Main 60596, Germany.
Ganymed Pharmaceuticals AG, Mainz 55131, Germany.
Cancers (Basel). 2015 Mar 19;7(1):503-37. doi: 10.3390/cancers7010503.
Signal transducers and activators of transcription (Stats) play central roles in the conversion of extracellular signals, e.g., cytokines, hormones and growth factors, into tissue and cell type specific gene expression patterns. In normal cells, their signaling potential is strictly limited in extent and duration. The persistent activation of Stat3 or Stat5 is found in many human tumor cells and contributes to their growth and survival. Stat5 activation plays a pivotal role in nearly all hematological malignancies and occurs downstream of oncogenic kinases, e.g., Bcr-Abl in chronic myeloid leukemias (CML) and Jak2(V617F) in other myeloproliferative diseases (MPD). We defined the mechanisms through which Stat5 affects growth and survival of K562 cells, representative of Bcr-Abl positive CML, and HEL cells, representative for Jak2(V617F) positive acute erythroid leukemia. In our experiments we suppressed the protein expression levels of Stat5a and Stat5b through shRNA mediated downregulation and demonstrated the dependence of cell survival on the presence of Stat5. Alternatively, we interfered with the functional capacities of the Stat5 protein through the interaction with a Stat5 specific peptide ligand. This ligand is a Stat5 specific peptide aptamer construct which comprises a 12mer peptide integrated into a modified thioredoxin scaffold, S5-DBD-PA. The peptide sequence specifically recognizes the DNA binding domain (DBD) of Stat5. Complex formation of S5-DBD-PA with Stat5 causes a strong reduction of P-Stat5 in the nuclear fraction of Bcr-Abl-transformed K562 cells and a suppression of Stat5 target genes. Distinct Stat5 mediated survival mechanisms were detected in K562 and Jak2(V617F)-transformed HEL cells. Stat5 is activated in the nuclear and cytosolic compartments of K562 cells and the S5-DBD-PA inhibitor most likely affects the viability of Bcr-Abl+ K562 cells through the inhibition of canonical Stat5 induced target gene transcription. In HEL cells, Stat5 is predominantly present in the cytoplasm and the survival of the Jak2(V617F)+ HEL cells is impeded through the inhibition of the cytoplasmic functions of Stat5.
信号转导子和转录激活子（Stats）在将细胞外信号（例如细胞因子、激素和生长因子）转化为组织和细胞类型特异性基因表达模式方面发挥着核心作用。在正常细胞中，其信号转导潜能在程度和持续时间上受到严格限制。在许多人类肿瘤细胞中发现 Stat3 或 Stat5 持续激活，并有助于它们的生长和存活。Stat5 激活在几乎所有血液恶性肿瘤中都起着关键作用，并发生在致癌激酶下游，例如慢性髓性白血病中的 Bcr-Abl 和其他骨髓增生性疾病中的 Jak2(V617F)。我们定义了 Stat5 影响 Bcr-Abl 阳性慢性髓性白血病代表细胞 K562 和 Jak2(V617F)阳性急性红细胞白血病代表细胞 HEL 生长和存活的机制。在我们的实验中，我们通过 shRNA 介导的下调来抑制 Stat5a 和 Stat5b 的蛋白表达水平，并证明了细胞存活对 Stat5 存在的依赖性。或者，我们通过与 Stat5 特异性肽配体相互作用来干扰 Stat5 蛋白的功能能力。该配体是一种 Stat5 特异性肽适体构建体，它包含整合到修饰的硫氧还蛋白支架中的 12 mer 肽，S5-DBD-PA。该肽序列特异性识别 Stat5 的 DNA 结合结构域（DBD）。S5-DBD-PA 与 Stat5 的复合物形成导致 Bcr-Abl 转化的 K562 细胞中核部分的 P-Stat5 强烈减少，并抑制 Stat5 靶基因。在 K562 和 Jak2(V617F)-转化的 HEL 细胞中检测到不同的 Stat5 介导的存活机制。Stat5 在 K562 细胞的核和胞质区室中被激活，并且 S5-DBD-PA 抑制剂很可能通过抑制经典 Stat5 诱导的靶基因转录来影响 Bcr-Abl+K562 细胞的活力。在 HEL 细胞中，Stat5 主要存在于细胞质中，并且 Jak2(V617F)+HEL 细胞的存活通过抑制 Stat5 的细胞质功能来受阻。
