Mechanism of leukemogenesis by constitutive active receptor tyrosine kinase

酪氨酸激酶的结构性活性突变是癌症的关键遗传异常。在血液系统恶性肿瘤中，c-Kit和Flt3等受体酪氨酸激酶的结构性活性突变被认为是急性髓系白血病的关键突变。我们研究了这些结构性活性受体酪氨酸激酶在白血病发生中的作用机制。由于受体酪氨酸激酶胞质区域中的酪氨酸残基调节激活和下游信号转导，因此我们研究了调节突变受体酪氨酸激酶结构性激活的关键酪氨酸残基。通过对结构活性突变体Flt3Asp838Val的每22个酪氨酸残基的Tyr-Phe突变分析，我们确定Tyr845、Tyr892和Tyr922是调节Flt3Asp835Val突变体激活的关键酪氨酸残基。Tyr 845Phe、Tyr892Phe和Tyr922Phe突变取消了Flt3 Asp835Val自身的激酶激活，导致完全信号转导、增殖和存活的抑制。通过将温度调至33℃，以及伴侣蛋白Cdc38和Hsp90的共表达，这些酪氨酸-Phe突变体被抑制的激酶活性被部分挽救。这些结果表明，Tyr845、Tyr892和Tyr922可能是维持Flt3Asp835Val突变体活性构象的关键酪氨酸残基。我们已经确定，酪氨酸残基Tyr719对c-Kit Asp814Val突变体的激活起关键作用，c-Kit Asp814Val突变体是Flt3 Asp835Val的相应突变体。综上所述，受体酪氨酸激酶的结构性活性突变体具有调节致癌活性的特异性酪氨酸残基，可能成为酪氨酸激酶抑制剂的新的特异性靶点。

Constitutive active mutants of tyrosine kinases are the key genetic abnormality of cancer. In hematological malignancies, constitutive active mutants of receptor tyrosine kinases such as c-Kit and FLT3 have been identified as the critical mutations in acute myeloid leukemia. We have studied the mechanism of leukemogenesis by these constitutive active receptor tyrosine kinases. Since tyrosine residues in the cytoplasmic domain of receptor tyrosine kinases regulate the activation and the downstream signal transduction, we investigated the critical tyrosine residues which regulate the constitutive activation of mutant receptor tyrosine kinases. By analyzing the Tyr-Phe mutations of each 22 tyrosine residue of FLT3 Asp838Val, constitutive active mutant of FLT3, we identified that Tyr845,Tyr892, and Tyr922 are the critical tyrosine residues which regulated the activation of FLT3Asp835Val mutant. The Tyr 845Phe,Tyr892Phe and Tyr922Phe mutations abolished the kinase activation itself of FLT3 Asp835Val, leading to the inhibition of full signal transduction, proliferation and survival. The suppressed kinase activity of these Tyr-Phe mutants were partially rescued by shifting the temperature to 33℃, and co-expression of chaperone proteins, Cdc38 and Hsp90. These results suggested that Tyr845,Tyr892 and Tyr922 may be the critical tyrosine residues which maintain the active conformation of FLT3 Asp835Val mutant. We have already identified that the tyrosine residue, Tyr7l9,critically regulated the activation of c-Kit Asp8l4Val mutant, which is the corresponding mutant to FLT3 Asp835Val. Taken together, the constitutive active mutants of receptor tyrosine kinase have the specific tyrosine residues which regulate the oncogenic activation, which may serve as the new specific targets of tyrosine kinase inhibitors.