Recent studies have shown that bone morphogenetic protein receptor 2 (BMPR2) regulates cell survival signaling events in cancer cells independent of the BMP type 1 receptor (BMPR1) or the Smad-1/5 transcription factor. Mutations in BMPR2 trafficking proteins leads to overactive BMP signaling, which leads to neurological diseases caused by BMPR2 stabilization of the microtubules. It is not known whether BMPR2 regulates the microtubules in cancer cells and what effect this has on cell survival. It is also not known whether alterations in BMPR2 trafficking effects activity and response to BMPR2 inhibitors. We utilized BMPR2 siRNA and the BMP receptor inhibitors JL5 and Ym155, which decrease BMPR2 signaling and cause its mislocalization to the cytoplasm. Using the JL5 resistant MDA-MD-468 cell line and sensitive lung cancer cell lines, we examined the effects of BMPR2 inhibition on BMPR2 mislocalization to the cytoplasm, microtubule destabilization, lysosome activation and cell survival. We show that the inhibition of BMPR2 destabilizes the microtubules. Destabilization of the microtubules leads to the activation of the lysosomes. Activated lysosomes further decreases BMPR2 signaling by causing it to mislocalizated to the cytoplasm and/or lysosome for degradation. Inhibition of the lysosomes with chloroquine attenuates BMPR2 trafficking to the lysosome and cell death induced by BMPR2 inhibitors. Furthermore, in MDA-MD-468 cells that are resistant to JL5 induced cell death, BMPR2 was predominately located in the cytoplasm. BMPR2 failed to localize to the cytoplasm and/or lysosome following treatment with JL5 and did not destabilize the microtubules or activate the lysosomes. These studies reveal that the inhibition of BMPR2 destabilizes the microtubules promoting cell death of cancer cells that involves the activation of the lysosomes. Resistance to small molecules targeting BMPR2 may occur if the BMPR2 is localized predominantly to the cytoplasm and/or fails to localize to the lysosome for degradation.

中文翻译：

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骨形态发生蛋白受体2抑制使微管不稳定，促进溶酶体活化和肺癌细胞死亡

最近的研究表明，骨形态发生蛋白受体 2 (BMPR2) 可独立于 BMP 1 型受体 (BMPR1) 或 Smad-1/5 转录因子调节癌细胞中的细胞存活信号传导事件。BMPR2 转运蛋白的突变导致 BMP 信号过度活跃，从而导致由 BMPR2 稳定微管引起的神经系统疾病。目前尚不清楚 BMPR2 是否调节癌细胞中的微管以及这对细胞存活有什么影响。也不知道 BMPR2 运输的改变是否会影响活性和对 BMPR2 抑制剂的反应。我们利用了 BMPR2 siRNA 和 BMP 受体抑制剂 JL5 和 Ym155，它们降低了 BMPR2 信号传导并导致其错误定位到细胞质。使用JL5抗性MDA-MD-468细胞系和敏感肺癌细胞系，我们检查了 BMPR2 抑制对 BMPR2 错误定位到细胞质、微管失稳、溶酶体活化和细胞存活的影响。我们表明抑制 BMPR2 会破坏微管的稳定性。微管的不稳定导致溶酶体的激活。活化的溶酶体通过使其错误定位到细胞质和/或溶酶体进行降解来进一步降低 BMPR2 信号传导。用氯喹抑制溶酶体可减弱 BMPR2 向溶酶体的转运和 BMPR2 抑制剂诱导的细胞死亡。此外，在对 JL5 诱导的细胞死亡具有抗性的 MDA-MD-468 细胞中，BMPR2 主要位于细胞质中。BMPR2 在用 JL5 处理后未能定位到细胞质和/或溶酶体，并且没有破坏微管的稳定性或激活溶酶体。这些研究表明，抑制 BMPR2 会破坏微管的稳定性，从而促进涉及溶酶体激活的癌细胞的细胞死亡。如果 BMPR2 主要定位于细胞质和/或未能定位于溶酶体进行降解，则可能会出现对靶向 BMPR2 的小分子的抗性。