Department of Human Pathology and Oncology, University of Siena, Siena, Italy.
Oncogene. 2012 Feb 16;31(7):929-38. doi: 10.1038/onc.2011.286. Epub 2011 Jul 25.
Malignant mesothelioma (MM) is a highly aggressive tumor of the serous membranes for which there is currently no effective curative modality. Recent data suggest that hyperactivation of the tyrosine kinase SRC has a key role in MM development and therefore this kinase represents an important molecular target for MM therapy. We tested new pyrazolo[3,4-d]pyrimidine SRC inhibitors on a panel of MM cell lines expressing the active form of SRC. These SRC inhibitors exerted a significant proapoptotic effect on MM cells without affecting the normal mesothelial cell line MET-5A, supporting a possible use of these SRC inhibitors for a safe treatment of MM. We also showed that SRC inhibitor-induced apoptosis occurred concomitantly with an increase in the nuclear stability of the cyclin-dependent kinase inhibitor p27. This finding is remarkable considering that loss of nuclear p27 expression is a well-established adverse prognostic factor in MM, and p27 nuclear localization is crucial for its tumor-suppressive function. Consistently, SRC inhibition seems to promote the increase in p27 nuclear level also by inactivating the AKT kinase and downregulating cyclin D1, which would otherwise delay p27 nuclear import and provoke its cytoplasmic accumulation. To determine whether p27 stabilization has a direct role in apoptosis induced by SRC inhibition, we stably silenced the CDKN1B gene, encoding p27, in MSTO-211H and REN mesothelioma cells by transduction with lentiviral vectors expressing short hairpin RNAs against the CDKN1B transcript. Strikingly, p27 silencing was able to suppress the apoptosis induced by these SRC inhibitors in both MM cell lines, suggesting that p27 has a crucial proapoptotic role in MM cells treated with SRC inhibitors. Our findings reveal a new mechanism, dependent on p27 nuclear stabilization, by which SRC inhibition can induce apoptosis in MM cells and provide a new rationale for the use of SRC inhibitors in MM therapy.
恶性间皮瘤（MM）是一种高度侵袭性的浆膜肿瘤，目前尚无有效的治疗方法。最近的数据表明，酪氨酸激酶 SRC 的过度激活在 MM 的发展中起着关键作用，因此该激酶代表了 MM 治疗的一个重要的分子靶点。我们在表达 SRC 活性形式的 MM 细胞系中测试了新型吡唑并[3,4-d]嘧啶 SRC 抑制剂。这些 SRC 抑制剂对 MM 细胞具有显著的促凋亡作用，而对正常间皮细胞系 MET-5A 没有影响，支持这些 SRC 抑制剂用于 MM 的安全治疗。我们还表明，SRC 抑制剂诱导的凋亡与细胞周期蛋白依赖性激酶抑制剂 p27 的核稳定性增加同时发生。考虑到核 p27 表达的丢失是 MM 中一个既定的不良预后因素，并且 p27 的核定位对于其肿瘤抑制功能至关重要，这一发现是值得注意的。一致地，SRC 抑制似乎通过使 AKT 激酶失活和下调 cyclin D1 来促进 p27 核水平的增加，否则这会延迟 p27 核输入并导致其细胞质积累。为了确定 p27 稳定化在 SRC 抑制诱导的凋亡中是否具有直接作用，我们通过转导表达针对 CDKN1B 转录本的短发夹 RNA 的慢病毒载体，在 MSTO-211H 和 REN 间皮瘤细胞中稳定沉默编码 p27 的 CDKN1B 基因。令人惊讶的是，p27 沉默能够抑制这两种 MM 细胞系中这些 SRC 抑制剂诱导的凋亡，表明 p27 在接受 SRC 抑制剂治疗的 MM 细胞中具有关键的促凋亡作用。我们的发现揭示了一种新的机制，该机制依赖于 p27 的核稳定化，通过该机制，SRC 抑制可以诱导 MM 细胞凋亡，并为 SRC 抑制剂在 MM 治疗中的应用提供了新的依据。
