Mechanisms of MEK/ERK growth arrest signaling

Raf/MEK/ERK通路在癌症中经常被解除调控，因此成为治疗的关键靶点。 尽管针对B-Raf和MEK1/2的先进抑制剂的最新进展改善了对 B-RafV600E，K黑色素瘤，这些肿瘤的耐药能力和内在耐药 对于这些抑制剂，许多其他MEK/ERK去调节的肿瘤类型需要额外的治疗策略。 因为肿瘤细胞有能力通过基因途径重新激活MEK/ERK来产生耐药性 相关信令网络的改变或反馈重排，预测当前 针对MEK/ERK抑制的治疗策略将不断受到挑战。有鉴于此，一个很有希望的 战略将是利用癌细胞的一个弱点(S)，这不可避免地与它们的异常有关 MEK/ERK活性。该项目的目标是确定mortalin(GRP75/HSPA9)，一种分子 HSP70家族中的伴侣蛋白可以选择性地诱导线粒体驱动的死亡 MEK/ERK失控肿瘤细胞的机制。在上一个资助期，我们发现 肿瘤中Mortalin上调是促进MEK/ERK介导的肿瘤细胞生长的关键机制 通过抑制该途径触发生长停滞的潜力而产生增殖信号。为了进一步推动 通过详细阐述mortalin在癌症中的功能，我们发现mortalin还可以通过以下方式促进肿瘤细胞的存活 调控线粒体生物能量学。Mortalin的后一种作用需要在 MEK/ERK信号转导的背景，因为我们初步研究的数据强烈表明 去死蛋白可选择性地诱导MEK/ERK异常的肿瘤细胞死亡 活性，包括对B-Raf抑制剂获得抗药性的B-RafV600E肿瘤细胞。而且，我们的 研究表明，mortalin耗竭通过调节MEK/ERK信号转导通路诱导肿瘤细胞死亡 线粒体的腺嘌呤核苷酸易位酶(ANT)和电压依赖性阴离子通道(VDAC) 这些通道对细胞生物能量学至关重要，但在下列情况下也可能变成强大的死亡机器 压力很大。因此，我们假设mortalin的一个关键功能是保护肿瘤细胞免受 MEK/ERK活性异常引起的线粒体生物能应激。进一步说，我们预测 Mortalin提供了选择性地触发MEK/ERK中线粒体死亡机制的独特靶点- 解除对肿瘤细胞的控制。为了验证这些假设，目标1将确定mortalin是否调节细胞 ANT/VDAC相关的线粒体通透性转换和钙离子从内质网流向内质网的死亡/存活 线粒体。目的2将确定mortalin是否抑制由 MEK/ERK失控肿瘤细胞的生物能量学应激。目标3将确定mortalin靶向 在体内能有效抑制MEK/ERK失控的肿瘤。所获得的结果将有助于定义 Mortain可促进MEK/ERK失控癌症的存活和增殖。

The Raf/MEK/ERK pathway is frequently deregulated in cancer, thus being a key target for therapy. Although recent development of advanced inhibitors targeting B-Raf and MEK1/2 has improved therapy of B-RafV600E,K melanoma, the ability of these tumors to develop drug resistance and the intrinsic resistance of many other MEK/ERK-deregulated tumor types to these inhibitors demand additional therapeutic strategies. Because tumor cells have the ability to develop drug resistances by reactivating MEK/ERK via genetic alterations or feedback rearrangement of the associated signaling network, it is predicted that current therapeutic strategies aiming MEK/ERK inhibition will be continuously challenged. Given that, one promising strategy would be to exploit a weakness(s) of cancer cells, which is inevitably associated with their aberrant MEK/ERK activity. The goal of this project is to determine whether mortalin (GRP75/HSPA9), a molecular chaperone in the HSP70 family, can be targeted to selectively induce mitochondria-driven death mechanisms in MEK/ERK-deregulated tumor cells. In the previous funding period, we discovered that mortalin upregulation in cancer is a key mechanism that facilitates MEK/ERK-mediated tumor cell proliferative signaling by suppressing the pathway’s potential to trigger growth arrest. In an effort to further elaborate mortalin functions in cancer, we discovered that mortalin can also facilitate tumor cell survival by regulating mitochondrial bioenergetics. This latter function of mortalin needs to be thoroughly evaluated in the context of MEK/ERK signaling because the data from our preliminary studies strongly suggest that mortalin deprivation can selectively induce robust cell death in tumor cells exhibiting aberrant MEK/ERK activity, including the B-RafV600E tumor cells that have acquired resistance to B-Raf inhibitors. Moreover, our data suggest that mortalin depletion induces cell death in MEK/ERK-deregulated tumor cells by regulating adenine nucleotide translocases (ANT) and voltage-dependent anion channel (VDAC), the mitochondrial channels that are critical for cellular bioenergetics but can also turn into powerful death machinery when stressed. We therefore hypothesize that a key function of mortalin is to protect tumor cells from mitochondrial bioenergetics stress caused by aberrant MEK/ERK activity. By extension, we predict that mortalin provides a unique target to selectively trigger mitochondrial death mechanisms in MEK/ERK- deregulated tumor cells. To test these hypotheses, Aim 1 will determine whether mortalin regulates cell death/survival via ANT/VDAC-associated mitochondrial permeability transition and Ca2+ flux from ER to mitochondria. Aim 2 will determine whether mortalin suppresses mitochondrial cell death caused by bioenergetics stress in MEK/ERK-deregulated tumor cells. Aim 3 will determine whether mortalin targeting can effectively suppress MEK/ERK-deregulated tumors in vivo. The obtained results will help define how mortain promotes survival and proliferation of MEK/ERK-deregulated cancers.