Functional Determinants of Metastatic Dormancy

描述（由申请人提供）：大多数癌症患者会在治疗后几十年死于播散性肿瘤细胞（dtc）的转移，这表明dtc以休眠、非增殖状态存活。我们的长期目标是确定调控dtc休眠的机制。我们假设(i)肿瘤细胞休眠（即生长停滞）可能发生在传播期间和/或之后，以响应由不适宜的组织微环境和/或治疗施加的应激信号；（ii）应激信号反过来激活一个强大的生存程序，有利于在休眠期间延长生存时间。利用HEp3头颈部鳞癌细胞作为实验模型，我们实验室发现了调节休眠肿瘤细胞生长停滞和生存能力的新机制。这些依赖于ERK1/2（有丝分裂）和p38a/b（应激）途径之间的信号平衡以及特定的下游基因表达程序。我们发现，在从体内到培养条件的适应过程中，HEp3癌细胞重编程以获得休眠表型，其特征是在体内重新注射时延长G0/G1停滞。我们发现(i)休眠HEp3细胞的生长停滞是由于p38a依赖于复杂转录因子（TF）网络的调节。在这个网络中，p53和BHLHB3是由p38转录诱导的，它们有助于沉默。p38a依赖性的tf FoxM1和c-Jun抑制进一步加强了G0/G1阻滞；后者可拮抗p53。我们还发现（ii） TF ATF6a通过控制mTOR激活的替代途径来调节休眠的存活成分。事实上，ATF6a上调小GTPase Rheb，这反过来诱导mTOR- s6k激活，对雷帕霉素的抗性和体内休眠肿瘤细胞的存活。因此，我们已经确定了促进休眠肿瘤细胞的静止和存活的基因和机制。我们还发现，HEp3 dtc在骨髓微环境中不能恢复增殖，而在原发部位和肺部则继续生长。这种显著的差异似乎是一种休眠程序。其基础是，这些细胞从骨髓中恢复并在培养中扩增后，再注射到动物体内时不能形成肿瘤。相反，它们在恢复生长之前会经历一个休眠期。我们假设与上述相似的机制允许dtc抵抗治疗或微环境诱导的细胞死亡，并在休眠状态下存活，这为患者转移性复发提供了一个来源。显然，诱导或延长dtc生长停止对患者有益，但阻断它们的生存机制将使它们在复发发生之前被根除。由于抗癌治疗的最终成功严格依赖于治疗或预防转移，因此迫切需要在这一领域取得进展，以提高对转移前体的治疗根除。我们相信这些发现具有重要意义，因为对DTC休眠的了解将对我们如何理解和治疗癌症产生重要影响。

DESCRIPTION (provided by applicant): Majority of cancer patients will die of metastases that develop from disseminated tumor cells (DTCs) sometimes decades after treatment, suggesting that DTCs survive in a dormant, non-proliferative state. Our long-term goal is to identify the mechanisms regulating dormancy of DTCs. We hypothesize that (i) tumor cell dormancy (i.e. growth arrest) may happen during and/or after dissemination in response to stress signals imposed by an inhospitable tissue microenvironment and/or by therapy and that (ii) stress signaling in turn activates a robust survival program that favors prolonged survival during the dormancy periods. Using an experimental model, HEp3 head and neck squamous carcinoma cells, our laboratory has identified novel mechanisms regulating the growth arrest and survival capacity of dormant tumor cells. These depend on the signaling balance between ERK1/2 (mitogenic) and p38a/b (stress) pathways and a specific downstream gene expression program. We showed that during adaptation from in vivo to culture conditions HEp3 carcinoma cells reprogram to acquire a dormant phenotype characterized by a prolonged G0/G1 arrest when re-injected in vivo. We discovered that (i) the growth arrest of dormant HEp3 cells is due to p38a-dependent regulation of a complex transcription factor (TF) network. In this network p53 and BHLHB3 are transcriptionally induced by p38 and they contribute to quiescence. The G0/G1 arrest is further enforced by p38a-dependent inhibition of the TFs FoxM1 and c-Jun; the latter antagonizes p53. We also found that (ii) the TF ATF6a regulates the survival component of dormancy by controlling an alternative pathway to mTOR activation Indeed, ATF6a upregulates the small GTPase Rheb, which in turn induces mTOR-S6K activation, resistance to Rapamycin and survival of dormant tumor cells in vivo. Thus, we have pinpointed genes and mechanisms contributing to both the quiescence and survival of dormant tumor cells. We also discovered that HEp3 DTCs but in the bone marrow microenvironment are unable to resume proliferation, while growth ensues in the primary site and lungs. This remarkable difference seems to be a program of dormancy. The basis for this is that upon recovery from the bone marrow and expansion in culture these cells are unable to form tumors when re-injected in animals. Instead they undergo a dormancy phase before resuming growth. We hypothesize that similar mechanisms to those described above allow DTCs to resist therapy- or microenvironment-induced cell death and to survive in a dormant state, providing a source of metastatic recurrences in patients. Clearly, inducing and or extending the growth arrest of DTCs would be beneficial for patients, but blocking their survival mechanisms would allow their eradication before recurrences can develop. Because eventual success of anti- cancer therapy depends strictly on curing or preventing metastases, progress in this field is urgently needed to improve the therapeutic eradication of metastatic precursors. We believe these findings are of significance, as knowledge on DTC dormancy will have an important impact on how we understand and treat cancer. PUBLIC HEALTH RELEVANCE: We will explore the gene programs regulating the induction of quiescence, the prolonged survival and chemotherapy resistance of dormant tumor cells. We will also study the activation of these mechanisms in disseminated tumor cells. These studies will provide insight into how to stop metastasis development.