Quiescence and epithelial-mesenchymal transition in HNSCC

大多数头颈部鳞状细胞癌(HNSCC)患者在治疗和切除原发肿瘤后几个月、几年甚至几十年内会死于播散性肿瘤细胞(DTC)的转移。在初次肿瘤切除后的几年内，大约50%的患者出现远处器官或局部复发，即使手术切缘没有癌症。这一潜伏期表明，在未来转移的部位，DTCs以休眠、非增殖的状态存活。这种状态被称为静止，这是一种未承诺的、可逆的生长停滞，可以由不同的、主要与压力相关的信号引起。导致这种静止的诱导和维持的因素，从而导致后来形成转移的因素，目前还没有得到严格的研究。大多数HNSCC患者患有肺和淋巴转移，而骨转移非常罕见。然而，在30%的HNSCC患者的骨髓中可以检测到DCs。为了首先到达这些遥远的部位，这些上皮细胞必须获得移动性。他们通过上皮间充质转化(EMT)实现这一点，EMT是一种高度保守的胚胎细胞程序，允许上皮细胞获得移动性和侵袭性等间充质特征。与此同时，细胞经历了细胞周期的停滞，限制了它们的增殖。最近研究表明，应激激活的蛋白激酶p38细胞在体内调节HNSCC长时间静止程序的诱导。在另一项研究中，p38的药理抑制导致EMT转录因子(TF)Snail、Slug和ZeB的基因表达减少。本研究证实了休眠的诱导与EMT中至关重要的转录因子的调节之间的可能联系。本研究的目的是确定DTCs进入和退出静止的调控机制，并阐明与导致或维持HNSCC中EMT的因素的可能联系。我将在已经建立的HNSCC小鼠模型中测试所提出的休眠调节剂是否与骨髓DCs的静止与肺和淋巴结内DCs的生长有关。我将进一步测试细胞因子TGFbeta2的上调是否在HNSCC静止期诱导中发挥作用，因为它已被确定为人类乳腺癌休眠基因信号的一部分，并需要维持骨髓干细胞处于静止期。由于TGFbeta信号也是EMT的已知诱导者，我将阐明已知的EMT和静止诱导转录因子之间是否存在串扰，了解这些DTC的静止是至关重要的。这样，我们也许有一天能够设计出一种治疗方法：(I)使DTC永久静止，从而使患者保持在慢性但无症状的微小残留病中，或(Ii)选择性地针对这些静止的DTC所部署的生存机制来根除它们。

The majority of head and neck squamous cell carcinoma (HNSCC) patients will die of metastases that develop from disseminated tumor cells (DTCs), months, years or even decades after treatment and removal of the primary tumor. Within years after primary tumor resection, approximately 50% of patients develop distant organ or loco regional recurrences, even if the surgical margins were free of cancer. This latency suggests that DTCs survive in a dormant, non-proliferative state at the site of future metastases. This state is known as quiescence, an uncommitted and reversible growth arrest that can be brought about by different, mostly stress associated, signals. The factors leading to induction and upkeep of this quiescence, and thus to the formation of metastases later on, have not been toughly investigated, yet. Most HNSCC patients suffer from lung and lymph node metastases, while bone metastases are very rare. Yet in >30% of HNSCC patients, DTCs are detectable in the bone marrow. In order to reach these distant sites in the first place, these epithelial cells have to acquire mobility. They achieve this through an epithelial mesenchymal transition (EMT), a highly conserved embryonic cellular program which allows epithelial cells to acquire mesenchymal traits like mobility and invasiveness. At the same time, cells undergo a cell-cycle arrest, limiting their proliferation.The stress activated protein kinase p38 cells was recently shown to regulate the induction of a program of prolonged quiescence in HNSCC in vivo. In a different study, the pharmacological inhibition of p38 led to a reduced gene expression of the EMT transcription factors (TF) Snail, Slug and ZEB. This research demonstrates a possible connection between the induction of dormancy and regulation of transcription factors crucial in EMT.The aim of this research is to identify the mechanisms regulating entry and exit of quiescence in DTCs and elucidate the possible connection with factors leading to or maintaining an EMT in HNSCC. I will test in an already established HNSCC mouse model, whether proposed dormancy regulators are linked to quiescence in bone marrow DTCs vs. growth of DTCs in lungs and lymphnodes. I will further test if the upregulation of the cytokine TGFbeta2 plays a part in HNSCC quiescence induction, since it has been identified as part of a dormancy gene signature in human breast cancer and is required to maintain bone marrow stem cells in quiescence. As TGFbeta signaling is also a known inducer of EMT, I will elucidate if there is crosstalk between known EMT and quiescence inducing transcription factors.It is of utmost importance to understand the quiescence of these DTCs. This way we may one day be able to devise a treatment that (I) either keeps the DTCs in permanent quiescence, thus keeping the patient in chronic yet asymptomatic minimal residual disease, or (II) selectively targets the survival mechanisms deployed by these quiescent DTCs to eradicate them.