肿瘤的生长和代谢可能会局限于某些氨基酸用于蛋白合成。最近已经被证明，某些类型的癌细胞依赖于甘氨酸、谷氨酰胺，亮氨酸，丝氨酸代谢和增殖。此外，运用左旋门冬酰胺酶诱导天冬酰胺缺乏，已经用于治疗急性淋巴细胞白血病。然而，本研究之前还不能在每个肿瘤中检测哪些氨基酸缺乏可以导致其生长受阻。
在2月25日的Nature中，研究者用核糖体分析来检测限制性氨基酸。他们开发了diricore，一种核糖体检测不同密*****子的步骤，用来评估特定氨基酸用于蛋白合成的可用性。
Diricore是基于核糖体分析检测（ribosome profiling）而开发的，核糖体分析是一种基于深度测序的技术可以定量地分析核苷酸翻译的方法。使用核酸酶消化mRNA时，在翻译过程中发挥作用的核糖体结合并保护了大约30bp的mRN段（RPF）。将细胞中这些被保护的mRN段构建成DNA文库，再使用测序仪对文库中所有的片段进行深度测序，最终得到了有关细胞中蛋白质翻译情况的图谱。而在此基础上如图，diricore运用RPF进行亚克隆测序和5末端密度两种互补的方法进行分析。
RPF的9,12和15位点分别对应核糖体的E，P和A位点
他们首先运用代谢抑制和营养缺乏分析验证了diricore的功能与抑制。值得注意的是使用左旋门冬酰胺酶在天冬酰胺密*****子诱导特殊diricore信号会引起高水平天冬酰胺合成酶（ASNS）。
然后研究者将diricore运用到肾癌上，从信号上发现脯氨酸是限制性的氨基酸。对于天冬酰胺来说，观察的结果与高水平的PYCR1，脯氨酸产生的一个关键酶相关。这提示了一个允许肿瘤扩增的代偿性的机制。PYCR1是由脯氨酸前体不足引起的，当脯氨酸缺乏时抑制�*************************缚梢砸种粕霭┫赴脑鲋场�
高水平的PYCR1经常在浸润性的乳腺癌中被观察到。在这个肿瘤的体内模型系统中，研究人员也发现了脯氨酸是限制性氨基酸。在限制生长的条件下，需要PYRC1来维持肿瘤生长。进一步研究表明，CRISPR介导的PYCR1的基因敲除可以阻碍这个模型系统中肿瘤的生长。
因此diricore可以用于揭示哪些对于癌细胞来说是限制性的氨基酸，寻找哪些能作为癌症治疗的重要代谢途径的靶点。
参考文献
Tumour-specific proline vulnerability uncovered by differential ribosome codon reading
文献检索：doi:10.1038/nature16982
文献期刊：Nature
Tumour growth and metabolic adaptation may restrict the availability of certain amino acids for protein synthesis. It has recently been shown that certain types of cancer cells depend on glycine, glutamine, leucine and serine metaboli to proliferate and survive. In addition, successful therapies using L-asparaginase-induced asparagine deprivation have been developed for acute lymphoblastic leukaemia. However, a tailored detection system for measuring restrictive amino acids in each tumour is currently not available. Here we harness ribosome profiling6 for sensing restrictive amino acids, and develop diricore, a procedure for differential ribosome measurements of codon reading. We first demonstrate the functionality and constraints of diricore using metabolic inhibitors and nutrient deprivation assays. Notably, treatment with L-asparaginase elicited both specific diricore signals at asparagine codons and high levels of asparagine synthetase (ASNS). We then applied diricore to kidney cancer and discover signals indicating restrictive proline. As for asparagine, this observation was linked to high levels of PYCR1, a key enzyme in proline production, suggesting a compensatory mechani allowing tumour expansion. Indeed, PYCR1 is induced by shortage of proline precursors, and its suppression attenuated kidney cancer cell proliferation when proline was limiting. High PYCR1 is frequently observed in invasive breast carcinoma. In an in vivo model system of this tumour, we also uncover signals indicating restrictive proline. We further show that CRISPR-mediated knockout of PYCR1 impedes tumorigenic growth in this system. Thus, diricore has the potential to reveal unknown amino acid deficiencies, vulnerabilities that can be used to target key metabolic pathways for cancer treatment.
