正常细胞和癌细胞之间在感应氨基酸波动机制上的差别，以及细胞最初感知和随后应答氨基酸限制的机制，仍然是悬而未决的问题。MAP4K3是一个介导氨基酸营养源到mTOR信号转导的蛋白激酶。有研究报道，MAP4K3在一个大规模的RNAi的基因筛选中，选择性地显示出对癌细胞的繁殖和生存的重要性。前期工作鉴定了一个受磷蛋白磷酸酶PP2A调控并对MAP4K3活化和mTOR激活是必要的自磷酸化位点(Ser170)；同时也鉴定了PP2A的靶向调控亚基PR61ε，它在氨基酸缺乏时结合到MAP4K3，提升了S170的脱磷酸化。可是，有关MAP4K3底物目前并不清楚。我们瞄准MAP4K3，采用一个改良的化学遗传的方法来系统筛选MAP4K3底物，该方法的特点是提升了免疫沉淀的有效性；通过研究这些底物，进一步阐明MAP4K3在应答氨基酸营养信号传导中的作用机制及新生物学功能，有助于评估治疗疾病诸如癌症的分子靶点的潜力。

It remains open questions as to whether the mechanisms responsible for sensing and responding to fluctuations in amino acids differ between normal and cancer cells, and what the mechanisms responsible for both the initial sensing and the subsequent responses to amino acid limitation are. MAP4K3 is identified as a protein kinase that mediates amino acid nutrient signaling to the mTOR pathway. Studies have reported that MAP4K3 was identified in a large-scale RNAi screen for gene selectively involved in cancer cell proliferation and survival. We previously identified a PP2A-regulated autophosphorylation site(Ser170) that is essential for MAP4K3 activity and mTORC1 activation. We also identified a PP2A targeting subunit PR61εthat binds to MAP4K3 after removing amino acids and promotes Ser170 dephosphorylation. However, substrates for MAP4K3 are unclear at present. We aim at MAP4K3 and systemic screen for MAP4K3 substrates by using an improved chemical genetic approach. The modified approaches will greatly improve immunoprecipitation efficiency. Identifying the direct targets of MAP4K3 will help to understand how MAP4K3 responds to amino acids signaling and its novel biological functions. It would aid in assessing the potential of these components as therapeutic molecular targets for the treatment of human diseases such as cancer.