Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, TX 79430, U.S.A.
Biochem J. 2021 Oct 29;478(20):3757-3774. doi: 10.1042/BCJ20210377.
PEPT1 is a proton-coupled peptide transporter that is up-regulated in PDAC cell lines and PDXs, with little expression in the normal pancreas. However, the relevance of this up-regulation to cancer progression and the mechanism of up-regulation have not been investigated. Herein, we show that PEPT1 is not just up-regulated in a large panel of PDAC cell lines and PDXs but is also functional and transport-competent. PEPT2, another proton-coupled peptide transporter, is also overexpressed in PDAC cell lines and PDXs, but is not functional due to its intracellular localization. Using glibenclamide as a pharmacological inhibitor of PEPT1, we demonstrate in cell lines in vitro and mouse xenografts in vivo that inhibition of PEPT1 reduces the proliferation of the cancer cells. These findings are supported by genetic knockdown of PEPT1 with shRNA, wherein the absence of the transporter significantly attenuates the growth of cancer cells, both in vitro and in vivo, suggesting that PEPT1 is critical for the survival of cancer cells. We also establish that the tumor-derived lactic acid (Warburg effect) in the tumor microenvironment supports the transport function of PEPT1 in the maintenance of amino acid nutrition in cancer cells by inducing MMPs and DPPIV to generate peptide substrates for PEPT1 and by generating a H+ gradient across the plasma membrane to energize PEPT1. Taken collectively, these studies demonstrate a functional link between PEPT1 and extracellular protein breakdown in the tumor microenvironment as a key determinant of pancreatic cancer growth, thus identifying PEPT1 as a potential therapeutic target for PDAC.
PEPT1 是一种质子偶联肽转运体，在 PDAC 细胞系和 PDX 中上调，在正常胰腺中表达很少。然而，这种上调与癌症进展的相关性及其上调的机制尚未得到研究。在此，我们表明，PEPT1 不仅在大量 PDAC 细胞系和 PDX 中上调，而且具有功能和转运能力。另一种质子偶联肽转运体 PEPT2 在 PDAC 细胞系和 PDX 中也过表达，但由于其在细胞内的定位而没有功能。我们使用格列本脲作为 PEPT1 的药理学抑制剂，在体外细胞系和体内小鼠异种移植中证明，抑制 PEPT1 可减少癌细胞的增殖。这些发现得到了使用 shRNA 进行的 PEPT1 基因敲低的支持，其中转运体的缺失显著减弱了癌细胞在体外和体内的生长，表明 PEPT1 对癌细胞的存活至关重要。我们还确定肿瘤微环境中的肿瘤源性乳酸（Warburg 效应）通过诱导 MMP 和 DPPIV 产生 PEPT1 的肽底物，并通过在质膜上产生 H+梯度来为 PEPT1 提供能量，从而支持 PEPT1 的转运功能，以维持癌细胞的氨基酸营养。总的来说，这些研究表明，PEPT1 与肿瘤微环境中外源蛋白降解之间存在功能联系，是胰腺癌生长的关键决定因素，从而确定 PEPT1 是 PDAC 的一个潜在治疗靶点。
