Abstract
Some endothelial cells in the tumor vasculature express a system L amino acid transporter, LAT1. To elucidate the role of LAT1 in tumor-related endothelial cells, tumor cells were injected into endothelial cell–specific LAT1 conditional knockout mice (Slc7a5flox/flox; Cdh5-Cre-ERT2), and we found that the shape of the tumor vasculature was normalized and the size and numbers of lung metastasis was reduced. TNF-α–induced expression of VCAM1 and E-selectin at the surface of HUVEC, both of which are responsible for enhanced monocyte attachment and premetastatic niche formation, was reduced in the presence of LAT1 inhibitor, nanvuranlat. Deprivation of tryptophan, a LAT1 substrate, mimicked LAT1 inhibition, which led to activation of MEK1/2-ERK1/2 pathway and subsequent cystathionine γ lyase (CTH) induction. Increased production of hydrogen sulfide (H2S) by CTH was at least partially responsible for tumor vascular normalization, leading to decreased leakiness and enhanced delivery of chemotherapeutic agents to the tumor.
Authors
Jun-ichi Suehiro, Toru Kimura, Toshiyuki Fukutomi, Hisamichi Naito, Yasuharu Kanki, Youichiro Wada, Yoshiaki Kubota, Nobuyuki Takakura, Hiroyuki Sakurai
Figure 2
LAT1 inhibition led to a decrease in intracellular tryptophan levels, resulting in suppression of TNF-α–mediated VCAM1 expression and monocyte adhesion via MEK1/2-ERK1/2 signaling cascade.
