# Glutamine transporter SLC1A5 inhibits autophagy-mediated CD276 degradation to promote esophageal cancer progression

## TL;DR

A glutamine transporter called SLC1A5 helps ESCC cancer cells by preventing the breakdown of CD276, a protein linked to cancer progression, through a process involving autophagy and reactive oxygen species.

## Contribution

This study reveals a novel mechanism where SLC1A5 inhibits autophagy-mediated CD276 degradation, promoting esophageal cancer progression.

## Key findings

- SLC1A5 stabilizes CD276 protein in ESCC cells by suppressing ROS-dependent autophagic degradation.
- Inhibiting glutamine metabolism reverses CD276-induced ESCC cell proliferation and tumor growth in mice.
- Combining SLC1A5 inhibition with CD276 knockout significantly reduces tumor volume in xenograft models.

## Abstract

CD276/B7-H3 is an immune checkpoint molecule often overexpressed in cancers, representing a potential therapeutic target. The underlying mechanisms for CD276 upregulation remain unclear. This study investigates how glutamine metabolism affects CD276 protein stability and esophageal squamous cell carcinoma (ESCC) progression.

CD276 and SLC1A5 expression were analyzed in 90 ESCC clinical tissues and TCGA/GEO datasets. CCK-8, colony formation, wound healing and transwell assays were performed in KYSE150 and KYSE450 cells. Autophagy was quantified by immunofluorescence and western blot. Mitochondrial reactive oxygen species (ROS) levels measured by flow cytometry. Rescue experiments used N-acetylcysteine (NAC) and chloroquine (CQ). Finally, antitumor effects of SLC1A5 inhibitor V9302 in the presence or absence of CD276 were evaluated in NOD/SCID mice (n = 5 per group) bearing KYSE150 xenografts.

CD276 and SLC1A5 upregulated in ESCC tissues (P < 0.05). CD276 overexpression enhanced ESCC cell proliferation and migration by 42.3% and 58.7%, respectively (P < 0.01). CQ but not MG-132 increased CD276 expression in ESCC cells. SLC1A5 stabilized CD276 protein without altering CD276 mRNA levels, by suppressing ROS-dependent autophagic degradation. NAC reversed ROS-induced CD276 degradation, while CQ abrogated CD276 downregulation upon glutamine metabolism inhibition. Inhibiting glutamine metabolism could reverse ESCC cell proliferation induced by CD276 overexpression. Moreover, combination of V9302 and CD276 knockout significantly reduced KYSE150 cell-derived xenograft tumor volume by 65.2% (95% CI 58.3–72.1%, P < 0.001) in NOD/SCID mice, without affecting mouse body weight (P > 0.05).

SLC1A5 enhances CD276 stability by suppressing ROS-autophagy signaling, promoting ESCC progression. Targeting glutamine metabolism to enhance CD276 degradation might be a novel therapeutic strategy for ESCC.