# Targeting cell surface GRP78-CD44v interaction suppresses cell migration in triple-negative breast cancer cells

## TL;DR

This study shows that targeting GRP78 on the cell surface can reduce migration in triple-negative breast cancer cells by interacting with CD44v.

## Contribution

The novel finding is that cell surface GRP78 interacts with CD44v to regulate cancer cell migration in triple-negative breast cancer.

## Key findings

- Over 70% of MDA-MB-231 TNBC cells express cell surface GRP78.
- Targeting GRP78 with antibody 76-E6 reduces CD44v expression and inhibits cell motility.
- GRP78-CD44v interaction is relevant in vivo in MDA-MB-231 tumor xenografts.

## Abstract

Triple-negative breast cancer (TNBC) is characterized by the absence of estrogen receptor (ER), progesterone receptor (PR), and HER-2 amplification, rendering it unresponsive to endocrine and HER2-targeted therapies. GRP78 (78 kDa glucose-regulated protein), a key endoplasmic reticulum (ER)-resident chaperone involved in protein folding and stress response, has been observed atypically localized on the cell surface of various cancer and stressed cell types, where it engages in non-canonical signaling and cellular functions. Cell surface GRP78 (csGRP78) is preferentially expressed in malignant cells relative to normal tissue, making it an attractive therapeutic target. In this study, we report that over 70% of MDA-MB-231 TNBC cells express csGRP78. Interestingly, MDA-MB-231 cells predominantly exhibit a distinct unipolar morphology, with csGRP78 prominently co-localizing with the variant isoform of CD44 (CD44v, containing variable exon 3) at the anterior region of the cell. Co-localizations of csGRP78 and CD44v were also observed in MDA-MB-231 tumor xenografts, supporting its relevance in vivo. Importantly, targeting csGRP78 with the monoclonal antibody 76-E6 downregulated CD44v expression, inhibited Src kinase signaling, disrupted cell morphology, and suppressed cell motility. We further mapped the epitope of GRP78 targeted by 76-E6. Together, our findings identify csGRP78 as a functional regulator of cell morphology and migration at least in part via a csGRP78-CD44v axis and underscore its potential as a therapeutic target in TNBC.

The online version contains supplementary material available at 10.1038/s41598-025-33441-5.