Abstract A047: Differential regulation of LRIG1 and tumor suppressive pathways in ancestrally distinct ER-negative breast cancer cell lines

Abstract Background: In the U.S., African American (AA) women have a 40% higher mortality rate from breast cancer than European American (EA) women, despite having a lower incidence rate. This disproportionate mortality burden is rooted in both environmental and genetic causes. We are interested in elucidating molecular and environmental mechanisms that may be contributing to these breast cancer disparities. Our recent study identified that higher neighborhood-level socioeconomic deprivation was associated with hypomethylation and decreased gene expression for LRIG1 (Leucine-rich repeats and immunoglobulin-like domains 1) in AA women. LRIG1 is a tumor suppressor associated with members of the ErbB family of receptor tyrosine kinases (RTKs), which includes the epidermal growth factor receptor (EGFR). This association of LRIG1 with EGFR is predicted to result in the degradation of these proteins through recruiting c-CBL, an E3 ubiquitin ligase, which leads to the suppression of pro-growth signaling. Objective: This project aims to determine differences in the protein expression and localization of LRIG1, EGFR, and c-CBL in the presence or absence of serum and/or proteasome inhibitor within estrogen receptor-negative (ER-) breast cancer cell lines derived from AA and EA women. We hypothesize that in the presence of serum and proteasome inhibitor, protein expression of LRIG1, EGFR, and c-CBL will increase in breast cancer cell lines derived from AA women compared to EA women. Methods: ER- cells lines HCC1806 (derived from an AA woman) and MDA-MB-231 (derived from an EA women) were cultured in the absence or presence of serum and/or proteasome inhibitor (MG-132). The levels of protein expression of LRIG1, EGFR, ERα, and c-CBL proteins were assessed using Western immunoblotting and densitometric analysis. The colocalization of LRIG1/EGFR in ER- cell lines treated with varying MG-132 concentrations (0-10 μM) was assessed through immunofluorescence (IF) cell staining. Results: Western immunoblotting revealed notable increases in LRIG1 and ERα expression with addition of serum and MG-132 in HCC1806 cells and less variation in MDA-MB-231 cells. These results may indicate that the proteasome inhibited by MG-132 degrades ERα and/or LRIG1 in HCC1806 more completely than in MDA-MB-231. IF staining demonstrated limited colocalization between LRIG1 and c-CBL and high colocalization between LRIG1 and EGFR. Further experiments will include using Western immunoblotting to measure the levels of ubiquitinated proteins in ER- cell lines treated with varying concentrations of MG-132. Conclusions: Our results provide insight into LRIG1 and EGFR co-expression in ER- breast cell lines from AA and EA women. We will also conduct co-immunoprecipitation followed by immunoblotting to validate LRIG1 association with EGFR in HCC1806 and MDA-MB-231 cells treated with serum and/or MG-132. Citation Format: Amber Yu, Angel H. Pajimola, Kayla S. Ingram, Brittany Jenkins-Lord. Differential regulation of LRIG1 and tumor suppressive pathways in ancestrally distinct ER-negative breast cancer cell lines [abstract]. In: Proceedings of the 18th AACR Conference on the Science of Cancer Health Disparities; 2025 Sep 18-21; Baltimore, MD. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2025;34(9 Suppl):Abstract nr A047.