Abstract 12: Deciphering the role of oncogenic integrin alpha 6B in aged mouse mammary epithelial cells

Abstract Breast cancer (BC) is the most diagnosed cancer in women with aging being the major risk factor. According to American Cancer Society (2024), an estimation of 310, 720 invasive BC and about 56, 500 cases of DCIS diagnosed among women in the USA, and the women die from BC are likely among age groups of 70 or older. Our previous report demonstrated that aging was associated with an increased number of basal epithelial cells (CD49fhiCD24low) and reduced luminal epithelial cells (CD49flowCD24hi) in mice. The CD49f (Integrin α6), a cell surface marker of mammary stem cells (MaSc), is enriched in the basal cell population of the mammary gland (MG). These cells have oligo-lineage differentiation potential, especially when transplanted into the cleared mammary fat pad (CFP). Integrin α6 has two variants with a different cytoplasmic domain, produced via alternative splicing (Isoforms: α6A & α6B). Recent scientific evidence suggests that α6B produced in transformed mammary cell lines was oncogenic. Previous studies from us and others showed CD49fhi aberrant stem cell-like cells in the luminal epithelium display more hyperplastic duct in the old mice, as well as tumor adjacent normal tissue from women with breast cancer. The mechanism underlying the expansion of CD49fhi cells during aging is unclear. It could be due to the proliferation of basal cells, or trans-differentiation of luminal cells. Henceforward, this study examines changes in the CD49f expression (and its isoforms) in the basal and luminal cell populations with aging in mice, hypothesizing that luminal cell attains basal cell signature by expressing more CD49f that contributes to hyperplasia in the aged mammary glands. To explore this hypothesis, we evaluated the gene and protein expression of Integrin α6 isoforms (α6A & α6B) across basal and luminal populations in FVB/NJ and C57Bl/6 aging mice using RT-PCR and Western blotting. Mammary cells were gated and sorted in FACS and used for RNA and protein studies. Our results revealed that aged basal and luminal cells express higher levels of ITGA6B mRNA transcript compared to ITGA6A in both the mice stains. Cell cycle analysis was performed using Hoechst to evaluate the cell cycle phase of each population using flow cytometry. The results showed that luminal cells from aged mice have a higher fraction of G2/M phase cells than those from young mice, suggesting an increased cell cycle in the aged luminal cells, which may be due to increased Integrin α6B. We are currently developing a method to measure Integrin α6B protein levels in young and aged mouse mammary luminal and basal cells. Our study provides the first evidence that aged CD49fhi cells, particularly those expressing α6B exhibit increased cell proliferation potential, revealing a potential target for breast cancer prevention. Citation Format: Thangarajeswari Mohan, Morgana McLaughlin, Jacob Mackay, Luzhe Sun. Deciphering the role of oncogenic integrin alpha 6B in aged mouse mammary epithelial cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 12.