Abstract P2-10-18: Deciphering racial disparities in breast cancer collagen reorganization by targeted extracellular matrix proteomics
Authors: Angel Peggi M , Saunders Janet , Jensen-Smith Heather , Bruner Evelyn , Ford Marvella E. , Berkhiser Savanna , Boxall Baylye , Bethard Jennifer , Ball Lauren E. , Yeh Elizabeth S. , Hollingsworth Michael A. , Mehta Anand S. , Marks Jeffrey R. , Nakshatri Harikrishna , Drake Richard R. 
Published: March 2020

Although European American women have a higher incidence of breast cancer, African American women have higher mortality rates with increased occurrence of lethal cancers at a younger age. Breast density, characterized by increases in stroma, is a risk factor for breast cancer and African American women have significantly greater odds of high breast density compared to European American women. Genomic profiling of breast cancer by ancestry shows that stromal collagen type genes vary based on African and European ancestry and correlate to differences in breast cancer progression and survival. Contemporary scientific literature describes breast cancer progression as being linked to a “collagen switch” whereby collagen fibers surrounding the tumor are re-organized during later tumor growth to facilitate metastatic spread of cancer activated fibroblasts. However, mechanisms facilitating the “collagen switch” remain mostly unknown, especially at a translational level. Additionally, collagen re-organization has not yet been evaluated for contributions to racial disparities in breast cancer. Our novel extracellular matrix proteomic studies on 17 patient lumpectomies depict that very specific sites on collagen protein types in breast tumor are post-translationally regulated by hydroxylation of proline (HYP) dependent on race (7 African American, 10 European American; no significant age or receptor status difference). By proteomic sequencing, distinct peptide sequences of collagen 1A1, collagen 1A2, and collagen 3A1 are modified by HYP and are significantly regulated when measured in African American versus European American breast tumors. From 16 collagen type proteins, 143 collagen peptides from all breast tumors were identified with HYP modifications (site probability ≥0.95). A total of 16% of the HYP peptides were unique to African American breast tumors. Imaging mass spectrometry that targets collagens reported that specific peptides sequences showed increased hydroxylation of proline in tumors compared to normal adjacent tissue. Interestingly, but not unexpected, translational and post-translational regulation did not always correlate with transcriptional regulation. Investigation on over 300 tissue microarray cores of breast tumor by second harmonic generation microscopy demonstrated significant ancestry-defined regulation of collagen fibers. For example, compared to breast tumor tissue cores of European American ancestry, African American breast tumor tissue cancer cores showed significant overall increases in collagen fibril length with decreased collagen fibril straightness (two-tailed student’s t-test p-value &lt;0.05). Imaging mass spectrometry that targets collagens done on the identical set of 300 ancestry-defined tissue microarray cores supports that ancestry of breast tumor correlates with site specific collagen modification by hydroxylation of prolines. For instance, COL3A1 peptide GPAGIPx GFPx shows a nearly 3-fold increase in African American breast tumors compared to European breast tumors (Mann-Whitney p-value ≤0.02; area under the receiver operating curve 0.81, p-value ≤0.0001; HYP site probability of 1.00 for each proline designated Px). Since HYP stabilizes collagen triple helices, we hypothesize that HYP alteration at specific sites in collagen protein types from African American breast tumors may reflect a change in collagen flexibility that contributes to an earlier metastatic collagen switch than in European American breast tumors. Current work determines ancestry-related changes in collagen fibers per breast cancer type and per normal adjacent tissue. To summarize, we provide the first evidence that post-translational regulation of collagen types may contribute to racial disparities in breast cancer.

Citation Format: Peggi M Angel, Janet Saunders, Heather Jensen-Smith, Evelyn Bruner, Marvella E. Ford, Savanna Berkhiser, Baylye Boxall, Jennifer Bethard, Lauren E. Ball, Elizabeth S. Yeh, Michael A. Hollingsworth, Anand S. Mehta, Jeffrey R. Marks, Harikrishna Nakshatri, Richard R. Drake. Deciphering racial disparities in breast cancer collagen reorganization by targeted extracellular matrix proteomics [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-10-18.