Breast stroma plays a significant role in breast cancer risk and progression yet remains poorly understood. In breast stroma, collagen is the most abundantly expressed protein and its increased deposition and alignment contributes to progression and poor prognosis. Collagen post-translation modifications such as hydroxylated-proline (HYP) control deposition and stromal organization. The clinical relevance of collagen HYP site modifications in cancer processes remains undefined due to technical issues accessing collagen from formalin-fixed, paraffin-embedded (FFPE) tissues. We previously developed a targeted approach for investigating collagen and other extracellular matrix proteins from FFPE tissue. Here, we hypothesized that immunohistochemistry staining for fibroblastic markers would not interfere with targeted detection of collagen stroma peptides and could reveal peptide regulation influenced by specific cell types. Our initial work demonstrated that stromal peptide peak intensities when using MALD-IMS following IHC staining (αSMA, FAP, P4HA3 and PTEN) were comparable to serial sections of nonstained tissue. Analysis of histology-directed IMS using PTEN on breast tissues and TMAs revealed heterogeneous PTEN staining patterns and suggestive roles in stromal protein regulation. This study sets the foundation for investigations of target cell types and their unique contribution to collagen regulation within extracellular matrix niches.

Past studies have identified that a unique type of matrix metalloproteinase, the membrane-type-1 MMP (MT1-MMP), is increased within the left ventricle (LV) of patients with dilated cardiomyopathy (DCM). However, the cellular and molecular basis for this induction of MT1-MMP with DCM is unknown. LV myocardial biopsies from nonfailing, reference normal patients (defined as LV ejection fraction >50%, elective coronary bypass surgery, no perfusion defect at biopsy site, n = 6) and DCM patients (LV ejection fraction <20%, at transplant, n = 5) were used to establish fibroblast cultures (FIBROS). Confluent LV FIBROS from culture passages 2–5 were measured with respect to MT1-MMP mRNA and protein levels and the distribution of the MT1-MMP mRNA pool in ribosomal fractions. Total MT1-MMP mRNA within DCM FIBROS increased by over 140%, and MT1-MMP protein increased by over 190% from reference normal FIBROS (both P < 0.05). MT1-MMP mRNA in monosome fractions decreased by over twofold in DCM FIBROS compared with reference normal ( P < 0.05) and remained lower in polyribosomal fractions (i.e., 15.7 ± 5.2 vs. 1.4 ± 0.6% in polysomal fraction 6, P < 0.05). These differences in DCM MT1-MMP FIBROS transcription and translation persisted throughout passages 2–5. The unique findings from this study demonstrated that elevated steady-state MT1-MMP mRNA and protein levels occurred in DCM FIBROS despite a decline in translational deficiency. These phenotypic changes in DCM fibroblasts may provide the basis for developing cell specific pharmacological targets for control of MT1-MMP expression.

Ductal carcinoma in situ (DCIS) is a heterogeneous breast disease that remains challenging to treat due to its unpredictable progression to invasive breast cancer (IBC). Contemporary literature has become increasingly focused on extracellular matrix (ECM) alterations with breast cancer progression. However, the spatial regulation of the ECM proteome in DCIS has yet to be investigated in relation to IBC. We hypothesized that DCIS and IBC present distinct ECM proteomes that could discriminate between these pathologies. Tissue sections of pure DCIS, mixed DCIS-IBC, or pure IBC (n = 22) with detailed pathological annotations were investigated by multiplexed spatial proteomics. Across tissues, 1,005 ECM peptides were detected in pathologically annotated regions and their surrounding extracellular microenvironments. A comparison of DCIS to IBC pathologies demonstrated 43 significantly altered ECM peptides. Notably, eight fibrillar collagen peptides could distinguish with high specificity and sensitivity between DCIS and IBC. Lesion-targeted proteomic imaging revealed heterogeneity of the ECM proteome surrounding individual DCIS lesions. Multiplexed spatial proteomics reported an invasive cancer field effect, in which DCIS lesions in closer proximity to IBC shared a more similar ECM profile to IBC than distal counterparts. Defining the ECM proteomic microenvironment provides novel molecular insights relating to DCIS and IBC.

Collagen stroma interactions within the extracellular microenvironment of breast tissue play a significant role in breast cancer, including risk, progression, and outcomes. Hydroxylation of proline (HYP) is a common post-translational modification directly linked to breast cancer survival and progression. Changes in HYP status lead to alterations in epithelial cell signaling, extracellular matrix remodeling, and immune cell recruitment. In the present study, we test the hypothesis that the breast cancer microenvironment presents unique PTMs of collagen, which form bioactive domains at these sites that are associated with spatial histopathological characteristics and influence breast epithelial cell signaling. Mass spectrometry imaging proteomics targeting collagens were paired with comprehensive proteomic methods to identify novel breast cancer-related collagen domains based on spatial localization and regulation in 260 breast tissue samples. As ancestry plays a significant role in breast cancer outcomes, these methods were performed on ancestry diverse breast cancer tissues. Lumpectomies from the Cancer Genome Atlas (TCGA; n=10) reported increased levels of prolyl 4-hydroxylase subunit alpha-3 (P4HA3) accompanied by spatial regulation of fibrillar collagen protein sequences. A concise set of triple negative breast cancer lumpectomies (n=10) showed spatial regulation of specific domain sites from collagen alpha-1(I) chain. Tissue microarrays identified proteomic alterations around post-translationally modified collagen sites in healthy breast (n=81) and patient matched normal adjacent (NAT; n=76) and invasive ductal carcinoma (n=83). A collagen alpha-1(I) chain domain encompassing amino acids 506-514 with site-specific proline hydroxylation reported significant alteration between patient matched normal adjacent tissue and invasive breast cancer. Functional testing of domain 506-514 on breast cancer epithelial cells showed proliferation, chemotaxis and cell signaling response dependent on site localization of proline hydroxylation within domain 506-514 variants. These findings support site localized collagen HYP forms novel bioactive domains that are spatially distributed within the breast cancer microenvironment and may play a role in ancestral traits of breast cancer.