Proteomic Profiling of Human Prostate Cancer-associated Fibroblasts (CAF) Reveals LOXL2-dependent Regulation of the Tumor Microenvironment*

Abstract

Mass spectrometry-based (phospho)proteomics identified a prominent hub associated with collagens, receptor tyrosine kinase discoidin domain-containing receptor 2 (DDR2), and lysyl oxidase-like 2 (LOXL2) from patient-matched cancer-associated fibroblasts (CAF) and non-malignant prostate fibroblasts (NPF). The functional role of LOXL2 in regulating ECM organization and migration of both CAF and co-cultured prostate cancer cells was validated with LOXL2 inhibitors. Our data provide the first demonstration that prostate CAF-dependent LOXL2 production controls prostate tumor cell motility, highlighting LOXL2 as an attractive therapeutic target.

Graphical Abstract

Highlights

• Quantitative (phoshpo)proteome of primary cell cultures of patient-matched prostate CAF and NPF.

• Key CAF-associated proteins validated using orthogonal methodologies.

• LOXL2 inhibitors D-penicillamine and PXS-S2A impaired CAF migration and ECM alignment.

• Pre-treatment with LOXL2 inhibitors impaired migratory capacity of RWPE-2 cells in co-culture.

Abstract

In prostate cancer, cancer-associated fibroblasts (CAF) exhibit contrasting biological properties to non-malignant prostate fibroblasts (NPF) and promote tumorigenesis. Resolving intercellular signaling pathways between CAF and prostate tumor epithelium may offer novel opportunities for research translation. To this end, the proteome and phosphoproteome of four pairs of patient-matched CAF and NPF were characterized to identify discriminating proteomic signatures. Samples were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with a hyper reaction monitoring data-independent acquisition (HRM-DIA) workflow. Proteins that exhibited a significant increase in CAF versus NPF were enriched for the functional categories “cell adhesion” and the “extracellular matrix.” The CAF phosphoproteome exhibited enhanced phosphorylation of proteins associated with the “spliceosome” and “actin binding.” STRING analysis of the CAF proteome revealed a prominent interaction hub associated with collagen synthesis, modification, and signaling. It contained multiple collagens, including the fibrillar types COL1A1/2 and COL5A1; the receptor tyrosine kinase discoidin domain-containing receptor 2 (DDR2), a receptor for fibrillar collagens; and lysyl oxidase-like 2 (LOXL2), an enzyme that promotes collagen crosslinking. Increased activity and/or expression of LOXL2 and DDR2 in CAF were confirmed by enzymatic assays and Western blotting analyses. Pharmacological inhibition of CAF-derived LOXL2 perturbed extracellular matrix (ECM) organization and decreased CAF migration in a wound healing assay. Further, it significantly impaired the motility of co-cultured RWPE-2 prostate tumor epithelial cells. These results indicate that CAF-derived LOXL2 is an important mediator of intercellular communication within the prostate tumor microenvironment and is a potential therapeutic target.