Osteopontin

Background: Bromodomain and extra-terminal domain (BET) inhibitors have shown profound efficacy against hematologic malignancies and solid tumors in preclinical studies. However, the underlying molecular mechanism in melanoma is not well understood. Here we identified secreted phosphoprotein 1 (SPP1) as a melanoma driver and a crucial target of BET inhibitors in melanoma. Methods: Bioinformatics analysis and meta-analysis were used to evaluate the SPP1 expression in normal tissues, primary melanoma, and metastatic melanoma. Real-time PCR (RT-PCR) and Western blotting were employed to quantify SPP1 expression in melanoma cells and tissues. Cell proliferation, wound healing, and Transwell assays were carried out to evaluate the effects of SPP1 and BET inhibitors in melanoma cells in vitro. A xenograft mouse model was used to investigate the effect of SPP1 and BET inhibitors on melanoma in vivo. Chromatin immunoprecipitation (ChIP) assay was performed to evaluate the regulatory mechanism of BET inhibitors on SPP1. Results: SPP1 was identified as a melanoma driver by bioinformatics analysis, and meta-analysis determined it to be a diagnostic and prognostic biomarker for melanoma. SPP1 overexpression was associated with poor melanoma prognosis, and silencing SPP1 suppressed melanoma cell proliferation, migration, and invasion. Through a pilot drug screen, we identified BET inhibitors as ideal therapeutic agents that suppressed SPP1 expression. Also, SPP1 overexpression could partially reverse the suppressive effect of BET inhibitors on melanoma. We further demonstrated that bromodomain-containing 4 (BRD4) regulated SPP1 expression. Notably, BRD4 did not bind directly to the SPP1 promoter but regulated SPP1 expression through NFKB2. Silencing of NFKB2 resembled the phenotype of BET inhibitors treatment and SPP1 silencing in melanoma. Conclusion: Our findings highlight SPP1 as an essential target of BET inhibitors and provide a novel mechanism by which BET inhibitors suppress melanoma progression via the noncanonical NF-κB/SPP1 pathway.

Vascular calcification (VC) is considered a common pathological process in various vascular diseases. Accumulating studies have confirmed that VC is involved in the inflammatory response in heart disease, and SPP1+ macrophages play an important role in this process. In VC, studies have focused on the physiological and pathological functions of macrophages, such as pro-inflammatory or anti-inflammatory cytokines and pro-fibrotic vesicles. Additionally, macrophages and activated lymphocytes highly express SPP1 in atherosclerotic plaques, which promote the formation of fatty streaks and plaque development, and SPP1 is also involved in the calcification process of atherosclerotic plaques that results in heart failure, but the crosstalk between SPP1-mediated immune cells and VC has not been adequately addressed. In this review, we summarize the regulatory effect of SPP1 on VC in T cells, macrophages, and dendritic cells in different organs' VC, which could be a potential therapeutic target for VC.

Osteopontin (OPN) is a non-collagenous protein involved in biomineralization of bone tissue. Beyond its role in biomineralization, we show that osteopontin is essential to the quality of collagen fibrils in bone. Transmission electron microscopy revealed that, in Opn-/- tissue, the organization of the collagen fibrils was highly heterogeneous, more disorganized than WT bone and comprised of regions of both organized and disorganized matrix with a reduced density. The Opn-/- bone tissue also exhibited regions in which the collagen had lost its characteristic fibrillar structure, and the crystals were disorganized. Using nanobeam electron diffraction, we show that damage to structural integrity of collagen fibrils in Opn-/- bone tissue and their organization causes mineral disorganization, which could ultimately affect its mechanical integrity. STATEMENT OF SIGNIFICANCE: This study presents new evidence about the role of osteopontin (OPN) - a non-collagenous protein - on the structure and organization of the organic and mineral matrix in bone. In previous work, osteopontin has been suggested to regulate the nucleation and growth of bone mineral crystals and to form sacrificial bonds between mineralized collagen fibrils to enhance bone's toughness. Our findings show that OPN plays a crucial role before mineralization, during the formation of the collagen fibrils. OPN-deficient bones present a lower collagen content compared to wild type bone and, at the tissue level, collagen fibrils organization can be significantly altered in the absence of OPN. Our results suggest that OPN is critical for the formation and/or remodeling of bone collagen matrix. Our findings could lead to the development of new therapeutic strategies of bone diseases affecting collagen formation and remodeling.

Poly (ADP-ribose) polymerase inhibitors (PARPis) benefit homologous recombination-deficient (HRD) malignancies, yet resistance remains a major challenge. Leveraging specimens from a prospective neoadjuvant niraparib monotherapy trial in treatment-naive, high-grade serous ovarian cancer, we integrated PhenoCycler-Fusion spatial profiling, scRNA-Seq, and multiplex immunohistochemistry to identify 2 therapeutic-modulated cellular neighborhoods: an IFN+ tumor cell-enriched niche that expands in resistant lesions and a niche enriched in tumor-associated macrophage (TAM) that persists but acquires enhanced immunosuppressive features. Mechanistically, sustained tumor cell-derived IFN induced osteopontin (SPP1) expression in TAMs via STAT signaling, creating immunosuppressive niches enriched in Tregs and myofibroblastic cancer-associated fibroblasts with intensified cell-cell interactions. SPP1 directly suppressed T cell signaling and effector function. High baseline SPP1+ cells predicted lower response rate (30.0% vs. 76.2%; P = 0.021) and shorter progression-free survival (median 13.5 vs. 28.3 months; P = 0.0006). In HRD mouse models, SPP1 blockade restored PARPi sensitivity, reversed acquired resistance, and enhanced T cell cytotoxicity-effects abrogated in immunodeficient mice, confirming immune dependence. These data establish a spatial IFN-SPP1 axis whereby persistent tumor cell IFN reprograms TAMs to promote PARPi resistance, position SPP1 as a key therapeutic target and prognostic biomarker for this therapy, and underscore therapeutic potential of microenvironment-targeted strategies to overcome PARPi resistance.