The tumor extracellular matrix (ECM) critically regulates cancer progression and treatment response. Expression of the basement membrane component collagen XVIII (ColXVIII) is induced in solid tumors, but its involvement in tumorigenesis has remained elusive. We show here that ColXVIII was markedly upregulated in human breast cancer (BC) and was closely associated with a poor prognosis in high-grade BCs. We discovered a role for ColXVIII as a modulator of epidermal growth factor receptor tyrosine kinase (ErbB) signaling and show that it forms a complex with ErbB1 and -2 (also known as EGFR and human epidermal growth factor receptor 2 [HER2]) and α6-integrin to promote cancer cell proliferation in a pathway involving its N-terminal portion and the MAPK/ERK1/2 and PI3K/AKT cascades. Studies using Col18a1 mouse models crossed with the mouse mammary tumor virus–polyoma virus middle T antigen (MMTV-PyMT) mammary carcinogenesis model showed that ColXVIII promoted BC growth and metastasis in a tumor cell–autonomous manner. Moreover, the number of mammary cancer stem cells was significantly reduced in the MMTV-PyMT and human cell models upon ColXVIII inhibition. Finally, ablation of ColXVIII substantially improved the efficacy of ErbB-targeting therapies in both preclinical models. In summary, ColXVIII was found to sustain the stemness properties of BC cells and tumor progression and metastasis through ErbB signaling, suggesting that targeting ColXVIII in the tumor milieu may have important therapeutic potential.

Basement membrane (BM) zone-associated collagen XV (ColXV) has been shown to suppress the malignancy of tumour cells, and its restin domain can inhibit angiogenesis. In human breast cancer, as well as in many other human carcinomas, ColXV is lost from the epithelial BM zone prior to tumour invasion. Here, we addressed the roles of ColXV in breast carcinogenesis using the transgenic MMTV-PyMT mouse mammary carcinoma model. We show here for the first time that the inactivation of Col15a1 in mice leads to changes in the fibrillar tumour matrix and to increased mammary tumour growth. ColXV is expressed by myoepithelial and endothelial cells in mammary tumours and is lost from the ductal BM along with the loss of the myoepithelial layer during cancer progression while persisting in blood vessels and capillaries, even in invasive tumours. However, despite the absence of anti-angiogenic restin domain, neovascularisation was reduced rather than increased in the ColXV-deficient mammary tumours compared to controls. We also show that, in robust tumour cell transplantation models or in a chemical-induced fibrosarcoma model, the inactivation of Col15a1 does not affect tumour growth or angiogenesis. In conclusion, our results support the proposed tumour suppressor function of ColXV in mammary carcinogenesis and reveal diverse roles of this collagen in different cancer types.

Key points: Extracellular matrix is highly remodelled in obesity and associates with the development of metabolic disorders, such as insulin resistance. Previously, we have shown that the lack of specific collagen XVIII isoforms impairs adipocyte differentiation in mice. Here, we show that mice lacking the medium and long isoforms of collagen XVIII develop insulin resistance and glucose intolerance and show elevated serum triglycerides and fat accumulation in the liver. We report that collagen XVIII‐deficient mice have increased heat production at low temperatures. These results reveal a new role for collagen XVIII in the regulation of glucose and lipid metabolism, and they expand the understanding of the development of metabolic disorders. Liver and adipose tissues play important roles in the regulation of systemic glucose and lipid metabolism. Extracellular matrix synthesis and remodelling are significantly altered in these tissues in obesity and type 2 diabetes. Collagen XVIII is a ubiquitous extracellular matrix component, and it occurs in three isoforms which differ in terms of molecular size, domain structure and tissue distribution. We recently showed that, in mice, the lack of collagen XVIII, and especially its medium and long isoforms, leads to reduced adiposity and dyslipidaemia. To address the metabolic consequences of these intriguing observations, we assessed whole‐body glucose homeostasis in mice challenged with a high‐fat diet and in normal physiological conditions. We observed that, in the high caloric diet, the overall adiposity was decreased by 30%, serum triglyceride values were threefold higher and the steatotic area in liver was twofold larger in collagen XVIII knockout mice compared with controls. We demonstrated that mice lacking either all three collagen XVIII isoforms, or specifically, the medium and long isoforms develop insulin resistance and glucose intolerance. Furthermore, we found that ablation of collagen XVIII leads to increased heat production in low temperatures and to reduction of the high blood triglyceride levels of the knockout mice to the level of wild‐type mice. Our data indicate that collagen XVIII plays a role in the regulation of glucose tolerance, insulin sensitivity and lipid homeostasis, principally through its ability to regulate the expansion of the adipose tissue. These findings advance the understanding of metabolic disorders.

Background: Modeling the pathophysiology of prostate cancer (PCa) remains a challenge and primary tissue-derived organoid cultures have emerged as promising models representing good tissue mimicry. Methods: We have established 36 PCa patient-derived organoid cultures that self-renew and can be maintained long-term. Using CRISPR-mediated genomic editing, selected PCa organoids were also genetically engineered to modulate their tumorigenic and self-renewal properties. We show that PCa organoids can also be readily utilized in drug sensitivity tests. In vivo, orthotopic xenograft studies were performed to recapitulate the original tumor phenotype. Finally, we performed scRNA and bulk RNA sequencing to show the multi-cellular involvement in PCa organoid self-renewal and tumorigenesis. Results: The morphological properties of cancer organoids were found to correlate with the disease grading. Importantly, detailed analyses of selected organoid lines indicated that they maintain the heterogeneity, gene expression profile, and histological architecture of their primary tumor-of-origin and recapitulate these features in vivo as xenografts. Finally, we show that α6-integrin expression is a requisite for the growth and long-term propagation of human PCa organoids while α2-integrin expression is dispensable. High expression levels of both α6- and α2-integrins have been documented in putative prostate epithelial stem cells which likely play an important role in PCa tumorigenesis. Our single-cell analysis identified a distinct cell population with a stem cell profile and high expression of α6- and α2-integrins. Discussion: Our data suggest that α6-integrin expression promotes PCa stem cell self-renewal and demonstrates the versatile biomedical utilities of PCa-derived organoid models.