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Integrin α11β1 is a collagen receptor that has been reported to be overexpressed in the stroma of non-small cell lung cancer (NSCLC) and of head and neck squamous cell carcinoma (HNSCC). In the current study, we further analyzed integrin α11 expression in 14 tumor types by screening a tumor tissue array while using mAb 203E3, a newly developed monoclonal antibody to human α11. Different degrees of expression of integrin α11 were observed in the stroma of breast, ovary, skin, lung, uterus, stomach, and pancreatic ductal adenocarcinoma (PDAC) tumors. Co-expression queries with the myofibroblastic cancer-associated fibroblast (myCAF) marker, alpha smooth muscle actin (αSMA), demonstrated a moderate level of α11+ in myCAFs associated with PDAC and HNSCC tumors, and a lack of α11 expression in additional stromal cells (i.e., cells positive for fibroblast-specific protein 1 (FSP1) and NG2). The new function-blocking α11 antibody, mAb 203E1, inhibited cell adhesion to collagen I, partially hindered fibroblast-mediated collagen remodeling and obstructed the three-dimensional (3D) migration rates of PDAC myCAFs. Our data demonstrate that integrin α11 is expressed in a subset of non-pericyte-derived CAFs in a range of cancers and suggest that α11β1 constitutes an important receptor for collagen remodeling and CAF migration in the tumor microenvironment (TME).

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Integrin α11β1 is a collagen-binding integrin, which is receiving increasing attention in the context of wound healing and fibrosis. Although α11β1 integrin displays similar collagen specificity to α2β1 integrin, both integrins have distinct in vivo functions. In this context, the contribution of α11 subunit cytoplasmic tail interactions to diverse molecular signals and biological functions is largely unknown. In the current study, we have deleted the α11 cytoplasmic tail and studied the effect of this deletion on α11 integrin function. Compared to wild-type cells, C2C12 cells expressing tail-less α11 attached normally to collagen I, but formed fewer focal contacts. α11-tail-less cells furthermore displayed a reduced capacity to invade and reorganize a 3D collagen matrix and to proliferate. Analysis of cell signaling showed that FAK and ERK phosphorylation was reduced in cells expressing tail-less α11. Inhibition of ERK and FAK activation decreased α11-mediated cell proliferation, whereas α11-mediated cell invasion was FAK-dependent and occurred independently of ERK signaling. In summary, our data demonstrate that the integrin α11 cytoplasmic tail plays a central role in α11 integrin-specific functions, including FAK-dependent ERK activation to promote cell proliferation.

Cell-specific expression of genes offers the possibility to use their promoters to drive expression of Cre-recombinase, thereby allowing for detailed expression analysis using reporter gene systems, cell lineage tracing, conditional gene deletion, and cell ablation. In this context, current data suggest that the integrin α11 subunit has the potential to serve as a fibroblast biomarker in tissue regeneration and pathology, in particular in wound healing and in tissue- and tumor fibrosis. The mesenchyme-restricted expression pattern of integrin α11 thus prompted us to generate a novel ITGA11-driver Cre mouse strain using a ϕC31 integrase-mediated knock-in approach. In this transgenic mouse, the Cre recombinase is driven by regulatory promoter elements within the 3 kb segment of the human ITGA11 gene. β-Galactosidase staining of embryonic tissues obtained from a transgenic ITGA11-Cre mouse line crossed with Rosa 26R reporter mice (ITGA11-Cre;R26R) revealed ITGA11-driven Cre expression and activity in mesenchymal cells in a variety of mesenchymal tissues in a pattern reminiscent of endogenous α11 protein expression in mouse embryos. Interestingly, X-gal staining of mouse embryonic fibroblasts (MEFs) isolated from the ITGA11-Cre;R26R mice indicated heterogeneity in the MEF population. ITGA11-driven Cre activity was shown in approximately 60% of the MEFs, suggesting that the expression of integrin α11 could be exploited for isolation of different fibroblast populations. ITGA11-driven Cre expression was found to be low in adult mouse tissues but was induced in granulation tissue of excisional wounds and in fibrotic hearts following aortic banding. We predict that the ITGA11-Cre transgenic mouse strain described in this report will be a useful tool in matrix research for the deletion of genes in subsets of fibroblasts in the developing mouse and for determining the function of subsets of pro-fibrotic fibroblasts in tissue fibrosis and in different subsets of cancer-associated fibroblasts in the tumor microenvironment.

Pathological myocardial hypertrophy in response to an increase in left ventricular (LV) afterload may ultimately lead to heart failure. Cell surface receptors bridge the interface between the cell and the ECM in cardiac myocytes and cardiac fibroblasts, and have been suggested to be important mediators of pathological myocardial hypertrophy. We identify for the first time that integrin α11 (α11) is preferentially upregulated amongst integrin beta 1 heterodimer-forming α subunits in response to increased afterload induced by aortic banding (AB) in wild type mice (WT). Mice were anesthetized in a chamber with 4% isoflurane and 95% oxygen before being intubated and ventilated with 2.5% isoflurane and 97% oxygen. For pre- and post-operative analgesia, animals were administered 0.02 mL buprenorphine (0.3 mg/mL) subcutaneously. Surprisingly, mice lacking α11 develop myocardial hypertrophy following AB comparable to WT. In the mice lacking α11, we further show a compensatory increase in the expression of another mechanoreceptor, syndecan-4, following AB compared to WT AB mice, indicating that syndecan-4 compensated for lack of α11. Intriguingly, mice lacking mechanoreceptors α11 and syndecan-4 show ablated myocardial hypertrophy following AB compared to WT mice. Expression of the main cardiac collagen isoforms col1a2 and col3a1 was significantly reduced in AB mice lacking mechanoreceptors α11 and syndecan-4 compared to WT AB.

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