| Fibulin‑3 (EFEMP1) is a secreted, disulfide‑rich extracellular matrix glycoprotein of the fibulin family that localizes to basement membranes and pericellular matrix in tissues such as retina, lung, vasculature, and bone, where it helps organize elastic and collagenous matrices and modulates cell–matrix adhesion, growth factor signaling, and stromal activation in a context‑dependent manner. The protein contains an N‑terminal signal peptide, a short unique segment, a series of tandem calcium‑binding EGF‑like domains, and a C‑terminal fibulin‑type module that mediates binding to ECM partners including fibronectin, collagens, elastin-associated components, and ECM1, allowing fibulin‑3 to participate in scaffold assembly and confer biomechanical stability to basement membranes. Fibulin‑3 promotes integrin‑dependent cell adhesion and spreading and supports cell–ECM attachment in multiple tissues; its presence influences the organization and cross‑linking of elastic fibers and basement membrane integrity, and EFEMP1 knockdown reduces adhesion and alters expression of ECM remodeling genes in tumor and stromal cells, pointing to a regulatory role in matrix composition and stiffness. In the eye, EFEMP1 is expressed by retinal pigment epithelium and choroidal tissues and contributes to Bruch’s membrane structure; disease-associated mutations such as R345W cause misfolding and impaired secretion, leading to intracellular and sub‑RPE accumulation of mutant fibulin‑3 and driving macular dystrophy, while gene expression profiling in age‑related macular degeneration shows upregulation of EFEMP1 in retinal–choroidal tissues and elevated serum fibulin‑3 in neovascular AMD, identifying it as a biomarker and potential driver of choroidal neovascularization. In cancer biology, fibulin‑3 acts as a matricellular regulator with tissue‑ and context‑dependent pro‑ and anti‑tumorigenic roles; in osteosarcoma and other solid tumors, EFEMP1 overexpression has been linked to enhanced invasion, lung metastasis, and matrix remodeling, where its depletion in osteosarcoma models reduces expression of ECM genes such as COL1A1, POSTN, MMP1, and MMP2 in lung fibroblasts, increases TIMP3, and diminishes tumor cell adhesion to preconditioned stroma, indicating that fibulin‑3 shapes a pro‑metastatic niche by reprogramming stromal ECM deposition and protease balance. Mechanistic work in cervical carcinoma and other epithelial cancers further shows that fibulin‑3 can induce epithelial–mesenchymal transition and activate PI3K–AKT–mTOR or Wnt/β‑catenin pathways, promote angiogenesis via VEGF upregulation, and associate with poor differentiation and unfavorable prognosis, although opposing tumor‑suppressive effects have been reported in some contexts, underscoring its role as a finely tuned ECM‑linked modulator of signaling rather than a uniformly oncogenic structural protein. Across ocular and oncologic systems, fibulin‑3/EFEMP1 therefore operates as an ECM organizer and matricellular signaling hub whose modular EGF‑like and fibulin domains coordinate interactions with ECM proteins, integrins, and growth factor pathways to maintain tissue architecture, regulate neovascular and metastatic programs, and generate disease‑specific expression and secretion patterns that are increasingly being explored as diagnostic and therapeutic targets. |
