Matricellular Proteins in Bladder Cancer: Context-Dependent Roles in Tumor Promotion and Suppression

Bladder cancer (BLCA) is a common and heterogeneous malignancy in which disease progression is driven not only by tumor-intrinsic alterations but also by dynamic interactions within the tumor microenvironment (TME). Increasing evidence positions the extracellular matrix (ECM) as a critical regulator of these processes. Matricellular proteins (MCPs), a group of nonstructural ECM-associated molecules, have emerged as key modulators of tumor-stroma communication. In BLCA, MCPs have been reported to display divergent, and in some cases opposing, associations or functions, with the same protein participating in both tumor promotion and suppression. Here, we review current evidence on the function of MCPs in BLCA and synthesize their bidirectional roles in carcinogenesis. MCPs contribute to tumor progression by promoting invasion, epithelial-mesenchymal transition (EMT), angiogenesis, and metastatic niche formation. At the same time, MCPs can restrain tumor growth by inhibiting angiogenesis, stabilizing ECM organization, inducing cell cycle arrest, and maintaining epithelial integrity. A key concept emerging from this body of evidence is the context-dependent functional plasticity of MCPs. We propose that MCP-associated phenotypes in BLCA may be influenced by contextual factors, including isoform diversity arising from alternative splicing and post-translational modifications, spatial compartmentalization within tumor and stromal niches, tumor microenvironmental composition, and molecular subtype. However, the level of supporting evidence differs substantially among MCPs, and direct BLCA-specific mechanistic evidence remains limited for many proposed relationships. These factors, therefore, provide a framework for interpreting divergent findings rather than representing universally established determinants of MCP function. Recognizing MCPs as context-sensitive regulators rather than fixed tumor-promoting or tumor-suppressing entities provides a unifying framework for understanding their roles in BLCA. This could be an important step for therapeutic targeting, encouraging effective strategies to consider and incorporate the molecular and microenvironmental context in which MCPs operate.