Friend or Foe? Unraveling the Dual Role of MMP-12 in Cancer Biology

Abstract

Matrix metalloproteinases (MMPs) have long been recognized as key mediators of tumor invasion and metastasis due to their capacity to degrade extracellular matrix components. However, clinical failure of broad-spectrum MMP inhibitors has revealed a more complex and context-dependent role for these proteases in cancer. Among them, macrophage metalloelastase, MMP-12, has emerged as a particularly intriguing enzyme with both tumor-promoting and tumor-suppressive functions. Predominantly expressed by tumor-associated macrophages, MMP-12 occupies a unique position at the interface of proteolysis, inflammation, and immune regulation within the tumor microenvironment. Accumulating evidence from experimental models and clinical studies demonstrates that MMP-12 can exert potent anti-tumorigenic effects, primarily through inhibition of angiogenesis. Mechanistically, MMP-12 generates angiostatin and other anti-angiogenic fragments, suppresses vascular endothelial growth factor signaling, and reduces tumor vascularization, thereby limiting tumor growth and metastatic expansion. In several cancer types, including lung, colorectal, and hepatocellular carcinoma, elevated MMP-12 expression has been associated with reduced tumor progression and improved patient outcomes. Conversely, MMP-12 can also promote tumor progression through extracellular matrix remodeling, facilitation of invasion, and modulation of inflammatory pathways, particularly in environments characterized by chronic inflammation or immunosuppressive macrophage phenotypes. These seemingly contradictory roles are governed by multiple context-dependent factors, including macrophage polarization, tumor type, disease stage, and microenvironmental cues such as hypoxia and cytokine signaling. In this review, we comprehensively examine the molecular regulation, functional mechanisms, and clinical relevance of MMP-12 in cancer. We highlight the dualistic nature of MMP-12 activity and discuss its implications for therapeutic strategies, emphasizing the need for selective and context-aware targeting approaches rather than broad inhibition of MMP activity.