Metallothionein-3 (MT3)

Metallothionein-3 (MT3) is a small, cysteine-rich intracellular protein unique among the metallothionein family, primarily known for its high affinity binding of essential metal ions such as zinc and copper[2]. MT3 is structurally characterized by a distinctive N-terminal TCPCP motif and a C-terminal EAAEAE insert, endowing it with functional properties diverging from other metallothioneins[2]. Notably, MT3 was originally identified as the "growth inhibitory factor" (GIF) in the brain, where it plays a significant role in the regulation of neuronal growth and has been implicated in Alzheimer's disease[2]. Unlike other metallothioneins (MT1/2), MT3 shows specialized biological functions: it modulates cell differentiation and polarity in renal epithelial cells (critical for vectorial active transport), regulates cytoskeletal dynamics through direct interaction with proteins like β-actin and myosin-9, and is essential for proper homeostasis of zinc and copper[1][2][3]. MT3 is also highly expressed in osteoclasts, where it regulates osteoclastogenesis and bone metabolism through molecular pathways involving reactive oxygen species (ROS) and transcriptional control (e.g., SP1 regulation)[3]. Its role in cellular protection against oxidative damage is context-dependent and remains an area of active investigation, showing both antioxidative and, in some settings, paradoxically pro-oxidative effects[2]. Variably involved in pathologies such as neurodegeneration, cancer, and metabolic bone diseases, MT3 is considered an emerging and multifunctional molecular target with potential relevance to therapy, yet it currently has no approved pharmacological modulators or established biomarkers for clinical monitoring[2][3].

Other names

Metallothionein-IIIMT-3GIFGrowth inhibitory factorGIFBGRIFZnMT3metallothionein 3 (growth inhibitory factor)metallothionein-III