Zinc is an important nutrient that is required for cell growth, differentiation and its survival. Zinc deficiency can cause growth retardation, immunodeficiency and other related health problems. Consequently, zinc homeostasis should be tightly controlled in individual cells. Zinc is identified as the most important in the immune system, while its detailed roles and mechanisms are yet to be resolved.

Zinc has been submitted to act as a kind of neurotransmitter. Furthermore, zinc has shown to bind and affect the activity of various signaling molecules, i.e. protein tyrosine phosphatases (PTPs). But, it has not been recognized whether zinc could act as an intracellular signaling molecule, specifically, a molecule whose intracellular status is modified in response to an extracellular stimulus. And it is also capable of transducing the extracellular stimulus into an intracellular signaling event.

It is proposed that zinc acts as a signaling molecule and there are minimum two kinds of zinc signaling: "late Zn signaling," a dependent on an alteration in the expression profile of zinc transporters, and "early Zn signaling," that includes a "Zinc wave" and is directly stimulated by an extracellular stimulus.

Source: Hirano T, Murakami M, Fukada T, Nishida K, Yamasaki S, Suzuki T. Roles of zinc and zinc signaling in immunity: zinc as an intracellular signaling molecule. Adv Immunol. 2008; 97:149-176. doi:10.1016/S0065-2776(08)00003-5