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Mild dietary zinc deprivation in humans and rodents has little effect on blood plasma zinc levels, and yet cellular consequences of zinc depletion can be detected in vascular and other tissues. We proposed that a zinc-regulated humoral factor might mediate the effects of zinc deprivation. Using a novel approach, primary rat vascular smooth muscle cells (VSMCs) were treated with plasma from zinc-deficient (<1 mg Zn/kg) or zinc-adequate (35 mg Zn/kg, pair-fed) adult male rats, and zinc levels were manipulated to distinguish direct and indirect effects of plasma zinc. Gene expression changes were analyzed by microarray and qPCR, and incubation of VSMCs with blood plasma from zinc-deficient rats strongly changed the expression of > 2500 genes, compared to incubation of cells with zinc-adequate rat plasma. We demonstrated that this effect was caused by a low-molecular-weight (~2-kDa) zinc-regulated humoral factor but that changes in gene expression were mostly reversed by adding zinc back to zinc-deficient plasma. Strongly regulated genes were overrepresented in pathways associated with immune function and development. We conclude that zinc deficiency induces the production of a low-molecular-weight humoral factor whose influence on VSMC gene expression is blocked by plasma zinc. This factor is therefore under dual control by zinc. [ABSTRACT FROM AUTHOR]

Messenger RNA trafficking, which provides a mechanism for local protein synthesis, is dependent oncis-acting sequences in the 3′ untranslated regions (3′UTRs) of the mRNAs concerned acting together withtrans-acting proteins. The C-MYC transcription factor is a proto-oncogene product involved in cell proliferation, differentiation and apoptosis. Localization of c-mycmRNA to the perinuclear cytoplasm and its association with the cytoskeleton is determined by a signal in the 3′UTR. Here we show the specific binding of atrans-acting factor to the perinuclear localization element in the 3′UTR of c-mycmRNA and identify this protein as annexin A2. Gel retardation and UV cross-linking experiments showed that proteins in fibroblast extracts formed complexes with the region of c-myc3′UTR implicated in localization; a protein of≈ 36 kDa exhibited specific, Ca2+-dependent binding. Binding was reduced by introduction of a mutation that abrogates localization. Using RNA-affinity columns followed by gel electrophoresis and mass spectrometry this protein was identified as annexin A2. The RNA–protein complex formed by cell extracts was further retarded by anti-(annexin A2). Purified annexin A2 bound to the same region of the c-myc3′UTR but binding was reduced by introduction of a mutation, as with cell extracts. It is proposed that binding of annexin A2 to the localization signal in the c-mycmRNA leads to association with the cytoskeleton and perinuclear localization. The data indicate a novel functional role for the RNA-binding properties of annexin A2 in perinuclear localization of mRNA and the association with the cytoskeleton. [ABSTRACT FROM AUTHOR]