Lung Lysyl Oxidase Regulation by Metal Ion Homeostasis

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PROJECT ABSTRACT. Lysyl oxidase (LO), a copper-(Cu) dependent enzyme, oxidizes peptidyl lysine residues in substrates, e.g., collagen, elastin and histone H1, essential for organization and stabilization of the extracellular matrix (ECM) and the cell nucleus. This enzyme has been identified as a tumor suppressor, for example, inhibiting transforming activity of ras, a proto oncogene. Thus, LO as an intra- and extracellular effector plays a critical role in human physiology and pathology. Chronic exposure of humans to cadmium (Cd), a heavy metal, either from occupational contamination or from cigarette smoke, induces emphysema and lung cancers. However, the mechanisms for Cd-elicited lung pathology remain poorly understood. LO as a metalloenzyme is susceptible to changes in cellular metal homeostasis. Previous studies by this lab investigating the phenotype change from Cd sensitive to Cd resistant of rat lung fibroblasts (RFL6) illustrated downregulation of LO by Cd at mRNA, protein and catalytic levels. Continuing studies further indicated that RFL6 cells in response to Cd displayed inhibition of LO transcription initiation and enhancement of LO mRNA decay both collectively contributing to decreased levels of steady-state LO mRNAs. These findings have led to a hypothesis that transcriptional control and regulation of the LO gene are critical targets for Cd insult and silencing of LO gene transcription by Cd is a key molecular basis for lung diseases. The overall goal of the proposed research is to test this hypothesis by achieving following specific aims: 1) to identify mechanisms for Cd silencing of the LO gene at the transcriptional level by examining Cd modulation of RNA polymerase II- directed LO pre-mRNA synthesis and processing, and of the LO promoter activation regulated by the core promoter; 2) to identify mechanisms for Cd silencing of the LO gene at the transcriptional level by examining Cd modulation of the LO promoter activation regulated by metal and redox-sensitive transcription factors and their cognate cis-elements, and determining LO promoter methylation to provide evidence for Cd epigenetic damage to LO DNA; 3) to identify mechanisms for Cd silencing of the LO gene at the posttranscriptional level by examining Cd effects on the 5'-capping and 3'-polyadenylation status of LO mRNA, and assessing Cd sensitive, LO mRNA stability-related cis-elements in the 3'-untranslation region and their corresponding binding proteins; and 4) to investigate biological consequences of Cd silencing of the LO gene in cell and animal models by examining effects of altered LO expression by Cd on substrate promoter activation and cell transformation in the cell model and assessing the active status of the major LO transcriptional and posttranscriptional machineries as well as aberrant methylation of the LO gene promoter in emphysematous and carcinogenic lungs of rats receiving Cd by chronic administration. The outcomes of the proposed research are expected to enhance our understanding of mechanisms of LO gene silence by Cd providing the basis for developing prophylaxis and treatment strategies for Cd-related lung diseases.