ABSTRACT
A defining hallmark of primary and metastatic cancers is the migration and invasion of malignant cells. These invasive properties involve altered dynamics of the cytoskeleton and one of its major structural components ß-actin. Here we identify AIM1 (absent in melanoma 1) as an actin-binding protein that suppresses pro-invasive properties in benign prostate epithelium. Depletion of AIM1 in prostate epithelial cells increases cytoskeletal remodeling, intracellular traction forces, cell migration and invasion, and anchorage-independent growth. In addition, decreased AIM1 expression results in increased metastatic dissemination in vivo. AIM1 strongly associates with the actin cytoskeleton in prostate epithelial cells in normal tissues, but not in prostate cancers. In addition to a mislocalization of AIM1 from the actin cytoskeleton in invasive cancers, advanced prostate cancers often harbor AIM1 deletion and reduced expression. These findings implicate AIM1 as a key suppressor of invasive phenotypes that becomes dysregulated in primary and metastatic prostate cancer.
Subject(s)
Actins/metabolism , Cell Movement , Crystallins/metabolism , Membrane Proteins/metabolism , Prostatic Neoplasms/metabolism , Actin Cytoskeleton/metabolism , Actins/genetics , Animals , Cell Line , Cell Line, Tumor , Crystallins/genetics , HEK293 Cells , Humans , Male , Membrane Proteins/genetics , Mice , Microscopy, Electron, Transmission , Microscopy, Fluorescence , Neoplasm Invasiveness , Neoplasm Micrometastasis , Prostatic Neoplasms/genetics , Prostatic Neoplasms/ultrastructure , Protein Binding , RNA Interference , Transplantation, HeterologousABSTRACT
BACKGROUND: Glutathione S-transferases (GSTs) metabolize drugs and xenobiotics. Yet despite high protein sequence homology, expression of π-class GSTs, the most abundant of the enzymes, varies significantly between species. In mouse liver, hepatocytes exhibit high mGstp expression, while in human liver, hepatocytes contain little or no hGSTP1 mRNA or hGSTP1 protein. π-class GSTs are known to be critical determinants of liver responses to drugs and toxins: when treated with high doses of acetaminophen, mGstp1/2+/+ mice suffer marked liver damage, while mGstp1/2-/- mice escape liver injury. METHODOLOGY/PRINCIPAL FINDINGS: To more faithfully model the contribution of π-class GSTs to human liver toxicology, we introduced hGSTP1, with its exons, introns, and flanking sequences, into the germline of mice carrying disrupted mGstp genes. In the resultant hGSTP1+mGstp1/2-/- strain, π-class GSTs were regulated differently than in wild-type mice. In the liver, enzyme expression was restricted to bile duct cells, Kupffer cells, macrophages, and endothelial cells, reminiscent of human liver, while in the prostate, enzyme production was limited to basal epithelial cells, reminiscent of human prostate. The human patterns of hGSTP1 transgene regulation were accompanied by human patterns of DNA methylation, with bisulfite genomic sequencing revealing establishment of an unmethylated CpG island sequence encompassing the gene promoter. Unlike wild-type or mGstp1/2-/- mice, when hGSTP1+mGstp1/2-/- mice were overdosed with acetaminophen, liver tissues showed limited centrilobular necrosis, suggesting that π-class GSTs may be critical determinants of toxin-induced hepatocyte injury even when not expressed by hepatocytes. CONCLUSIONS: By recapitulating human π-class GST expression, hGSTP1+mGstp1/2-/- mice may better model human drug and xenobiotic toxicology.
