Inflammatory Cytokines Induce Ubiquitination and Loss of the Prostate Suppressor Protein NKX3.1
Abstract
During the normal aging process in the prostate a variety of histologic changes are seen including regions termed inflammatory atrophy where mononuclear infiltrating cells are seen adjacent to atrophic glands. Moreover both clinical and subclinical prostatitis is a risk factor for the development of prostate cancer. This thesis describes a causative link between prostatic inflammatory processes and reductions in expression of the prostate suppressor protein NKX3.1. Reduction of the suppressor protein NKX3.1 by either loss of heterozygosity at 8p21, gene methylation or both is an early event in prostate cancer. We have found that the inflammatory cytokines TNF-alpha and IL-1beta induce rapid ubiquitination and proteasomal degradation of NKX3.1 in vitro. Within 2 hours of exposing LNCaP cells to TNF-alpha we observed marked reductions of either endogenous or exogenously expressed NKX3.1. Inhibitors of proteasomal degradation blocked the loss of NKX3.1 and allowed accumulation of NKX3.1 protein complexed with polyubiquitin. The C-terminal domain of NKX3.1 representing the 51 amino acids distal to the homeodomain can undergo posttranslational modification to regulate ubiquitination and turnover of NKX3.1. Deletion of the C-terminal domain results in prolonged protein half life and absence of ubiquitination in response to TNF-alpha. The C-terminus directs ubiquitination but is not the site for ubiquitin ligation since site-directed mutation of either or both of the two lysines (193 and 201) in the C-terminal domain affects neither ubiquitination nor protein half-life. The ubiquitination signal can be localized to amino acids (184-192) in the C-terminal domain and mutation of serine 185 prolonged NKX3.1 half-life but did not affect TNF-alpha induced ubiquitination. Mutation of serine 196 inhibited TNF-alpha induced ubiquitination and degradation demonstrating differential regulation of NKX3.1 levels by inflammatory cytokines versus basal protein turnover.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 2007
- Accession Number
- ADA477595
Entities
People
- Erin E. Muhlbradt
Organizations
- Georgetown University