4824

NKX3-1

BAPX2|NKX3|NKX3.1|NKX3A;NK3 homeobox 1;NKX3-1;NK3 homeobox 1

NK homeobox, family 3, A|NK3 transcription factor homolog A|NK3 transcription factor related, locus 1|homeobox protein NK-3 homolog A|homeobox protein Nkx-3.1

8p21.2

protein-coding

PURPOSE: NKX3.1 is an androgen regulated gene that is largely specific to the prostate for expression and it is predicted to encode a homeobox protein. Null alleles of NKX3.1 in mice results in impaired prostate development as well as hyperplasia and dysplasia of the prostate. In addition, the NKX3.1 gene maps to a region of high loss of heterozygosity in prostate cancer in humans, suggesting that NKX3.1 might have a direct role in prostate carcinogenesis, possibly functioning as a tumor suppressor protein. Previous studies of the levels of NKX3.1 mRNA or protein in prostate cancer specimens have resulted in conflicting findings. MATERIALS AND METHODS: To resolve this issue we assessed NKX3.1 expression by mRNA in situ analysis and immunohistochemistry on the same prostate cancer tissue arrays. RESULTS: Data showed that NKX3.1 mRNA and protein levels in prostate cancer specimens are correlated, suggesting that most regulation is at the transcriptional level. There was no correlation of NKX3.1 expression levels with tumor grade or clinical stage. In general there was a suggestion that worse clinical features at surgery were associated with lower IHC stain scores. In particular, extracapsular extension but not seminal vesicle invasion inversely correlated with NKX3.1 expression. CONCLUSIONS: Together these data suggest that NKX3.1 does not function as a typical tumor suppressor protein in prostate cancer but it may still have important regulatory roles during prostate cancer progression.

The NKX3.1 gene located at 8p21.2 encodes a homeodomain-containing transcription factor that acts as a haploinsufficient tumor suppressor in prostate cancer. Diminished protein expression of NKX3.1 has been observed in prostate cancer precursors and carcinomas. TOPORS is a ubiquitously expressed E3 ubiquitin ligase that can ubiquitinate tumor suppressor p53. Here we report interaction between NKX3.1 and TOPORS. NKX3.1 can be ubiquitinated by TOPORS in vitro and in vivo, and overexpression of TOPORS leads to NKX3.1 proteasomal degradation in prostate cancer cells. Conversely, small interfering RNA-mediated knockdown of TOPORS leads to an increased steady-state level and prolonged half-life of NKX3.1. These data establish TOPORS as a negative regulator of NKX3.1 and implicate TOPORS in prostate cancer progression.

Inflammation of the prostate is a risk factor for the development of prostate cancer. In the aging prostate, regions of inflammatory atrophy are foci for prostate epithelial cell transformation. expression of the suppressor protein NKX3.1 is reduced in regions of inflammatory atrophy and in preinvasive prostate cancer. Inflammatory cytokines tumor necrosis factor (TNF)-alpha and interleukin-1beta accelerate NKX3.1 protein loss by inducing rapid ubiquitination and proteasomal degradation. The effect of TNF-alpha is mediated via the COOH-terminal domain of NKX3.1 where phosphorylation of serine 196 is critical for cytokine-induced degradation. mutation of serine 196 to alanine abrogates phosphorylation at that site and the effect of TNF-alpha on NKX3.1 ubiquitination and protein loss. This is in contrast to control of steady-state NKX3.1 turnover, which is mediated by serine 185. mutation of serine 185 to alanine increases NKX3.1 protein stability by inhibiting ubiquitination and doubling the protein half-life. A third COOH-terminal serine at position 195 has a modulating effect on both steady-state protein turnover and on ubiquitination induced by TNF-alpha. Thus, cellular levels of the NKX3.1 tumor suppressor are affected by inflammatory cytokines that target COOH-terminal serine residues to activate ubiquitination and protein degradation. Our data suggest that strategies to inhibit inflammation or to inhibit effector kinases may be useful approaches to prostate cancer prevention.

BACKGROUND: ETS transcription factors regulate important signaling pathways involved in cell differentiation and development in many tissues and have emerged as important players in prostate cancer. However, the biological impact of ETS factors in prostate tumorigenesis is still debated. METHODOLOGY/PRINCIPAL FINDINGS: We performed an analysis of the ETS gene family using microarray data and real-time PCR in normal and tumor tissues along with functional studies in normal and cancer cell lines to understand the impact in prostate tumorigenesis and identify key targets of these transcription factors. We found frequent dysregulation of ETS genes with oncogenic (i.e., ERG and ESE1) and tumor suppressor (i.e., ESE3) properties in prostate tumors compared to normal prostate. Tumor subgroups (i.e., ERG(high), ESE1(high), ESE3(low) and NoETS tumors) were identified on the basis of their ETS expression status and showed distinct transcriptional and biological features. ERG(high) and ESE3(low) tumors had the most robust gene signatures with both distinct and overlapping features. Integrating genomic data with functional studies in multiple cell lines, we demonstrated that ERG and ESE3 controlled in opposite direction transcription of the Polycomb Group protein EZH2, a key gene in development, differentiation, stem cell biology and tumorigenesis. We further demonstrated that the prostate-specific tumor suppressor gene Nkx3.1 was controlled by ERG and ESE3 both directly and through induction of EZH2. CONCLUSIONS/SIGNIFICANCE: These findings provide new insights into the role of the ETS transcriptional network in prostate tumorigenesis and uncover previously unrecognized links between aberrant expression of ETS factors, deregulation of epigenetic effectors and silencing of tumor suppressor genes. The link between aberrant ETS activity and epigenetic gene silencing may be relevant for the clinical management of prostate cancer and design of new therapeutic strategies.