Transcription factor, which binds preferentially the consensus sequence 5'-TAAGT[AG]-3' and can behave as a transcriptional repressor. Plays an important role in normal prostate development, regulating proliferation of glandular epithelium and in the formation of ducts in prostate. Acts as a tumor suppressor controlling prostate carcinogenesis, as shown by the ability to inhibit proliferation and invasion activities of PC-3 prostate cancer cells. Interacts with serum response factor (SRF) (By similarity). Interacts with SPDEF (PubMed:11809674). Interacts with WDR77 (PubMed:12972618). Interacts with TOPORS which polyubiquitinates NKX3-1 and induces its proteasomal degradation (PubMed:18077445). Interacts with FEM1B (By similarity). Additional isoforms seem to exist. Highly expressed in the prostate and, at a lower level, in the testis. By androgens and, in the LNCaP cell line, by estrogens. Androgenic control may be lost in prostate cancer cells during tumor progression from an androgen-dependent to an androgen-independent phase. Ubiquitinated by TOPORS; monoubiquitinated at several residues and also polyubiquitinated on single residues. Belongs to the NK-3 homeobox family.