Ubiquitin-like protein modifications in prostate and breast cancer

Post-translational modifications by ubiquitin-like proteins have been implicated in the regulation of diverse cellular processes, including nuclear transport, transcription regulation, stress response and DNA repair. Ubiquitination is well characterized for its roles in regulating these cellular processes. As a newly identified member of ubiquitin-like proteins, the small ubiquitin-like modifier (SUMO) has received a great deal of attention for its functions distinct from ubiquitin. In particular, alterations of SUMO conjugation or sumoylation have been implicated in several human diseases, including cancer. Although little is known about the underlying mechanism of sumoylation-associated tumorigenesis, the modulation of nuclear receptor (NR)-mediated signaling pathways is likely to play a role in this aspect. NRs are a family of ligand dependent transcription factors which control cell growth and differentiation in many cell types, as well as during the development of cancer. In this review, we will discuss some basic aspects of sumoylation and how sumoylation modulates the NR-mediated gene expression, focusing on androgen receptor (AR) and estrogen receptor (ER), a key player in progression of prostate or breast cancer.