• Journal of Life Science
• /
• v.25 no.8
• /
• pp.947-952
• /
• 2015

Prostate apoptosis response-4 (Par-4) was originally identified in androgen-independent prostate cancer cells undergoing apoptosis. Par-4 is ubiquitously expressed in normal cells and tissues, but it is downregulated in several types of cancers. Par-4 is a 38 kDa tumor suppressor protein encoded by the PARW gene. Par-4 promotes apoptosis in a variety of cancerous cells, but not in normal cells. In this review, we focused on the structure, expression and function of Par-4 in apoptotic signaling pathway. Functional domains of Par-4 include two nuclear localization sequences (NLS), a leucine zipper (LZ) domain, a nuclear export sequence (NES) and selective for apoptosis in cancer cell (SAC) domain. Many studies have underlined the importance of Par-4 in preventing cancer development. The activity of Par-4 is differently regulated by localization of intracellular and extracellular Par-4. Intracellular Par-4 inhibits Akt- and NF-κB-mediated cell survival pathways and downregulates Bcl-2 expression. Extracellular Par-4 activates the extrinsic apoptotic pathway by binding to cell surface receptor GRP78, a stress response protein that is in the endoplasmic reticulum (ER). Endogenous Par-4 sensitizes cancer cells to various apoptotic stimuli, while exogenous Par-4 enhances SAC domain-dependent apoptosis in cancer cells, but not normal cells. Therefore, Par-4 is an attractive target for cancer therapy.

• Journal of Life Science
• /
• v.26 no.5
• /
• pp.614-619
• /
• 2016

The prostate-apoptosis-response-gene-4 (Par-4) protein has been identified as an effector of cell death in response to various apoptotic stimuli in prostate cancer cells. We found that overexpression of Par-4 by stable transfection inhibits cell migration and invasion in Caki cells. The expression of various matrix metalloproteinases (MMPs) has been implicated in the invasion and metastasis of cancer cells. In this study, we investigated whether ectopic expression of Par-4 modulates MMP-2 expression and activity in human renal carcinoma Caki cells. We found that overexpression of Par-4 markedly inhibited MMP-2 activity, but not MMP-9 activity. However, loss of the leucine zipper domain of Par-4 (Par-4 ΔLZ#1 and #2) did not inhibit MMP-2 activity. Further, knock-down of Par-4 with the corresponding siRNA resulted in increased invasion and metastasis of renal carcinoma Caki cells. Interestingly, overexpression or knock-down of Par-4 did not affect the expression levels of MMP-2 mRNA. Taken together, our findings suggest that Par-4 may inhibit MMP-2 activity through its post-transcriptional regulation in renal carcinoma Caki cells.