Tetramer formation by the caspase‐activated fragment of the Par‐4 tumor suppressor

• Published in: The FEBS journal Vol. 286; no. 20; pp. 4060 - 4073
• Main Authors: Clark, Andrea M., Ponniah, Komala, Warden, Meghan S., Raitt, Emily M., Smith, Benjamin G., Pascal, Steven M.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.10.2019
• Subjects: Apoptosis; Cancer; Caspase; Cell proliferation; coiled coil; disorder; Fluorescence; Ionic strength; Ions; Light scattering; Nuclei (cytology); par-4; Photon correlation spectroscopy; Prostate; Scattering; Size exclusion chromatography; Sodium chloride; Spectroscopy; tumor suppressor; Tumor suppressor genes; Tumors; Tyrosine; par-4; apoptosis; tumor suppressor; disorder; coiled coil
• ISSN: 1742-464X; 1742-4658
• DOI: 10.1111/febs.14955

The prostate apoptosis response‐4 (Par‐4) tumor suppressor can selectively kill cancer cells via apoptosis while leaving healthy cells unharmed. Full length Par‐4 has been shown to be predominantly intrinsically disordered in vitro under neutral conditions. As part of the apoptotic process, cellular Par‐4 is cleaved at D131 by caspase‐3, which generates a 24 kDa C‐terminal activated fragment (cl‐Par‐4) that enters the nucleus and inhibits pro‐survival genes, thereby preventing cancer cell proliferation. Here, the structure of cl‐Par‐4 was investigated using CD spectroscopy, dynamic light scattering, intrinsic tyrosine fluorescence, and size exclusion chromatography with mutli‐angle light scattering. Biophysical characterization shows that cl‐Par‐4 aggregates and is disordered at low ionic strength. However, with increasing ionic strength, cl‐Par‐4 becomes progressively more helical and less aggregated, ultimately forming largely ordered tetramers at high NaCl concentration. These results, together with previous results showing induced folding at acidic pH, suggest that the in vivo structure and self‐association state of cl‐Par‐4 may be strongly dependent upon cellular environment. The prostate apoptosis response‐4 (Par‐4) tumor suppressor has been shown to be largely disordered in vitro. Cleavage by caspase‐3, producing a C‐terminal 24 kDa fragment (cl‐Par‐4), is necessary for induction of apoptosis by Par‐4. Here, we show that while cl‐Par‐4 is largely disordered and aggregated under neutral conditions, at high ionic strength, cl‐Par‐4 forms a highly helical tetramer that may play a role in nuclear translocation and in the induction of apoptosis.