Identification of Pirh2D, an Additional Novel Isoform of Pirh2 Ubiquitin Ligase.

Pirh2 is an E3 ubiquitin ligase that promotes tumor suppressor p53 ubiquitination and proteasomal degradation. Recently, we have reported the identification and characterization of two novel isoforms of Pirh2 named Pirh2B and Pirh2C and accordingly, reclassified the full-length Pirh2 as Pirh2A. Both Pirh2B and C negatively regulate p53 and also exhibit interactions with MDM2. Here, we report the existence of an additional Pirh2 isoform that we have named Pirh2D. Translation of nucleotide sequence predicts Pirh2D to be composed of 75 amino acids with a molecular mass of 8493.74 Da. Thus, Pirh2D is a truncated protein that harbors 67 amino-terminal amino acids identical to those in Pirh2A, Pirh2B and Pirh2C and has 8 additional unique amino acids at the carboxyl-terminal end. Further studies are needed to determine whether Pirh2D also functions in a manner similar to Pirh2B and Pirh2C.