Characterization of novel elongated Parvulin isoforms that are ubiquitously expressed in human tissues and originate from alternative transcription initiation

In this study we confirm by RT-PCR the existence of a longer Parvulin isoform expressed in all tissues examined so far. This isoform contains a 5' extension including a 75 bp extended open reading frame with two coupled SNPs leading to amino acid substitutions Q16R and R18S. About 1% of all Parvulin mRNAs include the novel extension as quantified by real-time PCR. The human Parvulin promoter is TATA-less and situated in a CpG island typical for house keeping genes. Thus, different Parvulin mRNAs seem to arise by alternative transcription initiation. N-terminally extended Parvulin is protected from rapid proteinaseK degradation. In HeLa and HepG2 cell lysates two protein species of about 17 and 28 KDa are detected by an antibody against an epitope within the N-terminal extension. These two bands are also recognized by an antibody towards the PPIase domain of Parvulin. The longer Parvulin protein is encoded by the human genome but absent from rodent, bovine and non-mammalian genomes.Due to its molecular weight of 16.6 KDa we denote the novel Parvulin isoform as Par17 following the E. coli Par10 and human Par14 nomenclature. The N-terminal elongation of Par17-QR and Par17-RS suggests these isoforms to perform divergent functions within the eukaryotic cell than the well characterized Par14.Members of the parvulin family of peptidyl prolyl cis/trans isomerases (EC 5.2.1.8) are involved in mitotic regulatory mechanisms and cell proliferation [1-4]. The human genome only encodes two parvulin proteins – Pin1 and Parvulin. Pin1 is a well studied mitotic regulator involved in cell cycle and transcriptional regulation [1,4,5]. Overexpression of Pin1 was found in several tumor types [6,7]; inhibition of this enzyme leads to apoptosis in a Ras-transformed cell line [8]. The second member of the parvulin PPIase family, the 14 KDa protein Parvulin14 [9,10] (Par14 or PIN4), is assumed to be involved in cell cycle progression or chromatin remodeling [11,12]. Pin1 and Par14 sequences