Abstract
Activator protein-1 (AP-1) is an important bZIP transcription factor that regulates a series of physiological processes by specifically activating transcription of several genes, and one of its well-chartered functions in mammals is participating in bone mineralization. We isolated and cloned the complete cDNA of a Jun/AP-1 homolog from Pinctada fucata and called it Pf-AP-1. Pf-AP-1 had a highly conserved bZIP region and phosphorylation sites compared with those from mammals. A tissue distribution analysis showed that Pf-AP-1 was ubiquitously expressed in P. fucata and the mRNA level of Pf-AP-1 is extremely high in mantle. Pf-AP-1 expression was positively associated with multiple biomineral proteins in the mantle. The luciferase reporter assay in a mammalian cell line showed that Pf-AP-1 significantly up-regulates the transcriptional activity of the promoters of KRMP, Pearlin, and Prisilkin39. Inhibiting the activity of Pf-AP-1 depressed the expression of multiple matrix proteins. Pf-AP-1 showed a unique expression pattern during shell regeneration and pearl sac development, which was similar to the pattern observed for biomineral proteins. These results suggest that the Pf-AP-1 AP-1 homolog is an important transcription factor that regulates transcription of several biomineral proteins simultaneously and plays a role in P. fucata biomineralization, particularly during pearl and shell formation.
Highlights
Jun was once regarded as the Activator protein-1 (AP-1) gene[7,8]
Many of the modified Pf-AP-1 residues were highly conserved compared with those of human AP-1, residues phosphorylated by p21 protein-activated kinase 2 (PAK2; aa 7, 76, and 80), MAPK8, polo-like kinase 3 (PLK3; aa 51 and 61), dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 2 (DYRK2; aa 221), and glycogen synthase kinase 3-beta (GSK3-β ; aa 217 and 221), whereas aa 44 may be a potential acetylation site
Jun is a central component of all AP-1 complexes and forms homodimers and heterodimers with all other AP-1 family members
Summary
Jun was once regarded as the AP-1 gene[7,8]. Jun is called Jun/AP-1 or AP-1, in protein and antibody products[9]. There are many complex post-transcriptional modifications of Jun, which regulates Jun functions in cellular processes and diseases[10] It is antagonistic with JunB during fibroblast, keratinocyte, and granulocyte differentiation. Several studies have demonstrated that Jun is a key transcription factor during bone formation and reconstruction. The functions of more than 20 biomineral proteins have been studied, but little is known about the regulatory mechanism for their expression. We cloned and characterized the complete cDNA sequence of AP-1 from P. fucata and performed a series of analyses to investigate whether AP-1 could influence pearl and shell formation by regulating biomineral protein transcription. The AP-1 and biomineral protein gene expression patterns during shell regeneration and pearl sac development were determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis
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