Anti-PCSK1 monoclonal antibody, clone 4E3

Transcription factor cAMP responsive element-binding protein 3 like 1 (Creb3l1) is a non-classical endoplasmic reticulum stress molecule that is emerging as an important component for cellular homeostasis, particularly within cell types with high peptide secretory capabilities. We have previously shown that Creb3l1 serves an important role in body fluid homeostasis through its transcriptional control of the gene coding for antidiuretic hormone arginine vasopressin in the neuropeptide-rich magnocellular neurones of the supraoptic nucleus. In response to osmotic stimuli such as dehydration, vasopressin magnocellular neurones undergo remarkable transcriptome changes, including increased Creb3l1 expression, to ensure that the supply of vasopressin meets demand. To determine where else Creb3l1 fits into the secretory cell supply chain, we performed RNA-sequencing of Creb3l1 knockdown anterior pituitary mouse corticotroph cell line AtT20. The target chosen for further investigation was Pcsk1, which encodes proprotein convertase enzyme 1 (PC1/3). PC1/3 is crucial for processing of neuropeptides and peptide hormones such as pro-opiomelanocortin (POMC), proinsulin, proglucagon, vasopressin and oxytocin. Viral manipulations in supraoptic nuclei by over-expression of Creb3l1 increased Pcsk1, whereas Creb3l1 knockdown decreased Pcsk1 expression. In vitro promoter activity and binding studies showed that Creb3l1 was a transcription factor of the Pcsk1 gene binding directly to a G-box motif in the promoter. In the dehydrated rat anterior pituitary, Creb3l1 and Pcsk1 expression decreased in parallel compared to control, supporting our findings from manipulations in AtT20 cells and the supraoptic nucleus. No relationship was observed between Creb3l1 and Pcsk1 expression in the neurointermediate lobe of the pituitary, indicating a different mechanism of PC1/3 synthesis by these POMC-synthesising cells. Therefore, Creb3l1, by regulating the expression of Pcsk1, does not control the processing of POMC peptides in the intermediate lobe.

The postnatal proliferation and maturation of insulin-secreting pancreatic beta-cells are critical for glucose metabolism and disease development in adults. Elucidation of the molecular mechanisms underlying these events will be beneficial to direct the differentiation of stem cells into functional beta-cells. Maturation of beta-cells is accompanied by increased expression of MafA, an insulin gene transcription factor. Transcriptome analysis of MafA knockout islets revealed MafA is required for the expression of several molecules critical for beta-cell function, including Glut2, ZnT8, Granuphilin, Vdr, Pcsk1 and Urocortin 3, as well as Prolactin receptor (Prlr) and its downstream target Cyclin D2 (Ccnd2). Inhibition of MafA expression in mouse islets or beta-cell lines resulted in reduced expression of Prlr and Ccnd2, and MafA transactivated the Prlr promoter. Stimulation of beta-cells by prolactin resulted in the phosphorylation and translocation of Stat5B and an increased nuclear pool of Ccnd2 via Prlr and Jak2. Consistent with these results, the loss of MafA resulted in impaired proliferation of beta-cells at 4 weeks of age. These results suggest that MafA regulates the postnatal proliferation of beta-cells via prolactin signaling.