Action of Protein Disulfide Isomerase on Proinsulin Exit from Endoplasmic Reticulum of Pancreatic β-Cells

Abstract

Background:We have examined the effect of PDI knockdown in pancreatic ␤-cells. Results: Upon knockdown, proinsulin oxidation to form native disulfide bonds is enhanced and accompanied by improved exit from the ER with increased total insulin secretion. Conclusion:We hypothesize that PDI exhibits unfoldase activity for proinsulin. Significance: Unexpectedly, PDI increases retention of proinsulin within the ER of pancreatic ␤-cells.

Proinsulin Intermolecular Interactions during Secretory Trafficking in Pancreatic β Cells

“…Conditions that adversely affect ER export of proinsulin, including dysregulated mRNA translation, impaired ER-to-Golgi traffic (3,4), or alteration of the ER environment that impairs rate/efficiency of proinsulin monomer folding (5,6) promote insulin deficiency and glucose intolerance. Conversely, enhanced exit from the ER is correlated with increased protein entry into forming granules, (7) which, in ␤ cells, increases insulin production (8). These findings seem to imply that proinsulin egress from the ER is rate-limiting for insulin production.…”

ER-associated degradation is required for vasopressin prohormone processing and systemic water homeostasis

“…The notion that rather than prevent, the formation of proAVP aggregates or polymers. Given our own data and the current literature (3,33,56), we propose 2 possible modes of action for PDI in the context of proAVP ERAD, as illustrated in Figure 9C. PDI may act to reduce and unfold proAVP targeted for ERAD, which may result in the generation of unfolded substrates with highly reactive cysteine thiols.…”

“…Studies have suggested that PDI subserves a pro-folding role in WT cells (30,55), and more recently, studies have demonstrated that PDI, but not other members of the PDI family (ERp57 and ERdj5), may also participate in ERAD by feeding reduced protein substrates (e.g., Akita proinsulin and thyroglobulin) to the ERAD machinery (3,33,56 (20). Single-guide RNA (sgRNA) oligonucleotides were designed for human HRD1 (5′-GGA-CAAAGGCCTGGATGTAC).…”

“…PDI can act as a protein chaperone to help protein folding and stability (30,32) by interacting with substrates at different stages of the folding process, i.e., unfolded, partially folded, or native state (32), and also has a role in ERAD. Recent studies have suggested that PDI in the ER is able to reduce proinsulin disulfide bonds (33) and in this way may prime proinsulin Akita-mutant protein to unfold for Sel1L-Hrd1 ERAD (3). Adding further complexity to the function of PDI, another study suggested that the role of PDI in ERAD may be substrate dependent (34).…”

Impact of exposure to low concentrations of nitric oxide on protein profile in murine and human pancreatic islet cells

“…[27][28][29] Likewise, the unfolded protein response induced by NO could be also due to the regulation of protein disulfide isomerases (PDIA6 and P4HB (PDIA1) in HPI improving the protein folding including insulin for its accurate secretion. 30 Increments in ATP5A1, P4HB and HSPA8 and other proteins such as HSPD1, ATP6V1B1 and HSP90B1 were also detected in NO-treated, serum-deprived mouse pancreatic islets when compared with islets cultured under serum withdrawal, despite having used a different strategy for analyzing the spots (Table S1 and Figure S1). It is also relevant to note the existence of species differences in keratin expression.…”