Induction of ER stress by variants of the prohormone convertase 1 (PCSK1)-gene

Background & Hypotheses: Prohormone convertase 1 encoded by the PCSK1 gene processes and activates multiple prohormones such as proinsulin in the pancreas. Some variants within this gene are associated with polygenic obesity and rare mutations cause childhood obesity and abnormal glucose homeostasis.

The unfolded protein response (UPR) is a cellular mechanism protecting the cell against the effects of an accumulation of falsely folded proteins in the endoplasmic reticulum (ER). A continuously activated UPR leads to apoptosis.

We hypothesized that variants of PCSK1 can lead to falsely folded proteins and subsequently harm ß-cells by inducing ER-stress and apoptosis. This could link PCSK1 variants to diabetes, the most common comorbidity of obesity.

Methods: We used HEK-293 cells to investigate the influence of the PCSK1 missense variants S24C, R80Q, N221D, S307L and the exon missing variant ΔEx8 on maturation and secretion by western blot.

ER stress and UPR mediators like (P)eIF2α and ATF6 were evaluated by western blot and PCR.

Finally, the effect of overexpressed variants on apoptosis was assessed by flow cytometry.

Results: The S24C, R80Q and N221D variants were expressed and secreted like the wild type; no secretion was detectable for ΔEx8. We found a reduced maturation and secretion of S307L.

UPR and apoptosis markers were not elevated and the flow cytometry analysis did not show apoptosis induction.

Conclusion: Disturbances in maturation and secretion could be shown for ΔEx8 and S307L. Though, our data implicates that the variants have no effect on the induction of ER stress or apoptosis in HEK-293 cells.