Evaluating the Role of Piccolo Splice Variants in Regulated Secretion of Insulin from Rat Pancreatic Cells

Abstract

Secretion of insulin from pancreatic beta‐cells is required for proper glucose homeostasis; however, the molecular mechanism of insulin granule exocytosis has not been fully elucidated. In pancreatic beta‐cells, glucose‐induced insulin secretion is synergistically potentiated through an Epac2‐Rim2‐Piccolo signaling response mechanism. Both Piccolo and Rim2 were originally identified as active zone proteins in neurons and have been shown to regulate synaptic vesicle cycling and neurotransmitter signaling. A recent study showed that a number of active zone proteins, including Rim2 and Piccolo, are downregulated in human pancreatic islet cells isolated from patients with type 2 diabetes (T2D). Understanding the role of Piccolo in regulated secretion of insulin may provide valuable insights into the causes of T2D. The C‐terminal region of Piccolo contains a Ca2+‐binding C2A domain. It is likely that Piccolo may regulate secretion from insulin granule vesicles by serving as a Ca2+‐sensor. Alternative splicing of exons within the coding region of the C2A domain results in an exon‐skipping event generating either a splice variant that lacks the 27‐nucleotide exon 16 (short C2A) or a variant that retains this exon (long C2A). Exclusion of the 9 amino acid residue sequence in the short C2A domain results in enhanced Ca2+‐binding affinity. In this study, we sought to examine the differential roles of the short C2A and long C2A variants in Ca2+‐mediated insulin secretion from rat INS‐832/13 pancreatic beta‐cells. We demonstrate that INS‐832/13 cells express both long and short variants of the C2A domain and real‐time qPCR demonstrated differential expression of the variants. In addition, we examined the effects of overexpression of the short and long C2A domains on glucose‐stimulated insulin secretion from INS‐832/13 cells.Support or Funding InformationMaximizing Access to Research Careers Program at Fort Lewis College (NIH‐T34GM092711)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.