Differential processing of pro-glucose-dependent insulinotropic polypeptide in gut

Abstract

Glucose-dependent insulinotropic polypeptide (GIP) is a hormone released from enteroendocrine K cells in response to meals. Posttranslational processing of the precursor protein pro-GIP at residue 65 by proprotein convertase subtilisin/kexin type 1 (PC1/3) in gut K cells gives rise to the established 42-amino-acid form of GIP (GIP1–42). However, the pro-GIP peptide sequence contains a consensus cleavage site for PC2 at residues 52–55 and we identified PC2 immunoreactivity in a subset of K cells, suggesting the potential existence of a COOH-terminal truncated GIP isoform, GIP1–30. Indeed a subset of mouse and human K cells display GIP immunoreactivity with GIP antibodies directed to the mid portion of the peptide, but not with a COOH-terminal-directed GIP antibody, indicative of the presence of a truncated form of GIP. This population of cells represents ∼5–15% of the total GIP-immunoreactive cells in mice, depending on the region of intestine, and is virtually absent in mice lacking PC2. Amidated GIP1–30 and GIP1–42 have comparable potency at stimulating somatostatin release in the perfused mouse stomach. Therefore, GIP1–30 represents a naturally occurring, biologically active form of GIP.

Immunohistochemical characterisation of cells co-producing insulin and glucagon in the developing human pancreas

“…paraformaldehyde, embedded in paraffin and sectioned (Wax-it Histology Services, Vancouver, BC, Canada). Immunofluorescence staining was performed as previously described [9]. Non-commercial antibodies towards PDX1 were graciously provided by J. Habener (Massachusetts General Hospital, Boston, MA, USA) and C. Wright (Vanderbilt University, Nashville, TN, USA).…”

Overexpression of PAX4 reduces glucagon expression in differentiating hESCs

“…Immunostaining using primary and secondary antibodies described in Table 2, was performed as previously described. 4,35 Image acquisition and subsequent semi-automated nucleocentric quantification of immunostained slides was performed using an ImageXpress Micro TM automated microscope and associated MetaXpress NX software (Molecular Devices Corp.). Image acquisition of differentiating hESC cultures expressing eGFP was acquired using an Axiovert 200 microscope (Carl Zeiss Canada), Retiga 2000R CCD camera (Qimaging) controlled using Openlab 5.0 imaging software (Improvision).…”

Comparison of sub-chronic metabolic effects of stable forms of naturally occurring GIP(1-30) and GIP(1-42) in high fat fed mice

“…Recent studies by Fujita et al (2010a) have highlighted potential differential posttranslational processing of GIP in gut K-cells. Thus, processing of the precursor protein pro-GIP by prohormone convertase 1/3 (PC1/3) is known to yield the full-length GIP(1-42) molecule (Ugleholdt et al 2006).…”

“…Thus, processing of the precursor protein pro-GIP by prohormone convertase 1/3 (PC1/3) is known to yield the full-length GIP(1-42) molecule (Ugleholdt et al 2006). However, PC2 immunoreactivity has been identified in a sub-population of K-cells, which appears to result in the generation of the truncated GIP isoform, GIP(1-30) (Fujita et al 2010a). This distinct sub-set of cells represents w5-15% of the total GIP-immunoreactive cells in mice (Fujita et al 2010a).…”

“…However, PC2 immunoreactivity has been identified in a sub-population of K-cells, which appears to result in the generation of the truncated GIP isoform, GIP(1-30) (Fujita et al 2010a). This distinct sub-set of cells represents w5-15% of the total GIP-immunoreactive cells in mice (Fujita et al 2010a). Furthermore, immunohistochemical studies suggest that GIP is expressed in pancreatic islet a-cells and its secretion is under the control of PC2, again yielding the GIP(1-30) isoform (Fujita et al 2010b).…”