Immunohistochemical localization of eight phospholipase C isozymes in pancreatic islets of the mouse

Abstract

The possible involvement of phospholipase C (PLC) in the regulation of insulin secretion is not clearly understood and neither its isozymes expressed nor cellular localization in the pancreatic islets is known. By using specific monoclonal antibodies, we have investigated the expression and localization of eight different PLC isozymes, β1, β2, β3, β4, γ1, γ2, δ1, and δ2, in the pancreatic islets of adult mice. Immunohistochemical analysis carried out on paraffin embedded sections showed a distinct pattern of expression for each of the PLC isozymes. In the central part of the islets containing β cells, a high level of β4 and moderate levels of β3 and γ1 were expressed, whereas PLC-β1 and −γ1 were abundantly expressed in the exocrine pancreas. These results demonstrated the heterogeneity in expression of the phospholipase C isozymes in pancreatic islets. It is conceivable that these isozymes are coupled to different receptors and perform selective tasks in the regulation of insulin secretion for glucose homeostasis.

Phospholipase C‐β1 potentiates glucose‐stimulated insulin secretion

“…First, we confirmed the expression of PLC-b1 by performing immunohistochemistry analysis. Consistent with the previously published data (22,33), PLC-b1 was localized in both nucleus and cytosol in islet cells and was also detected in the nucleus in exocrine cells. However, a and d cells were either negative or weakly positive for PLC-b1 staining (Supplemental Fig.…”

“…The 4 PLC-b isozymes, PLC-b1 to -b4, differ in expression pattern and regulation. However, studies of PLC-b isozyme expression patterns have been controversial (22)(23)(24), with additional investigations necessary to determine the expression levels of individual PLC-b isozymes. First, to confirm the PLC-b isozyme expressed in pancreatic b cells, we assessed PLC-b isozyme expression patterns in MIN6 cells (55), a mouse pancreatic b-cell line, and in mouse primary pancreatic islets in which b cells are the major cell type by Western blotting (Fig.…”

Olfactory receptors are expressed in pancreatic β-cells and promote glucose-stimulated insulin secretion

“…To examine which isoform(s) of PLC is involved in OA-induced GSIS, we knocked down several PLC isoforms in MIN6 cells, followed by testing for the presence of GSIS enhancement in response to OA. We selected PLC isoforms reported to be expressed in pancreatic islets 26 or a β-cell line 27 and prepared specific siRNAs for each isoform. Specific siRNAs for Plc-β1 , -β3 , -β4 , -γ1 and -δ4 significantly suppressed the expressions of the corresponding Plc isoforms in MIN6 cells (Supplementary Fig.…”

Oscillatory control of insulin secretion

“…Whereas IP 3 mobilizes Ca 2+ from the ER, DAG plays an important role as activator of protein kinase C (PKC). PLC activity was early detected in rodent islets (Schrey and Montague, 1983;Dunlop and Larkins, 1986), and subsequent analyses have demonstrated islet expression of several PLC-β, -γ, and -δ isozymes Zawalich et al, 1995;Gasa et al, 1999;Zawalich and Zawalich, 2000;Kim et al, 2001a;Kim et al, 2001b). The importance of PLC activity for insulin secretion is underlined by the fact that the enzyme is activated not only after exposure of islets and β-cells to various G-protein coupled receptor stimuli, such as acetylcholine/carbachol (Best and Malaisse, 1983;Hellman and Gylfe, 1986a;Best et al, 1987;Biden et al, 1987;Gilon and Henquin, 2001) and ATP (Gylfe and Hellman, 1987;Blachier and Malaisse, 1988), but also after exposure to glucose (Axen et al, 1983;Best and Malaisse, 1983;Laychock, 1983;Montague et al, 1985) and depolarizing agents (Laychock, 1983;Mathias et al, 1985;Best et al, 1987;Biden et al, 1987;Zawalich and Zawalich, 1988 (Prentki et al, 1988;Gylfe, 1991;Hellman et al, 1992;Theler et al, 1992;Miura et al, 1996) and these oscillations are characterized by a much shorter period than the glucose-induced, slow oscillations described above.…”