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Dynamics of Glucose-Induced Localization of PKC Isoenzymes in Pancreatic ß-Cells

Diabetes-Related Changes in the GK Rat

¹ Endocrinology and Metabolism Service, Department of Medicine, The Hebrew University, Hadassah Medical Center, Jerusalem, Israel
² Department of Molecular Medicine, Endocrine and Diabetes Unit, Karolinska Institute and Hospital, Stockholm, Sweden

Address correspondence and reprint requests to Rafael Nesher, PhD, Endocrinology and Metabolism Service, Hebrew University, Hadassah Medical Center, P.O. Box 12000, 91120 Jerusalem, Israel. E-mail: rafael.nesher{at}huji.ac.il

Abbreviations: PKC, protein kinase C

Glucose metabolism affects most major signal pathways in pancreatic ß-cells. Multiple protein kinases, including protein kinase C (PKC) isoenzymes, are involved in these effects; however, their role is poorly defined. Moreover, the dynamics of kinase isoenzyme activation in reference to the biphasic insulin secretion is unknown. In perfused pancreas of Wistar rats, PKC staining was strongly associated with insulin staining, jointly accumulating in the vicinity of the plasma membrane during early first-phase insulin response. The signal declined before the onset of second phase and reappeared during second-phase insulin release as foci, only weekly associated with insulin staining; this signal persisted for at least 15 min after glucose stimulation. In the GK rat, glucose had minimal effect on ß-cell PKC. In control ß-cells, PKC stained as granulated foci with partial association with insulin staining; however, no glucose-dependent translocation was observed. In the GK rat, only minimal staining for PKC was observed, increasing exclusively during early first-phase secretion. In Wistar ß-cells, PKC concentrated near the nucleus, strongly associated with insulin staining, with dynamics resembling that of biphasic insulin response, but persisting for 15 min after cessation of stimulation. In GK rats, PKC staining lacked glucose-dependent changes or association with insulin. PKC exhibited bimodal dynamics in control ß-cells: during early first phase, accumulation near the cell membrane was observed, dispersing thereafter. This was followed by a gradual accumulation near the nucleus; 15 min after glucose stimulus, clear PKC staining was observed within the nucleus. In the GK rat, a similar response was only occasionally observed. In control ß-cells, glucose stimulation led to a transient recruitment of PKC, associated with first-phase insulin release, not seen in GK ß-cell. Data from this and related studies support a role for PKC in glucose-induced insulin granule recruitment for exocytosis; a role for PKC in activation of insulin granules for exocytosis and/or in the glucose-generated time-dependent potentiation signal for insulin release; and a dual function for PKC in initiating insulin release and in a regulatory role in the transcriptional machinery. Furthermore, diminished levels and/or activation of PKC, PKC, PKC, and PKC could be part of the defective signals downstream to glucose metabolism responsible for the deranged insulin secretion in the GK rat.

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