Human islets of Langerhans express the delta(c) isoform of calcium/calmodulin-dependent protein kinase II

Background There is considerable evidence that calcium/calmodulin-dependent protein kinase II (CaM kinase II) plays a key role in insulin secretion an d the enzyme provides a candidate gene for Type 2 diabetes. Since several i soforms of the enzyme exist, it is essential to define which are expressed by the beta-cell. Methods A human islet cDNA library in lambda ZAPII was screened with a prob e for the 5'-end of human gamma CaM kinase II. Since this region is very ho mologous between the different isoforms, it is expected that isoforms other than gamma would be detected. From each of the six positive clones obtaine d, DNA was prepared and subjected to PCEY using primers spanning the variab le region in which the main variability of CaM kinase II isoforms resides. PCR products were purified and sequenced in both directions. The beta-cell line MING was screened for CaM kinase II delta by reverse transcriptase-pol ymerase chain reaction (RT-PCR) and by Western blotting. Results The sequences of five of the human islet PCR products indicated tha t the clones corresponded to the gamma(B) isoform whose expression in human islets we have previously documented. The other PCR product, however, gave a sequence containing the variable domains II and VII characteristic of Ca M kinase II delta. This sequence and the absence of other domains in this r egion identified the clone as CaM kinase II delta(C). The expression of CaM kinase II delta in MING beta-cells was confirmed by RT-PCR and by Western blotting. Conclusions Human islets of Langerhans express the delta(C) isoform of CaM kinase II. Copyright (C) 1999 John Wiley & Sons, Ltd.