Cloning and quantitative determination of the human Ca2+/calmodulin-dependent protein kinase II (CaMK II) isoforms in human beta cells.
OBJECTIVE
The Ca2+/calmodulin-dependent protein kinase II (CaMK II) is highly expressed in pancreatic islets and associated with insulin secretion vesicles. The suppression of CaMK II disturbs insulin secretion and insulin gene expression. There are four isoforms of CaMK II, alpha to delta, that are expressed from different genes in mammals. Our aim was to identify the isoforms of CaMK II expressed in human beta cells by molecular cloning from a human insulinoma cDNA library and to assess its distribution in humans.


METHODS
The previously unknown complete coding sequences of human CaMK IIbeta and the kinase domain of CaMK IIdelta were cloned from a human insulinoma cDNA library. Quantitative determination of CaMK II isoform mRNA was carried out in several tissues and beta cells purified by fluorescence activated cell sorting and compared to the housekeeping enzyme pyruvate dehydrogenase.


RESULTS
We found CaMK IIbeta occurred in three splice variants and was highly expressed in endocrine tissues such as adrenals, pituitary and beta cells. Liver showed moderate expression but adipose tissue or lymphocytes had very low levels of CaMK IIbeta-mRNA. In human beta cells CaMK IIbeta and delta were expressed equally with pyruvate dehydrogenase whereas tenfold lower expression of CaMK IIgamma and no expression of CaMK IIalpha were found.


CONCLUSIONS
Although CaMK IIdelta is ubiquitously expressed, CaMK IIbeta shows preferential expression in neuroendocrine tissues. In comparison with the expression of a key regulatory enzyme in glucose oxidation, pyruvate dehydrogenase, two of the four CaM kinases investigated are expressed at equally high levels, which supports an important role in beta-cell physiology. These results provide the basis for exploring the pathophysiological relevance of CaMK IIbeta in human diabetes.
Rochlitz
H
H
Department of Internal Medicine, University Hospital Bergmannsheil, University of Bochum, Germany.
Voigt
A
A
Lankat-Buttgereit
B
B
Göke
B
B
Heimberg
H
H
Nauck
M A
MA
Schiemann
U
U
Schatz
H
H
Pfeiffer
A F
AF
D000273:Adipose Tissue / Q000201:enzymology; D000595:Amino Acid Sequence; D001483:Base Sequence; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000032:analysis* / Q000737:chemistry / Q000235:genetics*; D003001:Cloning, Molecular; D015870:Gene Expression; D015723:Gene Library; D006801:Humans; D007340:Insulinoma / Q000737:chemistry; D007515:Islets of Langerhans / Q000201:enzymology*; D007527:Isoenzymes / Q000032:analysis* / Q000235:genetics*; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000201:enzymology; D010190:Pancreatic Neoplasms / Q000737:chemistry; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis; D017385:Sequence Homology
D007527:Isoenzymes; D012333:RNA, Messenger; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases