R. Nissi et al., Prolyl 4-hydroxylase isoenzymes I and II have different expression patterns in several human tissues, J HIST CYTO, 49(9), 2001, pp. 1143-1153
Prolyl 4-hydroxylase plays a central role in the synthesis of all collagens
. We have previously reported that the recently identified Type II isoenzym
e is its main form in chondrocytes and possibly in capillary endothelial ce
lls, while Type I is the main form in many other cell types. We report here
that the Type II isoenzyme is clearly the main form in capillary endotheli
al cells and also in cultured umbilical vein endothelial cells, whereas no
Type I isoenzyme could be detected in these cells by immunostaining or West
ern blotting. The Type II isoenzyme was also the main form in cells of the
developing glomeruli in the fetal kidney and tubular structures of collecti
ng duct caliber in both fetal and adult kidney, in occasional sinusoidal st
ructures and epithelia of the bile ducts in the liver, and in some cells of
the decidual membrane that probably represented invasive cytotrophoblasts
in the placenta. Osteoblasts in a fetal calvaria, i.e., a bone developing b
y intramembranous ossification, stained strongly for both types of isoenzym
e. The Type I isoenzyme was the main form in undifferentiated interstitial
mesenchymal cells of the developing kidney, for example, and in fibroblasts
and fibroblastic cells in many tissues. Skeletal myocytes and smooth muscl
e cells appeared to have the Type I isoenzyme as their only prolyl 4-hydrox
ylase form. Hepatocytes expressed small amounts of the Type I enzyme and ve
ry little if any Type II, the Type I expression being increased in malignan
t hepatocytes and cultured hepatoblastoma cells. The data suggest that the
Type I isoenzyme is expressed especially by cells of mesenchymal origin and
in developing and malignant tissues, whereas the Type II isoenzyme is expr
essed, in addition to chondrocytes and osteoblasts, by more differentiated
cells, such as endothelial cells and cells of epithelial structures.