Regulation of alkaline phosphatase promoter activity by forkhead transcription factor FKHR

Tissue-Nonspecific Alkaline Phosphatase, a Possible Mediator of Cell Maturation: Towards a New Paradigm

Alkaline phosphatase (ALP) is a ubiquitous membrane-bound glycoprotein capable of providing inorganic phosphate by catalyzing the hydrolysis of organic phosphate esters, or removing inorganic pyrophosphate that inhibits calcification. In humans, four forms of ALP cDNA have been cloned, among which tissue-nonspecific ALP (TNSALP) (TNSALP) is widely distributed in the liver, bone, and kidney, making it an important marker in clinical and basic research. Interestingly, TNSALP is highly expressed in juvenile cells, such as pluripotent stem cells (i.e., embryonic stem cells and induced pluripotent stem cells (iPSCs)) and somatic stem cells (i.e., neuronal stem cells and bone marrow mesenchymal stem cells). Hypophosphatasia is a genetic disorder causing defects in bone and tooth development as well as neurogenesis. Mutations in the gene coding for TNSALP are thought to be responsible for the abnormalities, suggesting the essential role of TNSALP in these events. Moreover, a reverse-genetics-based study using mice revealed that TNSALP is important in bone and tooth development as well as neurogenesis. However, little is known about the role of TNSALP in the maintenance and differentiation of juvenile cells. Recently, it was reported that cells enriched with TNSALP are more easily reprogrammed into iPSCs than those with less TNSALP. Furthermore, in bone marrow stem cells, ALP could function as a "signal regulator" deciding the fate of these cells. In this review, we summarize the properties of ALP and the background of ALP gene analysis and its manipulation, with a special focus on the potential role of TNSALP in the generation (and possibly maintenance) of juvenile cells.

Regulation of PGC-1 promoter activity by protein kinase B and the forkhead transcription factor FKHR

Peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC-1) plays a major role in mediating hepatic gluconeogenesis in response to starvation, during which PGC-1 is induced by the cyclic AMP response element binding protein. Although it is observed that insulin counteracts PGC-1 transcription, the mechanism by which insulin suppresses the transcription of PGC-1 is still unclear. Here, we show that forkhead transcription factor FKHR contributes to mediating the effects of insulin on PGC-1 promoter activity. Reporter assays demonstrate that insulin suppresses the basal PGC-1 promoter activity and that coexpression of protein kinase (PK)-B mimics the effect of insulin in HepG2 cells. Insulin response sequences (IRSs) are addressed in the PGC-1 promoter as the direct target for FKHR in vivo. Coexpression of FKHR stimulates the PGC-1 promoter activity via interaction with the IRSs, while coexpression of FKHR (3A), in which the three putative PKB sites in FKHR are mutated, mainly abolishes the suppressive effect of PKB. Whereas deletion of the IRSs prevents the promoter stimulation by FKHR, that activity is still partially inhibited by insulin. These results indicate that signaling via PKB to FKHR can partly account for the effect of insulin to regulate the PGC-1 promoter activity via the IRSs.