چکیده (انگلیسی):

Background: The transcription factors NFATc1 and PU.1 play important roles in osteoclast development.
NFATc1 and PU.1 transactivate osteoclast-specific gene expression and a deficiency in NFATc1 or PU.1
genes causes osteopetrosis due to an insufficient development of osteoclasts. However, the existence of
cross-regulation between NFATc1 and PU.1 is largely unknown. In the present study, the role of PU.1 in
NFATc1 expression was investigated.
Methods: Osteoclasts were generated from mouse bone marrow cells. PU.1 knockdown was performed
with siRNA introduction. The mRNA levels in siRNA-introduced cells were determined by quantitative
RT-PCR. The involvement of PU.1 in the NFATc1 promoter was analyzed by using a chromatin immunoprecipitation
(ChIP) assay and a reporter assay. Retrovirus vector was used for enforced expression of
PU.1.
Results: Introduction of PU.1 siRNA into bone marrow-derived osteoclasts resulted in a decrease in
NFATc1 mRNA level. A ChIP assay showed that PU.1 bound to the NFATc1 promoter in osteoclasts. NFATc1
promoter activity was reduced in PU.1 knockdown cells as assessed by a reporter assay. PU.1 siRNA
introduction also downregulated the expression of osteoclast-specific genes and tartrate resistant acid
phosphatase (TRAP) activity. Enforced expression of PU.1 using a retrovirus vector increased NFATc1
expression and TRAP activity. When NFATc1 expression was knocked down by using siRNA, the induction
of osteoclast-specific genes and TRAP-positive cells was suppressed without affecting the expression
level of PU.1.
Conclusions: These results indicate that PU.1 is involved in osteoclast development by transactivating
NFATc1 expression via direct binding to the NFATc1 promoter.