Activation of protein kinase C accelerates murine osteoclastogenesis partly via transactivation of RANK gene through functional AP-1 responsive element in RANK gene promoter

CpG Methylation of Receptor Activator NF-κB (RANK) Gene Promoter Region Delineates Senescence-Related Decrease of RANK Gene Expression

While the rapid decrease in estrogen is well known as the main cause of postmenopausal osteoporosis in women, the precise pathogenesis of senile osteoporosis in the elderly regardless of gender is largely unknown. The age-related epigenetic regulation of receptor activator NF-κB (RANK) gene expression was investigated with the use of a high-passaged mouse osteoclast progenitor cell line, RAW264.7, as an in vitro model of aging. In the RAW264.7 cells after repeated passages, receptor RANK expression was downregulated, resulting in decreased soluble RANK ligand (sRANKL)-induced osteoclastogenesis, expression of tartrate-resistant acid phosphatase-5b (TRAcP) and cathepsin K (CTSK). Methylation-specific PCR and bisulfite mapping revealed hypermethylation of CpG-loci located in the RANK gene promoter in multiple-passaged cells. ICON probe-mediated in situ assessment of methylated-cytosine at the CpG loci revealed an increase in the percentage of methylated RAW264.7 cells in the RANK gene in a passage-dependent manner. Conversely, upon treatment with demethylating agent 5-aza-2-deoxycytidine (5-aza-dC), high-passaged RAW264.7 cells displayed restored expression of the RANK gene, osteoclastogenesis, TRAcP and CTSK. Ex vivo cultures of splenic macrophages from young (10.5 W) and aged (12 M) mice also showed that CpG methylation was predominant in the aged animals, resulting in reduced RANK expression and osteoclastogenesis. Reduced RANK expression by age-related accumulation of DNA methylation, albeit in a limited population of osteoclast precursor cells, might be, at least in part, indicative of low-turnover bone characteristic of senile osteoporosis.

SHIP1 deficiency causes inflammation-dependent retardation in skeletal growth

Inflammation and skeletal homeostasis are closely intertwined. Inflammatory diseases are associated with local and systemic bone loss, and post-menopausal osteoporosis is linked to low-level chronic inflammation. Phosphoinositide-3-kinase signalling is a pivotal pathway modulating immune responses and controlling skeletal health. Mice deficient in Src homology 2-containing inositol phosphatase 1 (SHIP1), a negative regulator of the phosphoinositide-3-kinase pathway, develop systemic inflammation associated with low body weight, reduced bone mass, and changes in bone microarchitecture. To elucidate the specific role of the immune system in skeletal development, a genetic approach was used to characterise the contribution of SHIP1-controlled systemic inflammation to SHIP1-dependent osteoclastogenesis. Lymphocyte deletion entirely rescued the skeletal phenotype in Rag2 -/- /Il2rg -/- /SHIP1 -/- mice. Rag2 -/- /Il2rg -/- /SHIP1 -/- osteoclasts, however, displayed an intermediate transcriptomic signature between control and Rag2 +/+ /Il2rg +/+ /SHIP1 -/- osteoclasts while exhibiting aberrant in vitro development and functions similar to Rag2 +/+ /Il2rg +/+ /SHIP1 -/- osteoclasts. These data establish a cell-intrinsic role for SHIP1 in osteoclasts, with inflammation as the key driver of the skeletal phenotype in SHIP1-deficient mice. Our findings demonstrate the central role of the immune system in steering physiological skeletal development.

RANK- NFATc1 signaling forms positive feedback loop on rank gene expression via functional NFATc1 responsive element in rank gene promoter

Receptor Activator of NF-κB (RANK) expressed on osteoclasts and their precursors is a receptor for RANK ligand (RANKL). Signals transduced by RANKL-RANK interaction induce genes essential for the differentiation and function of osteoclasts, partly through the direct binding of NFATc1, to target gene promoters. We have previously cloned a 6-kb fragment containing the 5'-flanking region of the mouse RANK gene and have demonstrated the presence of binding elements of hematological transcription factors, such as MITF, PU.1 and AP-1. Here, we demonstrated the presence of the functional NFATc1 responsive element on the RANK gene promoter. Transfection of an NFATc1-expression vector increased RANK mRNA that was subsequently nullified by NFATc1 knockdown. With the use of electrophoretic mobility shift assay (EMSA), an oligonucleotide (-388/-353) showed specific protein-DNA binding that was blockshifted with an anti-NFATc1 antibody and washed out with excess amounts of the cold consensus sequence. Co-transfection studies with the use of an NFATc1-expression vector and RANK promoter-reporter constructs showed that NFATc1 increased promoter activity 2-fold in RAW264.7 cells that was again nullified as disclosed by mutagenesis studies. Taken together, these results indicate that RANK transcription is positively regulated by the RANKL signal through the direct binding of NFATc1 to its specific binding site of the RANK gene promoter, and suggest the presence of a crucial positive feedback mechanism of gene expression that promotes accelerated terminal differentiation of RANK-positive committed precursors to mature osteoclasts.

Identification of calmodulin-like protein 5 as tumor-suppressor gene silenced during early stage of carcinogenesis in squamous cell carcinoma of uterine cervix

In the course of identifying the molecular mechanism that is related to strong cell-cell adhesion in stratified structures of the squamous epithelium, calmodulin-like protein 5 (CALML5) was identified as a spinous structure-associated protein by producing monoclonal antibodies with the use of the crude intercellular portion of squamous tissue as an immunogen and by subsequent morphologic screening. By electrophoretic mobility shift assay (EMSA) and a series of mutagenesis studies, two transcription factors, ZNF750 and KLF4, by binding in line to the CALML5 gene promoter, were found to play a central role in CALML5 transcription. Knockdown of CALML5 by siRNA in the A431 cell line that expresses high levels of CALML5 resulted in the acceleration of wound confluence in a scratch assay, indicating that CALML5 functions as a tumor-suppressor in uterine cervical cancer. Immunohistochemical evaluation of squamous intraepithelial lesions, carcinoma in situ (CIS) and invasive uterine cancer, revealed a reduction in CALML5 expression during the stages of CIS through various molecular pathways including the blockage of the nuclear translocation of KLF4. Conversely, restoration of the nuclear translocation of KLF4 by inhibiting ERK-signaling reactivated CALML5 expression in ME180 cells expressing low levels of CALML5. Thus, alteration of the p63-ZNF750-KLF4 axis may result in critical functional loss of CALM-related genes during cancer progression. Although the morphological association of CALML5 with the spiny-structure in relation to cell motility is not clear, evaluation of CALML5 expression provides a useful diagnostic indicator of differentiating dysplasia, preinvasive and invasive cervical cancers.