Two different baculovirus genes are known to be able to block apoptosis triggered upon infection of Spodoptera frugiperda cells with p35 mutants of the insect baculovirus Autographa californica nuclear polyhedrosis virus (AcMNPV): p35 (P35-encoding gene) of AcMNPV (R.

Microarray and real-time RT-PCR were used to examine expression changes in primary bone marrow cells and RAW 264.7 cells in response to RANKL. In silico sequence analysis was performed on a novel gene which we designate OC-STAMP. Specific siRNA and antibodies were used to inhibit OC-STAMP RNA and protein, respectively, and TRAP+ multinucleated osteoclasts were counted. Antibodies were used to probe bone tissues and western blots of RAW cell extracts +/− RANKL. cDNA overexpression constructs were transfected into RAW cells and the effect on RANKL-induced differentiation was studied. OC-STAMP was very strongly up-regulated during osteoclast differentiation. Northern blots and sequence analysis revealed 2 transcripts of 2 kb and 3.7 kb differing only in 3'UTR length, consistent with predictions from genome sequence. The mRNA encodes a 498 amino acid, multi-pass transmembrane protein that is highly conserved in mammals. It has little overall homology to other proteins. The carboxy-terminal 193 amino acids, however, are significantly similar to the DC-STAMP family consensus sequence. DC-STAMP is a transmembrane protein required for osteoclast precursor fusion. Knockdown of OC-STAMP mRNA by siRNA and protein inhibition by antibodies significantly suppressed the formation of tartrate-resistant acid phosphatase (TRAP) +, multinucleated cells in differentiating osteoclast cultures, with many TRAP + mononuclear cells present. Conversely, overexpression of OC-STAMP increased osteoclastic differentiation of RAW 264.7 cells. We conclude that OC-STAMP is a previously unknown, RANKL-induced, multi-pass transmembrane protein that promotes the formation of multinucleated osteoclasts.

The transcription factor Sp1 plays a key role in the activation of many cellular and viral gene promoters, including those that are regulated during the cell cycle. However, recent evidence indicates that Sp1 belongs to a larger family of factors which bind G/C box elements in order to either activate or repress transcription. Sp3, a member of this family, functions to repress transcriptional activation in two viral promoters, most likely by competing with Sp1 for GC box/Sp binding sites. However, the physiological role of Sp3 in the repression of endogenous cellular promoters has not been experimentally addressed. In the present study, we analyze the activity and binding of Sp3 on several eukaryotic promoters that contain G/C boxes and are known to be regulated during cellular proliferation and the cell cycle. Using antibodies specific for Sp1 and Sp3, we observe that both of these factors localize to the cell nucleus and have a similar, dispersed subnuclear distribution. Further, using gel mobility shift assays, we show that both Sp1 and Sp3 interact specifically with the histone H4 promoter. Transient cotransfections of Drosophila cells with Sp1 and Sp3 expression vectors and with the histone H4, thymidine kinase (TK), or dihydrofolate reductase (DHFR) promoters show that only the DHFR promoter, containing multiple functional GC boxes, displays Sp3 repression of Sp1 activation. In contrast, the single G/C boxes within the histone H4 or TK promoters, which confer transcriptional activation via Sp1 binding, are not responsive to repression by Sp3. Therefore, we demonstrate that the endogenous cellular DHFR promoter is selectively responsive to Sp3 repression. The data suggest that Sp3 may contribute to the control of proliferation- and/or cell-regulated promoters depending upon the context and/or number of functional Sp1 binding sites.

Transcription of the genes for the human.histone proteins H4, H3,.H2A, H2B, and Hi is activated at the G1/S phase transition of the cell cycle. We have previously shown that the promoter complex HiNF-D, which interacts with cell cycle control elements in multiple histone genes, contains the key cell cycle factors cyclin A, CDC2, and a retinoblastoma (pRB) protein-related protein. However, an intrinsic DNA-binding subunit for HiNF-D was not identified.Many genes that are up-regulated at the G1/S phase boundary are controlled by E2F, a transcription factor that associates with cyclin-, cyclin-dependent kinase-, and pRB-related proteins. Using gel-shift immunoassays, DNase I protection, and oligonucleotide competition analyses, we show that the homeodomain protein CDP/cut, not E2F, is the DNA-binding subunit of the HiNF-D complex. The HiNF-D (CDP/cut) complex with the H4 promoter is immunoreactive with antibodies against CDP/cut and pRB but not p107, whereas the CDP/cut complex with a nonhistone promoter (gp9l-phox) reacts only with CDP and p107 antibodies. Thus, CDP/cut complexes at different gene promoters can associate with distinct pRB-related proteins. Transient coexpression assays show that CDP/cut modulates H4 promoter activity via the HiNF-D-binding site. Hence, DNA replication-dependent histone H4 genes are regulated by an E2F-independent mechanism involving a complex of CDP/cut with cyclin A/CDC2/ RB-related proteins.Cell proliferation is initiated by a sequential series of growth factor-dependent events that activate cyclin-dependent kinases (CDKs), which mediate the onset of the cell cycle and progression into S phase (1, 2). There are two functional components to the G1/S phase transition point during the cell cycle. First, initiation of DNA replication necessitates adjustments in the activities of enzymes involved in nucleotide metabolism and DNA synthesis. Second, progression into early S phase requires induction of histone gene expression, because de novo synthesis of histone nucleosomal proteins is essential for the ordered packaging of newly replicated DNA into chromatin (3).Many genes that are functionally linked to cell cycle progression appear to be regulated by the E2F class of transcription factors, including genes encoding enzymes and regulatory factors involved in DNA synthesis (e.g., refs. 4-13). E2F factors are heterodimers composed of different pairs of E2F/DP proteins that are capable of forming higher order complexes with multiple cell cycle regulators including retinoblastoma protein (pRB)-related proteins (pRB/plO5, pRB-

Osteoclasts differentiate from hematopoietic mononuclear precursor cells under the control of both colony stimulating factor-1 (CSF-1, or M-CSF) and receptor activator of NF-B ligand (RANKL, or TRANCE, TNFSF11) to carry out bone resorption. Using high density gene microarrays, we followed gene expression changes in long bone RNA when CSF-1 injections were used to restore osteoclast populations in the CSF-1-null toothless (csf1 tl /csf1 tl ) osteopetrotic rat. We found that ovarian cancer G-protein-coupled receptor 1 (OGR1, or GPR68) was strongly up-regulated, rising >6-fold in vivo after 2 days of CSF-1 treatments. OGR1 is a dual membrane receptor for both protons (extracellular pH) and lysolipids. Strong induction of OGR1 mRNA was also observed by microarray, real-time RT-PCR, and immunoblotting when mouse bone marrow mononuclear cells and RAW 264.7 pre-osteoclast-like cells were treated with RANKL to induce osteoclast differentiation. Anti-OGR1 immunofluorescence showed intense labeling of RANKL-treated RAW cells. The time course of OGR1 mRNA expression suggests that OGR1 induction is early but not immediate, peaking 2 days after inducing osteoclast differentiation both in vivo and in vitro. Specific inhibition of OGR1 by anti-OGR1 antibody and by small inhibitory RNA inhibited RANKL-induced differentiation of both mouse bone marrow mononuclear cells and RAW cells in vitro, as evidenced by a decrease in tartrate-resistant acid phosphatase-positive osteoclasts. Taken together, these data indicate that OGR1 is expressed early during osteoclastogenesis both in vivo and in vitro and plays a role in osteoclast differentiation.The catabolic removal of bone during skeletal formation and remodeling requires the specialized activity of multinucleated osteoclasts. Osteoclasts differentiate by fusion of hematopoietic mononuclear precursors in response to systemic and local signals, in particular colony-stimulating factor-1 (CSF-1, 2 or M-CSF) and the tumor necrosis factor family member receptor activator of NF-B ligand (RANKL, or TRANCE, TNFSF11) (1). Excessive osteoclast activity systemically leads to osteopenias such as osteoporosis, whereas local hyperactivity can lead to osteolysis as seen in tumor metastases to bone or in prosthesis loosening. Hypoactivity of osteoclasts can lead to sclerosing bone disorders, for example in genetic conditions such as osteopetrosis.Osteoclast differentiation is a complex process that requires the coordinated action of many gene products, including not only extrinsic factors such as CSF-1 and RANKL, which are supplied by osteoblasts locally in bone tissue, but also intrinsic factors required for osteoclast function. Mononuclear precursors must migrate to sites where resorption is needed, fuse to form multinucleated pre-osteoclasts, and attach firmly to bone. They develop highly specialized cellular structures, including an actin ring that forms a tight seal with the bone surface, and a highly convoluted plasma membrane domain called the ruffled border, which is the site of extremely a...

Bone disease is a side effect of concern regarding chronic glucocorticoid (GC) administration. Most GC-treated patients exhibit a process of bone loss, frequently leading to osteoporosis, with increased fracture risk, especially in spinal vertebrae. Some GC-treated patients will develop osteonecrosis, a disease with distinct clinical and histopathological features, most often occurring underneath the articular surface of the femoral head. Remarkably, both of these GC-induced bone diseases are associated with osteoblast and osteocyte apoptosis, which is emerging as a potential primary pathogenic mechanism. Here, we review the evidence for osteoblast and osteocyte apoptosis in GC-induced bone disease and highlight current debates: (1) With recent reports describing the antiapoptotic effect of GCs in some in vitro osteoblast models, and with the known adverse effects of GCs on osteoblast cell cycle and differentiation, could the in vivo osteoblast apoptosis be an indirect rather than a direct effect of GCs? (2) What is the pathogenic relationship between GC-induced osteoporosis and osteonecrosis? Could the latter be a mere manifestation of the former? and (3) How does apoptosis fit into the traditional concept of ischemia as a key etiology in osteonecrosis? Regardless of the answers, recent studies with cells, animals, and humans point out bone cell apoptosis as a potential target in the design of treatment for GC-induced bone disease.

The fusion of monocyte/macrophage lineage cells into fully active, multinucleated, bone resorbing osteoclasts is a complex cell biological phenomenon that utilizes specialized proteins. OC-STAMP, a multi-pass transmembrane protein, has been shown to be required for pre-osteoclast fusion and for optimal bone resorption activity. A previously reported knockout mouse model had only mononuclear osteoclasts with markedly reduced resorption activity in vitro, but with paradoxically normal skeletal micro-CT parameters. To further explore this and related questions, we used mouse ES cells carrying a gene trap allele to generate a second OC-STAMP null mouse strain. Bone histology showed overall normal bone form with large numbers of TRAP-positive, mononuclear osteoclasts. Micro-CT parameters were not significantly different between knockout and wild type mice at 2 or 6 weeks old. At 6 weeks, metaphyseal TRAP-positive areas were lower and mean size of the areas were smaller in knockout femora, but bone turnover markers in serum were normal. Bone marrow mononuclear cells became TRAP-positive when cultured with CSF-1 and RANKL, but they did not fuse. Expression levels of other osteoclast markers, such as cathepsin K, carbonic anhydrase II, and NFATc1, were not significantly different compared to wild type. Actin rings were present, but small, and pit assays showed a 3.5-fold decrease in area resorbed. Restoring OC-STAMP in knockout cells by lentiviral transduction rescued fusion and resorption. N- and C-termini of OC-STAMP were intracellular, and a predicted glycosylation site was shown to be utilized and to lie on an extracellular loop. The site is conserved in all terrestrial vertebrates and appears to be required for protein stability, but not for fusion. Based on this and other results, we present a topological model of OC-STAMP as a 6-transmembrane domain protein. We also contrast the osteoclast-specific roles of OC- and DC-STAMP with more generalized cell fusion mechanisms.

Casein kinase II (CKII) of Saccharomyces cerevisiae contains two distinct catalytic subunits, ␣ and ␣, that are encoded by the CKA1 and -2 genes, respectively. We have constructed conditional alleles of the CKA1 gene. In contrast to cka1 cka2 ts strains, which exhibit a defect in both G 1 and G 2 /M cell cycle progression, cka1 ts cka2 strains continue to divide for three cell cycles after a shift to restrictive temperature and then arrest as a mixture of budded and unbudded cells with a spherical morphology. Arrested cells exhibit continued growth, a nonpolarized actin cytoskeleton, delocalized chitin deposition, and a significant fraction of multinucleate cell bodies, confirming the presence of a cell polarity defect in cka1 ts strains. The presence of budded as well as unbudded cells in the arrested population suggests that CKII is required for maintenance rather than establishment of cell polarity, although a role in both processes is also possible. The terminal phenotype of cka1 ts strains bears a strong resemblance to that of orb5 strains of Schizosaccharomyces pombe, which carry a temperature-sensitive CKII catalytic subunit mutation, but the underlying mechanism appears to be different in the two cases. These results establish a requirement for CKII in cell polarity in S. cerevisiae and provide the first evidence for functional specialization of CKA1 and -2.