Isolation and characterization of osteoclast precursors that differentiate into osteoclasts on calvarial cells within a short period of time

Osteoclasts are formed in cocultures of mouse calvarial cells and hematopoietic cells in the presence of osteotropic factors such as 1α,25-dihydroxyvitamin D₃ [1α,25(OH)₂D₃], parathyroid hormone (PTH) and prostaglandin E₂ (PGE₂). We isolated osteoclast precursors (OCPs) from the coculture and examined their characteristics. After coculture for 7 days of mouse calvarial cells and bone marrow cells in the absence of osteotropic factors, hematopoietic cells were recovered and applied to a Sephadex G-10 column. Cells which passed through the column were collected as OCPs. When OCPs were cultured on calvarial cell layers in the presence of 1α,25(OH)₂D₃, tartrate-resistant acid phosphatase (TRAP)–positive cells first appeared within 24 h, and their number increased thereafter. OCPs also differentiated into TRAP-positive cells within 48 h on the calvarial cell layer which had been pretreated with either 1α,25(OH)₂D₃, PTH, or PGE₂. Autoradiography using [¹²⁵I]-labeled calcitonin showed that TRAP-positive cells formed on the calvarial cell layer expressed calcitonin receptors. Direct contact between OCPs and calvarial cells was required for the differentiation of OCPs into TRAP-positive cells. Flow cytometric analysis revealed that OCPs were positive for Mac-1, Mac-2, and Gr-1 but negative for F4/80, B220 and CD3e. Calvarial cells obtained from macrophage-colony stimulating factor (M-CSF)–deficient osteopetrotic (op/op) mice did not support OCP formation. A cell preparation disaggregated from long bones of newborn mice contained OCPs that differentiated into TRAP-positive cells on calvarial cells within 48 h, but cell preparations of freshly isolated bone marrow cells and alveolar macrophages did not. These results suggest that OCPs are specific cells which are formed only in the bone microenvironment and that OCPs recognize a signal(s) expressed by stromal cells in response to osteotropic factors and differentiate into osteoclasts. J. Cell. Physiol. 177:26–35, 1998. © 1998 Wiley-Liss, Inc.     

Aspergillus salviicola,a new species from imported spice

A new species ofAspergillus, A. salviicola, has been isolated from Turkish sage, an imported spice in Japan. The species, characterized by white to rosy buff conidial heads, pinkish smooth-walled conidiophores, large biseriate aspergilla, globose smooth-walled conidia, absence of sclerotia and thermotolerant growth, is considered to represent an interface species in the subgenusCircumdati.     

A novel role for H-Ras in the regulation of very late antigen-4 integrin and VCAM-1 via c-Myc-dependent and -independent mechanisms.

Despite extensive studies on the crucial functions of Ras and c-Myc in cellular proliferation and transformation, their roles in regulating cell adhesion are not yet fully understood. Involvement of Ras in modulating integrin activity by inside-out signaling has been recently reported. However, in contrast to R-Ras, H-Ras was found to exhibit a suppressive effect. Here we show that ectopic expression of a constitutively active H-Rasv12, but not c-Myc alone, in a hemopoietic cell line induces activation of very late Ag-4 (VLA-4, alpha4beta1) integrin without changing its surface expression. Intriguingly, coexpression of H-Rasv12 and c-Myc in these cells results in not only the activation of VLA-4, but also the induction of expression of VCAM-1, the counterreceptor for VLA-4, thereby mediating a marked homotypic cell aggregation. In addition, H-Rasv12-induced VLA-4 activation appears to be partly down-regulated by coexpression with c-Myc. Our results represent an unprecedented example demonstrating a novel role for H-Rasv12 in the regulation of cell adhesion via c-Myc-independent and -dependent mechanisms.     

Ca2+-dependent maturation of subtilisin from a hyperthermophilic archaeon, Thermococcus kodakaraensis: the propeptide is a potent inhibitor of the mature domain but is not required for its folding

Subtilisin from the hyperthermophilic archaeon Thermococcus kodakaraensis KOD1 is a member of the subtilisin family. T. kodakaraensis subtilisin in a proform (T. kodakaraensis pro-subtilisin), as well as its propeptide (T. kodakaraensis propeptide) and mature domain (T. kodakaraensis mat-subtilisin), were independently overproduced in E. coli, purified, and biochemically characterized. T. kodakaraensis pro-subtilisin was inactive in the absence of Ca2+ but was activated upon autoprocessing and degradation of propeptide in the presence of Ca2+ at 80 degrees C. This maturation process was completed within 30 min at 80 degrees C but was bound at an intermediate stage, in which the propeptide is autoprocessed from the mature domain (T. kodakaraensis mat-subtilisin*) but forms an inactive complex with T. kodakaraensis mat-subtilisin*, at lower temperatures. At 80 degrees C, approximately 30% of T. kodakaraensis pro-subtilisin was autoprocessed into T. kodakaraensis propeptide and T. kodakaraensis mat-subtilisin*, and the other 70% was completely degraded to small fragments. Likewise, T. kodakaraensis mat-subtilisin was inactive in the absence of Ca2+ but was activated upon incubation with Ca2+ at 80 degrees C. The kinetic parameters and stability of the resultant activated protein were nearly identical to those of T. kodakaraensis mat-subtilisin*, indicating that T. kodakaraensis mat-subtilisin does not require T. kodakaraensis propeptide for folding. However, only approximately 5% of T. kodakaraensis mat-subtilisin was converted to an active form, and the other part was completely degraded to small fragments. T. kodakaraensis propeptide was shown to be a potent inhibitor of T. kodakaraensis mat-subtilisin* and noncompetitively inhibited its activity with a Ki of 25 +/- 3.0 nM at 20 degrees C. T. kodakaraensis propeptide may be required to prevent the degradation of the T. kodakaraensis mat-subtilisin molecules that are activated later by those that are activated earlier.     

MKK6-p38 MAPK signaling pathway enhances survival but not bone-resorbing activity of osteoclasts

Phosphorylated p38 mitogen-activating kinase (MAPK) is observed in osteoclasts under in vivo inflammatory situations. However, the role of p38 MAPK in osteoclast function has not been elucidated, because all external stimuli tested hitherto failed to induce the phosphorylation of p38 MAPK in osteoclasts in culture. In this study, a constitutively active form of MKK6 (MKK6CA) was expressed in osteoclasts using adenoviral gene transfer in vitro. MKK6CA expressed in osteoclasts phosphorylated p38 MAPK and enhanced the survival of osteoclasts. Dentine-resorbing activity of osteoclasts was not enhanced by the MKK6CA expression. These results suggest that p38 MAPK signaling plays a critical role in the survival of osteoclasts in inflammatory diseases.     

Crystallization and preliminary x-ray crystallographic analysis of galectin LEC-1 from Caenorhabditis elegans

Galectin LEC-1 isolated from the nematode Caenorhabditis elegans was the first galectin found in invertebrates and also the first tandem-repeat-type galectin identified, containing two homologous carbohydrate-binding sites. This galectin is localized most abundantly in the adult cuticle and possibly plays a role in the formation of epidermal layers. We succeeded in crystallizing LEC-1 composed of 279 amino acids with a calculated molecular weight of 31,809 Da under two independent sets of conditions as a result of extensive screening. The crystals grown under one set of conditions belong to the triclinic space group P1, with unit-cell parameters a = 48.44, b = 52.13, c = 64.24 A, alpha = 108.73, beta= 91.39, and gamma = 98.45 degrees and two protein molecules per unit cell. The crystals grown under the other set of conditions which included lactose belong to the monoclinic space group P2(1), with unit-cell parameters a = 52.90, b = 47.01, c = 66.16 A, and beta= 113.30 degrees and one protein molecule per asymmetric unit.     

Role of the IXI/V motif in oligomer assembly and function of StHsp14.0, a small heat shock protein from the acidothermophilic archaeon, Sulfolobus tokodaii strain 7

Small heat shock proteins (sHsps) are one of the most ubiquitous molecular chaperones. They are grouped together based on a conserved domain, the alpha-crystallin domain. Generally, sHsps exist as oligomers of 9-40 subunits, and the oligomers undergo reversible temperature-dependent dissociation into smaller species as dimers, which interact with denaturing substrate proteins. Previous studies have shown that the C-terminal region, especially the consensus IXI/V motif, is responsible for oligomer assembly. In this study, we examined deletions or mutations in the C-terminal region on the oligomer assembly and function of StHsp14.0, an sHsp from an acidothermophilic archaeon, Sulfolobus tokodaii strain 7. Mutated StHsp14.0 with C-terminal deletion or replacement of IIe residues in the IXI/V motif to Ala, Ser, or Phe residues could not form large oligomers and lost chaperone activity. StHsp14.0WKW, whose Ile residues in the IXI/V motif are changed to Trp, existed as an oligomer like that of the wild type. However, it dissociates to small oligomers and exhibits chaperone activity at relatively lowered temperature. Replacement of two Ile residues in the motif to relatively small residues, Ala or Ser, also resulted in the change of beta-sheet rich secondary structure and decrease of hydrophobicity. Interestingly, StHsp14.0 mutant with amino acid replacements to Phe kept almost the same secondary structure and relatively high hydrophobicity despite that it could not form an oligomeric structure. The results show that hydrophobicity and size of the amino acids in the IXI/V motif in the C-terminal region are responsible not only for assembly of the oligomer but also for the maintenance of beta-sheet rich secondary structure and hydrophobicity, which are important for the function of sHsp.