Populations of follicles in F344/N rats during aging

Follicular populations were investigated in female F344/N rats to better understand the aging process of the rat ovary. Ovaries dissected at various ages (spanning 1–36 months old) were submitted for histological examination. The total number of primordial, growing (primary and secondary), tertiary, and atretic follicles as well as corpora lutea (CL) were counted in hematoxylin–eosin- and azocarmine–aniline-blue-stained ovarian sections. The number of healthy follicles including primordial, growing and tertiary follicles decreased rapidly between the first and third months and gradually thereafter. CL were found in 3-month-old rats, and their number remained unchanged until 18 months of age, at which point it decreased. The number of atretic follicles started to increase in rats older than 18 months, which corresponded to the cessation of estrous cyclicity. Several healthy follicles and CL were observed even in 36-month-old rats.     

Cellulose-bound Peptide Arrays: Preparation and Applications

Spatial organization of metabolic enzymes may represent a general cellular mechanism to regulate metabolic flux. One recent example of this type of cellular phenomenon is the purinosome, a newly discovered multi-enzyme metabolic assembly that includes all of the enzymes within the de novo purine biosynthetic pathway. Our understanding of the components and regulation of purinosomes has significantly grown in recent years. This paper reviews the purine de novo biosynthesis pathway and its regulation, and presents the evidence supporting the purinosome assembly and disassembly processes under the control of G-protein-coupled receptor (GPCR) signaling. This paper also discusses the implications of purinosome and GPCR regulation in drug discovery.     

Desmoglein versus non-desmoglein signaling in pemphigus acantholysis: characterization of novel signaling pathways downstream of pemphigus vulgaris antigens

Although it is accepted that pemphigus antibody binding to keratinocytes (KCs) evokes an array of intracellular biochemical events resulting in cell detachment and death, the triggering events remain obscure. It has been postulated that the binding of pemphigus vulgaris IgG (PVIgG) to KCs induces "desmosomal" signaling. Because in contrast to integrins and classical cadherins, desmoglein (Dsg) molecules are not known to elicit intracellular signaling, and because PV patients also produce non-Dsg autoantibodies, we investigated the roles of both Dsg and non-desmoglein PV antigens. The time course studies of KCs treated with PVIgG demonstrated that the activity of Src peaked at 30 min, EGF receptor kinase (EGFRK) at 60 min, and p38 MAPK at 240 min. The Src inhibitor PP2 decreased EGFRK and p38 activities by approximately 45 and 30%, respectively, indicating that in addition to Src, PVIgG evokes other triggering events. The shrinkage of KCs (cell volume reduction) became significant at 120 min, keratin aggregation at 240 min, and an increase of TUNEL positivity at 360 min. Pretreatment of KCs with PP2 blocked PVIgG-dependent cell shrinkage and keratin aggregation by approximately 50% and TUNEL positivity by approximately 25%. The p38 MAPK inhibitor PD169316 inhibited these effects by approximately 15, 20, and 70%, respectively. Transfection of KCs with small interfering RNAs that silenced expression of Dsg1 and/or Dsg3 proteins, blocked approximately 50% of p38 MAPK activity but did not significantly alter the PVIgG-dependent rise in Src and EGFRK activities. These results indicate that activation of p38 MAPK is a late signaling step associated with collapse of the cytoskeleton and disassembly of desmosomes caused by upstream events involving Src and EGFRK. Therefore, the early acantholytic events are triggered by non-Dsg antibodies.     

Irreversible cross-linking of heme to the distal tryptophan of stromal ascorbate peroxidase in response to rapid inactivation by H2O2

Ascorbate peroxidase (APX) isoforms localized in the stroma and thylakoid membrane of chloroplasts play a central role in scavenging reactive oxygen species generated by photosystems. These enzymes are inactivated within minutes by H2O2 when the reducing substrate, ascorbate, is depleted. We found that, when the enzyme is inactivated by H2O2, a heme at the catalytic site of a stromal APX isoform is irreversibly cross-linked to a tryptophan residue facing the distal cavity. Mutation of this tryptophan to phenylalanine abolished the cross-linking and increased the half-time for inactivation from <10 to 62 s. In contrast with H2O2-tolerant peroxidases, rapid formation of the cross-link in APXs suggests that a radical in the reaction intermediate tends to be located in the distal tryptophan so that heme is easily cross-linked to it. This is the first report of a mutation that improves the tolerance of chloroplast APXs to H2O2.     

Production of a biologically active epidermal growth factor fusion protein with high collagen affinity

Collagen is generally incapable of capturing polypeptides such as growth factors in a specific manner. In this study, we established a collagen-binding growth factor (FNCBD-EGF) consisting of epidermal growth factor (EGF) and the fibronectin collagen-binding domain. A typical yield of FNCBD-EGF was approximately 200 microg/ml culture in an Escherichia coli expression system. This fusion protein bound to gelatin and fibrillar collagen sponges, and the bound protein was not effectively eluted even with 2 M NaCl. In addition, FNCBD-EGF bound to type I, II, III, or IV collagen-coated plates, and the specificity of binding was confirmed by competitive inhibition using fibronectin. FNCBD-EGF substantially stimulated cell growth after binding to collagen-coated culture plates, whereas EGF had no effect, indicating that this fusion protein acted as a collagen-associated growth factor. In an animal model of impaired wound healing, FNCBD-EGF, but not EGF, was retained with collagen sponges at wound sites 4 d after implantation, and repair of epidermis was observed underneath the sponges. These results suggested that our fusion protein with high collagen affinity would be useful for wound healing.     

Enhancement of secretion of human procollagen I in mouse HSP47-expressing insect cells

We previously demonstrated that insect cells were able to synthesize recombinant human procollagen I as triple-helical heterotrimers when transfected with cDNAs of both proalpha1(I) and proalpha2(I) chains. However, most of the heterotrimers were retained within the cells, unlike in the case of mammalian cells [Tomita, M., Kitajima, T., and Yoshizato, K. (1997) J. Biochem. 1061-1069]. In an attempt to improve the secretion of the heterotrimers, we introduced the putative collagen-specific chaperone HSP47 into this insect expression model. Mouse HSP47 produced by the insect cells bound intracellularly to both human proalpha1(I) and proalpha2(I) chains and enhanced the secretion of procollagen I heterotrimers. HSP47 was also coexpressed with either proalpha1(I) chains or proalpha2(I) chains, which showed that it enhanced the secretion of the former but not the latter. This selective effect of HSP47 was similarly observed in the cells treated with inhibitors of procollagen triple helix formation, indicating that HSP47 can also accelerate the secretion of non-helical procollagens. HSP47 did not change the intracellular solubility of proalpha1(I) and proalpha2(I) chains in 1% NP-40, eliminating the possibility that it prevents proalpha chains from aggregating into insoluble forms within the insect cells. We concluded that HSP47 can play a role in the secretion of alpha1(I)-procollagen chains in the insect cell model. The present study also demonstrated the dissimilarity in the mechanism of folding and secretion of the expressed procollagen I between the insect and mammalian cells.     

Biochemical characterization and functional analysis of two type II classic cadherins, cadherin-6 and -14, and comparison with E-cadherin

Classic cadherins can be grouped based on their deduced primary structures. Among them the type I cadherins have been well characterized; however, little is known about non-type I cadherins. In this study we characterized two human type II cadherins, cadherin-6 and cadherin-14, using a cDNA transfection system. They were each detected as two bands electrophoretically, were expressed on the external cell surface at cell-cell contact sites, and were associated with caten- ins. Direct sequencing of the N-terminal amino acids showed that the two bands of cadherin-14 corresponded to precursor and mature forms, whereas the two bands of cadherin-6 both had the N-terminal sequence of the mature form. Unlike type I cadherins, both cadherin-6 and -14 were not protected from trypsin degradation by Ca2+. We evaluated their adhesive functions by a long term cell aggregation method. The results suggest that both cadherin-6 and -14 have cell-cell binding strengths virtually equivalent to that of E-cadherin and that their binding specificities are distinct from that of E-cadherin. Cadherin-6 and -14 interacted with each other in an incomplete manner. They have a QAI tripeptide in the first extracellular subdomain instead of the HAV motif that is characteristic of type I cadherins and is intimately involved in the adhesive function. The QAI tripeptide, however, appeared not to be involved in the adhesive functions of cadherin-6 and -14.