An apical expression signal of the renal type IIc Na+-dependent phosphate cotransporter in renal epithelial cells.

The type IIc Na(+)-dependent phosphate cotransporter (NaPi-IIc) is specifically targeted to, and expressed on, the apical membrane of renal proximal tubular cells and mediates phosphate transport. In the present study, we investigated the signals that determine apical expression of NaPi-IIc with a focus on the role of the N- and the C-terminal tails of mouse NaPi-IIc in renal epithelial cells [opossum kidney (OK) and Madin-Darby canine kidney cells]. Wild-type NaPi-IIc, the cotransporter NaPi-IIa, as well as several IIa-IIc chimeras and deletion mutants, were fused to enhanced green fluorescent protein (EGFP), and their cellular localization was analyzed in polarized renal epithelial cells by confocal microscopy and by cell-surface biotinylation. Fluorescent EGFP-fused NaPi-IIc transporter proteins are correctly expressed in the apical membrane of OK cells. The apical expression of N-terminal deletion mutants (deletion of N-terminal 25, 50, or 69 amino acids) was not affected by truncation. In contrast, C-terminal deletion mutants (deletion of C-terminal 45, 50, or 62 amino acids) did not have correct apical expression. A more detailed mutational analysis indicated that a domain (amino acids WLHSL) in the cytoplasmic C terminus is required for apical expression of NaPi-IIc in renal epithelial cells. We conclude that targeting of NaPi-IIc to the apical cell surface is regulated by a unique amino acid motif in the cytoplasmic C-terminal domain.

Adenoid cystic carcinoma of the maxillary sinus with gradual histologic transformation to high-grade adenocarcinoma: a comparative report with dedifferentiated carcinoma.

We report a unique case of adenoid cystic carcinoma (ACC) of the maxillary sinus, with gradual histologic transformation from lower-grade ACC (cribriform and tubular types) to high-grade adenocarcinoma (HGA) showing a sequential histologic spectrum via solid-type ACC. A 74-year-old man presented with swelling and mild pain of the right cheek. CT scan showed a mass measuring approximately 4 cm, with marked bone destruction in the right maxillary sinus. A surgically resected specimen revealed that the tumor was comprised of three different components: HGA and solid-type ACC in the central portion and lower-grade ACC in the periphery. The tumor was discriminated from a dedifferentiated carcinoma or hybrid tumor. Autopsy specimens also demonstrated both solid-type ACC and HGA components in the lung and spleen. Immunohistochemically, positive staining of p53 protein was detected on both solid-type ACC and HGA cells, but cyclin D1 and HER2/neu was only seen in HGA cells. Solid-type ACC cells were immunoreactive for CD117 (c-kit), but lower-grade ACC and HGA cells were negative. This case suggests that the overexpression of CD117, p53 protein, cyclin D1, and HER2/neu might be involved in the progression from lower-grade ACC to solid-type ACC and HGA.

Implications of expansin-like 3 gene in Dictyostelium morphogenesis.

Dictyostelium harbors multiple expansin-like genes with generally unknown functions. Thus, we analyzed the expansin-like 3 (expL3) gene and found that its expression was reduced in a null mutant for a STATa gene encoding a transcription factor. The expression of expL3 was developmentally regulated and its transcript was spliced only in the multicellular stages. The expL3 promoter was activated in the anterior prestalk region of the parental strain and downregulated in the STATa null slug, although the expL3 promoter was still expressed in the prestalk region. The expL3 overexpressing strain exhibited delayed development and occasionally formed an aberrant structure, i.e., a fruiting body-like structure with a short stalk. The ExpL3-myc protein bound cellulose.

Unique uptake and efflux systems of inorganic phosphate in osteoclast-like cells.

During bone resorption, a large amount of inorganic phosphate (P(i)) is generated within the osteoclast hemivacuole. The mechanisms involved in the disposal of this P(i) are not clear. In the present study, we investigated the efflux of P(i) from osteoclast-like cells. P(i) efflux was activated by acidic conditions in osteoclast-like cells derived by the treatment of RAW264.7 cells with receptor activator of nuclear factor-kappaB ligand. Acid-induced P(i) influx was not observed in renal proximal tubule-like opossum kidney cells, osteoblast-like MC3T3-E1 cells, or untreated RAW264.7 cells. Furthermore, P(i) efflux was stimulated by extracellular P(i) and several P(i) analogs [phosphonoformic acid (PFA), phosphonoacetic acid, arsenate, and pyrophosphate]. P(i) efflux was time dependent, with 50% released into the medium after 10 min. The efflux of P(i) was increased by various inhibitors that block P(i) uptake, and extracellular P(i) did not affect the transport of [(14)C]PFA into the osteoclast-like cells. Preloading of cells with P(i) did not stimulate P(i) efflux by PFA, indicating that the effect of P(i) was not due to transstimulation of P(i) transport. P(i) uptake was also enhanced under acidic conditions. Agents that prevent increases in cytosolic free Ca(2+) concentration, including acetoxymethyl ester of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, 2-aminoethoxydiphenyl borate, and bongkrekic acid, significantly inhibited P(i) uptake in the osteoclast-like cells, suggesting that P(i) uptake is regulated by Ca(2+) signaling in the endoplasmic reticulum and mitochondria of osteoclast-like cells. These results suggest that osteoclast-like cells have a unique P(i) uptake/efflux system and can prevent P(i) accumulation within osteoclast hemivacuoles.

Large cell calcifying Sertoli cell tumor of the testis: comparative immunohistochemical study with Leydig cell tumor.

Large cell calcifying Sertoli cell tumor is a rare type of testicular tumor. Reported herein is a Japanese patient with this tumor not associated with Carney's complex. An 11-year-old boy was admitted to hospital because of left testicular enlargement, and radical orchiectomy was performed. Macroscopically, the tumor was well circumscribed and had a maximum diameter of approximately 2 cm. The cut surface showed a yellow-white solid mass. Histologically, the tumor was composed of large neoplastic cells with abundant eosinophilic cytoplasm with a tubular, trabecular, and solid arrangement and loose myxoid stroma with irregularly shaped calcification. Immunohistochemically, the tumor cells were positive for vimentin, S-100 protein, calretinin, inhibin-alpha, melan-A, and CD10, and type IV collagen and laminin were observed in the extracellular matrix around the tumor cells. The distributions of melan-A, CD10, and mitochondria were characteristically patchy; in contrast, they were diffusely distributed in the cytoplasm in a control case of Leydig cell tumor. The differences in immunostaining patterns for melan-A, CD10, and mitochondria as well as positivity for S-100 protein-beta might be useful diagnostic hallmarks of large cell calcifying Sertoli cell tumor for discrimination from Leydig cell tumor.

Some Cyanobacteria synthesize semi-amylopectin type alpha-polyglucans instead of glycogen.

It is widely accepted that green plants evolved the capacity to synthesize the highly organized branched alpha-polyglucan amylopectin with tandem-cluster structure, whereas animals and bacteria continued to produce random branched glycogen. Although most previous studies documented that cyanobacteria accumulate glycogen, the present study shows explicitly that some cyanobacteria such as Cyanobacterium sp. MBIC10216, Myxosarcina burmensis and Synechococcus sp. BG043511 had distinct alpha-polyglucans, which were designated as semi-amylopectin. The semi-amylopectin was intermediate between rice amylopectin and typical cyanobacterial glycogen in terms of chain length distribution, molecular size and length of the most abundant alpha-1,4-chain. It was also found that Cyanobacterium sp. MBIC10216 had no amylose-type component in its alpha-polyglucans. The evolutionary aspect of the structure of alpha-polyglucan is discussed in relation to the phylogenetic evolutionary tree of 16S rRNA sequences of cyanobacteria.

Starch-branching enzyme I-deficient mutation specifically affects the structure and properties of starch in rice endosperm.

We have isolated a starch mutant that was deficient in starch-branching enzyme I (BEI) from the endosperm mutant stocks of rice (Oryza sativa) induced by the treatment of fertilized egg cells with N-methyl-N-nitrosourea. The deficiency of BEI in this mutant was controlled by a single recessive gene, tentatively designated as starch-branching enzyme mutant 1 (sbe1). The mutant endosperm exhibited the normal phenotype and contained the same amount of starch as the wild type. However, the mutation apparently altered the fine structure of amylopectin. The mutant amylopectin was characterized by significant decrease in both long chains with degree of polymerization (DP) > or = 37 and short chains with DP 12 to 21, marked increase in short chains with DP < or = 10 (A chains), and slight increase in intermediate chains with DP 24 to 34, suggesting that BEI specifically synthesizes B1 and B2-3 chains. The endosperm starch from the sbe1 mutant had a lower onset concentration for urea gelatinization and a lower onset temperature for thermo-gelatinization compared with the wild type, indicating that the genetic modification of amylopectin fine structure is responsible for changes in physicochemical properties of sbe1 starch.