Beta4 integrin promotes osteosarcoma metastasis and interacts with ezrin.

The development of pulmonary metastasis is the major cause of death in osteosarcoma, and its molecular basis is poorly understood. In this study, we show that beta4 integrin is highly expressed in human osteosarcoma cell lines and tumor samples. Furthermore, highly metastatic MNNG-HOS cells have increased levels of beta4 integrin. Suppression of beta4 integrin expression by shRNA and disruption of beta4 integrin function by transfection of dominant-negative beta4 integrin was sufficient to revert this highly metastatic phenotype in the MNNG-HOS model without significantly affecting primary tumor growth. These findings suggest a role for beta4 integrin expression in the metastatic phenotype in human osteosarcoma cells. In addition, we identified a previously uncharacterized interaction between beta4 integrin and ezrin, a membrane-cytoskeletal linker protein that is implicated in the metastatic behavior of osteosarcoma. The beta4 integrin-ezrin interaction appears to be critical for maintenance of beta4 integrin expression. These data begin to integrate ezrin and beta4 integrin expression into a model of action for the mechanism of osteosarcoma metastases.

Alveolar soft-part sarcoma: a review and update.

Alveolar soft-part sarcoma (ASPS) is a rare, distinctive sarcoma, typically occurring in young patients. Although it displays a relatively indolent clinical course, the ultimate prognosis is poor and is often characterised by late metastases. Recently, our understanding of the genetic events underlying the pathogenesis of ASPS has greatly increased. The historical, histopathological, ultrastructural, immunohistochemical and genetic aspects of ASPS are reviewed in this article.

Grading of soft tissue sarcomas: the challenge of providing precise information in an imprecise world.

By identifying patients at greatest risk for distant metastasis and, hence, most likely to benefit from adjuvant therapy, the grading of sarcomas has been one of the most important contributions pathologists have made to the treatment of sarcomas. Over the years, many grading schemes have been proposed and validated as efficacious. The three-tier system proposed by the French Federation of Cancer Centres is precisely defined, easy to use, and is the most widely employed. However, no system performs perfectly on all sarcomas. Sarcomas that do not lend themselves well to grading include (i) those in which grade provides no incremental information over histological subtypes (e.g. well-differentiated liposarcoma/atypical lipomatous neoplasm, Ewing's sarcoma); (ii) tumours traditionally considered "ungradable" (e.g. epithelioid sarcoma, clear cell sarcoma, angiosarcoma); and (iii) sarcomas that customarily have been graded but in which grade has recently been shown not to correlate well with outcome (e.g. malignant peripheral nerve sheath tumour). Consequently, several sarcoma-specific risk stratification schemes have been proposed. The future may well witness a synthesis of these two approaches. Nomograms, which incorporate clinical, histological and demographic findings, have proved accurate in predicting disease-specific survival in sarcomas. Diagnosis and grading are increasingly based on tissue obtained by core needle biopsy, which poses new challenges for pathologists, particularly if neoadjuvant therapy is to be given. Grading on needle biopsies may require a two-tier grading system (i.e. low versus high grade) and a close dialogue with clinicians to resolve ambiguities.

Characterization of the distinct orthotopic bone-forming activity of 14 BMPs using recombinant adenovirus-mediated gene delivery.

Efficacious bone regeneration could revolutionize the clinical management of bone and musculoskeletal disorders. Although several bone morphogenetic proteins (BMPs) (mostly BMP-2 and BMP-7) have been shown to induce bone formation, it is unclear whether the currently used BMPs represent the most osteogenic ones. Until recently, comprehensive analysis of osteogenic activity of all BMPs has been hampered by the fact that recombinant proteins are either not biologically active or not available for all BMPs. In this study, we used recombinant adenoviruses expressing the 14 types of BMPs (AdBMPs), and demonstrated that, in addition to currently used BMP-2 and BMP-7, BMP-6 and BMP-9 effectively induced orthotopic ossification when either AdBMP-transduced osteoblast progenitors or the viral vectors were injected into the quadriceps of athymic mice. Radiographic and histological evaluation demonstrated that BMP-6 and BMP-9 induced the most robust and mature ossification at multiple time points. BMP-3, a negative regulator of bone formation, was shown to effectively inhibit orthotopic ossification induced by BMP-2, BMP-6, and BMP-7. However, BMP-3 exerted no inhibitory effect on BMP-9-induced bone formation, suggesting that BMP-9 may transduce osteogenic signaling differently. Our findings suggest that BMP-6 and BMP-9 may represent more effective osteogenic factors for bone regeneration.

Chemical modification and site-directed mutagenesis of conserved HXXH and PP-loop motif arginines and histidines in the murine bifunctional ATP sulfurylase/adenosine 5'-phosphosulfate kinase.

The sulfurylase domain of the mouse bifunctional enzyme ATP sulfurylase/adenosine 5'-phosphosulfate (APS) kinase contains HXXH and PP-loop motifs. To elucidate the functional importance of these motifs and of conserved arginines and histidines, chemical modification and site-directed mutagenesis studies were performed. Chemical modification of arginines and histidines with phenylglyoxal and diethyl pyrocarbonate, respectively, renders the enzyme inactive in sulfurylase, kinase, and overall assays. Data base searches and sequence comparison of bifunctional ATP sulfurylase/APS kinase and monofunctional ATP sulfurylases shows a limited number of highly conserved arginines and histidines within the sulfurylase domain. Of these conserved residues, His-425, His-428, and Arg-421 are present within or near the HXXH motif whereas His-506, Arg-510, and Arg-522 residues are present in and around the PP-loop. The functional role of these conserved residues was further studied by site-directed mutagenesis. In the HXXH motif, none of the alanine mutants (H425A, H428A, and R421A) had sulfurylase or overall activity, whereas they all exhibited normal kinase activity. A slight improvement in reverse sulfurylase activity (<10% residual activity) and complete restoration of forward sulfurylase was observed with R421K. Mutants designed to probe the PP-loop requirements included H506A, R510A, R522A, R522K, and D523A. Of these, R510A exhibited normal sulfurylase and kinase activity, R522A and R522K showed no sulfurylase activity, and H506A had normal sulfurylase activity but produced an effect on kinase activity (<10% residual activity). The single aspartate, D523A, which is part of the highly conserved GRD sequence of the PP-loop, affected both sulfurylase and kinase activity. This mutational analysis indicates that the HXXH motif plays a role only in the sulfurylase activity, whereas the PP-loop is involved in both sulfurylase and kinase activities. Residues specific for sulfurylase activity have also been distinguished from those involved in kinase activity.

Activity and stability of recombinant bifunctional rearranged and monofunctional domains of ATP-sulfurylase and adenosine 5'-phosphosulfate kinase.

Murine adenosine 3'-phosphate 5'-phosphosulfate (PAPS) synthetase consists of a COOH-terminal ATP-sulfurylase domain covalently linked through a nonhomologous intervening sequence to an NH2-terminal adenosine 5'-phosphosulfate (APS) kinase domain forming a bifunctional fused protein. Possible advantages of bifunctionality were probed by separating the domains on the cDNA level and expressing them as monofunctional proteins. Expressed protein generated from the ATP-sulfurylase domain alone was fully active in both the forward and reverse sulfurylase assays. APS kinase-only recombinants exhibited no kinase activity. However, extension of the kinase domain at the COOH terminus by inclusion of the 36 residue linker region restored kinase activity. An equimolar mixture of the two monofunctional enzymes catalyzed the overall reaction (synthesis of PAPS from ATP + SO42-) comparably to the fused bifunctional enzyme. The importance of the domain order and organization was demonstrated by generation of a series of rearranged recombinants in which the order of the two active domains was reversed or altered relative to the linker region. The critical role of the linker region was established by generation of recombinants that had the linker deleted or rearranged relative to the two active domains. The intrinsic stability of the various recombinants was also investigated by measuring enzyme deactivation as a function of time of incubation at 25 or 37 degrees C. The expressed monofunctional ATP-sulfurylase, which was initially fully active, was unstable compared with the fused bifunctional wild type enzyme, decaying with a t1/2 of 10 min at 37 degrees C. Progressive extension by addition of kinase sequence at the NH2-terminal side of the sulfurylase recombinant eventually stabilized sulfurylase activity. Sulfurylase activity was significantly destabilized in a time-dependent manner in the rearranged proteins as well. In contrast, no significant deactivation of any truncated kinase-containing recombinants or misordered kinase recombinants was observed at either temperature. It would therefore appear that fusion of the two enzymes enhances the intrinsic stability of the sulfurylase only.

A member of a family of sulfate-activating enzymes causes murine brachymorphism.

Sulfation is critical to the function of a wide variety of biomolecules. This common modification requires the enzymatic synthesis of an activated sulfate donor, phosphoadenosine-phosphosulfate (PAPS). In higher organisms PAPS synthesis is catalyzed by a bifunctional sulfurylase kinase (SK) polypeptide having both ATP-sulfurylase and adenosine-phosphosulfate kinase activities. We report the identification of a gene family encoding murine SK proteins with these two activities. A family member, SK2, colocalizes with the locus for the autosomal recessive murine phenotype brachymorphism. Brachymorphic mice have normal lifespans, but abnormal hepatic detoxification, bleeding times, and postnatal growth, the latter being attributed to undersulfation of cartilage proteoglycan. A missense mutation in the SK2 coding sequence of bm mice that alters a highly conserved amino acid residue destroys adenosine-phosphosulfate kinase activity and therefore the ability of SK2 to synthesize PAPS. We conclude that a family of SK genes are responsible for sulfate activation in mammals, that a mutation in SK2 causes murine brachymorphism, and that members of this gene family have nonredundant, tissue-specific roles.

Deletion and site-directed mutagenesis of the ATP-binding motif (P-loop) in the bifunctional murine ATP-sulfurylase/adenosine 5'-phosphosulfate kinase enzyme.

The P-loop is a common motif found in ATP- and GTP-binding proteins. The recently cloned murine ATP-sulfurylase/adenosine 5'-phosphosulfate (APS) kinase contains a P-loop (residues 59-66) in the APS kinase portion of the bifunctional protein. A series of enzymatic assays covering the multiplicity of functions of this unique protein (reverse ATP-sulfurylase, APS kinase, and an overall assay) were used to determine the effect of deleting or altering specific residues constituting this motif. In addition to the full-length cDNA construct (1MSK), two deletion mutants that progressively shortened the N terminus by 34 amino acids (2MSK) and 70 amino acids (3MSK) were designed to examine the effects of translation initiation before (2MSK) and after (3MSK) the P-loop. The 2MSK protein possessed sulfurylase and kinase activity equivalent to the full-length construct, but 3MSK exhibited no kinase activity and reduced sulfurylase activity. In light of the evident importance of this motif, a number of site-directed mutants were designed to investigate the contribution of key residues. Mutation of a highly conserved lysine in the P-loop to alanine (K65A) or arginine (K65R) or the following threonine (T66A) to alanine ablated APS kinase activity while leaving ATP-sulfurylase activity intact. Three mutations (G59A, G62A, and G64A) addressed the role of the conserved glycines as follows: G64A showed diminished APS kinase activity only, whereas G62A had no effect on either activity. G59A caused a significant decrease in ATP-sulfurylase activity without effect on APS kinase activity. A series of highly conserved flanking cysteines (Cys-53, Cys-77, and Cys-83) were mutated to alanine, but none of these mutations showed any effect on either enzyme activity.

Sulfate activation and transport in mammals: system components and mechanisms.

Extensive studies on the mammalian sulfate-activating enzymes and PAPS translocase have enhanced our understanding of the overall pathway of sulfate activation and utilization. Isolation of the PAPS-synthesizing activities from rat chondrosarcoma and preparation of stable non-hydrolyzable analogs of APS and PAPS have facilitated the kinetic characterization of mammalian ATP sulfurylase and APS kinase. These studies provided the basis for further experimental work showing that APS, the labile intermediate product, is channeled directly between the sulfurylase and kinase active sites. The defect in the brachymorphic mutant mouse lies in this channeling mechanism, thus interfering with efficient PAPS production. The rat chondrosarcoma ATP sulfurylase and APS kinase activities, in fact, reside in a single bifunctional cytoplasmic protein, which has now been cloned and expressed. The mechanism by which PAPS reaches its sites of utilization in the Golgi lumen has also been elucidated: The PAPS translocase is a 230-kDa integral Golgi membrane protein which functions as an antiport.

The isolation and characterization of cDNA encoding the mouse bifunctional ATP sulfurylase-adenosine 5'-phosphosulfate kinase.

Biosynthesis of the activated sulfate donor, adenosine 3'-phosphate 5'-phosphosulfate, involves the sequential action of two enzyme activities: ATP sulfurylase, which catalyzes the formation of adenosine 5'-phosphosulfate (APS) from ATP and free sulfate, and APS kinase, which subsequently phosphorylates APS to produce adenosine 3'-phosphate 5'-phosphosulfate. Oligonucleotide primers were derived from a human infant brain-expressed sequence tag putatively encoding a portion of APS kinase. Using these primers, reverse transcriptase-polymerase chain reaction was performed on mRNA from neonatal normal mice resulting in amplification of a 127-bp DNA fragment. This fragment was subsequently used to screen a mouse brain lambda gt11 cDNA library, yielding a 2.2-kb clone. Primers were designed from the 5'-end of the 2.2-kb clone, and 5'-rapid amplification of cDNA ends was used to obtain the translation start site. Sequence from the overlapping clones was assembled into a 2475-bp composite sequence, which contains a single open reading frame that translates into a 624-deduced amino acid sequence. Northern blots of total RNA from neonatal mice yielded a single message species at approximately 3.3 kb. Southern blot of genomic DNA digested with several restriction enzymes suggested the gene is present as a single copy. Comparison against sequence data bases suggested the composite sequence was a fused sulfurylase-kinase product, since the deduced amino acid sequence showed extensive homology to known separate sequences of both ATP sulfurylase and APS kinase from several sources. The first 199 amino acids corresponded to APS kinase sequence, followed by 37 distinct amino acids, which did not match any known sequence, followed by 388 amino acids that are highly homologous to known ATP sulfurylase sequences. Finally, recombinant enzyme expressed in COS-1 cells exhibited both ATP sulfurylase and APS kinase activity.