Curettage and cryosurgery for low-grade cartilage tumors is associated with low recurrence and high function

BACKGROUND

Chondrosarcomas of bone traditionally have been treated by wide or radical excision, procedures that may result in considerable lifelong disability. Grade 1 chondrosarcomas have little or no metastatic potential and are often difficult to distinguish from painful benign enchondromas. Curettage with adjuvant cryosurgery has been proposed as an alternative therapy for Grade 1 chondrosarcomas given the generally better function after the procedure. However, because it is an intralesional procedure, curettage and cryosurgery may be associated with higher rates of recurrence.

QUESTIONS/PURPOSES

We asked whether Grade 1 chondrosarcomas and enchondromas of uncertain malignant potential treated by curettage and cryosurgery are associated with low recurrence rates and high functional scores.

PATIENTS AND METHODS

We retrospectively reviewed the records of 46 patients with Grade 1 chondrosarcomas and enchondromas of uncertain malignant potential treated by curettage and cryosurgery. Forty-one patients had tumors of the long bones. Patients were followed a minimum of 18 months (average, 47.2. months; range, 18-134 months) for evidence of recurrence and for assessment of Musculoskeletal Tumor Society (MSTS) functional score.

RESULTS

Two of the 46 patients had recurrences in the original tumor site (4.3% recurrence rate), which subsequently were removed by wide excision, and both patients were confirmed to be disease-free 36 and 30 months, respectively, after the second surgery. The mean MSTS score was 27.2 of 30 points (median, 29 points).

CONCLUSIONS

Our observations show curettage with cryosurgery is associated with low recurrence of Grade 1 chondrosarcoma and high functional scores. Curettage with cryosurgery is a reasonable alternative to wide or radical excision as the treatment for Grade 1 chondrosarcomas, and allows for more radical surgery in the event of local recurrence.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Polymethylmethacrylate particle exposure causes changes in p38 MAPK and TGF-beta signaling in differentiating MC3T3-E1 cells

Periprosthetic osteolysis of joint replacements caused by wear debris is a significant complication of joint replacements. Polymethylmethacrylate (PMMA) particles have been shown to inhibit osteogenic differentiation, but the molecular mechanism has not been previously determined. In this study, we exposed differentiating MC3T3-E1 preostoblast cells to PMMA particles and determined the changes that occurred with respect to p38 mitogen-activated protein kinase (MAPK) activity and the transforming growth factor (TGF)-beta1 and bone morphogenetic protein (BMP) signaling pathways. In the absence of particles, MC3T3-E1 cells demonstrate activation of p38 MAPK on day 8 of differentiation; however, when treated with PMMA particles, differentiating MC3T3-E1 cells demonstrate the suppression of p38 activity on day 8 and show activation of p38 on days 1 and 4. On day 4 of particle exposure, the differentiating MC3T3-E1 cells show significant downregulation of TGF-beta1 expression, which is involved in osteoblast differentiation, and a significant upregulation of the expression of BMP3 and Sclerostin (SOST), which are negative regulators of osteoblast differentiation. By day 8 of particle exposure, the changes in TGF-beta1, BMP3, and SOST expression are opposite of those seen on day 4. This study has demonstrated the distinct changes in the molecular profile of MC3T3-E1 cells during particle-induced inhibition of osteoblast differentiation. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

Polymethylmethacrylate particles impair osteoprogenitor viability and expression of osteogenic transcription factors Runx2, osterix, and Dlx5

Polymethylmethacrylate (PMMA) particles have been shown to inhibit the differentiation of osteoprogenitor cells, but the mechanism of this inhibitory effect has not been investigated. We hypothesize that the inhibitory effects of PMMA particles involve impairment of osteoprogenitor viability and direct inhibition of transcription factors that regulate osteogenesis. We challenged MC3T3-E1 osteoprogenitors with PMMA particles and examined the effects of these materials on osteoprogenitor viability and expression of transcription factors Runx2, osterix, Dlx5, and Msx2. MC3T3-E1 cells treated with PMMA particles over a 72-h period showed a significant reduction in cell viability and proliferation as indicated by a dose- and time-dependent increase in supernatant levels of lactate dehydrogenase, an intracellular enzyme released from dead cells, a dose-dependent decrease in cell number and BrdU uptake, and the presence of large numbers of positively labeled Annexin V-stained cells. The absence of apoptotic cells on TUNEL assay indicated that cell death occurred by necrosis, not apoptosis. MC3T3-E1 cells challenged with PMMA particles during the first 6 days of differentiation in osteogenic medium showed a significant dose-dependent decrease in the RNA expression of Runx2, osterix, and Dlx5 on all days of measurement, while the RNA expression of Msx2, an antagonist of Dlx5-induced osteogenesis, remained relatively unaffected. These results indicate that PMMA particles impair osteoprogenitor viability and inhibit the expression of transcription factors that promote osteoprogenitor differentiation.

Ultrahigh molecular weight polyethylene wear debris inhibits osteoprogenitor proliferation and differentiation in vitro

Polyethylene wear debris induces progressive osteolysis by increasing bone degradation and suppressing bone formation. Polyethylene particles inhibit the function of mature osteoblasts, but whether polyethylene particles also interfere with the proliferation and differentiation of osteoprogenitor cells is unknown. In this study, we investigated the effects of ultrahigh molecular weight polyethylene (UHMWPE) particles on the osteogenic activity of primary murine bone marrow osteoprogenitors and MC3T3-E1 preosteoblastic cells in vitro. Submicron-sized UHMWPE particles generated from wear simulator tests were isolated from serum-containing solution by density gradient centrifugation. The particles were coated onto the surface of culture wells at concentrations of 0.038, 0.075, 0.150, 0.300, and 0.600% v/v in a layer of type I collagen matrix. Primary murine bone marrow cells and MC3T3-E1 preosteoblasts were seeded onto the particle-collagen matrix and induced to differentiate in osteogenic medium for 20 days. Exposure of both cell populations to UHMWPE particles resulted in a dose-dependent decrease in mineralization, proliferation, alkaline phosphatase activity, and osteocalcin production when compared with control cells cultured on collagen matrix without particles. Complete suppression of osteogenesis was observed at particle concentrations > or =0.150% v/v. This study demonstrated that UHMWPE particles inhibit the osteogenic activity of osteoprogenitor cells, which may result in reduced periprosthetic bone regeneration and repair.

Polymethylmethacrylate particles inhibit osteoblastic differentiation of MC3T3-E1 osteoprogenitor cells

Orthopedic wear debris has been implicated as a significant inhibitory factor of osteoblast differentiation. Polymethylmethacrylate (PMMA) particles have been previously shown to inhibit the differentiation of osteoprogenitors in heterogeneous murine marrow stromal cell cultures, but the effect of PMMA particles on pure osteoprogenitor populations remains unknown. In this study, we challenged murine MC3T3-E1 osteoprogenitor cells with PMMA particles during their initial differentiation in osteogenic medium. MC3T3-E1 cultures challenged with PMMA particles showed a gradual dose-dependent decrease in mineralization, cell number, and alkaline phosphatase activity at low particle doses (0.038-0.150% v/v) and complete reduction of these outcome parameters at high particle doses (> or =0.300% v/v). MC3T3-E1 cultures challenged with a high particle dose (0.300% v/v) showed no rise in these outcome parameters over time, whereas cultures challenged with a low particle dose (0.075% v/v) showed a normal or reduced rate of increase compared to controls. Osteocalcin production was not significantly affected by particles at all doses tested. MC3T3-E1 cells grown in conditioned medium from particle-treated MC3T3-E1 cultures showed a significant reduction in mineralization only. These results indicate that direct exposure of MC3T3-E1 osteoprogenitors to PMMA particles results in suppression of osteogenic proliferation and differentiation.

Polymethylmethacrylate particles inhibit osteoblastic differentiation of bone marrow osteoprogenitor cells

Aseptic implant loosening of total joint replacements often results from particle-mediated bone loss, which may be a combined effect of osteolysis and suppressed bone formation. Bone regeneration in the prosthetic bed depends on the activity of osteoblasts and their differentiation from osteoprogenitors in the bone marrow. This study investigated the effects of polymethylmethacrylate (PMMA) particles on the ability of bone marrow osteoprogenitors to differentiate into osteoblasts in vitro. Murine bone marrow cells challenged with PMMA particles on the first day of differentiation in osteogenic medium showed a dose-dependent decrease in osteoprogenitor proliferation, alkaline phosphatase expression, and mineralization. Undifferentiated bone marrow cells pretreated with PMMA particles in nonosteogenic medium for 5 days also showed a dose-dependent loss in osteogenic potential, which was sustained throughout subsequent growth in particle-free, osteogenic medium. Bone marrow cells challenged with PMMA particles after the fifth day of differentiation in osteogenic medium showed significant reductions in cellular proliferation, but not alkaline phosphatase expression and mineralization, indicating that bone marrow cells were most sensitive to particle treatment during the first 5 days of differentiation. This study demonstrated that PMMA particles inhibit osteoblastic differentiation of bone marrow osteoprogenitor cells, which may contribute to periprosthetic bone loss and implant failure.

Effects of a p38 MAP kinase inhibitor on bone ingrowth and tissue differentiation in rabbit chambers

The effects of an oral p38 mitogen-activated protein kinase (MAPK) inhibitor and polyethylene particles separately and together on tissue differentiation in the bone harvest chamber (BHC) in rabbits over a 3-week treatment period were investigated. The harvested tissue was analyzed histomorphometrically for markers of bone formation (percentage of bone area), osteoblasts (alkaline phosphatase staining), and osteoclasts (CD51, the alpha chain of the vitronectin receptor). Polyethylene particles decreased the percentage of bone ingrowth and staining for alkaline phosphatase. The p38 MAPK inhibitor alone decreased alkaline phosphatase staining. When the oral p38 MAPK inhibitor was given and the chamber contained polyethylene particles, there was a suppression of bone ingrowth and alkaline phosphatase staining. In contrast to oral non-steroidal anti-inflammatory drugs (NSAIDs) and local Interleukin-1 receptor antagonist (IL-1ra) administration, the oral p38 MAPK inhibitor alone did not suppress bone formation when given during the initial phase of tissue differentiation. Particle-induced inflammation and the foreign body reaction were not curtailed when the p38 MAPK inhibitor was given simultaneously with particles. Additional experiments are needed to establish the efficacy of p38 MAPK inhibitor administration on mitigating an established inflammatory and foreign body reaction that parallels the clinical situation more closely.

Kinetics of polymethylmethacrylate particle-induced inhibition of osteoprogenitor differentiation and proliferation

Periprosthetic bone loss induced by implant wear debris may be a combined effect of osteolysis and reduced bone formation resulting from particle-induced suppression of osteoprogenitor differentiation. This study investigated the time-dependent effects of polymethylmethacrylate (PMMA) particles on the osteogenic capability of bone marrow osteoprogenitor cells during the early phase of differentiation. Murine bone marrow cells were challenged with PMMA particles (0.30% v/v) on the first day of growth in osteogenic medium. Particles were removed from culture after 1, 3, and 5 days, respectively, after which cell growth in osteogenic medium was continued until the 15th day. Bone marrow osteoprogenitor cells exposed to particles during the first 5 days of differentiation showed complete, irreversible inhibition of proliferation, alkaline phosphatase expression, and mineralization. Osteoprogenitors exposed to particles for more than 5 days showed the same degree of inhibition, while those exposed to particles for less than 5 days showed a diminished inhibitory response. Conditioned medium from particle-treated cells did not suppress osteogenic development, demonstrating that suppression of osteogenesis was not due to secreted inhibitory factors. This study has shown that the early phase of osteoprogenitor differentiation is a crucial time period during which exposure to PMMA particles causes irreversible inhibition of osteogenesis.

Effects of orthopaedic wear particles on osteoprogenitor cells

Wear particles from total joint arthroplasties are constantly being generated throughout the lifetime of an implant. Since mesenchymal stem cells and osteoprogenitors from the bone marrow are the precursors of osteoblasts, the reaction of these cells to orthopaedic wear particles is critical to both initial osseointegration of implants and ongoing regeneration of the periprosthetic bed. Particles less than 5 microm can undergo phagocytosis by mature osteoblasts, with potential adverse effects on cellular viability, proliferation and function. The specific effects are dependent on particle composition and dose. Metal and polymer particles in non-toxic doses stimulate pro-inflammatory factor release more than ceramic particles of a similar size. The released factors inhibit markers of bone formation and are capable of stimulating osteoclast-mediated bone resorption. Mesenchymal stem cells and osteoprogenitors are also profoundly affected by wear particles. Titanium and polymethylmethacrylate particles inhibit bone cell viability and proliferation, and downregulate markers of bone formation in a dose- and time-dependent manner. Future studies should delineate the molecular mechanisms by which particles adversely affect mesenchymal stems cells and the bone cell lineage and provide strategies to modulate these effects.

Conformational States of Cytochrome P450cam Revealed by Trapping of Synthetic Molecular Wires

Members of the ubiquitous cytochrome P450 family catalyze a vast range of biologically significant reactions in mammals, plants, fungi, and bacteria. Some P450s display a remarkable promiscuity in substrate recognition, while others are very specific with respect to substrate binding or regio and stereo-selective catalysis. Recent results have suggested that conformational flexibility in the substrate access channel of many P450s may play an important role in controlling these effects. Here, we report the X-ray crystal structures at 1.8A and 1.5A of cytochrome P450cam complexed with two synthetic molecular wires, D-4-Ad and D-8-Ad, consisting of a dansyl fluorophore linked to an adamantyl substrate analog via an alpha,omega-diaminoalkane chain of varying length. Both wires bind with the adamantyl moiety in similar positions at the camphor-binding site. However, each wire induces a distinct conformational response in the protein that differs from the camphor-bound structure. The changes involve significant movements of the F, G, and I helices, allowing the substrate access channel to adapt to the variable length of the probe. Wire-induced opening of the substrate channel also alters the I helix bulge and Thr252 at the active site with binding of water that has been proposed to assist in peroxy bond cleavage. The structures suggest that the coupling of substrate-induced conformational changes to active-site residues may be different in P450cam and recently described mammalian P450 structures. The wire-induced changes may be representative of the conformational intermediates that must exist transiently during substrate entry and product egress, providing a view of how substrates enter the deeply buried active site. They also support observed examples of conformational plasticity that are believed be responsible for the promiscuity of drug metabolizing P450s. Observation of such large changes in P450cam suggests that substrate channel plasticity is a general property inherent to all P450 structures.

Renin-angiotensin system blockade in biopsy-proven allograft nephropathy

Allograft nephropathy leads to progressive renal injury and ultimate graft loss. In native kidney disease, the use of angiotensin-converting enzyme inhibitors (ACEi) or angiotensin receptor blockers (ARB) is beneficial in retarding the decline of renal function. We reviewed a cohort of renal transplant recipients who were prescribed either an ACEi or ARB for biopsy-proven allograft nephropathy. Patients were followed from time of initiation of ACEi/ARB and were stratified based on biopsy findings. Outcomes of interest included safety, allograft survival, renal function, and rate of renal function decline pre- and post-ACEi/ARB. The 5-year allograft survival after biopsy was 83%. Mean serum creatinine was 2.2 +/- 1.1 mg/dL (range 1.0 to 4.3) at time of biopsy and 2.6 +/- 1.2 mg/dL (1.2 to 6.5) at last follow-up. The mean slope of the creatinine versus time (SD) was 2.43 (7.93) in the 12 months prior to therapy and 1.45 (3.66) following therapy, with the absolute difference in slope -3.38 (6.06) (P =.0004). We conclude that treatment with ACEi/ARB is beneficial in the management of allograft nephropathy.

Regulation of the Expression of the Prostate-specific Antigen by Claudin-7

Claudins are a family of proteins involved in forming tight junctions between cells. Here we describe two forms of claudin-7 (CLDN-7), a full-length form of CLDN-7 with 211 amino-acid residues and a C-terminal truncated form with 158 amino-acid residues. These two forms of CLDN-7 are able to regulate the expression of a tissue-specific protein, the prostate-specific antigen (PSA), in the LNCaP prostate cancer cell line. We also found that the expression of CLDN-7 is responsive to androgen stimulation in the LNCaP cell line, suggesting that this protein is involved in the regulatory mechanism of androgen. Both forms of claudin-7 are expressed in human prostate, kidney and lung samples, and in most samples, the full-length form of claudin-7 was predominant. However, in some prostate samples from healthy individuals, the truncated form of claudin-7 is predominantly expressed. Our results demonstrated that unlike other claudins, CLDN-7 has both structural and regulatory functions, and the two forms of CLDN-7 may be related to cell differentiation in organ development.

Autologous chondrocyte implantation

Rationale for the treatment of cartilage damage in younger patients depends on a thorough understanding of the predisposing factors for the chondrosis and the stage of disease. Implantation with autologous cultured chondrocytes allows for resurfacing of larger defect areas with reproducibly good/excellent results in 90% of patients with isolated lesions of the femoral condyle. Patellar lesions also may be successfully treated (approximately 75% improved) but strict attention must be given to correction of malalignment. Results in patients with tibial and salvage lesions are encouraging; however, these results should be viewed with caution due to the small number of patients with 2-year follow-up. Autologous chondrocyte implantation involves an open technique with the inherent disadvantages of adhesions and a more prolonged recovery. However, these disadvantages must be weighed against the procedure's ability to produce a hyaline-type tissue with greater durability than fibrocartilage repairs produced by traditional marrow-stimulation techniques. We recommended matching the treatment procedure to patient expectations and lesion/demographic characteristics. Based on the available literature. algorithms have been published that recommend autologous chondrocyte implantation be reserved as first-line treatment for high-demand patients with large lesions (>2 cm2) and as revision therapy in patients with lesions of all sizes, regardless of patient demand, who have failed alternative marrow stimulation techniques.

Fluorescent probes for cytochrome p450 structural characterization and inhibitor screening

We have synthesized two luminescent probes (D-4-Ad and D-8-Ad) that target cytochrome P450cam. D-4-Ad luminescence is quenched by Förster energy transfer upon binding (Kd = 0.83 muM) but is restored when the probe is displaced from the active site by camphor. In contrast, D-8-Ad (Kd approximately 0.02 muM) is not displaced from the enzyme, even in the presence of a large excess of camphor. The 2.2 A resolution crystal structure of the D-8-Ad:P450cam complex reveals extensive hydrophobic contacts between the probe and the enzyme, which result from the conformational flexibility of the B', F, and G helices. Probes with properties similar to those of D-4-Ad potentially could be useful for screening P450 inhibitors.

Avian retrovirus DNA internal attachment site requirements for full-site integration in vitro

Concerted integration of retrovirus DNA termini into the host chromosome in vivo requires specific interactions between the cis-acting attachment (att) sites at the viral termini and the viral integrase (IN) in trans. In this study, reconstruction experiments with purified avian myeloblastosis virus (AMV) IN and retrovirus-like donor substrates containing wild-type and mutant termini were performed to map the internal att DNA sequence requirements for concerted integration, here termed full-site integration. The avian retrovirus mutations were modeled after internal att site mutations studied at the in vivo level with human immunodeficiency virus type 1 (HIV-1) and murine leukemia virus (MLV). Systematic overlapping 4-bp deletions starting at nucleotide positions 7, 8, and 9 in the U3 terminus had a decreasing detrimental gradient effect on full-site integration, while more internal 4-bp deletions had little or no effect. This decreasing detrimental gradient effect was measured by the ability of mutant U3 ends to interact with wild-type U3 ends for full-site integration in trans. Modification of the highly conserved C at position 7 on the catalytic strand to either A or T resulted in the same severe decrease in full-site integration as the 4-bp deletion starting at this position. These studies suggest that nucleotide position 7 is crucial for interactions near the active site of IN for integration activity and for communication in trans between ends bound by IN for full-site integration. The ability of AMV IN to interact with internal att sequences to mediate full-site integration in vitro is similar to the internal att site requirements observed with MLV and HIV-1 in vivo and with their preintegration complexes in vitro.

12-O-tetradecanoylphorbol-13-acetate (TPA)-induced c-Jun N-terminal kinase (JNK) phosphatase renders immortalized or transformed epithelial cells refractory to TPA-inducible JNK activity

c-Jun N-terminal kinase (JNK) regulates gene expression in response to various extracellular stimuli. JNK can be activated by the tumor promoting agent, 12-O-tetradecanoylphorbol-13-acetate (TPA) in normal human oral keratinocytes but not in human keratinocytes that have been immortalized (HOK-16B and HaCaT) or transformed (HOK-16B-Bap-T) nor in a cervical carcinoma cell line (HeLa). The refractory JNK activation response to TPA is not due a defect in the JNK pathway, because JNK can be activated by other stimuli, e.g. UV irradiation and an alkylating agent N-methyl-N'-nitrosoguanidine in these immortalized or transformed cells. More importantly, the refractory JNK and JNKK activation response to TPA can be restored by treatment of the cells with a combination of TPA and a protein-tyrosine phosphatase inhibitor, sodium orthovanadate. Furthermore, pretreatment of cells with TPA partially inhibited UV- or N-methyl-N'-nitrosoguanidine-induced JNK activity. These results suggest that a TPA-inducible, orthovanadate-sensitive protein-tyrosine phosphatase may specifically down-regulate JNK signaling pathway in these immortalized/transformed epithelial cells. In contrast, ERK and p38/Mpk2 are not regulated by this TPA-induced phosphatase. This putative protein-tyrosine phosphatase appears to be JNK pathway-specific.

ATF-2 has intrinsic histone acetyltransferase activity which is modulated by phosphorylation

Transcription factors carry functional domains, which are often physically distinct, for sequence-specific DNA binding, transcriptional activation and regulatory functions. The transcription factor ATF-2 is a DNA-binding protein that binds to cyclic AMP-response elements (CREs), forms a homodimer or heterodimer with c-Jun, and stimulates CRE-dependent transcription. Here we report that ATF-2 is a histone acetyltransferase (HAT), which specifically acetylates histones H2B and H4 in vitro. Motif A, which is located in the HAT domain, is responsible for the stimulation of CRE-dependent transcription; moreover, in response to ultraviolet irradiation, phosphorylation of ATF-2 is accompanied by enhanced HAT activity of ATF-2 and CRE-dependent transcription. These results indicate that phosphorylation of ATF-2 controls its intrinsic HAT activity and its action on CRE-dependent transcription. ATF-2 may represent a new class of sequence-specific factors, which are able to activate transcription by direct effects on chromatin components.

The E7 oncoprotein of human papillomavirus type 16 interacts with F-actin in vitro and in vivo

We report here that E7 oncoprotein of human papillomavirus type 16 (HPV-16) forms a complex in vivo and in vitro with actin, one of the components of the cellular cytoskeleton. The in vivo interaction was detected by immunofluorescent staining and confocal microscopic examination of normal human oral keratinocytes (NHOK) and CV-1 cells after transient expression of E7 employing the vaccinia virus-T7 RNA polymerase system and by coimmunoprecipitation from an immortalized, nontumorigenic cell line obtained after transfecting NHOK with the cloned HPV-16 DNA genome. The in vitro interaction was detected by cosedimentation of bacterially expressed E7 phosphorylated with rabbit reticulocyte lysate or purified casein kinase II (CKII) prior to incubation with F-actin. This interaction was inhibited if E7 phosphorylation by the rabbit reticulocyte lysate was prevented with heparin, a CKII inhibitor, or if the amino acids Ser-31 and Ser-32 in E7, which are phosphorylated by CKII, were replaced with amino acids that cannot be phosphorylated. Interestingly, a decrease in the amount of polymerized actin occurred in cells expressing E7.

Residual bladder dysfunction 2 to 10 years after acute transverse myelitis

OBJECTIVE

Acute transverse myelitis (ATM) is a relatively rare condition in children. The recovery rate is reported to be generally complete. In the current study, the long-term urological outcome of children with ATM was assessed.

METHODOLOGY

The medical records of children with ATM admitted to Queen Mary Hospital, Hong Kong, over the last 15 years, were reviewed.

RESULTS

The median age of the five children with ATM at the time of onset was 6 years (range = 2-12 years). The median length of follow up was 5 years (2-10 years). Four children recovered completely from paraparesis; two had no urinary symptoms with normal micturition. However, video-urodynamic studies 3 years after the acute onset revealed that four out of the five children, including one without any urinary symptom, suffered from residual bladder dysfunction - two from contractile neurogenic bladder and two from intermediate type of neurogenic bladder.

CONCLUSION

Residual bladder dysfunction is common in children suffering from ATM despite improvement of paraparesis and apparent lack of urological symptoms. Long-term follow up of urological function in these patients is recommended.

Retrovirus DNA termini bound by integrase communicate in trans for full-site integration in vitro

Integration of linear retrovirus DNA involves the concerted insertion of the viral termini (full-site integration) into the host chromosome. We investigated the interactions that occur between long terminal repeat (LTR) termini bound by avian retrovirus integrase (IN) for full-site integration in vitro. Wild-type (wt) or mutant LTR donors that possess gain-of-function ("G") or loss-of-function ("L") for full-site integration activity were used. G LTR termini are characterized as having significantly higher strand transfer activity than the wt and the L LTR termini. L LTR mutations are classified as partially or extremely defective for strand transfer activity. The L mutations were further classified by their ability to either permit or block the assembly of G or wt LTR termini into nucleoprotein complexes capable of full-site strand transfer. We demonstrated that avian myeloblastosis virus IN bound to G LTR termini increased the incorporation of partially defective L LTR termini into nucleoprotein complexes that were capable of full-site integration. The observed full-site integration activity of these assembled nucleoprotein complexes appeared to be influenced by each individual IN-LTR complex in trans. In contrast, extremely defective L LTR termini exhibited the ability to effectively block the assembly of wt LTR termini into nucleoprotein complexes capable of full-site strand transfer. Data from nonspecific DNA competition experiments suggested that IN had an apparent higher affinity for G LTR donor termini than for partially defective L LTR donor termini as measured by full-site integration activity. However, assembled nucleoprotein complexes containing either two G or two L LTR donors were stable, having a similar half-life of approximately 2 h on ice. The results suggest that LTR termini bound by IN exhibit an allosteric effect to modulate full-site integration in vitro. Similar regulatory controls also appear to exist in vivo between the wt U3 and wt U5 LTR termini in retroviruses as well as purified retrovirus preintegration complexes that promoted full-site integration in vitro.

Cutaneous rat wounds express c49a, a novel gene with homology to the human melanoma differentiation associated gene, mda-7

We have used DD-PCR (differential display-polymerase chain reaction) to identify new genes that are over- or underexpressed during wound repair. DD-PCR performed on excisional wounds identified the expression of rat c49a. Cloning and sequence analysis of the rat c49a gene revealed high homology to a novel human melanoma differentiation associated gene, mda-7. The human mda-7gene isolated from melanoma cell lines, has been linked with human melanoma differentiation, and growth suppression. Moreover, transfection of human mda-7 constructs into human tumor cells suppresses the growth and colony formation of tumor cells from diverse origins. To confirm and relatively quantitate expression of rat c49a gene during repair, specific primer, reduced cycle RT-PCR (reverse transcription-PCR) was performed. RT-PCR showed an approximately 9 to 12-fold elevation of rat c49a mRNA at 12 h to 5 days above nonwounded controls that gradually decreased to approximately 1.5 to 3-fold by day 14. Cloning and sequence analysis of the entire 1200 base pair c49a gene product showed 78% nucleotide homology to human mda-7. Immunohistochemistry studies localized rat C49A expression primarily to fibroblast-like cells at the wound edge and base. The marked up-regulation of rat c49a transcripts during the inflammatory and early granulation tissue phases of wound repair where cellular processes such as re-epithelialization, angiogenesis, and fibroplasia predominate--suggest that c49a is associated with proliferation of fibroblasts in wound healing.