Uncovering and engineering the mechanical properties of the adhesion GPCR ADGRG1 GAIN domain.

Key cellular functions depend on the transduction of extracellular mechanical signals by specialized membrane receptors including adhesion G-protein coupled receptors (aGPCRs). While recently solved structures support aGPCR activation through shedding of the extracellular GAIN domain, the molecular mechanisms underpinning receptor mechanosensing remain poorly understood. When probed using single-molecule atomic force spectroscopy and molecular simulations, ADGRG1 GAIN dissociated from its tethered agonist at forces significantly higher than other reported signaling mechanoreceptors. Strong mechanical resistance was achieved through specific structural deformations and force propagation pathways under mechanical load. ADGRG1 GAIN variants computationally designed to lock the alpha and beta subdomains and rewire mechanically-induced structural deformations were found to modulate the GPS-Stachel rupture forces. Our study provides unprecedented insights into the molecular underpinnings of GAIN mechanical stability and paves the way for engineering mechanosensors, better understanding aGPCR function, and informing drug-discovery efforts targeting this important receptor class.

Sea urchin maternal and embryonic U1 RNAs are spatially segregated in early embryos.

We have used in situ hybridization and cell fractionation methods to follow the distribution of U1 RNA and immunofluorescence microscopy to follow the distribution of snRNP proteins in oocytes, eggs, and embryos of several sea urchin species. U1 RNA and U1-specific snRNP antigens are concentrated in germinal vesicles of oocytes. Both appear to relocate after oocyte maturation because they are found primarily, if not exclusively, in the cytoplasm of mature unfertilized eggs. This cytoplasmic residence is maintained during early cleavage and U1 RNA is first detectable in nuclei of micromeres at the 16-cell stage. Between morula and gastrula stages the steady-state concentrations of both RNA and antigens gradually increase in nuclei and decrease in cytoplasm. Surprisingly, analysis of the distribution of newly synthesized U1 RNA shows that it does not equilibrate with the maternal pool. Instead new transcripts are confined to nuclei, while cytoplasmic U1 RNAs are of maternal origin. This lack of equilibration and the conversion of maternal U1 RNAs from nuclear species in oocytes to cytoplasmic in embryos suggests that these RNPs (or RNAs) are structurally altered when released to the cytoplasm at oocyte maturation.

In vitro growth inhibition of ovarian cancer cells by decorin: synergism of action between decorin and carboplatin.

In vitro studies showed that decorin, a small proteoglycan that is a normal component of the cell matrix involved in tissue scaffolding, effectively inhibited the growth of two ovarian cancer lines, SKOV3 and 2774. Using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay to measure cell growth, IC50s for decorin ranged from 150 to 400 microg/ml for the two cell lines. In contrast, the growth of tumor cells grown on an artificial cell matrix (Matrigel) was unaffected by decorin treatment, perhaps because of the decorin being irreversibly bound by matrix-associated collagen. Decorin-induced inhibition of ovarian tumor cells appeared to be associated with the increased expression of the cyclin-dependent kinase inhibitor p21Waf1/Cip1. Up-regulation of p21 expression was shown by Western blot analysis in decorin-treated ovarian cancer cells. No decorin-induced up-regulation of c-myc was seen, although decorin was reported to activate the epidermal growth factor receptor. Decorin was also shown to synergize with carboplatin to inhibit the growth of ovarian tumor cells. Additional studies are warranted to determine the role of decorin in the treatment of ovarian cancer.

Quantitative analysis of transforming growth factor beta 1 and 2 in ovarian carcinoma.

Transforming growth factor beta (TGF-beta) is an important family of cytokines that may promote tumor growth in vivo through several mechanisms including interference with antitumor T-cell immune responses, alteration of factors in the stroma and matrix, and the promotion of angiogenesis. TGF-beta isotypes have been detected in malignant and normal ovarian tissues. We have determined by quantitative immunohistochemistry the density of TGF-beta1, TGF-beta2, and human leukocyte antigen (HLA) Class I and Class II antigens on malignant cells in paired primary and metastatic specimens from 10 patients with ovarian carcinoma. Cryostat sections of specimens from the carcinomas and from normal ovaries of three women of similar age without ovarian cancer were stained respectively with specific antibodies to TGF-beta1, TGF-beta2, and HLA Class I and II antigens, and with isotype-matched control antibodies. Antigen density was quantitated blindly as mean absorbance on a SAMBA 4000 image analyzer. TGF-beta1 and TGF-beta2 were overexpressed in both primary and metastatic tumor specimens in comparison with normal ovarian tissue. No statistical correlation was found between the expression of TGF-beta1 or TGF-beta2 and HLA class I or HLA class II, which suggests that TGF-beta isotypes could have effects on the immune system other than down-modulation of these HLA molecules. Furthermore, the lack of association between levels of TGF-beta expression and the reduced expression of HLA molecules could suggest that tumor cells expressing both HLA and TGF-beta may be suitable targets for adaptive immunotherapy. Additional studies are necessary to determine whether TGF-beta expressed by ovarian cancer cells merits evaluation as a therapeutic target.

Transduction of rIL-2 expanded CD4+ and CD8+ ovarian TIL-derived T cell lines with the G1Na (neor) replication-deficient retroviral vector.

We have expanded ovarian tumor-infiltrating lymphocytes (TIL) in low concentrations of recombinant interleukin-2 (rIL-2) to conduct intraperitoneal adoptive immunotherapy trials in patients with ovarian cancer. We have previously demonstrated that certain T cell lines and clones derived from ovarian TIL exhibit in vitro autologous tumor-specific cytotoxicity and/or cytokine production (interferon-gamma, tumor necrosis factor-alpha) preferentially in response to autologous tumor cells. Studies that utilize a marker gene introduced into the DNA of TIL can provide useful information on specific uptake or localization of TIL at tumor sites and on the survival of TIL in vivo. We have conducted a series of preclinical experiments in which we have successfully transfected TIL with G1Na, which encodes the gene for neomycin phosphotransferase (neoR). NeoR was detected in at least 10% of CD8+ cells (mean = 10.4%) and between 2.5 and 20% of CD4+ TIL (mean = 8.5%). Transduction of ovarian TIL with G1Na caused no substantial changes to the T cell phenotypes or in vitro cytotoxicities against ovarian and hematogenous tumor cell targets, or on the rIL-2 requirements of TIL for growth and proliferation. In addition, the intact G1Na provirus in transduced TIL cells was rescuable by replication-competent retrovirus and was transferred into the genome of NIH-3T3 fibroblasts, which were rendered resistant to G418. An enhanced polymerase chain reaction (PCR) procedure utilizing detection by ethidium bromide staining was developed. The enhanced PCR detected 1 in 100,000 neoR-labeled cells. Furthermore, detection of the G1Na genome in transduced TIL by in situ hybridization with an RNA probe provided evidence for expression of the neoR gene in transduced TIL. Results obtained from these studies suggest that ovarian TIL-derived T cell lines transduced with the neoR gene post infection with the G1Na retroviral vector can be utilized to examine the in vivo trafficking pattern of ovarian TIL-derived T cell lines expanded in low concentrations of rIL-2 and their survival.

The role of cytokines in both the normal and malignant ovary.

Normal ovarian tissue is rich in cytokines. Cytokines and chemokines are important in the physiology of ovarian function and of ovulation. Cytokines and chemokines may recruit cytokine-producing lymphocytes to the site of a developing follicle, and cytokines appear to play an important role in pre and post follicle development. Most of the same cytokines that are found in normal ovarian tissue are also found in association with malignancy in contrast to their functions in normal tissues. It is reasonable to assume that the functions of cytokines associated with malignancy may serve to promote the unregulated growth if tumor cells and metastasis. It is also likely that cytokines produced by tumors will modulate immune responses that favor tumor progression. In the following review, we have highlighted those functions of cytokines that have been identified as having the most significant impact on tumor growth and development. By examining activities of these cytokines in normal and in malignant ovarian tissues, it is hoped that future possible avenues for investigation may be opened up and that the results of these investigations will lead to strategies that can modulate the production or the activity of the cytokines leading to the growth of tumors or their metastases. Such strategies now fall under the general discipline of bioimmunotherapy. This is an expanding discipline as more is learned about growth regulation in cancer, and with the availability and rapid development of new molecules for therapeutic approaches.

Structure of an unusual sea urchin U1 RNA gene cluster.

Genomic clones containing multiple copies of the Lytechinus variegatus U1 gene have been isolated from a gene library in the phage lambda EMBL3. These clones contain both types of U1 RNA gene repeats interspersed in the same 15-kb fragment. In addition, about 1/3 of the repeat units contain a 260-bp insert 460 bp prior to the first nucleotide of the U1 RNA sequence. The inserted sequence is abundant in the sea urchin genome as judged by Southern blots of genomic DNA. There are no repeated sequences flanking the insert. The insert occurs at the same position in the highly conserved 5'-flanking region at which a deletion has previously been reported.

RT-PCR quantitation of cytokine responses in vivo from specimens containing small numbers of cells during bioimmunotherapy.

A Standard Template method has been developed to carry out semiquantitative RT-PCR analysis on mRNA extracted from small specimens that contain low yields of RNA. Using easily prepared templates (made from previously tested reference specimens), standard calibration curves were generated for each of two cytokine products of interest, specifically IL-10 and IFN-gamma. Also, internal standardization was accomplished by quantitating a well-characterized housekeeping gene (GAPDH). Simple densitometry of the RT-PCR product did not demonstrate sufficient reliability for quantitation since a logarithmic relationship was shown between product and template input. Peritoneal exudate cell specimens that were obtained from ovarian cancer patients during intraperitoneal immunotherapy were utilized for the demonstration of IL-10 and IFN-gamma transcript in vivo. Briefly, this method consists of: (1) template preparation: a PCR product for the cytokine of interest is generated from a previously identified positive specimen, purified and stored at -20 degrees C. (2) RT-PCR: cDNAs are produced from RNA extracted from patient specimens. Replicates of each cDNA and serial dilutions of the corresponding template are amplified with primers specific for each cytokine of interest. (3) Quantitation: photographs are made of the PCR products displayed on an agarose gel and are analyzed by densitometry. Determinations of fold-differences in cytokine transcript expression are normalized to the mRNA content of each specimen (based on the expression of GAPDH).

Anomalies of the TGF-beta postreceptor signaling pathway in ovarian cancer cell lines.

Transforming growth factor-beta (TGF-beta) can cause cell cycle arrest, terminal differentiation, or apoptosis in most normal epithelial cells, whereas most malignant cell lines are resistant to TGF-beta. Mechanisms of resistance to TGF-beta caused by modulation of cell cycle regulators and/or inactivation of components of the TGF-beta signaling transduction pathway such as C-myc and Smad4 have been demonstrated in human pancreatic cancer and squamous cell carcinoma cell lines. But, this has not been shown in ovarian cancer. To investigate the potential association between loss of sensitivity to TGF-beta and expression status of transforming growth factor receptor II (T beta RII), Smad4, CDC25A and C-myc in fourteen cell lines derived from ovarian cancer, the expression levels of these genes were examined by semi-quantitative RT-PCR. Normal ovarian surface tissues were used as controls. Expression of T beta RII was detectable in all of fourteen cell lines. Expression of Smad4 was decreased in ten cell lines and nine cell lines overexpressed CDC25A, compared to normal controls. CDC25A gene was overexpressed in 88% (8/9) of tumorigenic cell lines as determined by xenografts in nude mice, and only in 20% (1/5) of non-tumorigenic cell lines (P < 0.05). C-myc was not overexpressed in any of these cell lines. The loss of sensitivity to TGF-beta of cell lines derived from ovarian cancers may be related to (1) a decreased expression of Smad4, which mediates TGF-beta induced growth inhibition; and/or (2) an overexpression of CDC25A. This overexpression correlates with increased tumorigenicity of ovarian cancer cell lines. The loss of sensitivity to TGF-beta is not associated with a lack of T beta RII.

Renal response to alterations in dietary phosphate in the young beagle.

Hyperphosphatemia is present in the young of many species compared to adult animals. We studied the renal response to alterations in dietary phosphate in 4- to 7-day-old beagle puppies. Puppies were phosphate restricted with oral aluminum hydroxide gel (Group I) or phosphate loaded with oral sodium phosphate (Group II). Puppies in both groups had hyperphosphatemia (Group I 8.6, Group II 12.2 mg/dl) relative to dogs (3.4--4.8 mg/dl). Plasma phosphate concentration (P) and rate of excretion of phosphate (Ep) were independent of glomerular filtration rate (GFR). At any filtered load of phosphate Ep was greater and rate of reabsorption less in Group II independent of P. The maximal rate of phosphate reabsorption (TmP) was higher in Group I (100 micrograms/ml GFR) than Group II (26 micrograms/ml GFR). Negative values for phosphate reabsorption in 4 animals support the presence of a secretory mechanism for phosphate. Relative hyperphosphatemia in the puppy is not secondary to a renal limitation in phosphate excretion. The 1- to 2-week-old puppy adjusts renal reabsorption of phosphate to maintain a concentration of phosphate in plasma higher than in the adult animal. The renal alterations in response to variations in dietary phosphate occur independently of plasma phosphate concentration, GFR, or filtered load of phosphate.

Neonatal lactic acidosis and renal failure: the role of peritoneal dialysis.

Lactic acidosis accompanied by acute renal failure in the newborn period was studied in two infants with circulatory insufficiency and hypoxia. Peritoneal dialysis was necessitated by anuria and serum potassium concentrations of 12.0 and 8.9 mEq/1. Plasma lactate concentration was 35 and 50 mM/1 and blood pH 7.23 and 7.18, respectively, at the time dialysis was instituted. Because of the uncontrollable anaerobic metabolism in these two patients, and the attendant inability to metabolize lactate, the use of commercial lactate-containing dialysates as a source of base was shown to be ineffective in correcting the acidosis and hypothesized to cause a worsening of metabolic acidosis due to a loss of bicarbonate from extracellular fluid into dialysate. Stabilization or improvement in the metabolic acidosis occurred with the utilization of a dilaysate containing bicarbonate with a gradient favoring movement of bicarbonate into, and lactate out of, extracellular fluid.

Identification of a new viral protein containing CAp30 and NCp10 sequences in murine and feline leukemia retroviruses.

Because Pr65gag is in part located in the nucleus and contains a putative bipartite nuclear targeting signal, we investigated the cellular location and structure of P55gag, a gag-encoded polyprotein known to lack the nucleocapsid (NC) protein NCp10. P55gag was found to be restricted to the cytoplasm of Moloney murine leukemia virus-infected cells. Of interest, P55gag was produced in cells infected by a viral protease deletion mutant and by a recombinant murine sarcoma virus known to lack the protease gene. Surprisingly, our structural and immunological studies indicated that P55gag also lacks carboxy-terminal residues of CAp30. During the course of studying P55gag, we detected a new viral protein within purified virus particles that contained NCp10 tryptic peptide sequences and a CAp30 tryptic peptide lacking in P55gag. This viral protein, which we have named nucleocapsid-related protein (NCRP), also contained antigenic epitopes present in CAp30 and NCp10. P55gag- and NCRP-like proteins were also observed in AKV murine leukemia virus and feline leukemia virus systems. The precise site of cleavage within Pr65gag that produces P55gag and NCRP is unknown but lies upstream of the CAp30-NCp10 junction within the carboxy-terminal domain of CAp30. The existence of a form of NCp10 containing carboxy-terminal CAp30 sequences raises interesting possibilities about its functional role in genomic RNA packaging and/or viral RNA dimerization.

Expression of costimulatory molecules CD80 and CD86 and their receptors CD28, CTLA-4 on malignant ascites CD3+ tumour-infiltrating lymphocytes (TIL) from patients with ovarian and other types of peritoneal carcinomatosis.

Costimulation of T lymphocytes by the leucocyte surface molecules CD80 and CD86 expressed on antigen-presenting cells (APC) is required for the development of T cell responses. The CD28 and CTLA-4 molecules on T cells serve as receptors for the CD80 and CD86 costimulatory antigens. We have examined the frequency of expression of CD80 (B7.1), CD86 (B7.2), CD28 and CTLA-4 surface antigens on TIL isolated from malignant ascites or peritoneal washings of 26 patients with ovarian carcinoma and five patients with non-ovarian peritoneal carcinomatosis. Expression of CD80 and CD86 antigen was detected by reverse transcription-polymerase chain reaction (RT-PCR), and by FACS analysis. Significantly higher proportions of intraperitoneal CD3+ cells expressed CD86 antigen than the CD80 antigen (14 +/- 9% versus 3 +/- 3%, P < 0.05). Moreover, CD3+CD86+ cells were significantly more frequent in the peritoneal fluid (14 +/- 9%) than in the peripheral blood (3 +/- 0.4%, P < 0.05) of ovarian patients or normal controls (3 +/- 1%). CTLA-4 and CD28 antigen were expressed, respectively, on 9 +/- 4% and 86 +/- 14% of ascitic CD3+ cells of ovarian cancer patients. Both CD80 and CD86 antigens were expressed primarily on HLA-DR+ ascites TIL and were present in a very low proportion of HLA-DR- ascites TIL. These HLA-DR+ cells may represent a population of lymphocytes that have been activated in vivo, and function as APC. An anti-CD86 MoAb or a combination of anti-CD86 and anti-CD80 MoAbs significantly inhibited the proliferation of cultured intraperitoneal TIL. We have shown that in addition to CD28 and CTLA-4, CD3+ intraperitoneal TIL express the costimulatory molecules CD80 and CD86. The expression of these molecules on T cells could be dependent upon certain factors in the tumour microenvironment that could determine the outcome of in vivo immune responses.

A developmental switch in sea urchin U1 RNA.

The sequence of U1 RNA has been determined in the eggs and embryos of two sea urchins, Lytechinus variegatus and Strongylocentrotus purpuratus. In both species the sequence of the U1 RNA changes as the embryos progress through development. The sequence of the major U1 RNA in the eggs of the two species differs in two nucleotides, while the sequence of the U1 RNA present in the late embryos and somatic tissue is identical in the two species. The U1 RNA in eggs and early embryos is primarily derived from the tandemly repeated gene set, which is not expressed in somatic tissues.

The significance of focal sclerotic lesions of glomeruli in children.

To establish the relationship between the type of focal sclerotic lesion of glomeruli and the development of progressive renal disease, the clinical courses of 20 children with focal segmental and 7 with focal global sclerosis were analyzed. Only five patients, all of them with focal segmental sclerosis, did not have the nephrotic syndrome, although all had proteinuria. Results suggest that patients with focal global sclerosis have a course identical to that of children with the minimal lesion form of nephrotic syndrome: onset in early childhood, response to steroid therapy, and a relapsing, nonprogressive course. Focal segmental sclerosis, in constrast, is characterized by older age at onset, high incidence of nephritic symptoms, lack of response to steroid therapy, and a progressive course with histologic and functional deterioration. Since most published reports have not distinguished between these two entities, a more favorable prognosis in focal segmental sclerosis may be inferred than is actually the case.

Temperature-sensitive viral RNA expression in Moloney murine sarcoma virus ts110-infected cells.

We examined the mos-specific intracellular RNA species in 6m2 cells, an NRK cell line nonproductively infected with the ts110 mutant of Moloney murine sarcoma virus. These cells present a normal phenotype at 39 degrees C and a transformed phenotype at 28 or 33 degrees C, expressing two viral proteins, termed P85gag-mos and P58gag, at 28 to 33 degrees C, whereas only P58gag is expressed at 39 degrees C. It has been previously shown that 6m2 cells contain two virus-specific RNA species, a 4.0-kilobase (kb) RNA coding for P58gag and a 3.5-kb RNA coding for P85gag-mos. Using both Northern blot and S1 nuclease analyses, we show here that the 3.5-kb RNA is the predominant viral RNA species in 6m2 cells grown at 28 degrees C, whereas only the 4.0-kb RNA is detected at 39 degrees C. During temperature shift experiments, the 3.5-kb RNA species disappears after a shift from 28 to 39 degrees C and is detected again after a shift back from 39 to 28 degrees C. By Southern blot analysis, we have detected only one ts110 proviral DNA in the 6m2 genome. This observation, as well as previously published heteroduplex and S1 nuclease analyses which showed that the 3.5-kb RNA species lacks about 430 bases found at the gag gene-mos gene junction in the 4.0-kb RNA, suggests that the 3.5-kb RNA is a splicing product of the 4.0-kb RNA. The absence of the 3.5-kb RNA when 6m2 cells are grown at 39 degrees C indicates that the splicing reaction is thermosensitive. The splicing defect of the ts110 Moloney murine sarcoma virus viral RNA in 6m2 cells cannot be complemented by acute Moloney murine leukemia virus superinfection, since no 3.5-kb ts110 RNA was detected in acutely superinfected 6m2 cells maintained at 39 degrees C. The spliced Moloney murine leukemia virus env mRNA, however, is found in acutely infected cells maintained at 39 degrees C, suggesting that the lack of ts110 viral RNA splicing at 39 degrees C is not due to an obvious host defect. In sharp contrast, however, 6m2 cells chronically superinfected with Moloney murine leukemia virus produce a 3.5-kb RNA species at 39 degrees C as well as at 28 degrees C and contain proviral DNAs corresponding to the two viral RNA species.(ABSTRACT TRUNCATED AT 400 WORDS)

Murine sarcoma virus ts110 RNA transcripts: origin from a single proviral DNA and sequence of the gag-mos junctions in both the precursor and spliced viral RNAs.

Our previous studies have argued persuasively that in murine sarcoma virus ts110 (MuSVts110) the gag and mos genes are fused out of frame due to a approximately 1.5-kilobase (kb) deletion of wild-type murine sarcoma virus 349 (MuSV-349) viral information. As a consequence of this deletion, infected cells grown at 39 degrees C appear morphologically normal, producing a 4-kb viral RNA and a truncated gag gene product, P58gag. At 33 degrees C, however, MuSVts110-infected cells appear transformed, producing two viral RNAs, about 4 and 3.5 kb in length, and two viral proteins, P58gag and P85gag-mos. Recent S1 nuclease analyses (Nash et al., J. Virol. 50:478-488, 1984) suggested strongly that at 33 degrees C about 430 bases surrounding the out-of-frame gag-mos junction and bounded by consensus splice donor and acceptor sites are excised from the 4-kb RNA to form the 3.5-kb RNA. As a result of this apparent splicing event, the gag and mos genes seemed to be fused in frame and allowed the translation of P85gag-mos. In the present study, DNA primers hybridizing to the MuSVts110 4- and 3.5-kb RNAs just downstream of the gag-mos junction points were used to sequence these junctions by the primer extension method. We observed that, relative to wild-type MuSV-349 5.2-kb RNA, the MuSVts110 4-kb RNA had suffered a 1,488-base deletion as a result of the fusion of wild-type gag gene nucleotide 2404 to wild-type mos gene nucleotide 3892. This gag-mos junction is out of frame, containing both TAG and TGA termination codons in the reading frame 42 and 50 bases downstream of the gag-mos junction, respectively. Thus, the MuSVts110 4-kb RNA can only be translated into a truncated gag precursor containing an additional C-terminal 14 amino acid residues derived from an alternate mos gene reading frame. Similar analyses of the MuSVts110 3.5-kb RNA showed a further loss of both gag and mos sequences over those deleted in the original 1,488-base deletion. In the MuSVts110 3.5-kb RNA, we found that gag nucleotide 2017 was fused to mos nucleotide 3936 (nucleotide 2449 in the MuSVts110 4-kb genome). This 431-base excised fragment is bounded exactly by in-frame consensus splice donor and acceptor sequences. As a consequence of this splice event, the TAG codon is excised and the restoration of the original mos gene reading frame allows the TGA codon to be bypassed.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular basis underlying phenotypic revertants of Moloney murine sarcoma virus MuSVts110.

We examined the molecular basis for phenotypic reversion in cells infected with a transformation mutant of murine sarcoma virus, MuSVts110. In MuSVts110-infected NRK cells (6m2 cells), the manifestation of the transformed phenotype at 33 degrees C and the normal phenotype at 39 degrees C is governed by thermosensitive splicing of the MuSVts110 primary transcript, a 4.0-kilobase (kb) RNA which contains the gag and mos genes joined out of frame. At 33 degrees C, selectively, the 4.0-kb RNA is processed to a spliced 3.5-kb RNA in which the gag and mos genes are rejoined in a continuous open reading frame, thus allowing synthesis of the P85gag-mos-transforming protein. In contrast, the MuSVts110 revertant cell lines (designated 54-5A4 and 204-3) appear transformed at all growth temperatures from 33 to 39 degrees C and express a P100gag-mos-transforming protein from an apparently unprocessed 4.0-kb viral RNA. In the current study we established both by S1 nuclease analysis and primer extension sequencing that the revertant 54-5A4 and 204-3 4.0-kb viral RNAs suffered a 5-base deletion at the intron-exon border of the 3' splice site. The effect of this deletion is twofold. First, because of the damage to the 3' splice site, the revertant viral 4.0-kb RNAs cannot be processed to the spliced 3.5-kb RNA and, consequently, cannot be translated to P85gag-mos. Second, the 5-base deletion excises an in-frame stop codon positioned at the intron-exon border in the parental RNA and restores the original mos gene reading frame. The net effect is to produce a continuous open reading frame from the gag, alternate mos, and authentic mos gene reading frames which are fused together in the revertant 4.0-kb RNA. This continuous open reading frame can be translated into the P100gag-mos-transforming protein at any growth temperature.

Focal segmental membranous glomerulonephropathy associated with other glomerular diseases.

In four patients with the nephrotic syndrome, renal biopsy revealed focal segmental membranous glomerulonephropathy (FSMGN) associated with the histologic patterns of "nil" disease (two cases), hereditary nephritis and diffuse diabetic glomerulosclerosis. The occurrence of FSMGN in association with other glomerular diseases, presumably unrelated to immune complex deposition, is infrequent in our experience. Rather than necessarily representing an early stage or milder form of membranous glomerulonephropathy, it may be an epiphenomenon. This interpretation has prognostic and therapeutic implications and raises important pathogenetic questions. In particular, this study suggests that in some instances, preexisting functional and structural abnormalities may play a role either in the deposition of preformed circulating immune complexes or in the local formation of immune complexes.