Posttranscriptionally mediated decreases in folylpolyglutamate synthetase gene expression in some folate analogue-resistant variants of the L1210 cell. Evidence for an altered cognate mRNA in the variants affecting the rate of de novo synthesis of the enzyme.

L1210 cell variants resistant to edatrexate (EDX) were isolated by selection in vivo during therapy with this folate analogue. Among the variants selected, seven (L1210/EDX-4 to -7 and L1210/EDX-12 to -14) were found to exhibit 2-23-fold lower levels of folylpolyglutamate synthetase (FPGS) activity compared with parental L1210 cells. Lower levels of FPGS activity in cell-free extract from these variants using EDX as substrate were characterized by the same relative decrease in value for Vmax with no change in apparent Km. The results of an analysis of FPGS activity in mixtures of variant and parental cell extract suggested that no endogenous inhibitors in the variant cells or stimulatory factors in parental cells accounted for the differences observed. Also, FPGS from variant and parental cells showed no difference in thermostability. Decreases in a 60-61-kDa protein as shown by immunoblotting with anti-FPGS peptide antibody were found to occur commensurately with the decrease in FPGS activity in cell extract from the variants compared with parental cells. However, no evidence was obtained for a difference in turnover of FPGS protein during measurement of the decay of FPGS activity in cycloheximide-treated variant and parental cells. In addition, Northern blotting of poly(A)+ RNA did not reveal any difference in the size or level of FPGS mRNA among these various cell types. Studies of in vitro translation of hybridization-selected FPGS mRNA from L1210 cells showed that both mitochondrial and cytosolic forms of FPGS were generated during the reaction. Moreover, FPGS mRNA from the variant cells was significantly less effective in mediating formation of the FPGS peptide product in a manner correlating with FPGS activity and protein found in the cytosol of the various cell types. These results suggest that FPGS gene expression in these variants is posttranscriptionally altered at the level of the cognate mRNA itself and that this alteration constitutively down-regulates the steady-state level of FPGS in these variants.

Different antifolate-resistant L1210 cell variants with either increased or decreased folylpolyglutamate synthetase gene expression at the level of mRNA transcription.

L1210 cell variants selected in the presence of the lipophilic dihydrofolate reductase inhibitor, metoprine, expressed increased levels of one-carbon, reduced folate transport inward (Sirotnak, F. M., Moccio, D. M., and Yang, C.-H. (1984) J. Biol. Chem. 259, 13139-13144). Growth of one of these variants (L1210/R69), with metoprine in the presence of decreasing concentrations of 1,L5-CHO-folateH4 (natural diastereoisomer of 5-formyl-tetrahydrofolate), resulted in the selection of other variants (L1210/R82, R83, and R84) with further reduction in one-carbon, reduced folate transport and in two cases (L1210/R83 and R84) with 3-8-fold increased folylpolyglutamate synthetase (FPGS) activity and folate compound polyglutamate formation in situ. Metoprine resistance was further increased, and the requirement for exogenous folate during growth was decreased as well in these variants. The increase in FPGS activity observed in L1210/R83 and R84 was characterized by 3- and 8-fold increases in value for Vmax with no change in Km and the same increase in a 60-61-kDa protein as shown by immunoblotting. Northern blotting revealed the same increases in these two variants in the level of a 2.3-kilobase FPGS mRNA when compared with control, while Southern blotting of genomic DNA did not reveal any increase in FPGS gene-copy number or restriction polymorphisms. Also, no difference in stability of FPGS mRNA was found between parental and variant cells. In contrast, nuclear run-on assays revealed differences among these cell types in the rate of FPGS mRNA transcription that correlated with increased FPGS activity, protein, and mRNA level in the variants. Similar studies with a transport-defective, methotrexate-resistant L1210 cell variant (L1210/R25) documented a 2-3-fold decrease in FPGS activity, protein, and mRNA levels that was accounted for by a decrease in FPGS mRNA transcription. These results provide the first examples of constitutively altered transcriptional regulation of FPGS activity associated with acquired resistance to antifolates.

Rapid decline in folylpolyglutamate synthetase activity and gene expression during maturation of HL-60 cells. Nature of the effect, impact on folate compound polyglutamate pools, and evidence for programmed down-regulation during maturation.

These studies in HL-60 cells examined the regulation of folylpolyglutamate synthetase (FPGS) activity at the level of gene expression during terminal maturation. Following addition of 210 mM Me2SO to cultures of HL-60 cells at a concentration that induces maturation of 85-90% of the cells, FPGS activity, but not folylpolyglutamate hydrolase (FPGH) activity, was reduced 2-7-fold within 1-5 days. The initial decline in FPGS activity preceded any effect of Me2SO on rate of growth and the increase in appearance of nitro blue tetrazolium-positive cells, a marker of cellular maturation, and the decrease after 5 days of exposure to Me2SO was solely accounted for by a 7-fold decrease in value for Vmax. The same time and concentration dependence for Me2SO was shown for the decline in FPGS activity, increase in nitro blue tetrazolium-positive cells, and decline in the level of a 2.1-kilobase FPGS mRNA during exposure to this inducer. This decline in FPGS mRNA was reversible when Me2SO was removed from the culture medium but only until that time when an appreciable number of cells were committed to terminal maturation. Following growth of HL-60 cells with [3H]MTX, used as a model folate compound, a large reduction in its intracellular polyglutamate pools was shown during maturation which quantitatively reflected the decline in FPGS activity as well as folate transport inward (Sirotnak, F.M., Jacobson, D.M., and Yang, C-H. (1986) J. Biol. Chem. 261, 11150-11156). Other data showed that folate status or obviation of the folate requirement during growth of these cells strongly influenced the rapidity of the onset of maturation following exposure to inducer. Overall, these results show that FPGS activity in HL-60 cells is a marker for proliferative capacity and that the underlying basis for the decline in FPGS activity during maturation is altered cognate gene expression which is manifested as early reversible and late irreversible phases. They also suggest that the coordinate reduction observed in folate transport, FPGS activity, dihydrofolate reductase, and probably other folate related enzymes by limiting macromolecular biosynthesis may be early programmed events in the maturation process that influence the switch from proliferation to senescence in these cells.

Coombs-positive autoimmune hemolytic anemia and postinfantile giant cell hepatitis in children.

We report a 23-month-old girl and a 9-month-old boy who presented with autoimmune hemolytic anemia followed by recurrent episodes of severe hepatitis. The first episode of hepatitis occurred 1 week and 15 months after presentation, respectively. Histologically, the livers showed loss of lobular architecture with diffuse giant cell transformation of hepatocytes and portal and pericellular fibrosis. The first patient died at 4 1/2 months after her initial presentation with a well-established micronodular cirrhosis. The second patient responded to steroid therapy and the hepatitis recurred when steroids were tapered. Postinfantile giant cell hepatitis may occur in association with Coombs-positive hemolytic anemia, it is thought to have an autoimmune mechanism, and early and sustained immunosuppression may control the progressive hepatocellular damage and prevent cirrhosis.

The CD59 antigen is a structural homologue of murine Ly-6 antigens but lacks interferon inducibility.

A cDNA encoding the human leukocyte antigen CD59 has been isolated from the erythroid cell line K-562 and its identity confirmed through expression in COS cells. Northern blotting reveals three message species of approximately 800, 1400 and 2000 bases in size, which are constitutively expressed in all lymphoid, erythroid, myeloid, and neural cell types tested thus far. Southern blotting of human DNA indicates a pattern consistent with the presence of a single gene, which has been mapped to chromosome 11 by somatic cell hybrids. Also, the finding of a transcriptionally active cross-hybridizing gene in monkey cells suggests conservation of CD59 sequences among primates. Comparison of the CD59 protein sequence with those of the Ly-6E and Ly-6C antigens discloses a similarity in overall structure, including the alignment of abundant cysteine residues, hydrophobic carboxy termini and conservation of amino acids surrounding the proposed phosphatidylinositol-glycan modification site for Ly-6 molecules. Unlike Ly-6, however, CD59 expression does not appear to be inducible with interferons. This, along with its limited homology and different tissue distribution, cast doubt upon the functional equivalence of CD59 and either of the well-characterized mouse Ly-6 proteins.

Analysis of three distinct Ly6-A-related cDNA sequences isolated from rat kidney.

Mouse Ly6A and Ly6C cDNA probes were hybridized to total RNA of rat tissues and, as in mouse, the highest level of Ly6-related transcripts was detected in kidney. Therefore, Ly6-related cDNA clones were isolated from a commercial rat kidney cDNA library in lambda gt11. Four of these (RK3, RK6, RK10, and RK11) have been fully characterized, and represent transcripts from three distinct genes. Each contains a reading frame encoding an amino acid sequence typical of the known Ly6 molecules: a 26aa leader (except in clone RK6 which has only two of its leader codons), followed by a sequence of 108 or 109aa containing 10 cysteines in excellent alignment with those of Ly6A. The three rat polypeptide sequences were more closely related to Ly6A than Ly6C, and more closely related to each other than to Ly6A. The most striking similarity between all these sequences is in the last 33aa at the C-terminal. Most of this is presumed to be cleaved off during post-translational addition of a phosphatidylinositol-glycan (PI-G) membrane anchor. Southern blot analysis of rat DNA probed with rat-Ly6 cDNA showed multiple band patterns indicative of a multigene family. No restriction fragment length polymorphism (RFLP) was evident amongst the six inbred rat strains tested. Anomalies in two of the rat cDNA clones, resulting from improper splicing of the original transcripts, correlated with Ly6Ca exon boundaries, thus suggesting conserved intron-exon organization.

I.29 lymphoma cells express a nonmutated VH gene before and after H chain switch.

The I.29 B cell lymphoma consists of IgM+ and IgA+ cells which express the same germ-line VH gene. IgA+ cells of the I.29 lymphoma were derived from the IgM+ cells by a typical H chain switch recombination event. The IgM+ cells can be induced with LPS to undergo H chain switching in culture. It has been proposed that the somatic hypermutation process is activated during H chain switch, since V genes expressed in IgG+ and IgA+ cells have more frequently undergone mutation than those expressed in IgM+ cells. We have investigated this question by sequencing VH genes expressed before and after H chain switch in the I.29 lymphoma. We have also sequenced the germ-line VH gene corresponding to the gene expressed by I.29 cells to determine whether the VH gene expressed in the IgM+ cells had already undergone somatic mutation. Our results indicate that somatic mutation was not activated in the precursor cell for the I.29 lymphoma, nor during isotype switch in I.29 cells. It is possible that cells of the I.29 lymphoma, or their precursor, have not received the signal which induces somatic mutation, or that I.29 cells belong to a subset of B cells that cannot be induced to undergo any (or much) somatic mutation.

N-terminal and cDNA characterization of murine lymphocyte antigen Ly-6C.2.

The Ly-6C.2 molecule was purified from K36 tumor cells by affinity chromatography and gel filtration. The electrophoretically homogeneous preparation, with m.w. 15,000, was tested with a panel of antibodies that confirmed the presence of the LY-6C.2 epitope. An N-terminal sequence of 39 amino acids was obtained showing 59% homology with the corresponding portion of the Ly-6A.2 polypeptide. Based on the least homologous (29%) 14 amino acid segment, an oligonucleotide probe was constructed, and Ly-6C.2 cDNA was cloned from a BW5147 cDNA library. A 794-base pair cDNA containing the entire coding region had 82% homology with Ly-6A.2 cDNA. The encoded polypeptide sequence of 131 amino acids containing a perfect correlation with the N-terminal sequence data was 63% homologous with that of Ly-6A.2. The greatest homology was in the leader, first 16 N-terminal and last 39 C-terminal amino acids. The latter are likely to be important in determining the attachment of glycophosphatidylinositol. Despite results indicating fewer disulfide constraints in the Ly-6C molecule, the predicted sequence contains 10 cysteine residues nearly perfectly matched with those predicted in Ly-6A.

Demonstration of phosphatidylinositol anchors on Ly-6 molecules by specific phospholipase C digestion and gel electrophoresis in octylglucoside.

Release by phosphatidylinositol-specific phospholipase C is frequently provided as evidence for membrane anchorage of a protein through phosphatidylinositol. Demonstration that the enzyme removes a lipophilic moiety from the protein is stronger evidence, and is presented here for members of the Ly-6 family of lymphocyte antigens: Ly-6A, C and E. Treatment of these molecules with the enzyme greatly increased their electrophoretic mobilities on polyacrylamide gels containing nonionic detergent. Furthermore, the mobilities of the digested, but not native Ly-6 molecules, were independent of detergent. This analytical method was applied to pure antigen, radiolabelled immunoprecipitate, or immunochemically detected Ly-6 antigens on blots.

Identical twins concordant for Crohn's disease.

Identical twin adolescent girls developed Crohn's disease within 15 months of each other. Clinical symptoms, growth retardation, barium studies, disease course, and pathologic findings at the time of resection were remarkably similar. Seventeen pairs of twins concordant for Crohn's disease have now been reported, but only four discordant pairs. Such observations lend support to a considerable genetic influence on the development and course of Crohn's disease.

Specificity of immunoglobulin heavy chain switch correlates with activity of germline heavy chain genes prior to switching.

IgM+ cells cultured from the I.29 B cell lymphoma can be induced with lipopolysaccharide (LPS) or, to a greater extent, with LPS plus anti-idiotype antibody to switch to IgG2a, IgE or IgA expression. The isotype switch is accompanied by rearrangement of immunoglobulin (Ig) heavy (H) chain genes. Here we demonstrate that the commitment of the I.29 IgM+ cells to switch to IgA appears to be manifested by hypomethylation of the alpha constant region genes in IgM+ cells, and by the presence of small amounts of RNAs transcribed from non-rearranged alpha gene(s) in IgM+ cells. The commitment to switch to IgE or IgG2a is also in accord with the presence of small amounts of RNA transcripts from the non-rearranged epsilon and gamma 2a genes, although the hypomethylation of the epsilon and gamma 2a genes is not as dramatic as that of the alpha genes. These results suggest that I.29 cells switch specifically to IgA, IgE or IgG2a due to the activation of the corresponding H chain constant region genes in IgM+ cells prior to the actual switch recombination event.

Atypical presentation of childhood acquired immune deficiency syndrome mimicking Crohn's disease: nutritional considerations and management.

A child with acquired immune deficiency syndrome became severely malnourished presumably as a result of multiple gastrointestinal infections, with numerous organisms including campylobacter, giardia, and cryptosporidium. These opportunistic infections preceded laboratory evidence of immune deficiency. Despite severe diarrhea and marked weight loss, there was no laboratory evidence of significant malabsorption. By using nasogastric feedings, we were successful in promoting a 60% weight gain, and a rise in serum albumin from 1.2 to 4.3 g/dl. While eventual outcome was not altered, this particular patient's clinical course was improved. We suggest that malnutrition should not be accepted as inevitable and that malabsorption should not be assumed in similar acquired immune deficiency syndrome patients. Appropriate studies for malabsorption should be done, and high caloric enteral feedings should be used whenever feasible.

Induction of immunoglobulin isotype switching in cultured I.29 B lymphoma cells. Characterization of the accompanying rearrangements of heavy chain genes.

The murine B cell lymphoma I.29 contains cells expressing surface IgM or IgA with identical heavy chain variable regions (9, 25, and D. Klein and J. Stavnezer, unpublished data). Purified IgM+ cells from the lymphoma have been adapted to culture and induced to switch to IgA, IgE, or IgG2 by treatment with lipopolysaccharide (LPS) or by treatment with a monoclonal anti-I.29 antiidiotype plus LPS. Clones of IgM+ cells have been obtained and induced to switch. Under optimal conditions, 30% of the cells in the culture expressed IgA 8 d after the inducers were added, and by 15 d 90% of the cells were IgA+. In actively switching cultures, up to 50% of the cells whose cytoplasm stained positively with anti-IgA stained simultaneously with anti-IgM, which indicates that the appearance of IgA+ cells in the cultures was due to isotype switching and not to clonal outgrowth. Examination by Southern blotting experiments of the Ig heavy chain genes in I.29 cells before and after switching revealed that isotype switching was accompanied by DNA recombinations that occurred within or immediately 5' to the tandemly repeated switch sequences. Within 3 d after the addition of inducers of switching, the nonexpressed chromosome underwent a variety of deletions or expansions within the S mu region, and a portion of the S alpha regions had undergone a 0.9-kb deletion. In cultures that contained at least 12% IgA+ cells, rearranged, expressed alpha genes, produced by recombination between the S mu region within the expressed mu gene and the S alpha region, were detected.

Rearrangements and deletions of immunoglobulin heavy chain genes in the double-producing B cell lymphoma I.29.

The B cell lymphoma I.29 consists of a mixture of cells expressing membrane-bound immunoglobulin M (IgM) (lambda) and IgA (lambda) of identical idiotypes. Whereas most of the cells express either IgM or IgA alone, 1 to 5% of the cells in this tumor express IgM and IgA simultaneously within the cytoplasm and on the cell membrane (R. Sitia et al., J. Immunol. 127:1388-1394, 1981; R. Sitia, unpublished data). When IgM+ cells are purified from the lymphoma and passaged in mice or cultured, a portion of the cells convert to IgA+. These properties suggest that some cells of the I.29 lymphoma may undergo immunoglobulin heavy chain switching, although it is also possible that the mixed population was derived by a prior switching event in a clone of cells. We performed Southern blotting experiments on genomic DNAs isolated from populations of I.29 cells containing variable proportions of IgM+ and IgA+ cells and on a number of cell lines derived from the lymphoma. The results were consistent with the deletion model for heavy chain switching, as the IgM+ cells contained rearranged mu genes and alpha genes in the germ line configuration on both the expressed and nonexpressed heavy chain chromosomes, whereas the IgA+ cells had deleted both mu genes and contained one rearranged and one germ line alpha gene. In addition, segments of DNA located within the intervening sequence 5' to the mu gene, near the site of switch recombination, were deleted from both the expressed and the nonexpressed chromosomes. Although mu genes were deleted from both chromosomes in the IgA+ cells, the sites of DNA recombination differed on the two chromosomes. On the expressed chromosome, Smu sequences were recombined with S alpha sequences, whereas on the nonexpressed chromosome, Smu sequences were recombined with S gamma 3 sequences.

Human skin fibroblasts from individuals genetically predisposed to cancer are sensitive to an SV40-induced T antigen display and transformation.

In the present study we have used a viral probe to determine the genetic susceptibility of fibroblastic cell strains derived from individuals with hereditary adenomatosis of the colon and rectum (ACR), an autosomal dominant trait. This report shows an increased sensitivity of apparently karyologically-normal diploid skin fibroblasts from ACR individuals to an SV40-induced T antigen display and transformation. None of the SV40-transformed cells grew as tumors in athymic mice and they all appeared to have a finite life span. The results suggest that the induction of T antigen positive cells by SV40 may be used as a marker of cancer risk in this cell system.

Effects of exogenous androgen treatment on X-chromatin.

In studying a possible hormonal influence on X-chromatin frequency, buccal smears from two groups of women, one on androgen therapy and one not on androgen therapy, were compared. Both groups were nonmenstruating, renal dialysis patients, 41 to 69 years of age. For each patient the X-chromatin frequency was determined from 100 analyzable and intact buccal mucosa cells. In determining X-chromatin frequency, stringent selection criteria were used, and a selection ratio was derived by dividing by 100 the total number of cells that were counted in order to discover 100 analyzable and intact cells. Using the Guard's staining technique, no significant difference could be demonstrated in either the X-chromatin frequency or the selection ratio between the women receiving androgens and those not receiving them.