Biomedical subjects
Publications and source records attributed to C M Croce.
We have localized a cDNA fragment that codes for human DNA polymerase-beta. Using somatic cell and in situ hybridization techniques, this cDNA was cloned by screening a human KM-3 cell cDNA library in lambda gt 11 for expression of fused beta-galactosidase-human DNA polymerase-beta proteins. We have mapped this human polymerase-beta gene to the short arm of chromosome 8 in the subregion 8p11----p12.
The human genes which code for Lipocortin I and Lipocortin II, proteins that inhibit phospholipase A2 (PLA2) activity, have been regionally localized in the human genome by chromosomal in situ hybridization and segregation analysis in somatic cell hybrids using cDNA clones for Lipocortin I and II. Lipocortin I, the 35 kd substrate for the epidermal growth factor (EGF) receptor/kinase, maps to chromosome region 9q11- greater than q22. The Lipocortin II cDNA probe detects at least four independently segregating loci which map to human chromosome regions 4q21-q31.1, 9pter-q34 proximal to c-abl, 10q proximal to 10q24 and 15q21-q22 proximal to the 15q22 translocation breakpoint characteristic of acute promyelocytic leukemia (APL). Thus, Lipocortin I and one locus detected by Lipocortin II cDNA are syntenic on chromosome 9; one Lipocortin II locus is perhaps not far from the genes for EGF and IL-2 on 4q; and another of the Lipocortin II loci is on 15q, perhaps not far from the APL breakpoint.
The protein encoded in a novel human oncogene isolated by transfection of Kaposi's sarcoma DNA is a growth factor with significant homology to basic and acidic FGFs. The genomic structure of this oncogene (designated K-FGF), as originally isolated, carried DNA rearrangements upstream and downstream of the coding region. The normally discontinuous sequence upstream of the K-FGF coding region derived from the 3' end of the c-fms gene and thus originated from human chromosome 5. In order to determine the normal chromosomal location of the K-FGF gene and of the DNA sequences adjacent to its 3' end, we have correlated the presence of these sequences with retention of specific human chromosome regions in rodent-human somatic cell hybrids. These experiments mapped the K-FGF gene to human chromosome region 11q13----11q23, and in situ hybridization localized it more precisely to region 11q13 near int-2, which also belongs to the FGF family. The sequence downstream of the gene in transfectants and discontinuous with K-FGF in normal human DNA derives from chromosome region 12p12----12q13, possibly near the int-1 locus.
Both the t(14; 18) and the t(11; 14) chromosomal translocations are associated with human B-cell neoplasms. Sequence analysis of the regions on chromosomes 18q- and 11q- involved in the joining of chromosomes 14 and 18 and of chromosomes 11 and 14 during their respective translocations indicates the involvement of the DH region. There is a deletion of the region between the involved D segment and the JH region, and extranucleotides are present at the joining sites on the 18q- and on the 11q- chromosomes. We have previously reported that the joining region on chromosome 14q+ involved in both the t(11; 14) and the t(14; 18) translocations are structurally identical. We now report that the joining regions on chromosomes 11q- and 18q- involved in these two different translocations are also identical. Thus, these translocations arose by the same mechanisms. The deletions of the region between the involved segment and the JH region must likely occur during either a D-J recombination event on the 18q- and 11q- chromosomes following the translocations or, alternatively, during the D-J recombination event that results in the translocation.
We have performed gene rearrangement studies on the leukemic blasts of a patient with acute pre-B-cell leukemia. The patient had a 5 year history of follicular lymphoma, which developed into acute pre-B-cell leukemia. The leukemic blasts revealed a karyotype with two translocations, t(8; 14) and t(14; 18), characteristic for Burkitt's lymphoma and follicular lymphoma. The cells are TdT positive, do not possess surface immunoglobulin, and they show immunoglobulin gene rearrangement. The mu heavy chain and kappa light chain constant (C mu and C kappa) loci are deleted, while the gamma and lambda light chain constant (C gamma and C lambda) region genes are rearranged. Both alleles of the heavy chain joining segment (JH) are rearranged on chromosome 14q+, one of them with the bcl-2 oncogene from chromosome 18. The breakpoint of the t(14; 18) translocation occurs in the major breakpoint cluster region in the 3' untranslated region of bcl-2. On chromosome 8 a c-myc rearrangement was mapped immediately 5' to the c-myc first exon in a region involved in sporadic Burkitt lymphoma. The data are consistent with our previous hypothesis on the evolution of B-cell malignancies: a rare pre-B cell develops a t(14; 18) translocation during immunoglobulin VDJ joining that results in an expansion of a follicular lymphoma clone carrying an activated bcl-2 gene. Within the clone of pre-B cells a second translocation, t(8; 14), occurs during heavy chain isotype switching that results in the deregulation of the c-myc involved in the translocation.
The transfection recombinant transforming gene, tre, originated from discontinuous human genetic elements after transfection of NIH3T3 cells with genomic DNA from a Ewing's sarcoma cell line. Probes for the three normally discontinuous human elements involved in the transfection recombinant were subcloned and used in conjunction with a panel of rodent-human hybrid cells to determine their normal location in the human genome. The leftmost (5') element derives from the long arm of chromosome 5 (5q); the internal fragment derives from human chromosome 18 proximal to the bcl-2 gene; and the rightmost (3') element derives from the long arm of chromosome 17 (17q) distal to an acute leukemia breakpoint at 17q21. In situ hybridization of the same probes to human metaphase chromosomes confirmed localization of these sequences to regions 5q23----q31, 18q12, and 17q12----q22.
Two types of Philadelphia (Ph') chromosome positive acute lymphoblastic leukemias (ALL) have been described. One shows rearrangements within the 5.8 kb breakpoint cluster region (bcr), which forms the mid-portion of the bcr gene, on chromosome 22, while the other carries rearrangements involving a more proximal region on chromosome 22. To understand the nature of the breakpoints on chromosome 22 in bcr rearrangement negative, Ph'-positive ALLs, we have cloned and sequenced the cDNA of the c-abl oncogene in such ALL cells. The 5' ends of the cDNA clones correspond to the normal sequences of the bcr gene first exon with two of the clones extending beyond the GCCATGG consensus sequence for the initiation of translation. The bcr sequence stops at nucleotide 1813 of the coding sequence of the bcr gene, while the c-abl sequence starts at the beginning of the second c-abl exon (nucleotide 227). Thus the joining point between bcr and c-abl is at the boundary between two exons, suggesting intronic fusion and the occurrence of a splicing event. Our current observations indicate that the Ph' translocation in bcr negative ALL involves bcr gene sequences, albeit only a proximal portion of those involved in CML. These genomic differences may be important factors in the pathogenesis of the distinct phenotypes of ALL and CML.
We have analyzed cells of the B lineage for expression of the Tp44 antigen, a 44,000 homodimer detected by monoclonal antibody 9.3 on approximately 80% of mature human T lymphocytes. Previous evidence has suggested that Tp44 may function as a receptor for accessory signals in T cell activation. High level Tp44 expression was observed on plasmacytomas grown in cell culture and on plasma cells from bone marrow biopsies of multiple myeloma patients. This antigen is not present on resting B cells from either peripheral blood or lymphoid organs, or on any other B cell tumor. The growth kinetics and Ig production in plasmacytomas are not affected by the binding of antibody 9.3. Moreover, the Tp44 molecule is co-expressed with PCA-1, an antigen characteristic of plasma cells, on peripheral blood B cells stimulated in vitro to differentiate toward plasma cells. Tp44 may represent a later stage of B cell differentiation than PCA-1 because unlike the PCA-1 antigen, this molecule could not be detected on any EBV-transformed cell line or Burkitt's lymphoma lines. The m.w. of the Tp44 molecule expressed on plasma cells and on T cells is identical, as determined by immunoprecipitation of radioiodinated cell surface proteins with monoclonal antibody 9.3. This antigen might be useful in studying the mechanism of growth and differentiation of human B cells, the heterogeneity within plasma cell populations, and B cell interactions with other components of the immune system.
The bcl-2 and c-myc proto-oncogenes are brought into juxtaposition with the immunoglobulin heavy chain locus in particular B-cell lymphomas, resulting in high levels of constitutive accumulation of their messenger RNAs. Precisely how the products of the bcl-2 and c-myc genes contribute to tumorigenesis is unknown, but observations that c-myc expression is rapidly induced in nonneoplastic lymphocytes upon stimulation of proliferation raise the possibility that this proto-oncogene is involved in the control of normal cellular growth. In addition to c-myc, the bcl-2 proto-oncogene also was expressed in normal human B and T lymphocytes after stimulation with appropriate mitogens. Comparison of the regulation of the expression of these proto-oncogenes demonstrated marked differences and provided evidence that, in contrast to c-myc, levels of bcl-2 messenger RNA are regulated primarily through transcriptional mechanisms.
We have cloned the mouse bcl-2 (mbcl-2) genomic locus and analyzed it in detail. The gene is comprised of two exons separated by more than 15 kb. Two species of mRNAs are produced, and DNA sequencing analysis shows that they code for two proteins differing at their C terminus: a 7.5 kb transcript codes for a polypeptide of 236 amino acids, mbcl-2 alpha, and a 2.4 kb transcript, which derives from the 5' exon only, codes for a protein of 199 amino acids, mbcl-2 beta. The gene is characterized by very long (5' about 1.4 kb, and 3' about 5.1 kb) untranslated regions surrounding the relatively short coding region. We have mapped the 5' end of the mbcl-2 mRNAs by S1 protection analysis, and we have analyzed the promoter region. The expression of the mbcl-2 gene was analyzed in different cell lines and in mouse tissues. Expression is tissue-specific in adult tissues: spleen and thymus express the highest level of mbcl-2 transcripts. The mbcl-2 gene maps to mouse chromosome 1.
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The mouse PIM-1 gene has been implicated in the evolution of retrovirus-associated mouse lymphomas. We have initiated a study of the human PIM-1 gene because of its potential importance as a human oncogene. We have isolated genomic and cDNA clones for this gene and characterized this locus in detail. The predicted PIM-1 protein is 313 amino acids in length. It has homology to a number of the protein kinases but does not have a transmembrane region. The amino acid corresponding to tyrosine-416 of pp60v-src is a tyrosine (position 198), which is consistent with the hypothesis that PIM-1 is a tyrosine kinase rather than a serine-threonine kinase. The PIM-1 gene was found to have six exons and five introns derived from 5 kb of genomic DNA. The site of transcription initiation was localized by S1 nuclease protection studies which indicated that the mature PIM-1 mRNA was approximately 2.7 kb in length. The promotor of this gene had no TATA or CAAT box but did have multiple GC boxes (CCGCCC) that might bind the Sp1 protein. The PIM-1 gene was expressed in myeloid and B lymphoid cell lines, but not in T lymphoid and nonhemopoietic lines. This initial characterization of PIM-1 will allow us to define its role in normal and malignant hematolymphoid differentiation.
Vasoactive intestinal peptide (VIP) is a regulatory neuropeptide involved in a wide variety of functions, among them vasodilation, smooth muscle relaxation, sweat secretion, gastrointestinal peristalsis, and pancreatic function. A deficient VIP-innervation of sweat glands was recently described as a possible pathogenic factor in sweating of cystic fibrosis (CF) patients. To investigate a possible role for a defective VIP-gene in cystic fibrosis, we have used a panel of rodent-human hybrid cells, retaining defined complements of human chromosomes to localize the VIP-gene to the human chromosome region 6p21----6qter. As the CF gene was recently mapped to chromosome 7, we conclude that the VIP-gene is not the primary gene defect in this disease.
Human leukemic T cells carrying a t(10;14)(q24;q11) chromosome translocation were fused with mouse leukemic T cells, and the hybrids were examined for genetic markers of human chromosomes 10 and 14. Hybrids containing the human 10q+ chromosome had the human genes for terminal deoxynucleotidyltransferase that has been mapped at 10q23-q25 and for C alpha [the constant region of TCRA (the alpha-chain locus of the T-cell antigen receptor gene)], but not for V alpha (the variable region of TCRA). Hybrids containing the human 14q- chromosome retained the V alpha genes. Thus the 14q11 breakpoint in the t(10;14) chromosome translocation directly involves TCRA, splitting the locus in a region between the V alpha and the C alpha genes. These results suggest that the translocation of the C alpha locus to a putative cellular protooncogene located proximal to the breakpoint at 10q24, for which we propose the name TCL3, results in its deregulation, leading to T-cell leukemia. Since hybrids with the 10q+ chromosome also retained the human terminal deoxynucleotidyltransferase gene, it is further concluded that the terminal deoxynucleotidyltransferase locus is proximal to the TCL3 gene, at band 10q23-q24.
Somatic cell hybrids were obtained between human T and B cells and tested for the expression of differentiated traits of both cell lineages. The T-cell parent SUP-T1 is CD3-, CD4+, CD1+, CD8+, is weakly positive for HLA class I determinants, and has an inversion of chromosome 14 due to a site-specific recombination event between an immunoglobulin heavy-chain variable gene and the joining segment of the T-cell receptor alpha chain. The B-cell parent, the 6-thioguanine- and ouabain-resistant mutant GM1500, is a lymphoblastoid cell line that secretes IgG2, kappa chains, and expresses B1, B532, and HLA class I and II antigens. All hybrids expressed characteristics of B cells (Ig+, B1+, B532+, EBNA+, HLA antigens), whereas only CD4 among the T-cell markers was expressed. The level of T-cell receptor beta-chain transcript was greatly reduced and no RNA of the chimeric T-cell receptor alpha-chain joining segment-immunoglobulin heavy-chain variable region was detected. Southern blot analysis indicated that absence of T-cell differentiation markers in the hybrids was not due to chromosomal loss. Rather, some B-cell-specific factor present in the hybrids may account for the suppression.
Recent molecular analyses of Burkitt lymphomas carrying the t(8;14) chromosome translocation have indicated that a dichotomy exists regarding the molecular mechanisms by which the translocations occur. Most sporadic Burkitt tumors carry translocations that apparently arise due to mistakes in the immunoglobulin isotype-switching process. In contrast, there is evidence that the translocations of most endemic Burkitt lymphomas occur as a consequence of aberrant V-D-J recombination of variable, diversity, and joining gene segments, catalyzed by the recombinase enzymes. This phenomenon was first noted in follicular lymphomas and chronic lymphocytic leukemias of the B-cell lineage and has been described in T-cell malignancies as well. In each of these cases, analysis of the nucleotide sequence at chromosome breakpoints demonstrated the involvement of immunoglobulin heavy chain JH or T-cell-receptor alpha-chain J alpha gene segments in the translocation. We now have cloned and sequenced both the 8q- and 14q+ translocation breakpoints deriving from the t(8;14) translocation of the endemic Burkitt lymphoma line Daudi. Our data show that the translocation resulted from a reciprocal exchange between the DH region on chromosome 14 and sequences far 5' of the MYC protooncogene on chromosome 8. Features of the nucleotide sequences surrounding the breakpoint further implicate the V-D-J joining machinery in the genesis of chromosome translocations in endemic Burkitt lymphomas and, more generally, in other lymphoid malignancies as well.
A probe derived from the 3' region of the BCR gene (breakpoint cluster region gene) detects four distinct loci in the human genome. One of the loci corresponds to the complete BCR gene, whereas the others contain a 3' segment of the gene. After HindIII cleavage of human DNA, these four loci are detected as 23-, 19-, 13-, and 9-kilobase-pair fragments, designated BCR4, BCR3, BCR2, and BCR1, respectively, with BCR1 deriving from the original complete BCR gene. All four BCR loci segregate 100% concordantly with human chromosome 22 in a rodent-human somatic cell hybrid panel and are located at chromosome region 22q11.2 by chromosomal in situ hybridization. The BCR2 and BCR4 loci are amplified in leukemia cell line K562 cells, indicating that they fall within the amplification unit that includes immunoglobulin lambda light chain locus (IGL) and ABL locus on the K562 Philadelphia chromosome (Ph1); additionally, in chronic myelogenous leukemia-derived mouse-human hybrids retaining a Ph1 chromosome in the absence of the 9q+ and normal chromosome 22, BCR2 and BCR4 loci are retained, whereas the 3' region of BCR1 and the BCR3 locus are lost, indicating that BCR3 is distal to BCR1 on chromosome 22. Similarly, in mouse-human hybrids retaining a Ph1 chromosome derived from an acute lymphoblastic leukemia-in the absence of the 9q+ and 22, only BCR2 and BCR4 loci are retained, indicating that the breakpoint in this acute lymphoblastic leukemia, as in chronic myelogenous leukemia, is proximal to the BCR1 3' region, but distal to the IGLC locus and the BCR2 and BCR4 3' loci. Thus, the order of loci on chromosome 22 is centromere----BCR2, BCR4, and IGL----BCR1----BCR3----SIS, possibly eliminating BCR2 and BCR4 loci as candidate targets for juxtaposition to the ABL gene in the acute lymphoblastic leukemia Ph1 chromosome.