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Comments on a study that discussed the role of multiplex methylation-specific polymerase chain reaction (PCR) assay in detecting promoter hypermethylation in multiple genes in breast cancer. Flaws of the PCR-based technique; Contribution of promoter hypermethylation to tumorigenesis; Importance of detecting abnormal methylation patterns to the diagnosis of the disease.

An abstract of the article "Hypermethylated genes as biomarkers of breast cancer," by M. J. Fackler, V. Stearns, S. A. Khan and S. Sukumar, is presented.

Background: Formation of single strand breaks in DNA is a constant process, estimated to occur 10,000 times per day in each cell, either from endogenous biosynthetic errors or from interference by endogenous or exogenous agents. Base excision repair in some cases may be impaired or may be exceeded by the rate of DNA damage, leading to cancer. Nick translation of with labeled nucleotides can be used as a quantitative indicator of SSBs. Methods: Healthy women were recruited through the Love-Avon Army of Women and breast clinics of Northwestern and John Hopkins Universities. Digital or digitized mammograms were evaluated for percent density using Cumulus software. The medians (ranges) were age 51 (36 to 60); BMI 28.2 (18.7 to 51.3); life-time Gail estimate 12.5 (5.6 to 28.3); % breast density 16.5 (2.4 to 52.5); Masood score 13 (0 to 18). Breast tissue was obtained by random fine needle aspiration (rFNA). Specimens were rinsed into ice-cold phosphate buffered saline and were stored at -80°C. Thawed samples were centrifuged at 2200 g for 60 min. A kit from Norgen Inc., was used to separate DNA, RNA, and protein from the pellet. The lipids were extracted with ethyl acetate-hexane (3:2) from the supernatant fluid, and triglycerides were precipitated from cold 90% methanol, leaving a purified lipid fraction containing the steroids. Steroids were then fractionated by HPLC on a C18 column, and estradiol was analyzed by a radioimmunoassay. Blood was obtained at the same time as the rFNA samples and was frozen prior to analysis. An aliquot containing 200 ng of DNA (260/280 ratio 1.3 to 2.3) was taken for the nick translation assay. Incorporation of free nucleotides at SSBs with dCTP labeled with³H was catalyzed by Polymerase I from E. coli. A quality control preparation prepared from calf thymus DNA and a reagent blank without DNA was included with each set of 6 samples. Incorporation of³HdCTP was linear with dose of DNA and reached a maximal at 30 min. Separation of free from incorporated³H-dCTP was accomplished by gel chromatography on an 80 x 15 mm column. The concordance of interassay values was 0.96. Results: Incorporation of nucleotides into DNA ranged from 0.03 to 8.59 pmol/μg, median 0.63 pmol/μg DNA. The association with other factors associated with breast cancer is shown in the Table. A significant correlation, was found with % breast density, life-time risk by the Gail model, but not serum estradiol concentrations. Conclusions: Assessment of SSBs by the nick translation procedure may be a useful indicator of breast cancer risk. Future studies will relate this method with actual risk as assessed by analysis of pre-diagnosis specimens with subsequent occurrence of breast cancer. [ABSTRACT FROM AUTHOR]

CD34 is a cell-surface transmembrane protein expressed specifically at the stem/progenitor stage of lymphohematopoietic development that appears to regulate adhesion. To elucidate intracellular signals modified by CD34, we designed and constructed glutathione-S-transferase (GST)- fusion proteins of the intracellular domain of full-length CD34 (GST-CD34i(full)). Precipitation of cell lysates using GST-CD34i(full) identified proteins of molecular mass 39, 36, and 33 kd that constitutively associated with CD34 and a 45-kd protein that associated with CD34 after adhesion. By Western analysis, we identified the 39-kd protein as CrkL. In vivo, CrkL was coimmunoprecipitated with CD34 using CD34 antibodies, confirming the association between CrkL and CD34. CD34 peptide inhibition assays demonstrated that CrkL interacts at a membrane-proximal region of the CD34 tail. To identify the CrkL domain responsible for interaction with CD34, we generated GST-fusion constructs of adapter proteins including GST-CrkL3' (C-terminal SH3) and GST-CrkL5' (N-terminal SH2SH3). Of these fusion proteins, only GST-CrkL3' could precipitate endogenously expressed CD34, suggesting that CD34 binds the C-terminal SH3 domain of CrkL. Interestingly, there appears to be differential specificity between CrkL and CrkII for CD34, because GST-CD34i(full) did not precipitate CrkII, a highly homologous Crk family member. Furthermore, GST-CD34i(full) did not bind c-Abl, c-Cbl, C3G, or paxillin proteins that are known to associate with CrkL, suggesting that CD34 directly interacts with the CrkL protein. CD34i(full) association with Grb or Shc adapter proteins was not detected. Our investigations shed new light on signaling pathways of CD34 by demonstrating that CD34 couples to the hematopoietic adapter protein CrkL. (Blood. 2001;97:3768-3775)

The classical definition of lymphohematopoietic stem cells (LHSC), the most primitive progenitors of all blood cells, requires that they have the capacity for self-renewal and for the long-term production of all blood cell lineages. However, other characteristics of LHSC have been debated. Our previous data suggested that mouse LHSC are very slowly proliferating cells that generate delayed multilineage engraftment, while "radioprotection" (rapid engraftment that will prevent early death from radiation-induced marrow aplasia) results from more committed progenitors. Alternatively, some groups have reported that mouse LHSC are responsible for both radioprotection and long-term repopulation of all blood cell lineages. A possible explanation for this difference is that cells with the capacity for long-term production of all blood cell lineages are biologically heterogeneous. We now show that 10 LHSC can generate all blood cell lineages for the lifetime of the animal. However, these cells lacked radioprotection and spleen colony-forming activity. LHSC were identified and isolated by their small size, their lack of expression of antigens characteristic of mature blood cell lineages, and their high expression of aldehyde dehydrogenase. In addition, these cells were found to express undetectable or low levels of many antigens presumed to mark LHSC, including Thy-1, Ly-6A/E (Sca-1), c-kit, and CD34. There appears to be at least two classes of LHSC with the capacity for long-term production of all blood cell lineages: one that generates both radioprotection and long-term engraftment and one that produces delayed but durable engraftment. Our data suggest that this latter class may represent a very primitive class of LHSC.

CD34 is expressed on human and murine hematopoietic stem and progenitor cells and its clinical usefulness for isolation of stem/progenitor cells has been well established. Although expression of CD34 is regulated in a developmental stage-specific manner, the function of CD34 is not known. Recently we have shown that both a full-length and truncated form of CD34 protein is expressed by hematopoietic cells (Blood 84:691, 1994). To test whether failure to suppress either form of CD34 could affect terminal myeloid differentiation, we constitutively expressed these CD34 proteins in murine M1 myeloid leukemia cells, which can be terminally differentiated to macrophages by treatment with interleukin-6 of leukemia inhibitory factor. Surprisingly our results show that forced expression of the full-length but not the truncated form of CD34 impedes terminal differentiation by these agents. Because the difference between the two forms of CD34 protein resides in the length of their respective cytoplasmic tail domains, our findings strongly suggest that the cytoplasmic domain region of full-length CD34 is responsible for the observed maturation arrest phenotype. These findings suggest a potential negative regulatory role for full-length CD34 in hematopoietic cell differentiation and may explain, at least in part, the block in maturation observed in CD34+ acute myeloid leukemia.

CD34 is expressed on human hematopoietic stem and progenitor cells, and its clinical usefulness for the purification of stem cells has been well established. However, a similar pattern of expression for murine CD34 (mCD34) has not yet been determined. Two polyclonal anti-mCD34 antibodies that specifically recognize both endogenous and recombinant murine CD34 were developed to characterize the mCD34 protein and to determine its pattern of expression on murine cell lines and hematopoietic progenitor cells. Fluorescence-activated cell sorter analysis showed that mCD34 is expressed on NIH/3T3 embryonic fibroblasts, PA6 stromal cells, embryonic stem cells, M1 leukemia cells, and a subpopulation of normal bone marrow cells. Murine CD34 was found to be a glycoprotein expressed on the cell surface as either a full-length (approximately 100 kD) or truncated (approximately 90 kD) protein in NIH/3T3 and PA6 cells. Recombinant full-length CD34, when expressed in the CHO-K1 cell line, had a molecular weight of approximately 105 kD. Full-length CD34 expressed on M1 leukemia cells, had a higher apparent molecular weight (110 kD). These results suggest that there are glycosylation differences between CD34 expressed by different cell types. The full-length form, but not the truncated form, is a phosphoprotein that is hyperphosphorylated in response to 12-0-Tetradecanoyl phorbol 13-acetate treatment, suggesting potential functional differences between the two forms. Selection of the 3% highest-expressing CD34+ bone marrow cells enriched for the hematopoietic precursors that form colony-forming unit-spleen (CFU-S), CFU-granulocyte-macrophage, and burst-forming unit-erythroid. Transplantation of lethally irradiated mice with these cells demonstrated both short- and long-term repopulating ability, indicating that this population contains both functional hematopoietic progenitors and the putative stem cell. These antibodies should be useful to select for murine hematopoietic stem cells.

The precursors of all blood cell lineages are contained within the 1-3% of bone marrow cells which express the CD34 antigen, and this population can reconstitute the hematopoietic system of lethally irradiated animals and humans. A potential regulatory role for the CD34 antigen in progenitor cell function and differentiation was indicated by our recent findings that the CD34 antigen can be phosphorylated in vivo to high stoichiometry in primitive CD34+ cell-lines by activated protein kinase C. To exclude the possibility that these effects were restricted to cell-lines, we have performed similar experiments on fresh cells from a patient with drug-resistant acute lymphoblastic leukemia. Similar to our previous findings, we found the CD34 antigen to be hyperphosphorylated in lymphoblasts labeled in the presence of active phorbols. The same peptides which were hyperphosphorylated in phorbol-stimulated cell-lines were also phosphorylated in phorbol-stimulated lymphoblasts. These data indicate that CD34 is a substrate molecule for PKC in fresh CD34+ lymphoblasts and underline the role of modulators of PKC activity in the biology of primitive leucocytes.

CD34 is a transmembrane sialoglycoprotein expressed by early hematopoietic progenitor cells as well as endothelial cells. Previously we found that CD34 is rapidly and stoichiometrically phosphorylated by activated protein kinase C (PKC) (Fackler, M.J., Civin, C.I., Sutherland, D.R., Baker, M.A., and May, W.S. (1990) J. Biol. Chem. 265, 11056-11061). In the present study, we find dose-dependent up-regulation of CD34 surface expression following treatment of normal human CD34+ bone marrow progenitor cells, cord blood-derived KMT-2, or KG1 a myeloid leukemia cells with the PKC activator 12-O-tetradecanoylphorbol-13-acetate. Up-regulation begins within 1 min of treatment, is maximal by 30 min, is maintained for at least 3 h, and is associated with CD34 hyperphosphorylation. A specific inhibitor of PKC, 2,6-diamino-N-(1[1-(1-oxotridecyl)-2-piperadinyl]methyl)h exan-amide (NPC 15437), blocks both up-regulation and hyperphosphorylation of CD34. CD34 up-regulation is independent of transcription and/or translation and results from the recruitment of preformed intracellular CD34. The endocytosis rate of surface CD34 is unaltered by 12-O-tetradecanoylphorbol-13-acetate. Thus, activation of PKC mediates increased surface expression of the CD34 molecule possibly as a result of phosphorylation of CD34.

The interrelationship between proliferation, differentiation, and activation responses of hematopoietic progenitor cells and mature blood cells is complex. Therefore, we are only now learning what role colony-stimulating factors play in the regulation of normal hematopoiesis in vivo and in the dysregulation of hematopoiesis in leukemia. Recent advantages in molecular hematology have opened the door to the therapeutic administration of recombinant growth factors. Through continued preclinical trials in animals and by clinical trials in humans, a better understanding of the precise target cells and mechanisms of action of hematopoietic growth factors will improve the therapeutic index of administering colony-stimulating factors. Better understanding of hematopoietic growth factors will, in turn, suggest novel approaches to therapy of acute lymphoblastic leukemia.

Immunologic strategies for removal of malignant cells from autologous marrow grafts by "negative selection" (i.e., "purging") requiring multiple specific monoclonal antibodies for each tumor type. "Positive selection" of marrow stem cells for grafting is a possible alternative strategy, using a monoclonal antibody which selectively recognizes lymphohematopoietic stem cells. The human hematopoietic progenitor cell antigen, CD34, is an integral cell membrane glycoprotein of approximately 115 kD, which has been molecularly cloned and sequenced. Although its function has not been determined, the glycoprotein has been characterized biochemically, including preliminary epitope mapping. Collective results from several laboratories indicate that CD34 monoclonal antibodies (My10, BI-3C5, 12.8, etc.) have the appropriate specificity to warrant testing their utility in positive selection for autologous bone marrow transplantation. First, precursors for all human hematopoietic lineages assayed (including most CFU-GM, BFU-E, CFU-MEG, CFU-EO, CFU-MIX or CFU-GEMM, pre-CFU, CFUBLAST, and terminal transferase+ B [and probably T] lymphoid precursors) are CD34+. Second, only 1.5% (mean) of low density human marrow mononuclear cells express CD34; mature human blood and marrow cells are CD34-. Endothelial cells are the only fixed tissue cells which express CD34. Third, the expression of CD34 in malignancies appears to parallel normal cellular expression: of hematopoietic malignancies, some acute leukemias and chronic myelogenous leukemia blasts are CD34+, but chronic lymphois leukemias, lymphomas, myelomas and non-hematopoietic malignancies are uniformly CD34-. Fourth, it appears feasible to isolate CD34+ cells from clinical marrow harvest samples in large scale, using either columns or immunomagnetic microspheres. Fifth, recent studies in very small numbers of non-human primates and human patients suggest that isolated CD34+ cells include the true hematopoietic stem cell, since transplantation of CD34+ cells, into myeloblated recipients results in at least short-term hematopoietic engraftment. It is anticipated that transplantation of CD34+ marrow cells may have broad applicability in clinical bone marrow transplantation.

The anti-My-11 murine monoclonal antibody reported on in this work identifies a KG-1a cell surface glycoprotein with apparent molecular mass of 210,000 daltons. Peripheral blood B-lymphocytes, and a novel subset of T-lymphocytes (not coinciding with helper or cytotoxic subsets) express My-11 antigen; granulocytes, red cells, and platelets are antigen negative. In normal bone marrow, lymphoid progenitors (TdT positive) and most granulocyte-monocyte progenitors express My-11, but erythroid and multilineage progenitors are My-11 negative. Approximately half of acute leukemia blast cell specimens are My-11 positive. The My-11 antigen distinguishes between lymphohematopoietic cells on the basis of lineage, and assists in the purification of hematopoietic progenitor cells and the subclassification of leukemias and normal lymphocytes.