Enrichment and identification of fetal trophoblast cells from first trimester maternal cervical lavage and uterine blood specimens

First trimester prenatal diagnosis of fetal aneuploidies is an active area of research despite years of disappointing data employing maternal peripheral blood samples. To remedy this situation we have investigated other first trimester maternal specimens attempting to find a consistent fetal cell source. Using our previously established positive enrichment procedure along with a commercially available depletion method, fetal trophoblast cells were identified employing immunocytochemistry using an antibody cocktail or by using mRNA in-situ hybridization employing a cocktail of trophoblast specific probes. Fetal origin of positively identified cells was verified using interphase fluorescent in-situ hybridization (FISH) for X and Y-chromosomes. Artificial model systems were established that indicated yields of trophoblast cells and allowed the enrichment procedure to be optimized for minimal losses from maternal specimens. We demonstrate herein that blood drawn from maternal vessels near the placental implantation site to be the most consistent source of fetal cells from any first trimester maternal specimen described to date. In addition, a high yield of multinucleated syncytiotrophoblast cells was obtained using a cell depletion strategy to enrich the target cells. The safety of the procedure or even the clinical utility of blood drawn from maternal vessels near the placental implantation site is yet to be demonstrated.

Inconsistency of fetal trophoblast cells in first trimester maternal peripheral blood prevents non-invasive fetal testing using this cell target

We have investigated whether maternal peripheral blood from the first trimester of pregnancy is a reliable source of identifiable trophoblast cells. The cells were enriched from 30 ml of venous blood, with multiple antibodies shown previously to enrich trophoblasts and a new cocktail based on known trophoblast surface features. Three different magnetic solid phases were tested to enrich trophoblasts, and both positive and negative cell enrichment strategies were examined. The cells were identified as trophoblast by morphology coupled with immunocytochemistry to co-localize cytokeratin with one of three IGF-II, PAI-1 or hPLH proteins or by in-situ hybridization with a mixture of 50 oligos directed to eight different expressed genes, alpha-HCG, IGF-II, PAI-1, HASH2, hPLH, p57(KIP2), PP5, H-19. While these tools worked beautifully in chorionic villi cell/sprout preparations and tissue sections, we could not detect and identify any trophoblasts in maternal peripheral blood even if the maternal peripheral blood was drawn 5-20 min following termination of pregnancy or from individuals maintaining the pregnancy. Based on our own experience and that of some reports in the literature, trophoblasts do not appear to be a viable candidate for fetal screening using maternal peripheral blood as the source. It is important to note that while trophoblast deportation is a biological phenomenon that has been described repeatable, they do not provide a means to perform prenatal genetic diagnosis.

High-density hapten labeling and HRP conjugation of oligonucleotides for use as in situ hybridization probes to detect mRNA targets in cells and tissues

Oligonucleotides that carry a detectable label can be used to probe for mRNA targets in in situ hybridization experiments. Oligonucleotide probes (OPs) have several advantages over cDNA probes and riboprobes. These include the easy synthesis of large quantities of probe, superior penetration of probe into cells and tissues, and the ability to design gene- or allele-specific probes. One significant disadvantage of OPs is poor sensitivity, in part due to the constraints of adding and subsequently detecting multiple labels per oligonucleotide. In this study, we compared OPs labeled with multiple detectable haptens (such as biotin, digoxigenin, or fluorescein) to those directly conjugated with horseradish peroxidase (HRP). We used branching phosphoramidites to add from two to 64 haptens per OP and show that in cells, 16-32 haptens per OP give the best detection sensitivity for mRNA targets. OPs were also made by directly conjugating the same oligonucleotide sequences to HRP. In general, the HRP-conjugated OPs were more sensitive than the multihapten versions of the same sequence. Both probe designs work well both on cells and on formaldehyde-fixed, paraffin-embedded tissues. We also show that a cocktail of OPs further increases sensitivity and that OPs can be designed to detect specific members of a gene family. This work demonstrates that multihapten-labeled and HRP-conjugated OPs are sensitive and specific and can make superior in situ hybridization probes for both research and diagnostic applications.

Identification of differentially expressed mRNAs in human fetal liver across gestation

Differential gene expression, with its precise start and stop times, is believed to be critical for the programmed development of new cells and tissues. Within the developing fetus, one tissue of particular interest is fetal liver. This organ undergoes rapid changes in the pathway toward liver development in utero since it is also the major site of hematopoiesis, until bone marrow hematopoiesis predominates. Believing that patterns would emerge from the bi-weekly large-scale inspection of expressed genes in the fetal liver, we employed differential display reverse transcription-polymerase chain reaction (DDRT-PCR) as ourprimary inspection tool. Using DDRT-PCR, we isolated cDNAs differentially expressed throughout fetal liver development and in adult liver. We displayed approximately 25 000 cDNAs from 10 and 24 week fetal liver and adult liver. From this initial screen, we determined that approximately 0.1-1% of the mRNA population undergoes expression changes. We extracted, purified and sequenced 25 differentially displayed cDNA bands. Fourteen cDNAs had similarities to known genes, while 11 cDNAs were not similar to any characterized gene. The differentially expressed cDNAs from known genes present in fetal liver include alpha-fetoprotein, stem cell factor, erythroid alpha-spectrin, 2,3-bisphosphoglycerate mutase, insulin-like growth factor-2, porphobilinogen deaminase and Mac30. The differentially expressed cDNAs present in adult liver but not in 10 week fetal liver were nicotinamide deaminase, human fibrinogen-related protein and alpha-acid glycoprotein. The majority of differentially expressed genes found during this effort appear to be turned on during organogenesis, however, some genes were found that are apparently turned off completely.

Human breast cancer progression can be regulated by dominant trans-acting factors in somatic cell hybridization studies

Human breast cancer is often characterized by a progression to an ER (estrogen receptor)-negative, estrogen-independent, antiestrogen-resistant, EGFR (epidermal growth factor receptor)-positive, and highly metastatic phenotype. The molecular and biochemical mechanisms behind this progression are not well defined. Most studies of breast cancer have focused on one or another aspect or this progression but have not found a common pathway. By constructing stable and complete human-human somatic cell fusions between a highly metastatic, undifferentiated, ER-negative line of melanoma lineage and the estrogen-dependent, ER-positive MCF-7 line, this study produced hybrids that were ER negative, highly expressive of EGFR, estrogen independent, estrogen unresponsive, fully tumorigenic, and highly metastatic. ER negativity was on the basis of complete suppression of ER transcription as evidenced by Northern blot analysis and nuclear run-on assay, not on the basis of gene rearrangement. EGFR positivity was not due to gene amplification or rearrangement but rather to increased EGFR transcription. Mechanisms, including ras activation, fibroblast growth factor 4 expression, and human DNA methyltransferase activation causing ER promoter methylation, which are respectively known to induce estrogen-independent growth, induce spontaneous metastasis, and decrease ER levels in breast carcinoma experimentally, were not mechanisms operating in the hybrids. This model demonstrates that many of the common denominators of human breast carcinoma progression can be regulated by dominant trans-acting factors.

Protein kinase C-beta is required for macrophage differentiation of human HL-60 leukemia cells

The requirement for protein kinase C (PKC)-beta in phorbol 12-myristate 13-acetate (PMA)-induced macrophage differentiation of human HL-60 promyelocytic leukemia cells was studied by using the variant HL-525, which is deficient in PKC-beta and is resistant to PMA-induced differentiation. Transfecting these resistant HL-525 cells with expression vectors containing either PKC-beta I or PKC-beta II cDNA resulted in clones that displayed PKC-beta transcript levels similar to or higher than those of the parental HL-60 cells or cells from a PMA-susceptible HL-60 clone, HL-205. These productive transfectants also exhibited PMA-induced cell attachment and spreading, inhibition of cell replication, reactivity to the OKM1 monoclonal antibody, and the ability to phagocytize opsonized beads, which are all characteristic macrophage markers. No PMA-induced differentiation markers were observed in any of the PKC-beta I or PKC-beta II transfectants that did not exhibit an increased PKC-beta RNA level or in cells transfected with control plasmids. These results indicate that restoration of the PKC-beta isozyme deficiency by productive gene transfection causes HL-525 cells to revert to a phenotype like that of the parental HL-60 cells, which is characterized by susceptibility to PMA-induced macrophage differentiation. Therefore, we can conclude that PKC-beta is one of the essential elements in the PMA-induced signal transduction pathway which leads to macrophage differentiation in HL-60 cells and perhaps in other related cell types.

Alterations in gene expression and signal transductions in human melanocytes and melanoma cells

The development of techniques to cultivate human primary melanocytes in vitro has provided the technical foundation for understanding the biology of this cell. Human melanocytes require various growth factors and agents for proliferation in vitro. These compounds activate two major signal transduction pathways: a calcium- and phospholipid-dependent (protein kinase C or PKC) pathway and a cyclic AMP (cAMP)-dependent (protein kinase A or PKA) pathway. Alterations in these signal transduction pathways coupled with changes in specific genes (protooncogenes, growth factors, and tumor suppressor genes) have been observed in human melanoma cells compared with normal melanocytes. Our own work indicates that loss in the expression of the PKC beta II isotype is a common, if not universal, alteration that occurs early in human melanocyte transformation. In this review, we concentrate on alterations in the signal transduction pathways in human melanocytes and melanoma cells and delineate how an understanding of these changes may allow us to understand the molecular mechanisms involved in human melanocyte transformation.

Protein kinase C beta expression in melanoma cells and melanocytes: differential expression correlates with biological responses to 12-O-tetradecanoylphorbol 13-acetate

Normal human melanocytes require 12-O-tetradecanoylphorbol 13-acetate (TPA) for prolonged growth in vitro. In contrast, the growth of human malignant melanoma cells is often inhibited by TPA. In this study, we have confirmed and extended these observations. Since protein kinase C (PKC) is an important mediator of the effects of TPA, we have investigated the nature of this differential growth response by examining PKC expression and activity in primary cultures of human neonatal melanocytes and metastatic melanoma cell strains. PKC, when measured by immunoreactivity or a functional assay, was found to be more abundant in melanoma cells than in melanocytes. When specific isotypes were examined by Northern analysis, PKC-alpha and -epsilon were expressed in both melanocytes and melanoma. PKC-beta was expressed in melanocytes, but was undetectable by Northern analysis in 10 out of 11 melanoma cell strains. Southern analysis revealed that no gross deletions or rearrangements of the PKC-beta gene had occurred. These data suggest that down-regulation of the PKC-beta gene occurs frequently during the process of transformation of melanocytes. Furthermore, differential expression of PKC isotypes may explain the different effects of TPA on melanocyte and melanoma cell growth.

Differences in basic fibroblast growth factor RNA and protein levels in human primary melanocytes and metastatic melanoma cells

Cultivation of human melanocytes requires several growth factors for cell proliferation. For example, basic fibroblast growth factor (bFGF) is an essential growth agent for melanocyte proliferation in vitro and has been proposed to be an autocrine growth factor in human melanoma cells. Studies using either anti-bFGF antibodies or antisense oligonucleotides partially inhibited the proliferation of human melanoma cells. However, one group was unable to detect bFGF RNA transcripts in human melanoma cells using a human complementary DNA probe. These contradictory results prompted us to investigate the bFGF gene expression in human primary melanocytes and metastatic melanoma cells using Southern, Northern, and Western blot analyses. No gross rearrangements in the bFGF gene were detected in the genomic DNA. Although high levels of bFGF RNA transcripts were detected in melanocytes, no bFGF protein was detected using Western blot analysis. In contrast, melanoma cells expressed much lower levels of bFGF RNA transcripts, and cells from three of four cell strains synthesized the multiple isoforms of bFGF protein. In one of the melanoma cell strains, no bFGF protein was detected using Western blot analysis. Although three of four melanoma cell strains expressed bFGF protein, this molecule does not appear to function as an autocrine growth factor, and expression of the bFGF protein was not a consistent alteration in all melanoma cell strains.

Expression of c-jun, jun-B, and c-fos proto-oncogenes in human primary melanocytes and metastatic melanomas

Analysis of the regulation of c-jun, jun-B, and c-fos RNA transcript expression was performed in human primary melanocytes and metastatic melanoma cell strains. The medium requirements for human melanocyte in vitro growth are phorbol esters, agents that elevate intracellular cAMP levels, hormones, and growth factors. Cellular jun, jun-B, and c-fos gene expression are known to be affected by growth promoting agents. In primary melanocytes, the expression of c-jun, jun-B, and c-fos RNA transcripts was dependent on the growth-promoting agents present in the medium. Uniformly high c-jun, jun-B, and c-fos RNA transcript levels were observed in melanocytes cultivated in complete medium. Higher levels of c-jun RNA transcripts and low levels of c-fos RNA transcripts were observed in melanocytes cultivated in plain medium. In contrast, a range of c-jun, jun-B, and c-fos RNA transcript levels was detected in metastatic melanoma cell strains cultivated in medium with or without serum. In general, an increase in jun-B and c-fos RNA transcript expression and a decrease in c-jun RNA transcript expression was observed in metastatic melanomas compared to neonatal melanocytes. These data suggest a potential role for c-jun, jun-B, and c-fos genes in the transformation of melanocytes to malignant melanoma.

The differential expression of protein kinase C genes in normal human neonatal melanocytes and metastatic melanomas

Expression of protein kinase C (PKC) genes (alpha, beta, gamma and epsilon) was measured in cultured normal human neonatal melanocytes and metastatic melanoma cell strains. Three of the PKC isotypes (alpha, beta and epsilon) were constitutively expressed in neonatal melanocytes. Protein kinase C beta RNA transcripts were induced in neonatal melanocytes cultivated in medium with serum and 12-O-tetradecanoylphorbol-13-acetate (TPA). In contrast, PKC alpha and epsilon RNA transcripts were detected in melanocytes cultivated in medium without serum and TPA, but were repressed in melanocytes cultivated in medium with serum and TPA. Only PKC alpha and epsilon RNA transcripts were detected in the melanoma cell strains and the PKC RNA transcript expression levels varied among the five metastatic melanomas. In four metastatic melanoma cell strains, PKC alpha and epsilon RNA transcript expression levels were repressed by serum, but in one melanoma cell strain, PKC alpha and epsilon RNA transcript expression levels were induced by serum. Protein kinase C gamma RNA transcripts were not detected in either the melanocytes or melanoma cell strains. These data suggest an alteration of PKC isotype gene expression in the progression of primary melanocytes to metastatic melanoma. The absence of the PKC beta RNA transcripts and altered expression of PKC alpha and epsilon isotypes in particular may be a feature in the transformation of human primary melanocytes.

An analysis of DNA replication in synchronized CHO cells treated with benzo[a]pyrene diol epoxide

Synchronized Chinese hamster ovary (CHO) cells treated with (+/-)7 beta,8 alpha- dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-dihydrobenzo[a]pyrene (BP diol epoxide I) were used to test the 'block-gap' model of replicative bypass repair in mammalian cells. One feature of the model is that carcinogenic or mutagenic DNA adducts act as blocks to the DNA replication fork on the leading strand. Using synchronized CHO cells, the rate of S phase progression by BrdUrd labeling of newly replicated DNA was measured. The rate of S phase progression was reduced by 22% and 42%, when the cells were treated at the G1/S boundary with 0.33 and 0.66 microM BP diol epoxide I, respectively. Using the pH step alkaline elution assay, it was found that the reduced rate of S phase progression was due to a delay in the appearance of multiple replicon size nascent DNA. This observation was consistent with the frequency of BP-DNA adducts present in the leading strand. A second feature of the 'block-gap' model is that the adduct-induced blockage on the lagging strand will produce gaps. It was determined by the use of high-resolution agarose gel electrophoresis, that the ligation of Okazaki size replication intermediates was blocked in a dose-dependent manner in BP diol epoxide I treated, synchronized CHO cells. These data are consistent with a block to the leading strand of DNA replication at DNA-carcinogen adducts. An inhibition of the ligation of Okazaki size fragments by BP diol epoxide I implies a block to replication of the DNA lagging strand leading to gap formation. The data presented here are, therefore, supportive of the 'block-gap' model of replicative bypass repair in carcinogen damaged mammalian cells.