Paul M. Kraemer

Heparin releases heparan sulfate from the cell surface.

Abstract Heparan sulfate of the cell surface of cultured Chinese hamster cells (line CHO) was promptly released when the cells were incubated with balanced salt solutions containing heparin. The released heparan sulfate included multichain proteoglycan of high molecular weight. The data suggest that the cell-surface localization of heparan sulfate is dependent, at least in part, upon cell-surface receptors with binding sites for the sugar chain moieties of sulfated glycosaminoglycans.

DNA Constancy in Heteroploidy and the Stem Line Theory of Tumors

Cellular DNA was measured by high-speed flow microfluorometry in mammalian diploid and heteroploid cell populations stained by the fluorescent Feulgen procedure. Heteroploid cells with elevated modal chromosome number showed the expected increase in modal DNA content. However, the variability of DNA content was the same in diploid and heteroploid cell populations despite the large variability of chromosome number in the latter populations. This suggests that heteroploidy may include defects in the chromosomal condensation and kinetochore development systems.

High molecular-weight heparan sulfate from the cell surface

Abstract Heparan sulfate fragments with molecular weight of 135,000 (as determined by equilibrium sedimentation analysis) were isolated from the trypsinate of Chinese hamster cells (line CHO) grown in culture. Evidence is presented which suggests that the intracellular heparan sulfate species with molecular weight of 10,000 to 20,000 were degradation products of the larger species. We propose that the native cell-surface heparan sulfate, in its physiological location, could serve as a nonspecific “screen” to the exposure of specific, topographically adjacent, cell-surface sites.

Detachment variants of Chinese hamster cells: Hyaluronic acid as a modulator of cell detachment

Abstract Variants of the Chinese hamster cell line CHO have been isolated and characterized with respect to attachment and trypsin- or EGTA-mediated detachment kinetics, cell morphologies, and the complex carbohydrates (labeled with [3H]glucosamine) of the cell surface. The variant which was more readily detached from the substratum exhibited a more rounded cell shape and had three times more label as hyaluronic acid on the cell surface than the parental cell. The slowly detaching variant had a morphology similar to the parental cell but only half the radioactivity ascribable to hyaluronic acid. Endogenous levels of cAMP were unaltered in the variants. Exogenous dbcAMP caused the cells to elongate and flatten but did not alter the characteristic detachment kinetics. The role of hyaluronic acid as a modulator of the cell substratum interface is discussed.

SV40 T antigen induced chromosomal changes reflect a process that is both clastogenic and aneuploidogenic and is ongoing throughout neoplastic progression of human fibroblasts

In human fibroblasts, the expression of SV40 large T antigen is known to cause a variety of chromosomal aberrations and especially dicentric chromosomes. In some cases, the later aberrations have been reported to be reversible telomeric associations. We report here aberration and chromosome number studies of twenty-nine T antigen positive lineages, studied from their initiation by transfection of T antigen sequences into human diploid fibroblasts, until crisis or immortalization occurred or, in some cases until the lines became tumorigenic in nude mice. The data show that T antigen consistently produced chromosomal instability of both number and structure by an active process that began before transformation indicators were positive and continued throughout neoplastic progression. The most frequently observed aberrations were dicentric chromosomes, which were shown to be true dicentrics by examination by in situ hybridization with telomeric sequences. These data are consistent with the hypothesis that T antigen causes human fibroblasts to become neoplastically transformed by successive rounds of chromosomal mutation and lineage evolution.

Frequent deletions in nine newly immortal human cell lines

Nine newly immortal lines of human fibroblasts transfected with SV40 T antigen were examined for recurrent chromosome losses. In order of decreasing frequency, all nine lines had three or more of the following minimal deletions specifically associated with the immortalization event: del(6)(q21), del(3)(p24), del(1)(p34), del(4)(p25), del(5)(p14), del(11)(p11), del(11)(q14), del(12)(p12), and del(14)(p?). Many other chromosome changes were not clearly associated with immortalization, but were acquired during other stages of this multistep model of neoplastic transformation. We propose that these chromosome loci associated with immortalization are candidates for the location of genes involved in cellular senescence.

Population analysis of arrested human diploid fibroblasts by flow microfluorometry

Abstract Confluent cultures of human diploid fibroblasts were maintained for 28 days with medium containing 0.5% serum. Periodically during this time cells were exposed to 3H-thymidine for 72 h; harvested; and analysed by flow microfluorometric, ‘cell sorting’, and autoradiographic techniques. The results showed that cells cultured under these conditions maintain a stable population distribution similar to that occurring when a population reaches confluency in medium containing 10% serum. Low labeling indices, sparce grain densities, and the presence of some mitotic cells indicated that a limited amount of cell-cycle traverse did occur but that both the S and G2 phases were prolonged. This new state of reduced mitotic activity with prolonged cell-cycle times may mimic the long-term inhibition of cell-cycle traverse of expanding tissues in vivo.

Elevated cell-surface hyaluronate in substrate-attached cells☆

CHO cells, an anchorage-independent Chinese hamster cell line, synthesize and deposit more hyaluronic acid into the cell-surface material when attached to substrate than when growing in suspension. The difference cannot be explained by differences in turnover, cellular localization, or secretion. Evidently the anchorage state per se stimulates hyaluronic acid synthesis.

Spontaneous in vitro neoplastic evolution: Recurrent chromosome changes of newly immortalized Chinese hamster cells

Spontaneous neoplastic progression in cultured Chinese hamster cells was studied at the earliest stage possible. Eighteen independent newly immortalized cell populations (from six individual Chinese hamsters) were characterized for karyotype instability. Colonies were selected from initial sparse platings of adult or fetal cells and were expanded for study. The chromosomes from these newly established cell lines were studied using a combination of G-banding and flow karyotype analysis. At a slightly later passage, the 18 cell lines were tested for tumorigenicity in nude mice. Frequent recurring chromosome changes were observed in the karyotypes. The most frequent changes were either total or partial trisomy of chromosome #3 (83%) and trisomy of chromosome #5 (61%). Only 4 of 18 clones (22%) were tumorigenic at the time of testing, and these had long latent periods. The presence of recurrent chromosome changes did not obligate these cell lines to become tumorigenic, but the karyotype instability appeared to be an indicator of the ongoing process of neoplasia.

Spontaneous in vitro neoplastic evolution: Selection of specific karyotypes in Chinese hamster cells

Recurrent cytogenetic changes occurred reproducibly in vitro during the spontaneous neoplastic evolution of cultured Chinese hamster cells. In particular, excess 3q material appeared shortly after immortalization in numerous independent trials. By contrast, when clones were isolated at the earliest possible time after immortalization, a wide spectrum of types of cytogenetic evolution followed, which also resulted in transformed and tumorigenic cells. Clones with stable distinct colonial morphologies were used to demonstrate growth rate interactions when subpopulations compete. We conclude that specific recurring karyotypes are associated with specific stem lines with transient growth advantage during the early stages of in vitro carcinogenesis. Stem lines with other karyotypic change or no detectable karyotypic change are almost equally capable of undergoing the entire spontaneous neoplastic process in vitro.