Contact inhibition and gene expression in HTC-L cell hybrid lines

Density-dependent regulation of growth in somatic hybrids between normal Chinese hamster fibroblasts and V79-8 (G1-) cells

The purpose of this work was to determine the relationship between the presence of a G1 period in the mitotic cycle and a cell's ability to respond to density-dependent regulation of growth (DDR). Somatic hybrids were obtained between normal fibroblasts from newborn Chinese hamsters, which show a strong response to DDR, and V79-8 Chinese hamster cells, which are insensitive to DDR. Two variant V79-8 sublines were used, one reported to lack a G1 period (G1-) and the other with a G1 period (G1+). Fourteen hybrid clones were isolated in selective medium and analysed for growth properties and cell cycle parameters; their hybrid nature was supported by chromosome counts. All hybrid clones, irrespective of whether a V79-8 G1- or G1+ cell was one of the parents, showed pronounced DDR and had G1 periods of various lengths. Previous experiments had shown the absence of G1 to be dominant in somatic hybrids between V79-8 G1- and G1+ cell lines. Our results may mean that the G1- property provided by V79-8 is unable to overcome the very long G1 of normal fibroblasts, or in cells that can be arrested in G1 in response to DDR, some function prevents the dominant effect of the G1- cell on at least part of the G1 period.

Somatic cell fusion in the study of glucocorticoid action

The basic phenomena of cell fusion and hybrid cell formation are briefly described and the potential of somatic cell hybridization in studies on the expression of differentiated cellular functions is discussed. The technique of cell hybridization has been applied to two types of cellular responses to glucocorticoids. The induction of specific proteins has been investigated in hybrids of inducible cells with uninducible cells. Most studies dealt with the liver-specific enzyme tyrosine aminotransferase, whose inducibility was extinguished in the majority of the hybrids between hepatoma and nonliver cells. However, upon chromosome segregation, inducibility reappeared in some of these hybrid cells. The current ideas about cellular control of inducibility are discussed. The other major glucocorticoid-responsive system investigated in cell hybridization studies consists of lymphoid cells which are killed when exposed to the steroid. Such sensitive cells were hybridized with several types of glucocorticoid-resistant lymphoid lines, and sensitivity was found to be dominant over resistence. Hybrids between sensitive and resistant lymphoid cells, however, showed an increase in the frequency at which resistance occurred as compared to the rate observed with the wild-type parental cells. No complementation to steroid sensitivity was found in hybrids between different types of resistant cells with defects in the glucocorticoid-specific receptor system.

Expression of transformation in cell hybrids. II. Nonsuppression of the transformed phenotype in hybrids between a chemically transformed and nontransformed derivatives of Balb/3T3

Hybrid clones derived from a nitrosocarbaryl-transformed Balb/3T3 cell line, Clone H, and a nontransformed cell line THO2 resemble the transformed parent in the clone morphology, higher saturation density, colony formation in medium with reduced serum concentration, growth in agarose and ability to form clones on Balb/3T3 monolayer. Results are discussed in the framework of genetic models which permit or require dominant mutations for the expression of transformed phenotype.

Growth characteristics in vitro of hybrids between normal and transformed cell lines

Sensitivity to the inhibition of division during cell crowding in vitro was determined for hybrids between normal and tumor cell populations of human and mouse origin. Interspecies hybrids were more sensitive to cell crowding than intraspecies hybrids. The results suggest that the inhibition of cell division due to crowding was more dependent upon the species of origin rather than on the normal or transformed character of the parental cell lines of the hybrid cell populations.

Glycopeptides from epithelial cell mutants: temperature sensitive for the transformation phenotype

Fucose-labelled glycopeptides obtained from the cell surfaces of normal and transformed epithelial cells were compared by co-chromatography on Sephadex G-50. The material obtained from epithelial cells transformed in vitro or from hepatoma cells in culture elutes earlier than the fucose-containing glycopeptides obtained from normal rat epithelial cells. A mutant (TS 223) of a transformed epithelial cell that is temperature-sensitive for maintenance of the transformed phenotype, varies in its Sephadex G-50 profile of cell surface glycopeptides when grown at the permissive (36 degrees C) or the non-permissive temperature (40 degrees C). When grown and labelled at 36 degrees C the gel filtration profile of the glycopeptides resembles that of transformed cells. At 40 degrees C there is an enrichment of later eluting glycopeptides. These differences are more striking in confluent-phase cultures than in log-phase culture. The differences are reversible following upward or downward shifts in growth temperature although there appears to be a lag of at least 6 h before the alteration can be demonstrated by these procedures.

Delayed malignancy and altered growth properties of somatic cell hybrids between rat hepatoma and mouse L-cells

Somatic cell hybrids of mouse L-cells with rat HTC cells were studied for their growth properties in vitro and tumorigenicity in vivo. Three hybrid clones were selected for detailed study. All were delayed in tumor formation in nude mice compared with the parent lines despite their varied growth properties in vitro. One clone was sensitive to density dependent inhibition of growth (DDIG) and had a relatively low saturation density. A second clone was not sensitive to DDIG and had a higher saturation density. The third clone had atypical morphology, was insensitive to DDIG, and had a relatively high saturation density. All of the clones studied produced colonies suspended in agarose gel which were much smaller than those of the parents incubated for the same period of time. Only the pattern of growth in agarose gel corresponded to the delayed tumor formation in vivo of the hybrids. Sensitivity to DDIG and saturation density were not consistent with tumor growth. The hybrid clone that was sensitive to DDIG was the only one of the three that had a nearly complete set of chromosomes derived from each of the parents. The chromosome numbers of all three clones were unchanged after growth in agarose or as tumors in the nude mice.

Hybridization of a human myeloma permanent cell line with mouse cells

A population of hybrid cells derived from the fusion of a permanent human myeloma cell line, which secretes complete IgE, and a subline of mouse L cells, did not secrete IgE as evidenced by sensitive immunosorbent tests. Also, the hybrid cells were observed not to contain intracellular IgE (epsilon or lambda chains) in amounts to be detectable by fluorescent antibody techniques. The doubling times and cell cycle parameters of the hybrid cells were found to be similar to those of the slow-growing parental human myeloma cells, in addition, the growth of the hybrid cells was characterized by a higher degree of contact inhibition than the parent mouse cells.

The control of serum protein synthesis in hepatoma-fibroblast hybrids

Hybrids between mouse hepatoma cells (which secrete several serum proteins) and mouse or rat fibroblasts (which do not secrete these proteins) produce transferrin and the third component of complement (C3) like the parental hepatoma cells, while they do not secrete either albumin or alpha-fetoprotein (AFP). This lack of albumin and AFP secretion is probably due to a lack of synthesis, rather than to a simple defect in secretion. The cessation of albumin and AFP production is not dependent upon the parental fibroblast nor upon the selection conditions; it is best explained by a shut-off synthesis and could thus reflect the existence of a regulatory mechanism. This would imply a difference between the control of albumin and AFP synthesis and that of transferrin and C3 synthesis. On the other hand, in agreement with Peterson and Weiss (1972), hybrids between rat hepatoma cells and mouse fibroblasts continue to product rat albumin. This suggests that the mouse hepatoma cells differ from the rat hepatoma cells in the way they control albumin production.