Dedifferentiated variants of a rat hepatoma: Analysis by cell hybridization

Abstract

Two independent dedifferentiated variants, H5 and FaoflC2, derived from the Reuber H35 hepatoma, produce trans-acting diffusible substances(s) that extinguish the expression of liver-specific proteins when hybridized with a well-differentiated cell line of the same origin (Fao and Fu5-5, respectively). H5 x Fao hybrids show total and stable extinction of four liver functions and clonal variability in the expression of three others. FaoflC2 x Fu5-5 hybrids are initially flat (like FaoflC2 cells), and die in glucose-free medium where survival requires expression of hepatic gluconeogenic enzymes, but then evolve to hepatoma-like and finally round morphology; these latter cells express all liver functions analyzed including the gluconeogenic enzymes. Two exceptional clones that remained flat long enough for complete analysis showed extinction of all hepatic functions not expressed by FaoflC2 cells. We conclude that this transitory extinction reflects the action and then loss of extinguishing factor(s) contributed by FaoflC2. When crossed with BW1-J mouse hepatoma cells. FaoflC2 causes stable extinction of mouse aldolase B. We propose that production of extinguishing factor(s) is the rule for dedifferentiated variants.

Chromatin repeat length correlates with phenotypic expression in hepatoma cells, their dedifferentiated variants, and somatic hybrids.

“…p4 and H5 cells fail to express the entire group of seven hepatic functions that we study, whereas FaoflC2 cells continue to express one of them; no striking karyotypic modification characterizes these clones (10). The isolation and characterization of the HF and pF hybrids have been described (11,12).…”

“…Each is an independent dedifferentiated variant clone whose cells fail to express most or all of the seven liver-specific functions analyzed. The (12). The repeat length of one of these subclones, HF1-5, is shown in Fig.…”

A liver-specific factor essential for albumin transcription differs between differentiated and dedifferentiated rat hepatoma cells.

“…Interestingly, C2Rev7, a revertant cell line derived from C2 that reexpresses albumin and other liver-specific proteins, showed the disappearance of the parental C2 complex and the reappearance of the hepatic-type CI complex. Most instructive is the analysis of the PE56 binding activity in a somatic hybrid, HFl, between Fao and H5 that causes extinction of the expression of the set of tissue-specific functions that characterizes the differentiated parent (Deschatrette et al 1979). As shown in Figure 2A, in FIFl only the C2 faster-migrating complex is observed.…”

Determinants of rat albumin promoter tissue specificity analyzed by an improved transient expression system.

“…Hepatoma cell lines are clonal descendants of line H4IIEC3 (43) derived from the Reuber H35 rat hepatoma (44). The clones used here have been described elsewhere (12,13). FR3T3 (45) and Rat2 (48) are rat fibroblast cell lines.…”