Liver-specific RNA metabolism in hepatoma cells: variations in transcription rates and mRNA levels.

Abstract

The transcription rate and abundance of several liver-specific mRNAs as well as mRNAs common to many cel types were compared in a series of rodent hepatoma cell lines, normal liver cells, and primary hepatocyte cultures. The rat hepatoma cell line, Fao, which displays a liver-specific phenotype, contained eight of eight liver-specific mRNAs examined. However, the transcription rates of most liver-specific mRNAs were found to be low (1 to 30%) compared with normal liver in this and other differentiated cell lines. This low rate is similar to the transcription rates of liver-specific mRNA sequences measured in primary cultures of hepatocytes. Several variant ceU lines that had lost differentiated traits contained few or none of the liver-specific mRNAs; clonal descendents which had regained differentiated function regained the tissue-specific mRNAs as a group, but at various concentrations. Because all of the changes observed in mRNA levels were not accompanied by parallel changes in transcription of the same sequences, differential posttranscriptional stabilization of the liver-specific mRNAs must also occur in the different cell lines. These results qualify the utility of cultured cell lines in the study of tissue-specific transcriptional control, but raise the possibility that posttranscriptional mechanisms act in cooperation with transcriptional controls to bring the level of tissue-specific mRNAs closer to those found in liver cells.Cell lines derived from liver tumors have been widely used in attempts to study various processes that normally occur in hepatocytes, including the mechanisms of tissue-specific gene control. Particular hepatoma clones secrete or contain numerous liver-specific plasma proteins and enzymes and have been considered well differentiated (13). Studies using these clones and the tools of somatic cell genetics (12,23,34) and molecular genetics (4, 24, 25) have provided evidence that many liver functions are regulated in these cells in a concerted manner. For example, cell lines can be selected which no longer produce the two liver-specific enzymes central to the ability of normal hepatocytes to synthesize glucose (1, 2). Loss of the ability of variant cells grow without glucose is accompanied by the loss of other liver functions (e.g., serum albumin production) (23). When revertant cell lines are then selected for their ability to grow in glucose-free medium, the expression of many or all of these other liver functions is regained (12).However, two important and general questions about these experiments, and cultured differentiated cell lines in general, remain unanswered. First, do immortalized, aneuploid, and culture-adapted cells exhibit patterns of gene control that resemble normal differentiated cells, or do they diverge in some potentially instructive way? For example, is the amount of a given liver-specific gene product in a well-differentiated hepatoma cell line quantitatively similar to that seen in the normal liver? How many separate liver functions are retained?Second, when he...

Expression of six mouse major urinary protein genes in the mammary, parotid, sublingual, submaxillary, and lachrymal glands and in the liver.

“…However, whether the expression of a given gene is controlled in different tissues by distinct regulatory elements and distinct trans-acting regulatory factors is not yet known. Likewise, even though the MUP II, IV, and V mRNAs are processed in the same manner in all tissues, the same species of MUP mRNAs may, in different tissues, exhibit different stability (6,12).…”

Non-receptor-mediated actions are responsible for the lipid-lowering effects of iodothyronines in FaO rat hepatoma cells

“…This 'minimum deviation' hepatoma cell line has been shown to secrete albumin, to maintain a number of other hepatocyte-specific differentiation markers, and to respond to hormonal stimulation as adult primary hepatocytes (Clayton et al 1985, Lauris et al 1986.…”

“…FaO cell line is a well-differentiated liver cell line maintaining a number of hepatocyte-specific markers (Clayton et al 1985, Lauris et al 1986). Cells were grown in Coon's modified Ham's F12 medium supplemented with 10% FBS (Euroclone, Milan, Italy), 100 U/ml penicillin, and 0 .…”

The mouse albumin promoter and a distal upstream site are simultaneously DNase I hypersensitive in liver chromatin and bind similar liver-abundant factors in vitro.

“…Previous studies found a liver-specific hypersensitive site 2.8 kb upstream of the rat albumin promoter (Babiss et al 1986;Turcotte et al 1986;Nahon et al 1987;Tratner et al 1987); this site is in a position similar to the site found at -3.5 kb in mice by Pinkert et al (1987) and in this study. Rodent hepatoma cell lines transcribe the al bumin gene at a much lower rate than liver (Clayton et al 1985b); in such cells the gene is weakly hypersensi tive at the promoter, and not at all at the expected -2.8-kb (Babiss et al 1986;Nahon et al 1987) or -3.5-kb (Y. Bergman and K. Zaret, unpubl. ) sites.…”