Expression of a growth arrest specific gene (gas‐6) during liver regeneration: Molecular mechanisms and signalling pathways

Abstract

A set of growth arrest-specific (gas) genes negatively regulated by serum has been identified. To define the role of gas genes in a model of cell proliferation in vivo we analyzed the expression of one of these genes (gas-6) during liver regeneration after partial hepatectomy (PH). We found that gas-6 mRNA was down-regulated 4 hours after PH, within the G0 to G1 transition. Later on, gas-6 mRNA increased over the level found in normal liver with a peak at 16 hours, before the onset of DNA synthesis. This surge was probably triggered by an inflammatory response caused by the surgical trauma, because an increase of similar extent occurring with the same time course was present in livers of sham-operated and turpentine-treated rats. Comparison of mRNA steady state levels with nuclear transcription rates indicated that gas-6 expression is post-transcriptionally regulated. As we found that down-regulation of gas-6 expression was prevented by treatment with Actinomycin D, a labile protein might be involved in the determination of gas-6 mRNA stability. To investigate the mitogenic signals controlling gas-6 expression during liver regeneration we treated hepatectomized rats with a specific alpha-1-adrenoceptor blocker (prazosin) as well as with drugs which modify intracellular calcium levels. The decrease of gas-6 mRNA 4 hours after PH was prevented by prazosin and by neomycin, an inhibitor of calcium release from endogenous stores. These findings suggest that down-regulation of gas-6 expression during hepatic regeneration is triggered by catecholamines interaction with alpha-1-adrenergic receptors and by subsequent calcium release. In addition we found that the rise of gas-6 gene expression occurring at 16 hours after PH was not affected by prazosin but was inhibited by trifluoperazine. Therefore, we suggest that up-regulation of gas-6 gene expression is mediated by the interaction of calcium with calmodulin, independently of catecholamines.

Posttranscriptional and Posttranslational Regulation of C/EBPδ in G0 Growth-arrested Mammary Epithelial Cells

“…In fact, both C/EBP␦ and gas-1 mRNAs exhibited stabilization during cell cycle reentry in response to transcriptional inhibitors in two mouse MEC lines, HC11 and COMMA D (later data not shown). Posttranscriptional control is known to play a major role in the regulation of gas family members in many cell types (61,66,67). Our results parallel previous work that shows an increase in gas-1 and gas-6 mRNA stability after cell cycle re-entry and treatment with actinomycin D of fibroblastic cell lines (61,66,67).…”

“…Posttranscriptional control is known to play a major role in the regulation of gas family members in many cell types (61,66,67). Our results parallel previous work that shows an increase in gas-1 and gas-6 mRNA stability after cell cycle re-entry and treatment with actinomycin D of fibroblastic cell lines (61,66,67). Furthermore, actinomycin D treatment of Schwann cells during cell cycle re-entry stabilized the gas-3 mRNA (68).…”

Analysis of EPC‐1 growth state–dependent expression, specificity, and conservation of related sequences

“…The induction of EPC-1 upon entry of WI-38 fibroblasts into the Go state is similar to the induction of the growth-arrest-specific (gas) genes in NIH 3T3 cells. Either serum deprivation or density-dependent contact inhibition will cause both EPC-1 and the gas genes to be expressed in amounts far in excess of basal levels (Schneider et al, 1988;Manfioletti et al, 1990;Brancolini et al, 1992;Del Sal et al, 1992;Ferrero et al, 1994). In most cases, the gas genes are downregulated much more rapidly than EPC-I, usually within 10 h after serum stimulation.…”

Molecular Regulation of Liver Regenerationa

“…Thus, the role of poly(A) tail shortening in modulating the decay rates of the gap junction connexin 32 and ornithine decarboxylase mRNAs was investigated at 0 and 12 hours post‐PH. These times reflect when their respective transcript stabilities are oppositely regulated 48–55 . The rate of poly(A) tail removal was increased for both transcripts coincident with decreased mRNA stability.…”

“…Transcriptional and/or posttranscriptional processes control the steady‐state expression of mRNAs, yet for many of the induced transcripts, substantial changes in transcriptional activity are not observed (T 2). In fact, numerous genes expressed in the regenerating liver are probably controlled at the posttranscriptional level, including those modulated at the immediate‐early phase of the cell cycle 16,47–57 . Posttranscriptional control of mRNA expression occurs primarily by nuclear processing of heterogeneous nuclear (hn) RNA, nucleocytoplasmic transport of mature mRNA and mRNA stability.…”