In this study we have investigated the molecular mechanism by which sodium butyrate modulates gene expression when added to cultured cells. As a model system we used hepatoma tissue culture cells in which sodium butyrate treatment increases histone H1°mRNA level and decreases c-myc mRNA level. Because we observed that stimulation of histone H1°gene expression could take place in the absence of protein neosynthesis, we hypothesized that sodium butyrate induced a posttranslational modification of a factor involved in the transcription process. Using different types of well known kinase and phosphatase inhibitors, we studied the implication of kinase or phosphatase activity in this pathway. Interestingly, cell treatment with potent serine-threonine-phosphatase inhibitors, calyculin A or okadaic acid, prevented the regulation of both histone H1°and c-myc gene expressions by sodium butyrate. On the other hand, the tyrosine phosphatase inhibitor, vanadate, or the protein kinase C inhibitor, staurosporine, did not significantly modify sodium butyrate effects. Using protein phosphatase 1 and 2A for in vitro assays, we found a 45% increase of phosphatase activity after cell treatment by sodium butyrate, possibly due to a protein phosphatase 1-type protein phosphatase. These data strongly suggest that signaling pathway(s) triggered by sodium butyrate to modulate gene expression involve(s) a serine-threonine-phosphatase activity.

A novel protein was extracted with 5% perchloric acid from rat liver and kidney. It is absent from other rat organs. Its apparent molecular mass is 23 kDa as determined by HPLC gel filtration. A single band, corresponding to 10 kDa, was observed after SDSPAGE, suggesting that the protein consists of two subunits with similar molecular masses.This protein can neither be phosphorylated by ATP, nor acetylated. The sequence of the cDNA encoding this protein was determined. Southern-blot analysis showed that the corresponding gene spanned at least 10 kb and contained at least five introns. Zoo-blot analysis at medium stringency strongly suggests that the gene has been conserved during evolution. The amino-acid sequence of this protein with a highly conserved region is similar to that of a heat-shock protein.High-mobility group (HMG) proteins are major chromatin components in all higher organisms. During the study of rat chromatin we have isolated from liver a novel protein which is co-extracted with the HMG protein by 5% perchloric acid.This protein does not meet the criteria that characterize the HMG protein group : monomeric structure, bipolar distribution of charged amino acids [ 1, 21. Since this protein is expressed at a high level in liver and kidney, but present in very low amounts in, or even absent from, other organs, it constitutes a good model for the study of tissue-specific regulation of protein synthesis.In this study we describe the purification of the protein whose apparent molecular mass is 23 kDa and which consists of two 10-kDa subunits, and the cloning and sequencing of the corresponding cDNA.This cDNA consists of 859 bp. The first half of the deduced polypeptide sequence presents 27% similarity with a region of the 83-90-kDa heat-shock protein (hsp) which is highly conserved from Drosophila to man [3 -51.

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