AND ALDO BERNELLI-ZAZZERA called ''heat shock proteins'' (hsps). [4][5][6][7][8][9] Not only the response to The expression of hsp70-the inducible member of the temperature is conserved but the heat-inducible proteins are corresponding heat shock gene family-of the oxidative conserved as well; among them, the hsp70 family of hsps are stress marker gene heme oxygenase (HOx), and of the particularly important for amount, constancy of induction, immediate early response genes c-fos and c-jun has been and possible role as cellular thermometer regulating the exstudied in FAO hepatocarcinoma cells depleted of polypression of all hsps. [10][11][12] Heat shock has additional effects on amines and exposed to heat shock. Depletion of polymessenger RNA (mRNA) stability and translational control, amines was obtained in short-term experiments (24-48 which contribute to the preferential expression of hsps. Behours) by the use of a-difluoromethylornithine (DFMO), cause of their rapid induction, most of the studies on hsps a classical inhibitor of ornithine decarboxylase (ODC),
have emphasized this characteristic response to heat but or of the combination of the newly available inhibitors of ODC and S-adenosylmethionine decarboxylase, i.e., many hsps are also constitutively expressed. The main func-(2R,5R)-hept-6-yne-2,5-diamine (MAP) and 5-{[(Z)-4tion of constitutive and inducible hsps is to regulate the foldaminobut-2-enyl]methylamino}-5-deoxyadeno-sine (Abing of newly synthesized protein and to help in their refolding eAdo). Under our experimental conditions polyamine imduring or after cell injury. 8,9 balance was realized without appreciable growth arrest
In addition to exposure to heat, other noxious agents, conand impaired expression of growth-related genes. Denected in some way with protein malfolding or denaturation, creases of putrescine and spermidine 48 hours after can induce the synthesis of hsps 13 and may also be relevant DFMO prevented the induction of hsp70 messenger RNA to liver cell pathology. 14,15 Indeed, it has been recognized that (mRNA), whereas depletion of spermidine and spermine ''the heat-shock response is for hepatologists, too'' 16 and that obtained with MAP/AbeAdo decreased intensity and duthe application of hsps to clinical medicine is on the horiration of post-heat shock accumulation of hsp70 mRNA. zon. 17,18 The induction of hsp70 mRNA starts with the activa-Inductions of HOx, c-jun and c-fos were also inhibited. tion of the heat shock transcription factor (HSF), which binds Because MAP/AbeAdo caused also an intracellullar accuto the consensus sequence heat shock element (HSE) present mulation of putrescine, we tested the effect of exogenous in the promoter of heat shock genes and transactivates the putrescine, which was found to stabilize the mRNAs for gene. In some circumstances, however, the binding is not hsp70 and c-jun. Hsp70 and HOx are thought to play a followed by the appearance of hsp70 mRNA, 19,20 which argues protective role, and the proteins of c-jun and c-fos constifor the need of permissive conditions inside the cell.
tute the transcription factor activator protein-1, which
The present investigation was undertaken to study the inis involved in the transcription of many defensive prodfluence of polyamine depletion on the induction of hsp70 and ucts. Therefore, the integrity of polyamine pool seems other stress genes in heat-exposed cells. Polyamines (putresto be a necessary permissive condition for an effective cine, spermine, and spermidine) are ubiquitous polycations response of the cells to adverse environmental changes. that have numerous, unique interactions in eukaryotic cells. (HEPATOLOGY 1996;24:150-156.)
The length of the backbone, net charge at physiological pH and charge distribution of polyamines favor their interaction with large anionic molecules, such as DNA, RNA, and phos-Increasing the temperature of cells or organisms several pholipids. [21][22][23] Therefore, polyamines exert relevant functions degrees above the level of their normal growth elicits a rein the processes of transcription, splicing, and stabilization sponse that includes a battery of metabolic and morphological of molecular secondary structures, for instance those of DNA changes, comprehensively designated as ''heat shock reand RNA. 21,22,24,25 These regulatory roles of polyamines are sponse.'' [1][2][3] The most relevant and best studied aspect of this important when the cell must restrict its activities to the response is a reprogramming of gene expression charactersynthesis of an essential set of proteins, as in response to ized by the induction of a small set of genes, coding for the soheat shock. 25 A further reason for investigating the relationship between imbalance of intracellular polyamine pool and activation of Abbreviations: hsps, heat shock proteins; mRNA, messenger RNA; HSF, heat shock heat-shock genes comes from some data of the literature, transcription factor; HSE, heat shock element; FAO, ; DFMO, a-difluoromethylornithine;
showing that polyamine depletion prevents the induction of ODC, ornithine decarboxylase; MDL, Merrell Dow Laboratories; MAP, (2R, SR)-hept-6-ynethe immediate-early genes c-fos, c-jun, and c-myc by mito-2, 5-diamine; AbeAdo, 5-{[(Z)-4-aminobut-2-enyl]methylamino}-5-deoxyadenosine; HOx, heme oxygenase.
gens, viral products, or tumor growth. [26][27][28][29] Because c-fos and From the