Thermic effects on the expression of human lymphocyte genes

Repression of hsp90β Gene by p53 in UV Irradiation-induced Apoptosis of Jurkat Cells

Tumor suppressor p53 has been implicated in cell stress response and determines cell fate of either growth arrest or apoptosis. Heat shock proteins (Hsps) expressed under stress usually confer survival protection to the cell or interruption in the apoptotic pathways. Although Hsp90 can physically interact with p53, whether or not the hsp90 gene is influenced downstream of p53 in UV irradiation-induced apoptosis remains unclear. We have found that the level of p53 is elevated with the decline of Hsp90 in UV-irradiated cells and that malfunction of Hsp90, as inhibited by geldanamycin, enhances the p53-involved UV irradiation-induced apoptosis. In addition, the expression of the hsp90beta gene was reduced in both UV-irradiated and wild type p53-transfected cells. These results suggest a negative correlation between the trans factor p53 and a chaperone gene hsp90beta in apoptotic cells. Mutation analysis demonstrated that the p53 binding site in the first exon was indispensable for p53 regulation on the hsp90beta gene. In addition, with p53 bound at the promoter of the hsp90beta gene, mSin3a and p300 were differentially recruited in UV irradiation-treated or untreated Jurkat cells in vivo. The evidence of p53-repressed hsp90beta gene expression in UV-irradiated cells shed light on a novel pathway of Hsp90 in the survival control of the stressed cells.

PKCϵ Is a Unique Regulator for hsp90β Gene in Heat Shock Response

An early event in cellular heat shock response is the transmittance of stress signals from the cell surface into the nuclei, resulting in the induction of heat shock proteins (Hsps). Protein kinase C (PKC) has been implicated as a key player in transducing stress signals. However, mechanism(s) by which PKC regulates heat shock-induced events remains largely unknown. Here we present data that pan-PKC inhibitor GF109203X, but not classic PKC inhibitor Gö6976, specifically repressed heat shock-induced accumulation of mRNA as well as promoter activity of hsp90 beta, but not hsp90 alpha, in Jurkat cells. Subcellular fractionation studies revealed that heat shock exclusively induced PKC-epsilon membrane translocation. Consistently, expression of a constitutively active PKC-epsilon(A159E) resulted in an enhanced promoter activity of hsp90 beta upon heat shock, whereas a dominant-negative PKC-epsilon(K437R) abolished this effect. In contrast, constitutively active-PKC-alpha or dominant-negative-PKC-alpha had no effects on heat shock induction of the gene. The effect of PKC-epsilon on hsp90 beta expression seems to be stimuli-specific, as phorbol myristate acetate-mediated hsp90 beta expression was PKC-epsilon-independent. We conclude that PKC-epsilon is specifically required in the signaling pathway leading to the induction of hsp90 beta gene in response to heat shock.

Differential hypersensitivity to DNase I in the regulatory region of human hsp90 beta gene in heat shock and constitutive expression

DNase I hypersensitivity analysis is a useful tool to investigate impact of structure changes in chromatin on the expression of a gene. In order to unravel chromatin regulation on human hsp90 beta gene, differential sensitivity to DNase I in non-treated and heat-shocked Jurkat cells are examined. Four major hypersensitive sites at -120/-20 bp (HS1), +360 bp (HS2), +630/+780 bp (HS4) and around +1020 bp (HS5) with respect to the transcription start site of hsp90 beta gene have been identified. The HS1 is shared by both constitutive and heat shock, while the intronic sites of HS4 and HS5 are elicited by heat shock and HS2 is illustrated only in constitutive expression. In addition, distal HSs at around 8.7 kb upstream and 6.8 kb downstream are found in both constitutive and heat shock expression, which indicate that the boundaries of the hsp90 beta gene extend for some 16 kb. The HS patterns confirm chromatin regulation in the expression of hsp90 beta gene under various treatments.

Regulation of human hsp90alpha gene expression

Mammalian HSP90alpha and HSP90beta are encoded by two individual genes. On the basis of the upstream sequences of the human hsp90alpha gene, GenBank accession number U25822, we have constructed CAT reporter plasmids driven by individual fragments of the hsp90alpha gene. We found that (1) the proximal heat shock element complex located at -96/-60 enhances hsp90alpha promoter expression; (2) heat shock induction depends upon the coexistence of distal heat shock element at -1031/-1022 and the proximal heat shock element complex of the hsp90alpha gene; (3) unlike hsp90beta, downstream sequences of the transcription start site inhibit hsp90alpha expression. We conclude that the regulatory mechanisms for the expression of hsp90alpha and hsp90beta genes are different.

Essential role of the first intron in the transcription of hsp90beta gene

The human HSP90 gene family contains introns. There are two typical heat shock elements (HSE) in the first intron of human hsp90beta gene. As detected by chloramphenicol acetyl transferase (CAT) reporter activity assays, the HSE-containing intron is essential in maintaining high constitutive expression and is critical for heat shock inducibility of the human hsp90beta gene. Cellular heat shock factor 1 (HSF 1) shows much higher binding affinity toward the intronic HSEs in comparison to an atypical HSE in the 5' flanking sequence. Novel initiation sites found in the first intron probably also contribute to constitutive and heat-inducible expression of the hsp90beta gene in Jurkat cells.

A method for simultaneous detection of the transcripts of different cellular genes

In this paper, a method for preparing radioactive-labelled first-strand cDNA has been described and the major procedures and reaction conditions have been studied. Some advantages provided by this method for simultaneously detecting the expression of multiple cellular genes are discussed.