In Vivo Growth of a Murine Lymphoma Cell Line Alters Regulation of Expression of HSP72

Abstract

We have identified a murine B-cell lymphoma cell line, CH1, that has a much-diminished capacity to express increased levels of heat shock proteins in response to heat stress in vitro. In particular, these cells cannot synthesize the inducible 72-kDa heat shock protein (HSP72) which is normally expressed at high levels in stressed cells. We show here that CH1 fails to transcribe HSP72 mRNA after heat shock, even though the heat shock transcription factor, HSF, is activated correctly. After heat shock, HSF from CH1 is found in the nucleus and is phosphorylated, trimerized, and capable of binding the heat shock element. We propose that additional signals which CH1 cells are unable to transduce are normally required to activate hsp72 transcription in vitro. Surprisingly, we have found that when the CH1 cells are heated in situ in a mouse, they show normal expression of HSP72 mRNA and protein. Therefore, CH1 cells have a functional hsp72 gene which can be transcribed and translated when the cells are in an appropriate environment. A diffusible factor present in ascites fluid is capable of restoring normal HSP72 induction in CH1 cells. We conclude that as-yet-undefined factors are required for regulation of the hsp72 gene or, alternatively, that heat shock in vivo causes activation of hsp70 through a novel pathway which the defect in CH1 has exposed and which is distinct from that operating in vitro. This unique system offers an opportunity to study a physiologically relevant pathway of heat shock induction and to biochemically define effectors involved in the mammalian stress response.

Methylation-associated Transcriptional Silencing of the Major Histocompatibility Complex-linked hsp70 Genes in Mouse Cell Lines

“…13). More recently, the same deficiency was found in a glucocorticoid-resistant rat hepatoma clone (14) and in the murine lymphoma line CH1, where, interestingly, hsp70 heat shock responsiveness was restored when the cells were grown as a tumor and heated in situ (15). Based on results of gel shift analyses and/or transfection studies, a trans-acting defect, possibly in HSF, was proposed as the cause for the lack of hsp70 responsiveness in the MEL, MPC-11, PCC4, and PCC7 mouse lines (11)(12)(13).…”

“…Based on results of gel shift analyses and/or transfection studies, a trans-acting defect, possibly in HSF, was proposed as the cause for the lack of hsp70 responsiveness in the MEL, MPC-11, PCC4, and PCC7 mouse lines (11)(12)(13). In the case of the rat hepatoma clone, a defect specific to the hsp70 gene itself was one of the possibilities considered (14), and, in the case of CH1 cells, a requirement for additional regulatory factors to activate hsp70 expression was suggested (15). None of the previous studies has identified the exact nature of the defect, however.…”

Inducible heat shock protein 70 expression as a potential predictive marker of metastasis in breast tumors

“…Because Hsp70 confers cell protection against different stresses, it has been hy-pothesized that this protein plays a protective role in tumor growth in vivo (Barnes et al 2001;Ravagnan et al 2001). Indeed, CH1 lymphoma cells in culture methylate and silence their Hsp70 promoter, but upon injection into a mouse Hsp70 production in the CH1 cells is restored (Davidson et al 1995). These data suggest that Hsp70 is needed for in vivo tumor progression.…”

HSP70.1 and -70.3 are required for late-phase protection induced by ischemic preconditioning of mouse hearts

“…Sham preconditioned animals subjected only to general anesthesia and a paramedian sternotomy were not protected against infarction. Moreover, sham IP had no effect on HSP70.1 and HSP70.3 mRNA or protein expression but did increase HSF activation in the nucleus compared with negative controls (unpublished observation), an event that has been shown to be insufficient to result in HSP70 translation (5). These data suggest that in an open-chest mouse model, sham operation may induce a minor stress that initiates cell signaling pathways but is insufficient to induce de novo HSP70.1 or HSP70.3 transcription or translation.…”