The human Hsp70 family encompasses at least 11 genes which encode a group of highly related proteins. These proteins include both cognate and highly inducible members, at least some of which act as molecular chaperones. The location of cognate Hsp70s within all the major subcellular compartments is an indication of the importance of these proteins. The expression of several inducible Hsp70 genes is also an indication of the importance of these proteins in the stress response. The existence of multiple genes and protein isoforms has created confusion in the identification and naming of particular family members. We have compiled, from the literature, a list of genes and genetic loci and produced a two-dimensional protein map of the known human Hsp70 family members. This will enable researchers in the field to quickly and reliably identify human Hsp70s. We have also devised a more rational nomenclature for these genes and gene products which, subject to general acceptance, could be extended to Hsp70 families from other species.

We found that PPM1D, encoding a serine/threonine protein phosphatase, lies within an epicenter of the region at 17q23 that is amplified in breast cancer. We show that overexpression of this gene confers two oncogenic phenotypes on cells in culture: attenuation of apoptosis induced by serum starvation and transformation of primary cells in cooperation with RAS.

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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.

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