Hsp90 as a capacitor of both genetic and epigenetic changes in the genome during cancer progression and evolution

Abstract

In this chapter, we focus on the role of the chaperone protein Hsp90 as a capacitor for morphological variation that is released during times of stress. Hsp90 helps to fold numerous client proteins, which constitute a veritable who's who of important signaling molecules, such as Akt, Raf, Src, chromatin-modifying proteins, nuclear hormone receptors, and kinetochore assembly proteins. We first review evidence that Hsp90 functions trans-generationally as a capacitor for morphological variation via both genetic and epigenetic means: in the former by revealing cryptic genetic variation and in the latter by generating heritable epialleles. Then we discuss two mechanisms by which altered Hsp90 function can mutate DNA: transposon mobilization, and chromosomal aneuploidy. Next, we hypothesize how beneficial cryptic epigenetic variation might be stabilized, or locked in place, by the directed DNA-level mutation of epigenetically assimilated epialleles. Finally, we describe how Hsp90 functions intra-generationally within an organism's lifetime by releasing cryptic phenotypic variation during development in a stressful environment, and how this can be hijacked during the progression of diseases such as cancer.