Cytosolic Hsp90α and its mitochondrial isoform Trap1 are differentially required in a breast cancer model

The Hsp90 family of molecular chaperones includes the cytosolic isoforms Hsp90 alpha and Hsp90 beta, and the mitochondrial isoform Trap1. Hsp90 alpha/beta support a large number of client proteins in the cytoplasm and the nucleus whereas Trap1 regulates oxidative phosphorylation in mitochondria. Many of the associated proteins and cellular processes are relevant to cancer, and there is ample pharmacological and genetic evidence to support the idea that Hsp90 alpha/beta and Trap1 are required for tumorigenesis. However, a direct and comparative genetic test in a mouse cancer model has not been done. Here we report the effects of deleting the Hsp90 alpha or Trap1 genes in a mouse model of breast cancer. Neither Hsp90 alpha nor Trap1 are absolutely required for mammary tumor initiation, growth and metastasis induced by the polyoma middle T-antigen as oncogene. However, they do modulate growth and lung metastasis in vivo and cell proliferation, migration and invasion of isolated primary carcinoma cells in vitro. Without Hsp90 alpha, tumor burden and metastasis are reduced, correlating with impaired proliferation, migration and invasion of cells in culture. Without Trap1, the appearance of tumors is initially delayed, and isolated cells are affected similarly to those without Hsp90 alpha. Analysis of expression data of human breast cancers supports the conclusion that this is a valid mouse model highlighting the importance of these molecular chaperones.