Highlights

• eHsp90 induces prostate cancer cell motility, suppresses E-cadherin, and induces EMT events

• eHsp90 induces tumor growth and invasion in animal models of prostate cancer

• eHsp90 is found in patient tumors and correlates with an invasive gene signature

• Goal is to identify the key effectors of eHsp90-driven tumor cell invasion and metastasis

 

Salient Findings

There is an urgent need to uncover new factors involved in cancer progression. We have shown

that eHsp90 may play an important role in this process (Hance MW et al., JBC 2012). To investigate this, prostate cancer cells lines were used as a model. We assessed the levels of secreted eHsp90 in 4 matched pairs of prostate cancer cell lines (Fig. 3A).

 

Each cell pair consisted of a non-metastatic (green bars) and metastatic (red bars) counterpart. In all instances, the metastatic cell lines exhibited higher secretion of eHsp90. To evaluate this in a functional context, Hsp90 protein was added to ARCaPE cells, a model for a tumorigenic, but poorly metastatic cell type. As shown (Fig. 3B), addition of Hsp90 protein (to mimic eHsp90 secretion), stimulates ARCaPE cancer cell motility. ARCaPM cells are the metastatic counterpart to ARCaPE. The blockade of eHsp90 function by a small molecule inhibitor (NPGA), dramatically decreases ARCaPM cancer cell motility.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A proposed model of eHsp90 function is shown (Fig. 5). eHsp90 (purple diamonds) can initiate signaling through its receptor LRP1 to activate the ERK kinase. This leads to the transcriptional upregulation of several key EMT effector genes (shown in yellow circle) that promote a mesenchymal phenotype and associated aggressive behavior. eHsp90 may also bind to other targets, such as proteolytic MMP proteins, to facilitate their activation. MMP activation also activates ERK signaling and participates in a feed-forward pathway to promote EMT events.

 

Ongoing and Future Research

We are now evaluating the role of eHsp90 in more complex models. The creation of our genetic model for eHsp90 secretion has allowed us to embark on utilization of animal models. In our pilot studies, we find that eHsp90 promotes tumor growth and tumor cell invasion (Fig. 6). We are also collaborating with a clinical group to obtain patient samples of prostate cancer tissue. The term prostatectomy is a surgical procedure wherein patients opt to remove their prostate following the identification of cancer tissue. This tissue is separated and sorted into cancer cell populations demonstrating either high or low surface eHsp90 expression (Fig. 7). The gene expression profiles for these respective tumor cell populations can then be analyzed for genes and/or microRNAs that correlate with poor prognosis. Thus, we can evaluate the potential clinical role of eHsp90 in prostate cancer progression.

 

We are now working to identify key effectors of eHsp90 function. Target genes of interest are being modulated and functionally evaluated in our xenograft models. We are also exploring the role of microRNAs (miRs) in this process. MiRs are small (approximately 22 nucleotide) double stranded RNAs that post-transcriptionally regulate gene expression and play key roles in cancer progression. We are also evaluating the role of epigenetic repressors, which function to compact the chromatin structure, thereby impeding the transcription of tumor-suppressor genes. It is well known that cancers exhibit a broad deregulation of epigenetic modifiers, several of which play key roles in EMT events. An overall schema of our integrated approaches to evaluate eHsp90 function in prostate cancer is shown (Fig. 8). These integrated approaches are expected to uncover key effectors of eHsp90-driven tumor cell invasion and metastasis, which may lead to new therapeutic approaches in prostate cancer and other solid malignancies.