Enolase 2 is a key player in prostate cancer bone metastasis

Prostate cancer (PCa) is the most frequently diagnosed cancer in men which patients with distance bone metastases have high mortality. ENO2 is an important enzyme in the glycolysis process that most cancer cells rely on and also a widely-used biomarker for various neuroendocrine cancers, but there are no studies to determine whether ENO2 is functionally involved in PCa progression and metastasis. Therefore, we hypothesize that ENO2 positively contributes to PCa bone metastasis.
To test the hypothesis, a systematic review and meta-analysis were initially conducted to examine the association between ENO2 expression and PCa progression. Clinical and in vitro studies included suggested that high ENO2 expression is significantly associated with more malignant forms of PCa and is not influenced by different treatments. Retrospective and bioinformatic studies further identified higher ENO2 expression in both PCa metastases and benign prostate tissue, more importantly correlates with reduced survival rates. This finding was supported by in vitro examining the expression of ENO2 in various PCa and benign prostate tissue cells and data suggested that, the expression of ENO2 was upregulated not only in highly metastatic PCa cell lines but also in benign prostate tissue cells. This is possible due to the unique feature of glucose metabolism in prostate and PCa, demonstrated by the data that glucose supplement influenced ENO2 expression and cellular behaviors in both PCa and benign prostate tissue cells but in a different manner.
To further elucidate the functional contribution of ENO2 to PCa progression, PCa cell lines, 22Rv1 and PC3, were selected for transient knock down and genetic knock out studies. Knockdown of ENO2 by siRNA reduced cell viability and proliferation but increased apoptosis compared to mock-transfected controls at 48 hours post- transfection. Successful knockout of ENO2 in two clones in both PC3 and 22Rv1 cells was verified at both mRNA and protein levels. Genetic knockout of ENO2 significantly reduced viability, proliferation, migration, and invasion, but had no impact on apoptosis. In a murine xenograft model systemically injected with human PC3 cells, knocking out the ENO2 gene reduced the occurrence of bone metastases, decreased tumour burden, and protected bone from tumour induced destructions. Further bulk RNA sequencing on PC3 and 22Rv1 knockout cells and subsequent bioinformatic analysis suggested that ENO2 is not only a key component of glycolysis but also promotes the progression of PCa by regulating key pathways such as the E2F pathway.
In conclusion, ENO2 functionally contributes to PCa bone metastasis and offers the potential as a pharmaceutical target for developing ENO2 oriented treatments in fighting this deadly disease.