Carboxypeptidase Cathepsin X Defines a Multifunctional Role of Gamma- Enolase in Cancer
Author(s): Tjasa Vi?in Zlobec, Anja Pišlar, Ib Jarle Christensen, Hans Jorgen Nielsen, Pika Meško Brguljan, Janko Kos
Gamma-enolase enzymatic activity is involved in glycolysis, a prevalent process in cancer cell metabolism. Additionally, gamma-enolase has a pro-survival function, exhibited through the active site at the C-terminal end of the molecule. This activity is regulated by cysteine peptidase cathepsin X, which cleaves two amino acids at C-terminal end of gamma-enolase. In clinical practice, the determination of gamma-enolase as a tumour marker does not differ between total, uncleaved and C-terminally cleaved forms. However, levels of uncleaved gamma-enolase alone may provide additional clinical information. In this study we analysed cathepsin X, C- terminally uncleaved and total gamma-enolase in tumour cell lines and sera from 255 patients with colorectal cancer (CRC) by western blot, immunoprecipitation, enzymatic activity, ELISAs and ECLIA. Results show that uncleaved gamma-enolase, rather than total gamma- enolase, exhibits different levels in cells, being the highest in those, derived from metastatic sites or highly invasive tumours. Gamma-enolase is secreted into the extracellular space predominantly as an uncleaved form and levels were congruent to those within the cells. Furthermore, levels of uncleaved gamma-enolase in cells are inversely related to cathepsin X protein level and its enzymatic activity. Uncleaved gamma-enolase is also predominant form in sera of patients with CRC. Both forms exhibit similar stage dependent distribution, with slightly elevated levels in stage IV patients. Higher levels of total gamma-enolase are significantly related to shorter survival in patients with metastatic CRC. Results support evidence of additional pro-survival function of gamma-enolase in cancer. Future studies should focus on analysis of uncleaved gamma-enolase in tumour samples, which may provide additional relations to clinical indicators of disease progression.