Elevated levels of mitochondrial mortalin and cytosolic HSP70 in blood as risk factors in patients with colorectal cancer

Abstract

Mortalin/GRP75 is a ubiquitous mitochondrial chaperone related to the cytosolic heat shock protein 70 (HSP70). It protects cells from senescence and apoptosis and is overexpressed in cancer cells. Cell resistance to complement-dependent cytotoxicity depends on mortalin and during complement attack mortalin is released from cells. Our goal was to determine whether cancer patients have circulating mortalin in blood. The significance of mortalin in blood to survival prospects of colorectal cancer patients was evaluated. Occurrence of extracellular soluble HSP70 (sHSP70) is documented. We developed a sensitive ELISA for mortalin. The association between mortalin level and survival was subjected to the Cox proportional hazards analysis (univariate and multivariate analyses). Mortalin concentration in serum of colorectal cancer patients was 10-214 ng/ml. Survival data of the patients were known from an earlier study of sHSP70 in these samples. Cox regression analysis indicated that high mortalin (>60 ng/ml) is a risk factor for shorter survival. Serum levels of sHSP70 and mortalin in patients were independent variables. Concurrence of high sHSP70 and mortalin was associated with rapid disease progression (HR = 4, 2.04-8.45, p < 0.001). Addition of high sHSP70 and mortalin to a baseline model of age, sex and TNM stage, significantly (p < 0.001) enhanced the risk score to 8 (3.26-20.46). This is the first demonstration of circulating mortalin in cancer patients. Analysis of mortalin in blood, and even more so of mortalin and sHSP70, adds a high prognostic value to the TNM stage and will identify colorectal cancer patients at high risk of poor survival.