Extracellular, cell-permeable survivin inhibits apoptosis while promoting proliferative and metastatic potential

Abstract

The tumour microenvironment is believed to be involved in development, growth, metastasis, and therapy resistance of many cancers. Here we show survivin, a member of the inhibitor of apoptosis protein (IAP) family, implicated in apoptosis inhibition and the regulation of mitosis in cancer cells, exists in a novel extracellular pool in tumour cells. Furthermore, we have constructed stable cell lines that provide the extracellular pool with either wild-type survivin (Surv-WT) or the previously described dominant-negative mutant survivin (Surv-T34A), which has proven pro-apoptotic effects in cancer cells but not in normal proliferating cells. Cancer cells grown in conditioned medium (CM) taken from Surv-WT cells absorbed survivin and experienced enhanced protection against genotoxic stresses. These cells also exhibited an increased replicative and metastatic potential, suggesting that survivin in the tumour microenvironment may be directly associated with malignant progression, further supporting survivin's function in tumourigenesis. Alternatively, cancer cells grown in CM taken from the Surv-T34A cells began to apoptose through a caspase-2-and caspase-9-dependent pathway that was further enhanced by the addition of other chemo-and radiotherapeutic modalities. Together our findings suggest a novel microenvironmental function for survivin in the control of cancer aggressiveness and spread, and should result in the genesis of additional cancer treatment modalities.

Tumor-Released Survivin Induces a Type-2 T Cell Response and Decreases Cytotoxic T Cell Function, in Vitro

“…Uptake of Survivin by malignant cells has been shown to increase their proliferative rate [34]. To determine if Survivin uptake has a similar effect on T cells, we analyzed their proliferation using the cell-cycle-associated nuclear antigen Ki-67 [38], CFSE staining and BrdU incorporation.…”

“…Recent studies have demonstrated that uptake of Survivin by cancer cells leads to a more aggressive phenotype [34]. To determine if tumor-infiltrating T cells would also be able to take up tumor-released Survivin, FLAG-HA-tagged Survivin was collected from cancer cell culture medium using dualaffinity purification and added to T cell cultures.…”

“…Peripheral blood mononuclear cells (PBMCs) were isolated from normal, cancer-free donors and CD3 + T cells isolated by magnetic separation. Using FLAG-HA-Survivin released by POZn-WT-Survivin HeLa S cells as previously described [34] and at a non-toxic concentration (Supplementary Figure 1), we analyzed for both surface binding and intracellular uptake of Survivin in T cells. Cells were cultured for 24 h in control R10 or FLAG-HA-Survivin medium and stained for confocal microscopy with anti-HA and anti-actin.…”

“…Much evidence points to tumor-released factors such as tumor proteins and cytokines [9,32,33]. One tumor antigen recently shown to be released from cancer cells into the extracellular space is the inhibitor of apoptosis (IAP) protein Survivin [34,35]. Within the cancer cell, Survivin functions to prevent cell death in response to apoptotic signals [36,37].…”

“…Within the cancer cell, Survivin functions to prevent cell death in response to apoptotic signals [36,37]. In its extracellular context, Survivin is released and taken up by surrounding malignant cells, which increases their proliferative rate, resistance to therapy and their invasive potential [34]. Here we show a novel role for tumor-released Survivin as a modulator of the T cell response, capable of inhibiting their proliferation and inducing a shift to a type 2 response, similar to that observed in cancer patients.…”