Characterization of the role of IL-6 in the progression of prostate cancer

BACKGROUND

We recently identified IL-6, a pleiotropic cytokine implicated in the neoplastic process of a variety of neoplasms, as a mediator of prostate cancer morbidity. In the present study, we investigated the expression of members of the IL-6 supergene family and related cytokines and the potential role of IL-6 in prostate cancer growth regulation.

METHODS

Five established human prostate cancer cell lines were screened by ELISA for production of granulocyte colony-stimulating factor (G-CSF), leukemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF), oncostatin M (OSM), tumor necrosis factor (TNF), interleukin-1 (IL-1), and granulocyte macrophage colony-stimulating factor (GM-CSF). Expression of the ligand-binding component of the IL-6 receptor, IL-6Rp80, was evaluated by ELISA and RT-PCR. Sequential immunoprecipitation and immunoblotting were performed to assay for expression of the signal-transducing component of the IL-6 receptor, gp130. The effects of IL-6 on cell growth were assessed by MTT assays.

RESULTS

The three hormone-refractory cell lines, DU-145, TSU, and PC-3, secreted distinct combinations of cytokines (DU-145: IL-6, GM-CSF; TSU: IL-6, LIF; PC-3: IL-6, G-CSF, LIF, IL-1, GM-CSF), each uniformly expressing IL-6. In contrast, neither of the two hormone-dependent cell lines, LNCaP-ATCC and LNCaP-GW, secreted significant quantities of any of the cytokines analyzed. None of the cell lines secreted detectable quantities of OSM, CNTF, or TNF. All cell lines, irrespective of hormone status, expressed both Il-6Rp80 and gp130. Addition of IL-6 in vitro inhibited growth of hormone-dependent cells, but had no effect on hormone-refractory lines. Anti-IL-6 neutralizing antibody inhibited growth of hormone-refractory cells.

CONCLUSIONS

IL-6 appears to undergo a functional transition from paracrine growth inhibitor to autocrine growth stimulator during progression of prostate cancer to the hormone-refractory phenotype.

Impaired expression and function of signal-transducing zeta chains in peripheral T cells and natural killer cells in patients with prostate cancer

Detection of functional, circulating T cells and NK cells may serve as a clinical test for the selection of individuals who can benefit from immunotherapy. Incidence of the T-cell receptor zeta (TCRdelta) chain within these populations appears to correlate with adequate effector cell function. In patients with advanced malignancy, the absence or reduced expression of delta chain has been documented. Flow cytometric analysis in the present study revealed a significant reduction in delta chain expression in peripheral blood lymphocytes (PBL) of 14 of 22 prostate cancer patients (P < 0.000001) as compared to normal donors, apparent in both T cells (CD3+, CD4+, CD8+), and NK (CD16+) cells. Compared to normal donor PBL, patient PBL cultured in the presence of CD3 and CD28, also demonstrated reduced expression of CD69 and/or CD25, and in some cases, failed to activate at all. Furthermore, evidence of cell proliferation in activation-stimulated patient PBL was muted: average PCNA positivity equaled 14%, a marked difference from what was observed in normal donors (P < 0.0002). In 8 of 16 samples of PBL, where delta expression was originally low, delta levels returned to the normal range after 48 hour culture in serum-free medium, suggesting that the loss of delta is reversible and may be caused by a tumor-derived substance. These data support the premise that monitoring the expression of delta in a cancer patient may provide a unique insight into the immune status and functionality of the individual, with the potential to redirect or augment therapies and ultimately alter prognosis.