Furthermore, we wish to thank Georg Sch?fer for evaluating the TMA. its role in therapy resistance has not yet been determined. Here we investigate the influence of interleukin-4 on primary epithelial cells from prostate cancer patients. Our data demonstrate an increase in the clonogenic potential of these cells when cultured in the presence of interleukin-4. In addition, a Phospho-Kinase Array revealed that in contrast to previously published work, signal transducer and activator of transcription6 (STAT6) is the only signalling molecule activated after interleukin-4 treatment. Using the STAT6-specific inhibitor AS1517499 we could confirm the role of STAT6 in increasing colony-forming frequency. However, clonogenic recovery assays revealed that interleukin-4 does not rescue the effects of either irradiation or docetaxel treatment. We therefore propose that although the interleukin-4/STAT6 axis AFP464 does not appear to be involved in therapy resistance, it does play a crucial role in the colony-forming abilities of the basal cell population in prostate cancer. IL-4 may therefore contribute to disease relapse by providing a niche that is favourable for the clonogenic growth of prostate cancer stem cells. Introduction Prostate cancer (PCa) is one of the most frequent malignancies in males.1 Treatment is strongly AFP464 dependent on tumour stage, patient age, overall patient health and tumour risk assessment.2, 3, 4 The most commonly used treatment options for PCa are radical prostatectomy, radiation therapy, multiple endocrine therapies and chemotherapy with docetaxel. Although most PCa patients respond initially to androgen deprivation treatment, the cancer inevitably recurs and progresses to highly aggressive castration-resistant PCa, for which only palliative therapeutic options exist.3, 5 However, AFP464 the exact mechanism behind the development of castration-resistant PCa is still unclear. One possible reason for this progression is that currently used therapies have only been designed to target androgen receptor-positive luminal cells in the cancer.5 However, several studies have demonstrated that a small population of primitive cells with a basal phenotype (characterized by AR?, CD49f+, CD44+, CKs 5/14+ and p63+ markers) exist within the tumour, and have the capacity to evade current therapies.6, 7, 8 These rare cells (<1%) have been shown to possess a higher regenerative potential and express tumour markers (including AMACR and theTMPRSS2-ERG fusion gene).9, 10, 11 Similar to benign prostate tissue, the basal cells (CD44+/CD49f+) from malignant areas can further be subgrouped by high expression of 21 integrin complex (CD49b), which results in a rapid adhesion to collagen.12 The basal compartment can also be further fractionated into stem cells (SC, CD49bhigh/CD133+), the highly proliferative transit-amplifying cells (TA, CD49bhigh/CD133?) and committed basal cells (CB, CD49blow/CD133?).5, CD80 10 CB cells have also been reported in several studies as intermediate cells, and harbour luminal and basal markers, such as cytokeratins 5, 14 and 18.5, 10 Interestingly, SC isolated from malignant areas (cancer stem cells, CSC) are highly invasive, have a shorter population doubling time and a distinct messenger RNA (mRNA) and microRNA profile compared to normal SC, and in addition can form tumours in mice.10, 11, 13 Recent clinical studies have demonstrated that inflammation is not only linked to the development of cancer, but is also an indicator of poor prognosis.8, 14 Chronic inflammation has been AFP464 associated with the production of a variety of cytokines by inflammatory cells, including interleukin (IL)-1, IL-6 and IL-4.15 In addition to the action on immune cells, cytokines modulate the different cells types within the tumour microenvironment, and are able to induce cell transformation.15 For example, increased IL-6 levels have been observed in PCa tissues, and are suggested to influence growth and survival pathways.16 IL-6 expression levels in prostate tissue also (i) correlate with Gleason score and biochemical recurrence, (ii) influence tumour initiation and (iii) affect clonogenic recovery after docetaxel treatment of PCa stem-like cells.16, 17, 18 IL-4 is a multifunctional cytokine that plays a critical role in the regulation of immune responses.19 Cytokine binding to the IL4R alpha-chain (IL4R) subunit results in the activation of mediators of cell growth, resistance to apoptosis, gene activation and differentiation.19 The activated signal pathways include AKT, p44/42 MAPK, NF-B and the JAK/STAT6 pathways, which represents the main mediator of IL-4 signalling in immune cells.19 Elevated levels of IL-4 (normally produced by tumour-infiltrating lymphocytes) have been documented in patients with progressive PCa,20, 21, 22 and studies using PCa cell lines have demonstrated that IL-4 activates NF-B and androgen receptor in a.