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Cytokines and adhesion receptors are key mediators in the dialog occurring between thymic epithelial cells (TEC) and thymocytes and regulating T cell maturation and epithelial embryonic differentiation. Among cytokines, IL-6 can be critical in the thymus, fostering proliferation, differentiation and/or survival of both TEC and thymocytes. We have previously reported in human normal TEC that clustering of the laminin receptor alpha6beta4 integrin induced by thymocyte contact or monoclonal antibody-mediated cross-linking regulates IL-6 gene expression via activation of NF-kappaB and NF-IL6 transactivators. Here we show that alpha6beta4 integrin activates p38 mitogen-activated protein kinase (MAPK) and that p38 is essential for IL-6 gene expression. In fact, beta4 cross-linking activated p38 and extracellular signal-regulated kinase (ERK) MAPK, Rac1, p21-activated protein kinase 1 (PAK1) and MAPK kinases (MKK) 3/MKK6. However, pharmacological blockade of p38 or ERK demonstrated that p38 inhibition abrogated both basal and beta4 integrin-induced production of IL-6 preventing NF-kappaB and NF-IL6 activation, whereas ERK inhibition reduced IL-6 production, hampering only NF-kappaB activation. Overall, our results indicate that p38 MAPK and alpha6beta4 integrin, expressed by TEC throughout their life, are critical regulators of the intrathymic availability of a cytokine controlling fate and functions of cells governing development and maintenance of thymic architecture and immune responses.

The interleukin-6 (IL-6) and the chemokine CCL5 are implicated in the development and progression of several forms of tumours including that of the prostate. The expression of the prostate specific membrane antigen (PSMA) is augmented in high-grade and metastatic tumors. Observations of the clinical behaviour of prostate tumors suggest that the increased secretion of IL-6 and CCL5 and the higher expression of PSMA may be correlated. We hypothesized that PSMA could be endowed with signalling properties and that its stimulation might impact on the regulation of the gene expression of IL-6 and CCL5. We herein demonstrate that the cross-linking of cell surface PSMA with specific antibodies activates the small GTPases RAS and RAC1 and the MAPKs p38 and ERK1/2 in prostate carcinoma LNCaP cells. As downstream effects of the PSMA-fostered RAS-RAC1-MAPK pathway activation we observed a strong induction of NF-kB activation associated with an increased expression of IL-6 and CCL5 genes. Pharmacological blockade with specific inhibitors revealed that both p38 and ERK1/2 participate in the phenomenon, although a major role exerted by p38 was evident. Finally we demonstrate that IL-6 and CCL5 enhanced the proliferative potential of LNCaP cells synergistically and in a dose-dependent manner and that CCL5 functioned by receptor-mediated activation of the STAT5-Cyclin D1 pro-proliferative pathway. The novel functions attributable to PSMA which are described in the present report may have profound influence on the survival and proliferation of prostate tumor cells, accounting for the observation that PSMA overexpression in prostate cancer patients is related to a worse prognosis. [ABSTRACT FROM AUTHOR]