The Wilms' tumor gene product (WT1) modulates the response to 1,25-dihydroxyvitamin D3 by induction of the vitamin D receptor

The Wilms' tumor gene (wt1) encodes a transcription factor involved in urogenital development, in particular in renal differentiation, and in hematopoietic differentiation. Differentiation of a number of solid tumor and leukemic cells lines can be mediated by 1,25-dihydroxyvitamin D(3). This is predominantly mediated by the nuclear receptor for 1,25-dihydroxyvitamin D(3), the vitamin D receptor (VDR). In initial experiments addressing a possible link between WT1 and VDR, we observed a correlated expression of WT1 and VDR mRNA in samples from renal tissues. HT29 colon carcinoma cells, stably transfected to express WT1, exhibited elevated endogenous VDR levels compared with control cells transfected with a control construct. Elevated VDR expression was found in wt1-transfected human embryonic kidney 293 cells, as well. In transient cotransfection experiments, we observed an activation of a vdr promoter reporter by WT1 through a WT1 recognition element, indicating transcriptional regulation of the vdr gene expression by WT1. The responsive sequence element was specifically bound by wild-type, but not by mutated WT1, in electrophoretic mobility shift assays. HT29 colon carcinoma cells, which respond to 1,25-dihydroxyvitamin D(3) with slow induction of growth arrest, were investigated for the influence of WT1 on 1,25-dihydroxyvitamin D(3)-mediated growth suppression. Although HT29 cells transfected with a control construct responded moderately to 1,25-dihydroxyvitamin D(3), the response of HT29 cells expressing WT1 was strikingly enhanced. Stimulation with dihydroxyvitamin D(3) caused an up to 3-fold reduction in the growth rate of different HT29 clones expressing WT1 as compared with control cells lacking WT1 expression. Thus, induction of VDR by WT1 leads to an enhanced response to 1,25-dihydroxyvitamin D(3). We conclude that the vitamin D receptor gene is a target for transcriptional activation by WT1, suggesting a possible physiological role of this regulatory pathway.

The CD30 ligand and CD40 ligand regulate CD54 surface expression and release of its soluble form by cultured Hodgkin and Reed-Sternberg cells

The membrane-bound proteins CD30 ligand (CD30L), CD40L and 4-1BBL are members of the tumor necrosis factor (TNF) superfamily. They are expressed mainly by activated T cells. Primary and cultured Hodgkin and Reed-Sternberg (H-RS) cells, regarded as the malignant components of Hodgkin's disease (HD), display high levels of the counter-receptors for these ligands, ie CD30, CD40 and 4-1BB. CD30L and CD40L are known to share some biological activities that can be linked to the unbalanced secretion of cytokines seen in HD. In addition, cell contact-dependent molecules such as adhesion or activation antigens are critically involved in T cell/H-RS cell interactions. Primary and cultured H-RS cells frequently overexpress intercellular adhesion molecule-1 (ICAM-1/CD54), BB-1 (B7-1/CD80) and B70/B7-2 (CD86). Here we show that CD30L and CD40L, but not 4-1BBL upregulate CD54 expression by cultured H-RS cells on the mRNA and protein level, as a result of transcriptional gene activation. Furthermore, enhanced CD54 surface expression by these cells is accompanied by increased shedding of surface-bound CD54, as evidenced by high levels of the 82 kDa soluble (s) CD54 form detectable in culture supernatants after specific stimulation. Addition of CD30L in combination with CD40L to cultured H-RS cells additively enhanced CD54 surface expression and its shedding. These results may give a plausible explanation why sCD54 serum levels are increased in patients with HD.