Genetic defects in the Wnt-1 signaling pathway contribute to human tumor progression and are especially prevalent in colorectal cancer. We screened mouse C57MG cells to isolate mRNAs induced by Wnt-1 and identified Stra6, an mRNA known to be up-regulated by retinoic acid. Up-regulation of Stra6 mRNA was also observed in hyperplastic mammary tissue and mammary gland tumors from transgenic mice expressing Wnt-1 and in human tumors that frequently harbor defects in Wnt-1 signaling. Stimulation of C57MG cells with retinoic acid plus Wnt-1 resulted in expression of Stra6 transcript to levels greatly exceeding that observed with either stimulus alone. This synergy could be explained in part by the up-regulation of retinoic acid receptor-gamma that was observed in response to Wnt-1 signaling. Accordingly, treatment of human colorectal cancer cell lines with retinoic acid resulted in the up-regulation of Stra6 mRNA and accumulation of Stra6 protein at the cell membrane. The data support a model in which Wnt-1 signaling synergizes with retinoids to activate retinoic acid receptor-gamma-responsive genes in human cancers.

Both glial cell line-derived neurotrophic factor (GDNF) and its recently discovered congener, neurturin (NTN), have been shown to excert neuroprotective effects on lesioned nigral dopamine (DA) neurons when administered at the level of the substantia nigra. In the present study, we have explored the relative in vivo potency of these two neurotrophic factors using two alternative routes of administration, into the striatum or the lateral ventricle, which may be more relevant in a clinical setting. In rats subjected to an intrastriatal (IS) 6-hydroxydopamine (6-OHDA) lesion, GDNF and NTN were injected every third day for 3 weeks starting on the day after the 6-OHDA injection. GDNF provided almost complete (90-92%) protection of the lesioned nigral DA neurons after both IS and intracerebroventricular (ICV) administration. NTN, by contrast, was only partially effective after IS injection (72% sparing) and totally ineffective after ICV injection. Although the trophic factor injections protected the nigral neurons from lesion-induced cell death, the level of expression of the phenotypic marker, tyrosine hydroxylase (TH), was markedly reduced in the rescued cell bodies. The extent of 6-OHDA-induced DA denervation in the striatum was unaffected by both types of treatment; consistent with this observation, the high rate of amphetamine-induced turning seen in the lesioned control animals was unaltered by either GDNF or NTN treatment. In the GDNF-treated animals, and to a lesser extent also after IS NTN treatment, prominent axonal sprouting was observed within the globus pallidus, at the level where the lesioned nigrostriatal axons are known to end at the time of onset of the neurotrophic factor treatment. The results show that GDNF is highly effective as a neuroprotective and axon growth-stimulating agent in the IS 6-OHDA lesion model after both IS and ICV administration. The lower efficacy of NTN after IS, and particularly ICV, administration may be explained by the poor solubility and diffusion properties at neutral pH.

Myelin oligodendrocyte glycoprotein (MOG) is a transmembrane glycoprotein expressed on the surface of central nervous system (CNS) myelin membranes, which has been shown to induce experimental autoimmune encephalomyelitis (EAE) in rodents. Here we describe the induction of EAE in SJL and (PLJ X SJL)F1 mice with truncated human recombinant MOG (thr-MOG, amino acids 1-120) which has been expressed in insect cells in soluble form. We show that in SJL mice, immunization with thr-MOG produces an immune response to the 1-30 and the 81-110 regions of the MOG molecule. We also demonstrate effective treatment of thr-MOG-induced EAE in SJL mice with intravenous injections of a single peptide, MOG 91-110. These results support the possibility of treating MS using an antigen dependent approach.

By transfecting 3T3 TK- fibroblasts with a plasmid DNA containing the MMTV LTR promotor and the thymidine kinase gene, we have isolated TK+ clones that contain only one copy of the recombinant DNA. The newly acquired DNA is integrated at different sites in each TK+ clones and can be amplified as a tandem repeat in some cases. The basal level of expression of the newly acquired LTR sequence is variable among the TK+ clones studied. Among those producing detectable amounts of MMTV RNA, we found that transcription is initiated from the LTR promotor and that the synthesis is stimulated by a short dexamethasone treatment. In addition, the presence of tandem repeated LTR DNA does not amplify the MMTV RNA synthesis. Endogenous LTR sequences have been found to be methylated, whereas we show that the newly integrated sequences, both as single copy and tandem repeats, remain unmethylated. Thus, non-methylation of MMTV LTR DNA is necessary but not significant to allow its transcription. Our results suggest that the level of LTR promotor activity could be modulated by the nature of its integration site within the cellular genome.