[Alternative splicing--principles, functional consequences and therapeutic implications]. / Alternatives Spleißen--Prinzipien, funktionelle Konsequenzen und therapeutische Relevanz.

Protein-coding genes in higher eukaryotes are transcribed as pre-mRNA in which the coding regions (exons) are separated by non-coding segments (introns). The exons are connected to form the mature mRNA in a process called splicing. In the case of alternative splicing an exon can be either included or skipped from the mature transcript leading to formation of several mRNAs from a single pre-mRNA. As over 90 % of all human genes are alternatively spliced, alternative splicing dramatically increases proteome diversity and fulfills important regulatory functions. This is underlined by mutations that interfere with splicing regulation and directly correlate with the formation of several diseases. Correction of these disturbed splicing processes has emerged as a promising therapeutic concept and has led to the development of several drugs that are currently being tested in clinical trials.

Tumour necrosis factor-alpha inhibits adipogenesis via a beta-catenin/TCF4(TCF7L2)-dependent pathway.

Tumour necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine, is a potent negative regulator of adipocyte differentiation. However, the mechanism of TNF-alpha-mediated antiadipogenesis remains incompletely understood. In this study, we first confirm that TNF-alpha inhibits adipogenesis of 3T3-L1 preadipocytes by preventing the early induction of the adipogenic transcription factors peroxisome proliferator-activated receptor-gamma (PPARgamma) and CCAAT/enhancer binding protein-alpha (C/EBPalpha). This suppression coincides with enhanced expression of several reported mediators of antiadipogenesis that are also targets of the Wnt/beta-catenin/T-cell factor 4 (TCF4) pathway. Indeed, we found that TNF-alpha enhanced TCF4-dependent transcriptional activity during early antiadipogenesis, and promoted the stabilisation of beta-catenin throughout antiadipogenesis. We analysed the effect of TNF-alpha on adipogenesis in 3T3-L1 cells in which beta-catenin/TCF signalling was impaired, either via stable knockdown of beta-catenin, or by overexpression of dominant-negative TCF4 (dnTCF4). The knockdown of beta-catenin enhanced the adipogenic potential of 3T3-L1 preadipocytes and attenuated TNF-alpha-induced antiadipogenesis. However, beta-catenin knockdown also promoted TNF-alpha-induced apoptosis in these cells. In contrast, overexpression of dnTCF4 prevented TNF-alpha-induced antiadipogenesis but showed no apparent effect on cell survival. Finally, we show that TNF-alpha-induced antiadipogenesis and stabilisation of beta-catenin requires a functional death domain of TNF-alpha receptor 1 (TNFR1). Taken together these data suggest that TNFR1-mediated death domain signals can inhibit adipogenesis via a beta-catenin/TCF4-dependent pathway.