Browsing by Author "Heissmeyer, Vigo"

The pentaspan protein CD133 (Prominin-1) is part of the signature of tumour-initiating cells for various cancer entities. The aim of the present study was to investigate the impact of ectopic CD133 expression on tumourigenic properties of otherwise CD133-negative, non-tumourigenic cells in vitro and in vivo. CD133 was stably transfected into human embryonic kidney 293 (HEK293) which was then sorted for the expression of CD133. The effects of CD133 on cell proliferation were assessed upon standard cell counting of sorted cells at various time points. Severe combined immunodeficient (SCID) mice (n = 30) were injected with HEK293 CD133(high) and CD133(low) transfectants (5 x 10(3), 1 x 10(5), or 5 x 10(6) cells per injection). The expression of CD133, Ki67, CD44s, CD44v6, and EpCAM was analysed upon immunohistochemical staining of cryosections with specific antibodies. In vitro, ectopic expression of CD133 did influence neither cell proliferation nor cell cycle distribution of otherwise CD133-negative HEK293 cells. However, CD133(high) cells generated tumours in vivo in SCID mice with at least 1,000-fold increased frequency compared to CD133(low) cells. Tumour load was also significantly increased in CD133(high) cells as compared to those tumours formed by high numbers of CD133(low) cells. Immunohistochemistry stainings disclosed no changes in Ki67, CD44s, CD44v6, or EpCAM once tumours were formed by either cell type. CD133 induces tumour-initiating properties in HEK293 cells in vivo and is potentially involved in the regulation of tumourigenicity. Future research will aim at the elucidation of molecular mechanisms of CD133-induced tumourigenicity.

BACKGROUND: The pentaspan protein CD133 (Prominin-1) is a predictive marker and part of the signature of tumour-initiating cells (TICs) for various cancer entities. METHODS: The correlation of CD133 expression with clinical parameters was assessed in primary samples of head and neck squamous cell carcinomas (n = 98) and normal mucosas (n = 24). RESULTS: A gradual and inversely proportional correlation between CD133 expression in primary tumours and decreased overall survival was observed, along with a positive correlation with the presence of lymph node metastases. CONCLUSIONS: CD133 has the potential of being a novel clinically relevant prognostic marker for head and neck malignancies, which is possibly involved in regulation of tumourigenicity.

The regulation of thymocyte development by RNA-binding proteins (RBPs) is largely unexplored. We identify 642 RBPs in the thymus and focus on Arpp21, which shows selective and dynamic expression in early thymocytes. Arpp21 is downregulated in response to T cell receptor (TCR) and Ca2+ signals. Downregulation requires Stim1/Stim2 and CaMK4 expression and involves Arpp21 protein phosphorylation, polyubiquitination and proteasomal degradation. Arpp21 directly binds RNA through its R3H domain, with a preference for uridine-rich motifs, promoting the expression of target mRNAs. Analysis of the Arpp21-bound transcriptome reveals strong interactions with the Rag1 3'-UTR. Arpp21-deficient thymocytes show reduced Rag1 expression, delayed TCR rearrangement and a less diverse TCR repertoire. This phenotype is recapitulated in Rag1 3'-UTR mutant mice harboring a deletion of the Arpp21 response region. These findings show how thymocyte-specific Arpp21 promotes Rag1 expression to enable TCR repertoire diversity until signals from the TCR terminate Arpp21 and Rag1 activities.