Orthopedia expression during Drosophila melanogaster nervous system development and its regulation by microRNA-252

During brain development of Drosophila melanogaster many transcription factors are involved in regulating neural fate and morphogenesis. In our study we show that the transcription factor Orthopedia (Otp), a member of the 57B homeobox gene cluster, plays an important role in this process. Otp is expressed in a stable pattern in defined lineages from mid-embryonic stages into the adult brain and therefore a very stable marker for these lineages. We determined the abundance of the two different otp transcripts in the brain and hindgut during development using qPCR. CRISPR/Cas9 generated otp mutants of the longer protein form significantly affect the expression of Otp in specific areas. We generated an otp enhancer trap strain by gene targeting and reintegration of Gal4, which mimics the complete expression of otp during development except the embryonic hindgut expression. Since in the embryo, the expression of Otp is posttranscriptionally regulated, we looked for putative miRNAs interacting with the otp 3'UTR, and identified microRNA-252 as a candidate. Further analyses with mutated and deleted forms of the microRNA-252 interacting sequence in the otp 3'UTR demonstrate an in vivo interaction of microRNA-252 with the otp 3'UTR. An effect of this interaction is seen in the adult brain, where Otp expression is partially abolished in a knockout strain of microRNA-252. Our results show that Otp is another important factor for brain development in Drosophila melanogaster.

Identification and Tissue-Specific Characterization of Novel SHOX-Regulated Genes in Zebrafish Highlights SOX Family Members Among Other Genes

SHOX deficiency causes a spectrum of clinical phenotypes related to skeletal dysplasia and short stature, including Léri-Weill dyschondrosteosis, Langer mesomelic dysplasia, Turner syndrome, and idiopathic short stature. SHOX controls chondrocyte proliferation and differentiation, bone maturation, and cellular growth arrest and apoptosis via transcriptional regulation of its direct target genes NPPB, FGFR3, and CTGF. However, our understanding of SHOX-related pathways is still incomplete. To elucidate the underlying molecular mechanisms and to better understand the broad phenotypic spectrum of SHOX deficiency, we aimed to identify novel SHOX targets. We analyzed differentially expressed genes in SHOX-overexpressing human fibroblasts (NHDF), and confirmed the known SHOX target genes NPPB and FGFR among the most strongly regulated genes, together with 143 novel candidates. Altogether, 23 genes were selected for further validation, first by whole-body characterization in developing shox-deficient zebrafish embryos, followed by tissue-specific expression analysis in three shox-expressing zebrafish tissues: head (including brain, pharyngeal arches, eye, and olfactory epithelium), heart, and pectoral fins. Most genes were physiologically relevant in the pectoral fins, while only few genes were also significantly regulated in head and heart tissue. Interestingly, multiple sox family members (sox5, sox6, sox8, and sox18) were significantly dysregulated in shox-deficient pectoral fins together with other genes (nppa, nppc, cdkn1a, cdkn1ca, cyp26b1, and cy26c1), highlighting an important role for these genes in shox-related growth disorders. Network-based analysis integrating data from the Ingenuity pathways revealed that most of these genes act in a common network. Our results provide novel insights into the genetic pathways and molecular events leading to the clinical manifestation of SHOX deficiency.

Activity patterns of proteasome subunits reflect bortezomib sensitivity of hematologic malignancies and are variable in primary human leukemia cells

Proteasomal proteolysis relies on the activity of six catalytically active proteasomal subunits (beta1, beta2, beta5, beta1i, beta2i and beta5i). Applying a functional proteomics approach, we used a recently developed activity-based, cell-permeable proteasome-specific probe that for the first time allows differential visualization of individual active proteasomal subunits in intact primary cells. In primary leukemia samples, we observed remarkable variability in the amounts of active beta1/1i-, beta2/2i- and beta5/5i-type of subunits, contrasting with their constant protein expression. Bortezomib inhibited beta5- and beta1-type, but to a lesser extend beta2-type of subunits in live primary cells in vitro and in vivo. When we adapted the bortezomib-sensitive human acute myeloid leukemia cell line HL-60 to bortezomib 40 nM (HL-60a), proteasomal activity profiling revealed an upregulation of active subunits, and residual beta1/beta5-type of activity could be visualized in the presence of bortezomib 20 nM, in contrast to control cells. In a panel of cell lines from hematologic malignancies, the ratio between beta2-type and (beta1 + beta5)-type of active proteasomal polypeptides mirrored different degrees of bortezomib sensitivity. We thus conclude that the proteasomal activity profile varies in primary leukemia cells, and that the pattern of proteasomal subunit activity influences the sensitivity of hematologic malignancies toward bortezomib.

The HIV protease inhibitor ritonavir and the proteasome inhibitor bortezomib induce synergistic cytotoxicity on soft tissue sarcoma cells in vitro

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Background: HIV-protease inhibitors like Ritonavir produces regressions in HIV-associated Kaposi‘s sarcoma, reportedly due to proteasome inhibition. We have here assessed the effect of Ritonavir and the proteasome inhibitor Bortezomib on the viability and proteasome activity of the soft tissue sarcoma cell lines RD (rhabdomyosarcoma) and A-673 (ewing‘s sarcoma) in vitro. Methods: Cytotoxixity was assessed by MTS-test. To directly dissect proteasome activity in viable sarcoma cells, we used a recently developed cell-permeable affinity label that for the first time allows to assess the individual activity profile of the different catalytically active proteasomal subunits in living cells (Berkers et al., Nature Methods, May 2005). Results: Both types of cells were resistant towards Bortezomib and Ritonavir monotherapy at therapeutic concentrations (20 nM for Bortezomib, 20μM for Ritonavir). Ritonavir induced cytotoxicity in sarcoma cell lines with an IC50 of 40μM. The combination of clinically meaningful concentrations of Ritonavir (20μM) with Bortezomib (10–20 nM) induced robust synergistic cytotoxicity in both sarcoma cell lines. Using affinity labelling of proteasome activity, we directly demonstrate that a) Botezomib abrogates beta5, but also beta1-proteosomal activity in sarcoma cells and b) that Ritonavir at 20μM does not affect proteasom activity. Conclusions: We here present the first analysis of active proteasomal subunits in living human sarcoma cell lines. Ritonavir and Velcade induce synergistic cytotoxicity at clinically meaningful concentrations in vitro, which is not mediated through a direct effect of Ritonavir on proteasome activity. Based on our data, the synergistic combination of Ritonavir and Bortezomib might warrant further clinical testing in soft tissue sarcoma in vivo.

No significant financial relationships to disclose.