Transcriptional activation of candidate paused genes after partial hepatectomy.

Partial hepatectomy is a model of acute liver injury that is known to induce a strong reprogrammation of gene expression. Transcriptional induction of Immediate Early Genes is extremely fast and this would be due to the release of RNA Polymerase II poised for elongation at 'paused' genes. Using bioinformatic analysis, we identified 23 genes sharing features of paused genes before hepatectomy, and with predicted quick and strong expression induction after. This transcriptional dynamic, confirmed by RT-qPCR for Jun , Fos , Btg2, is very precocious. RNA Pol II CTD Ser2 hyperphosphorylation indicates a switch to productive elongation and release from transcriptional pause.

An alternative D. melanogaster 7SK snRNP.

BACKGROUND: The 7SK small nuclear RNA (snRNA) found in most metazoans is a key regulator of P-TEFb which in turn regulates RNA polymerase II elongation. Although its primary sequence varies in protostomes, its secondary structure and function are conserved across evolutionary distant taxa. RESULTS: Here, we describe a novel ncRNA sharing many features characteristic of 7SK RNAs, in D. melanogaster. We examined the structure of the corresponding gene and determined the expression profiles of the encoded RNA, called snRNA:7SK:94F, during development. It is probably produced from the transcription of a lncRNA which is processed into a mature snRNA. We also addressed its biological function and we show that, like dm7SK, this alternative 7SK interacts in vivo with the different partners of the P-TEFb complex, i.e. HEXIM, LARP7 and Cyclin T. This novel RNA is widely expressed across tissues. CONCLUSION: We propose that two distinct 7SK genes might contribute to the formation of the 7SK snRNP complex in D. melanogaster.

Improvement of the rituximab-induced cell death by potentiation of the store-operated calcium entry in mantle cell lymphoma cell lines.

Mantle Cell Lymphoma (MCL) is one of the worst lymphomas with a median overall survival of 3 to 4 years. Even if the use of rituximab was a great step in therapy, patients commonly develop resistance and relapse. New therapies or complement of existing therapies should be developed. Using spectrofluorimetry, we found that the resting cytosolic Ca2+ ion concentration [Ca2+]cyt of MCL patients cells and MCL cell lines was increased. This increase is correlated with a larger store-operated calcium entry (SOCE) amplitude which is responsible for the Ca2+ ions influx. Furthermore, using a SOCE potentiating agent, we demonstrated that in the MCL Rec-1 cell line, the SOCE is already activated in resting conditions. Interestingly, this potentiating agent alone, by disturbing the SOCE, induced the apoptosis of Rec-1 cells with the same efficacy than rituximab. The use of the potentiating agent in addition to rituximab strengthens the rituximab-induced apoptosis of rituximab-sensitive Granta-519 and Rec-1 cells. However, this potentiating agent cannot convert the Jeko-1 rituximab-resistant to a rituximab-sensitive cell line. Our results confirm that the use of compound acting on the Ca2+ homeostasis could be a new target of interest in complement to existing therapies.

Functional Interaction between HEXIM and Hedgehog Signaling during Drosophila Wing Development.

Studying the dynamic of gene regulatory networks is essential in order to understand the specific signals and factors that govern cell proliferation and differentiation during development. This also has direct implication in human health and cancer biology. The general transcriptional elongation regulator P-TEFb regulates the transcriptional status of many developmental genes. Its biological activity is controlled by an inhibitory complex composed of HEXIM and the 7SK snRNA. Here, we examine the function of HEXIM during Drosophila development. Our key finding is that HEXIM affects the Hedgehog signaling pathway. HEXIM knockdown flies display strong phenotypes and organ failures. In the wing imaginal disc, HEXIM knockdown initially induces ectopic expression of Hedgehog (Hh) and its transcriptional effector Cubitus interuptus (Ci). In turn, deregulated Hedgehog signaling provokes apoptosis, which is continuously compensated by apoptosis-induced cell proliferation. Thus, the HEXIM knockdown mutant phenotype does not result from the apoptotic ablation of imaginal disc; but rather from the failure of dividing cells to commit to a proper developmental program due to Hedgehog signaling defects. Furthermore, we show that ci is a genetic suppressor of hexim. Thus, HEXIM ensures the integrity of Hedgehog signaling in wing imaginal disc, by a yet unknown mechanism. To our knowledge, this is the first time that the physiological function of HEXIM has been addressed in such details in vivo.