Transcription factor GATA‐1 is essential for red blood cell maturation and, therefore, for survival of developing mouse embryos. GATA‐1 is also expressed in megakaryocytes, mast cells, eosinophils, ...multipotential hematopoietic progenitors and Sertoli cells of the testis, where its functions have been elusive. Indeed, interpretation of gene function in conventional knockout mice is often limited by embryonic lethality or absence of mature cells of interest, creating the need for alternate methods to assess gene function in selected cell lineages. Emerging strategies for conditional gene inactivation through site‐specific recombinases rely on the availability of mouse strains with high fidelity of transgene expression and efficient, tissue‐restricted DNA excision. In an alternate approach, we modified sequences upstream of the GATA‐1 locus in embryonic stem cells, including a DNase I‐hypersensitive region. This resulted in generation of mice with selective loss of megakaryocyte GATA‐1 expression, yet sufficient erythroid cell levels to avoid lethal anemia. The mutant mice have markedly reduced platelet numbers, associated with deregulated megakaryocyte proliferation and severely impaired cytoplasmic maturation. These findings reveal a critical role for GATA‐1 in megakaryocyte growth regulation and platelet biogenesis, and illustrate how targeted mutation of cis‐elements can generate lineage‐specific knockout mice.
The transcription factor GATA-1 coordinates multiple events during terminal erythroid cell maturation. GATA-1 participates in the transcription of virtually all erythroid-specific genes, blocks ...apoptosis of precursor cells, and controls the balance between proliferation and cell cycle arrest. Prior studies suggest that the function of GATA-1 is mediated in part through association with transcriptional cofactors. CREB-binding protein (CBP) and its close relative p300 serve as coactivators for a variety of transcription factors involved in growth control and differentiation. We report here that CBP markedly stimulates GATA-1's transcriptional activity in transient transfection experiments in nonhematopoietic cells. GATA-1 and CBP also coimmunoprecipitate from nuclear extracts of erythroid cells. Interaction mapping pinpoints contact sites to the zinc finger region of GATA-1 and to the E1A-binding region of CBP. Expression of a conditional form of adenovirus E1A in murine erythroleukemia cells blocks differentiation and expression of endogenous GATA-1 target genes, whereas mutant forms of E1A unable to bind CBP/p300 have no effect. Our findings add GATA-1, and very likely other members of the GATA family, to the growing list of molecules implicated in the complex regulatory network surrounding CBP/p300.
Blood cell development relies on the expansion and maintenance of haematopoietic stem and progenitor cells in the embryo. By gene targeting in mouse embryonic stem cells, we demonstrate that the ...transcription factor GATA-2 plays a critical role in haematopoiesis, particularly of an adult type. We propose that GATA-2 regulates genes controlling growth factor responsiveness or the proliferative capacity of early haematopoietic cells.
Previous work established non-inferiority of switching participants who were virologically suppressed from daily oral standard of care to monthly long-acting intramuscular injections of cabotegravir ...plus rilpivirine over 96 weeks following a cabotegravir plus rilpivirine oral lead-in. Here, we report an evaluation of switching participants from standard of care oral regimens to long-acting cabotegravir plus rilpivirine via direct-to-injection or oral lead-in pathways.
This study reports the week 124 results of the FLAIR study, an ongoing phase 3, randomised, open-label, multicentre (11 countries) trial. Antiretroviral therapy (ART)-naive participants who were virologically suppressed (HIV-1 RNA <50 copies per mL) during the 20-week induction phase with standard of care were randomly assigned (1:1) to continue the standard of care oral regimen or switch to long-acting cabotegravir plus rilpivirine (283 per group) in the 100-week maintenance phase. Randomisation was stratified by sex at birth and baseline (pre-induction) HIV-1 RNA (<100 000 or ≥100 000 copies per mL). Participants randomly assigned to long-acting therapy at baseline received a cabotegravir (30 mg) plus rilpivirine (25 mg) once daily oral lead-in for at least 4 weeks before first injection and could choose to continue long-acting cabotegravir (400 mg) plus rilpivirine (600 mg) every 4 weeks from week 100 or withdraw. At week 100, participants in the oral comparator ART group, in discussion with the investigator, could elect to switch to long-acting therapy (extension switch population), either direct-to-injection or with a 4 week oral lead-in (oral lead-in group), or withdraw. Week 124 endpoints included plasma HIV-1 RNA 50 or more copies per mL and less than 50 copies per mL (US Food and Drug Administration FDA Snapshot), confirmed virological failure (two consecutive HIV-1 RNA ≥200 copies per mL), and safety and tolerability. The study is registered at ClinicalTrials.gov, NCT02938520.
Screening occurred between Oct 27, 2016, and March 24, 2017. At week 100, 232 (92%) of 253 participants transitioned to long-acting cabotegravir plus rilpivirine in the extension phase (111 48% in the direct-to-injection group and 121 52% in the oral lead-in group; extension switch population). 243 (86%) of the 283 who were randomly assigned to the long-acting therapy group continued the long-acting regimen into the extension phase. One (<1%) participant in each extension switch group had 50 or more HIV-1 RNA copies per mL; 110 (99%) participants in the direct-to-injection group and 113 (93%) participants in the oral lead-in group remained suppressed (HIV-1 RNA <50 copies per mL) at the week 124 Snapshot. The lower suppression rates in the oral lead-in group were driven by non-virological reasons. For participants in the randomly assigned long-acting group, 227 (80%) of 283 participants remained suppressed; at the week 124 Snapshot, 14 (5%) participants had HIV-1 RNA 50 or more copies per mL, including five additional participants since the week 96 analysis. The remaining 42 (15%) participants in the randomly assigned long-acting group had no virological data. Adverse events leading to withdrawal were infrequent, occurring in three (1%) participants in the extension switch population (one in the direct-to-injection group and two in the oral lead-in group) after 24 weeks of cabotegravir plus rilpivirine therapy, and 15 (5%) participants in the randomly assigned long-acting group up to 124 weeks of therapy. No deaths occurred in the extension phase. Overall, cabotegravir plus rilpivirine adverse event type, severity, and frequency were similar across all groups. Injection site reactions were the most common adverse event, occurring after 914 (21%) of 4442 injections in the extension switch population and 3732 (21%) of 17 392 injections in the randomly assigned long-acting group. Injection site reactions were mostly classified as mild-to-moderate in severity and decreased in incidence over time. Four (2%) of 232 participants in the extension switch population and seven (2%) of 283 in the randomly assigned long-acting group withdrew due to injection-related reasons.
After 24 weeks of follow-up, switching to long-acting treatment with or without an oral lead-in phase had similar safety, tolerability, and efficacy, supporting future evaluation of the simpler direct-to-injection approach. The week 124 results for participants randomly assigned originally to the long-acting therapy show long-acting cabotegravir plus rilpivirine remains a durable maintenance therapy with a favourable safety profile.
ViiV Healthcare and Janssen Research & Development.
XBP-1 is a CREB/ATF family transcription factor highly expressed in hepatocellular carcinomas. Here we report that XBP-1 is essential for liver growth. Mice lacking XBP-1 displayed hypoplastic fetal ...livers, whose reduced hematopoiesis resulted in death from anemia. Nevertheless, XBP-1-deficient hematopoietic progenitors had no cell-autonomous defect in differentiation. Rather, hepatocyte development itself was severely impaired by two measures: diminished growth rate and prominent apoptosis. Specific target genes of XBP-1 in the liver were identified as alphaFP, which may be a regulator of hepatocyte growth, and three acute phase protein family members. Therefore, XBP-1 is a transcription factor essential for hepatocyte growth.
There is a need for more convenient, less frequent treatment to help address challenges associated with daily oral HIV treatment in people living with HIV, including stigma, pill burden, drug-food ...interactions, and adherence. The phase 3 ATLAS and FLAIR studies showed non-inferiority of long-acting cabotegravir and rilpivirine dosed every 4 weeks compared with standard oral therapy for the maintenance of virological suppression in adults with HIV-1 over 48 weeks. We present the 96-week findings.
FLAIR is a randomised, phase 3, open-label, multicentre study done in 11 countries investigating whether switching to long-acting cabotegravir and rilpivirine is non-inferior to daily dolutegravir, abacavir, and lamivudine in virologically suppressed adults living with HIV-1. Antiretroviral therapy (ART)-naive participants received induction therapy with daily oral dolutegravir (50 mg), abacavir (600 mg), and lamivudine (300 mg) for 20 weeks. After 16 weeks, participants with less than 50 HIV-1 RNA copies per mL were randomly assigned (1:1) to continue the standard of care regimen (standard care group) or switch to receive daily oral cabotegravir 30 mg and rilpivirine 25 mg for at least 4 weeks followed by long-acting cabotegravir 400 mg and rilpivirine 600 mg, administered as two 2 mL intramuscular injections, every 4 weeks for at least 96 weeks (long-acting group). Randomisation was stratified by baseline (preinduction) HIV-1 RNA (<100 000 or ≥100 000 copies per mL) and sex at birth and used GlaxoSmithKline-verified randomisation software (RandAll NG, version 1.3.3) for treatment assignment. The primary endpoint was the proportion of participants with plasma HIV-1 RNA of 50 copies per mL or more assessed as per the US Food and Drug Administration (FDA) Snapshot algorithm at week 48, which has been reported previously. Here, we report the proportion of participants with 50 or more HIV-1 RNA copies per mL using the FDA Snapshot algorithm at week 96 (intention-to-treat population; non-inferiority margin 6%). The trial is registered with ClinicalTrials.gov, NCT02938520.
Between Oct 27, 2016, and March 24, 2017, 809 participants were screened. 631 (78%) participants entered the induction phase and 566 (70%) were randomly assigned to either the standard care group (283 50% participants) or the long-acting group (283 50%). Median age was 34 years (IQR 29 to 43), 62 (11%) were 50 years or older, 127 (22%) were women (sex at birth), and 419 (74%) were white. At week 96, nine (3%) participants in each arm had 50 or more HIV-1 RNA copies per mL, with an adjusted difference of 0·0 (95% CI -2·9 to 2·9), consistent with non-inferiority established at week 48. Across both treatment groups, adverse events leading to withdrawal were infrequent (14 5% participants in the long-acting group and four 1% in the standard care group). Injection site reactions were the most common adverse event, reported by 245 (88%) participants in the long-acting group; their frequency decreased over time. Median injection site reaction duration was 3 days (IQR 2 to 4), and 3082 (99%) of 3100 reactions were grade 1 or 2. No deaths occurred during the maintenance phase.
The 96-week results reaffirm the 48-week results, showing long-acting cabotegravir and rilpivirine continued to be non-inferior compared with continuing a standard care regimen in adults with HIV-1 for the maintenance of viral suppression. These results support the durability of long-acting cabotegravir and rilpivirine, over an almost 2-year-long period, as a therapeutic option for virally suppressed adults with HIV-1.
ViiV Healthcare and Janssen Research and Development.
Chromosomal translocations associated with malignancies often result in deregulated expression of genes encoding transcription factors. In human T-cell leukaemias such regulators belong to diverse ...protein families and may normally be expressed widely (for example, Ttg-1/rbtn1, Ttg-2/rbtn2), exclusively outside the haematopoietic system (for example, Hox11), or specifically in haematopoietic cells and other selected sites (for example, tal-1/SCL, lyl-1). Aberrant expression within T cells is though to interfere with programmes of normal maturation. The most frequently activated gene in acute T-cell leukaemias, tal-1 (also called SCL), encodes a candidate regulator of haematopoietic development, a basic-helix-loop-helix protein, related to critical myogenic and neurogenic factors. Here we show by targeted gene disruption in mice that tal-1 is essential for embryonic blood formation in vivo. With respect to embryonic erythropoiesis, tal-1 deficiency resembles loss of the erythroid transcription factor GATA-1 or the LIM protein rbtn2. Profound reduction in myeloid cells cultured in vivo from tal-1 null yolk sacs suggests a broader defect manifest at the myelo-erythroid or multipotential progenitor cell level.
The hematopoietic transcription factor GATA-1 is essential for development of the erythroid and megakaryocytic lineages. Using the conserved zinc finger DNA-binding domain of GATA-1 in the yeast two- ...hybrid system, we have identified a novel, multitype zinc finger protein,
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ATA-1 (FOG), which binds GATA-1 but not a functionally inactive mutant lacking the amino (N) finger. FOG is coexpressed with GATA-1 during embryonic development and in erythroid and megakaryocytic cells. Furthermore, FOG and GATA-1 synergistically activate transcription from a hematopoietic-specific regulatory region and cooperate during both erythroid and megakaryocytic cell differentiation. These findings indicate that FOG acts as a cofactor for GATA-1 and provide a paradigm for the regulation of cell type-specific gene expression by GATA transcription factors.
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