Correction: Foxf Genes Integrate Tbx5 and Hedgehog Pathways in the Second Heart Field for Cardiac Septation.

[This corrects the article DOI: 10.1371/journal.pgen.1004604.].

Foxf genes integrate tbx5 and hedgehog pathways in the second heart field for cardiac septation.

The Second Heart Field (SHF) has been implicated in several forms of congenital heart disease (CHD), including atrioventricular septal defects (AVSDs). Identifying the SHF gene regulatory networks required for atrioventricular septation is therefore an essential goal for understanding the molecular basis of AVSDs. We defined a SHF Hedgehog-dependent gene regulatory network using whole genome transcriptional profiling and GLI-chromatin interaction studies. The Forkhead box transcription factors Foxf1a and Foxf2 were identified as SHF Hedgehog targets. Compound haploinsufficiency for Foxf1a and Foxf2 caused atrioventricular septal defects, demonstrating the biological relevance of this regulatory network. We identified a Foxf1a cis-regulatory element that bound the Hedgehog transcriptional regulators GLI1 and GLI3 and the T-box transcription factor TBX5 in vivo. GLI1 and TBX5 synergistically activated transcription from this cis-regulatory element in vitro. This enhancer drove reproducible expression in vivo in the posterior SHF, the only region where Gli1 and Tbx5 expression overlaps. Our findings implicate Foxf genes in atrioventricular septation, describe the molecular underpinnings of the genetic interaction between Hedgehog signaling and Tbx5, and establish a molecular model for the selection of the SHF gene regulatory network for cardiac septation.

A novel murine allele of Intraflagellar Transport Protein 172 causes a syndrome including VACTERL-like features with hydrocephalus.

The primary cilium is emerging as a crucial regulator of signaling pathways central to vertebrate development and human disease. We identified atrioventricular canal 1 (avc1), a mouse mutation that caused VACTERL association with hydrocephalus, or VACTERL-H. We showed that avc1 is a hypomorphic mutation of intraflagellar transport protein 172 (Ift172), required for ciliogenesis and Hedgehog (Hh) signaling. Phenotypically, avc1 caused VACTERL-H but not abnormalities in left-right (L-R) axis formation. Avc1 resulted in structural cilia defects, including truncated cilia in vivo and in vitro. We observed a dose-dependent requirement for Ift172 in ciliogenesis using an allelic series generated with Ift172(avc1) and Ift172(wim), an Ift172 null allele: cilia were present on 42% of avc1 mouse embryonic fibroblast (MEF) and 28% of avc1/wim MEFs, in contrast to >90% of wild-type MEFs. Furthermore, quantitative cilium length analysis identified two specific cilium populations in mutant MEFS: a normal population with normal IFT and a truncated population, 50% of normal length, with disrupted IFT. Cells from wild-type embryos had predominantly full-length cilia, avc1 embryos, with Hh signaling abnormalities but not L-R abnormalities, had cilia equally divided between full-length and truncated, and avc1/wim embryos, with both Hh signaling and L-R abnormalities, were primarily truncated. Truncated Ift172 mutant cilia showed defects of the distal ciliary axoneme, including disrupted IFT88 localization and Hh-dependent Gli2 localization. We propose a model in which mutation of Ift172 results in a specific class of abnormal cilia, causing disrupted Hh signaling while maintaining L-R axis determination, and resulting in the VACTERL-H phenotype.

Induction of the small heat shock protein alphaB-crystallin by genotoxic stress is mediated by p53 and p73.

The small heat shock protein alphaB-crystallin is a molecular chaperone that is induced by stress and protects cells by inhibiting protein aggregation and apoptosis. To identify novel transcriptional regulators of the alphaB-crystallin gene, we examined the alphaB-crystallin promoter for conserved transcription factor DNA-binding elements and identified a putative response element for the p53 tumor suppressor protein. Ectopic expression of wild-type p53 induced alphaB-crystallin mRNA and protein with delayed kinetics compared to p21. Additionally, the induction of alphaB-crystallin by genotoxic stress was inhibited by siRNAs targeting p53. Although the p53-dependent transactivation of an alphaB-crystallin promoter luciferase reporter required the putative p53RE, chromatin immunoprecipitation failed to detect p53 binding to the alphaB-crystallin promoter. These results suggested an indirect mechanism of transactivation involving p53 family members p63 or p73. DeltaNp73 was dramatically induced by p53 in a TAp73-dependent manner, and silencing p73 suppressed the transcriptional activation of alphaB-crystallin by p53. Moreover, ectopic expression of DeltaNp73alpha (but not other p73 isoforms) increased alphaB-crystallin mRNA levels in the absence of p53. Collectively, our results link the molecular chaperone alphaB-crystallin to the cellular genotoxic stress response via a novel mechanism of transcriptional regulation by p53 and p73.

Regulation of alphaB-crystallin gene expression by the transcription factor Ets1 in breast cancer.

Recent studies indicate that the small heat shock protein alphaB-crystallin is expressed in poor prognosis basal-like breast tumors and likely contributes to their aggressive phenotype. However, the mechanisms underlying the deregulated expression of alphaB-crystallin in basal-like tumors are poorly understood. Using a bioinformatics approach, we identified a putative DNA binding motif in the human alphaB-crystallin promoter for the proto-oncogene Ets1, a member of the ETS transcription factor family that bind to DNA at palindromic ETS-binding sites (EBS). Here we demonstrate that ectopic expression of Ets1 activates the alphaB-crystallin promoter by an EBS-dependent mechanism and increases alphaB-crystallin protein levels, while silencing Ets1 reduces alphaB-crystallin promoter activity and protein levels. Chromatin immunoprecipitation analyses showed that endogenous Ets1 binds to the alphaB-crystallin promoter in basal-like breast cancer cells in vivo. Interrogation of publically available gene expression data revealed that Ets1 is expressed in human basal-like breast tumors and is associated with poor survival. Collectively, our results point to a previously unrecognized link between the oncogenic transcription factor Ets1 and alphaB-crystallin in basal-like breast cancer.

Celastrols as inducers of the heat shock response and cytoprotection.

Alterations in protein folding and the regulation of conformational states have become increasingly important to the functionality of key molecules in signaling, cell growth, and cell death. Molecular chaperones, because of their properties in protein quality control, afford conformational flexibility to proteins and serve to integrate stress-signaling events that influence aging and a range of diseases including cancer, cystic fibrosis, amyloidoses, and neurodegenerative diseases. We describe here characteristics of celastrol, a quinone methide triterpene and an active component from Chinese herbal medicine identified in a screen of bioactive small molecules that activates the human heat shock response. From a structure/function examination, the celastrol structure is remarkably specific and activates heat shock transcription factor 1 (HSF1) with kinetics similar to those of heat stress, as determined by the induction of HSF1 DNA binding, hyperphosphorylation of HSF1, and expression of chaperone genes. Celastrol can activate heat shock gene transcription synergistically with other stresses and exhibits cytoprotection against subsequent exposures to other forms of lethal cell stress. These results suggest that celastrols exhibit promise as a new class of pharmacologically active regulators of the heat shock response.