Taspase1-dependent TFIIA cleavage coordinates head morphogenesis by limiting Cdkn2a locus transcription

The general transcription factors (GTFs) of RNA polymerase II and their roles in plant development and stress responses

In eukaryotes, general transcription factors (GTFs) enable recruitment of RNA polymerase II (RNA Pol II) to core promoters to facilitate initiation of transcription. Extensive research in mammals and yeast has unveiled their significance in basal transcription as well as in diverse biological processes. Unlike mammals and yeast, plant GTFs exhibit remarkable degree of variability and flexibility. This is because plant GTFs and GTF subunits are often encoded by multigene families, introducing complexity to transcriptional regulation at both cellular and biological levels. This review provides insights into the general transcription mechanism, GTF composition, and their cellular functions. It further highlights the involvement of RNA Pol II-related GTFs in plant development and stress responses. Studies reveal that GTFs act as important regulators of gene expression in specific developmental processes and help equip plants with resilience against adverse environmental conditions. Their functions may be direct or mediated through their cofactor nature. The versatility of GTFs in controlling gene expression, and thereby influencing specific traits, adds to the intricate complexity inherent in the plant system.

Disruption of common ocular developmental pathways in patient-derived optic vesicle models of microphthalmia

Genetic perturbations influencing early eye development can result in microphthalmia, anophthalmia, and coloboma (MAC). Over 100 genes are associated with MAC, but little is known about common disease mechanisms. In this study, we generated induced pluripotent stem cell (iPSC)-derived optic vesicles (OVs) from two unrelated microphthalmia patients and healthy controls. At day 20, 35, and 50, microphthalmia patient OV diameters were significantly smaller, recapitulating the "small eye" phenotype. RNA sequencing (RNA-seq) analysis revealed upregulation of apoptosis-initiating and extracellular matrix (ECM) genes at day 20 and 35. Western blot and immunohistochemistry revealed increased expression of lumican, nidogen, and collagen type IV, suggesting ECM overproduction. Increased apoptosis was observed in microphthalmia OVs with reduced phospho-histone 3 (pH3+) cells confirming decreased cell proliferation at day 35. Pharmacological inhibition of caspase-8 activity with Z-IETD-FMK decreased apoptosis in one patient model, highlighting a potential therapeutic approach. These data reveal shared pathophysiological mechanisms contributing to a microphthalmia phenotype.

Multi-omics analysis of a case of congenital microtia reveals aldob and oxidative stress associated with microtia etiology

BACKGROUND

Microtia is reported to be one of the most common congenital craniofacial malformations. Due to the complex etiology and the ethical barrier of embryonic study, the precise mechanisms of microtia remain unclear. Here we report a rare case of microtia with costal chondrodysplasia based on bioinformatics analysis and further verifications on other sporadic microtia patients.

RESULTS

One hundred fourteen deleterious insert and deletion (InDel) and 646 deleterious SNPs were screened out by WES, candidate genes were ranked in descending order according to their relative impact with microtia. Label-free proteomic analysis showed that proteins significantly different between the groups were related with oxidative stress and energy metabolism. By real-time PCR and immunohistochemistry, we further verified the candidate genes between other sporadic microtia and normal ear chondrocytes, which showed threonine aspartase, cadherin-13, aldolase B and adiponectin were significantly upregulated in mRNA levels but were significantly lower in protein levels. ROS detection and mitochondrial membrane potential (∆ Ψ m) detection proved that oxidative stress exists in microtia chondrocytes.

CONCLUSIONS

Our results not only spot new candidate genes by WES and label-free proteomics, but also speculate for the first time that metabolism and oxidative stress may disturb cartilage development and this might become therapeutic targets and potential biomarkers with clinical usefulness in the future.

Taspase1 Facilitates Topoisomerase IIβ-Mediated DNA Double-Strand Breaks Driving Estrogen-Induced Transcription

The human protease Taspase1 plays a pivotal role in developmental processes and cancerous diseases by processing critical regulators, such as the leukemia proto-oncoprotein MLL. Despite almost two decades of intense research, Taspase1's biology is, however, still poorly understood, and so far its cellular function was not assigned to a superordinate biological pathway or a specific signaling cascade. Our data, gained by methods such as co-immunoprecipitation, LC-MS/MS and Topoisomerase II DNA cleavage assays, now functionally link Taspase1 and hormone-induced, Topoisomerase IIβ-mediated transient DNA double-strand breaks, leading to active transcription. The specific interaction with Topoisomerase IIα enhances the formation of DNA double-strand breaks that are a key prerequisite for stimulus-driven gene transcription. Moreover, Taspase1 alters the H3K4 epigenetic signature upon estrogen-stimulation by cleaving the chromatin-modifying enzyme MLL. As estrogen-driven transcription and MLL-derived epigenetic labelling are reduced upon Taspase1 siRNA-mediated knockdown, we finally characterize Taspase1 as a multifunctional co-activator of estrogen-stimulated transcription.

Dual activity inhibition of threonine aspartase 1 by a single bisphosphate ligand

Therapy resistance remains a challenge for the clinics. Here, dual-active chemicals that simultaneously inhibit independent functions in disease-relevant proteins are desired though highly challenging. As a model, we here addressed the unique protease threonine aspartase 1, involved in various cancers. We hypothesized that targeting basic residues in its bipartite nuclear localization signal (NLS) by precise bisphosphate ligands inhibits additional steps required for protease activity. We report the bisphosphate anionic bivalent inhibitor 11d, selectively binding to the basic NLS cluster (220KKRR223) with high affinity (K D = 300 nM), thereby disrupting its interaction and function with Importin α (IC50 = 6 μM). Cell-free assays revealed that 11d additionally affected the protease's catalytic substrate trans-cleavage activity. Importantly, functional assays comprehensively demonstrated that 11d inhibited threonine aspartase 1 also in living tumor cells. We demonstrate for the first time that intracellular interference with independent key functions in a disease-relevant protein by an inhibitor binding to a single site is possible.

Oxidative Stress-Induced Cellular Senescence in Aging Retina and Age-Related Macular Degeneration

Aging leads to a gradual decline of function in multiple organs. Cataract, glaucoma, diabetic retinopathy, and age-related macular degeneration (AMD) are age-related ocular diseases. Because their pathogenesis is unclear, it is challenging to combat age-related diseases. Cellular senescence is a cellular response characterized by cell cycle arrest. Cellular senescence is an important contributor to aging and age-related diseases through the alteration of cellular function and the secretion of senescence-associated secretory phenotypes. As a driver of stress-induced premature senescence, oxidative stress triggers cellular senescence and age-related diseases by inducing senescence markers via reactive oxygen species and mitochondrial dysfunction. In this review, we focused on the mechanism of oxidative stress-induced senescence in retinal cells and its role in the pathogenesis of AMD.

Recognition of a Flexible Protein Loop in Taspase 1 by Multivalent Supramolecular Tweezers

Many natural proteins contain flexible loops utilizing well-defined complementary surface regions of their interacting partners and usually undergo major structural rearrangements to allow perfect binding. The molecular recognition of such flexible structures is still highly challenging due to the inherent conformational dynamics. Notably, protein-protein interactions are on the other hand characterized by a multivalent display of complementary binding partners to enhance molecular affinity and specificity. Imitating this natural concept, we here report the rational design of advanced multivalent supramolecular tweezers that allow addressing two lysine and arginine clusters on a flexible protein surface loop. The protease Taspase 1, which is involved in cancer development, carries a basic bipartite nuclear localization signal (NLS) and thus interacts with Importin α, a prerequisite for proteolytic activation. Newly established synthesis routes enabled us to covalently fuse several tweezer molecules into multivalent NLS ligands. The resulting bi- up to pentavalent constructs were then systematically compared in comprehensive biochemical assays. In this series, the stepwise increase in valency was robustly reflected by the ligands' gradually enhanced potency to disrupt the interaction of Taspase 1 with Importin α, correlated with both higher binding affinity and inhibition of proteolytic activity.

The Senescence Markers p16INK4A, p14ARF/p19ARF, and p21 in Organ Development and Homeostasis

It is widely accepted that senescent cells accumulate with aging. They are characterized by replicative arrest and the release of a myriad of factors commonly called the senescence-associated secretory phenotype. Despite the replicative cell cycle arrest, these cells are metabolically active and functional. The release of SASP factors is mostly thought to cause tissue dysfunction and to induce senescence in surrounding cells. As major markers for aging and senescence, p16INK4, p14ARF/p19ARF, and p21 are established. Importantly, senescence is also implicated in development, cancer, and tissue homeostasis. While many markers of senescence have been identified, none are able to unambiguously identify all senescent cells. However, increased levels of the cyclin-dependent kinase inhibitors p16INK4A and p21 are often used to identify cells with senescence-associated phenotypes. We review here the knowledge of senescence, p16INK4A, p14ARF/p19ARF, and p21 in embryonic and postnatal development and potential functions in pathophysiology and homeostasis. The establishment of senolytic therapies with the ultimate goal to improve healthy aging requires care and detailed knowledge about the involvement of senescence and senescence-associated proteins in developmental processes and homeostatic mechanism. The review contributes to these topics, summarizes open questions, and provides some directions for future research.

A Bivalent Supramolecular GCP Ligand Enables Blocking of the Taspase1/Importin α Interaction

Taspase1 is a unique protease not only pivotal for embryonic development but also implicated in leukemia as well as solid tumors. As such, it is a promising target in cancer therapy, although only a limited number of Taspase1 inhibitors lacking general applicability are currently available. Here we present a bivalent guanidiniocarbonyl-pyrrole (GCP)-containing supramolecular ligand that is capable of disrupting the essential interaction between Taspase1 and its cognate import receptor Importin α in a concentration-dependent manner in vitro with an IC50 of 35 μM. Here, size of the bivalent vs the monovalent construct as well as its derivation with an aromatic cbz-group arose as critical determinants for efficient interference of 2GC. This was also evident when we investigated the effects in different tumor cell lines, resulting in comparable EC50 values (∼40-70 μM). Of note, in higher concentrations, 2GC also interfered with Taspase1's proteolytic activity. We thus believe to set the stage for a novel class of Taspase1 inhibitors targeting a pivotal protein-protein interaction prerequisite for its cancer-associated proteolytic function.

OUP accepted manuscript

BACKGROUND

TASP1 encodes an endopeptidase activating histone methyltransferases of the KMT2 family. Homozygous loss-of-function variants in TASP1 have recently been associated with Suleiman-El-Hattab syndrome. We report six individuals with Suleiman-El-Hattab syndrome and provide functional characterization of this novel histone modification disorder in a multi-omics approach.

METHODS

Chromosomal microarray/exome sequencing in all individuals. Western blotting from fibroblasts in two individuals. RNA sequencing and proteomics from fibroblasts in one individual. Methylome analysis from blood in two individuals. Knock-out of tasp1 orthologue in zebrafish and phenotyping.

RESULTS

All individuals had biallelic TASP1 loss-of-function variants and a phenotype including developmental delay, multiple congenital anomalies (including cardiovascular and posterior fossa malformations), a distinct facial appearance and happy demeanor. Western blot revealed absence of TASP1. RNA sequencing/proteomics showed HOX gene downregulation (HOXA4, HOXA7, HOXA1 and HOXB2) and dysregulation of transcription factor TFIIA. A distinct methylation profile intermediate between control and Kabuki syndrome (KMT2D) profiles could be produced. Zebrafish tasp1 knock-out revealed smaller head size and abnormal cranial cartilage formation in tasp1 crispants.

CONCLUSION

This work further delineates Suleiman-El-Hattab syndrome, a recognizable neurodevelopmental syndrome. Possible downstream mechanisms of TASP1 deficiency include perturbed HOX gene expression and dysregulated TFIIA complex. Methylation pattern suggests that Suleiman-El-Hattab syndrome can be categorized into the group of histone modification disorders including Wiedemann-Steiner and Kabuki syndrome.

Closantel is an allosteric inhibitor of human Taspase1

Dimerization of Taspase1 activates an intrinsic serine protease function that leads to the catalytic Thr234 residue, which allows to catalyze the consensus sequence Q^-3X^-2D^-1⋅G¹X²D³D⁴, present in Trithorax family members and TFIIA. Noteworthy, Taspase1 performs only a single hydrolytic step on substrate proteins, which makes it impossible to screen for inhibitors in a classical screening approach. Here, we report the development of an HTRF reporter assay that allowed the identification of an inhibitor, Closantel sodium, that inhibits Taspase1 in a noncovalent fashion (IC₅₀ = 1.6 μM). The novel inhibitor interferes with the dimerization step and/or the intrinsic serine protease function of the proenzyme. Of interest, Taspase1 is required to activate the oncogenic functions of the leukemogenic AF4-MLL fusion protein and was shown in several studies to be overexpressed in many solid tumors. Therefore, the inhibitor may be useful for further validation of Taspase1 as a target for cancer therapy.

Disruption of the interaction between TFIIAαβ and TFIIA recognition element inhibits RNA polymerase II gene transcription in a promoter context-dependent manner

General transcription factors and core promoter elements play a pivotal role in RNA polymerase II (Pol II)-mediated transcription initiation. In the previous work, we have defined a TFIIA recognition element (IIARE) that modulates Pol II-directed gene transcription in a promoter context-dependent manner. However, how TFIIA interacts with the IIARE and whether the interaction between TFIIA and the IIARE is involved in the regulation of gene transcription by Pol II are not fully understood. In the present study, we confirm that both K348 and K350 residues in TFIIAαβ are required for the interaction between TFIIAαβ and the IIARE. Disruption of the interaction between them by gene mutations dampens TFIIAαβ binding to the AdML-IIARE promoter and the transcriptional activation of the promoter containing a IIARE in vitro and in vivo. Stable expression of the TFIIAαβ mutant containing both K348A and K350A in the cell line with endogenous TFIIAαβ silence represses endogenous gene expression by reducing the occupancies of TFIIAαβ, TBP, p300, and Pol II at the promoters containing a IIARE. The findings from this study provide a novel insight into the regulatory mechanism of gene transcription mediated by TFIIA and the IIARE.

EMT-inducing transcription factor ZEB1-associated resistance to the BCL-2/BCL-XL inhibitor is overcome by BIM upregulation in ovarian clear cell carcinoma cells

Ovarian clear cell carcinoma (OCCC) is an aggressive subtype of epithelial ovarian cancer, which generally exhibits chemoresistance. Effective therapy for OCCC is currently unavailable, requiring the development of new therapeutic strategies. ABT-263 (navitoclax), an inhibitor of the anti-apoptotic BCL-2/BCL-X_L, has a potent ability of inducing death in cancer cells; however, the therapeutic effect of ABT-263 in OCCC remains unclear. Epithelial cells undergo epithelial-mesenchymal transition (EMT) to acquire a mesenchymal phenotype, which is known to contribute to the development of resistance against therapeutic agents. In this study, we revealed that the sensitivity of OCCC cells to ABT-263 was associated with the epithelial/mesenchymal status of the cells. While the OCCC cells with an epithelial phenotype were ABT-263-sensitive, those with a mesenchymal phenotype were ABT-263-resistant, which was accompanied by an insufficient expression of the pro-apoptotic BH3 protein BIM. Mechanistically, the EMT-inducing transcription factor, ZEB1 down-regulated BIM transcription by binding to BIM promoter, resulting in resistance to ABT-263. It is noteworthy that ZEB1-associated ABT-263 resistance was overcome by an HDAC inhibitor, FK228 (romidepsin), through the up-regulation of BIM. In summary, our study provides evidence for a mechanism for ABT-263 resistance in OCCC cells as well as a potential therapeutic strategy to overcome it.

TASP1 mutation in a female with craniofacial anomalies, anterior segment dysgenesis, congenital immunodeficiency and macrocytic anemia

Background

Threonine Aspartase 1 (Taspase 1) is a highly conserved site‐specific protease whose substrates are broad‐acting nuclear transcription factors that govern diverse biological programs, such as organogenesis, oncogenesis, and tumor progression. To date, no single base pair mutations in Taspase 1 have been implicated in human disease.

Methods

A female infant with a new pattern of diagnostic abnormalities was identified, including severe craniofacial anomalies, anterior and posterior segment dysgenesis, immunodeficiency, and macrocytic anemia. Trio‐based whole exome sequencing was performed to identify disease‐causing variants.

Results

Whole exome sequencing revealed a normal female karyotype (46,XX) without increased regions of homozygosity. The proband was heterozygous for a de novo missense variant, c.1027G>A predicting p.(Val343Met), in the TASP1 gene (NM_017714.2). This variant has not been observed in population databases and is predicted to be deleterious.

Conclusion

One human patient has been reported previously with a large TASP1 deletion and substantial evidence exists regarding the role of several known Taspase 1 substrates in human craniofacial and hematopoietic disorders. Moreover, Taspase 1 deficiency in mice results in craniofacial, ophthalmological and structural brain defects. Taken together, there exists substantial evidence to conclude that the TASP1 variant, p.(Val343Met), is pathogenic in this patient.

Homozygous loss-of-function variants of TASP1, a gene encoding an activator of the histone methyltransferases KMT2A and KMT2D, cause a syndrome of developmental delay, happy demeanor, distinctive facial features, and congenital anomalies

We report four unrelated children with homozygous loss-of-function variants in TASP1 and an overlapping phenotype comprising developmental delay with hypotonia and microcephaly, feeding difficulties with failure-to-thrive, recurrent respiratory infections, cardiovascular malformations, cryptorchidism, happy demeanor, and distinctive facial features. Two children had a homozygous founder deletion encompassing exons 5-11 of TASP1, the third had a homozygous missense variant, c.701 C>T (p.Thr234Met), affecting the active site of the encoded enzyme, and the fourth had a homozygous nonsense variant, c.199 C>T (p.Arg67*). TASP1 encodes taspase 1 (TASP1), which is responsible for cleaving, thus activating, the lysine methyltransferases KMT2A and KMT2D, which are essential for histone methylation and transcription regulation. The consistency of the phenotype, the critical biological function of TASP1, the deleterious nature of the TASP1 variants, and the overlapping features with Wiedemann-Steiner and Kabuki syndromes respectively caused by pathogenic variants in KMT2A and KMT2D all support that TASP1 is a disease-related gene.

A Strategy To Isolate Modifiers of Caenorhabditis elegans Lethal Mutations: Investigating the Endoderm Specifying Ability of the Intestinal Differentiation GATA Factor ELT-2

The ELT-2 GATA factor normally functions in differentiation of the C. elegans endoderm, downstream of endoderm specification. We have previously shown that, if ELT-2 is expressed sufficiently early, it is also able to specify the endoderm and to replace all other members of the core GATA-factor transcriptional cascade (END-1, END-3, ELT-7). However, such rescue requires multiple copies (and presumably overexpression) of the end-1p::elt-2 cDNA transgene; a single copy of the transgene does not rescue. We have made this observation the basis of a genetic screen to search for genetic modifiers that allow a single copy of the end-1p::elt-2 cDNA transgene to rescue the lethality of the end-1end-3 double mutant. We performed this screen on a strain that has a single copy insertion of the transgene in an end-1end-3 background. These animals are kept alive by virtue of an extrachromosomal array containing multiple copies of the rescuing transgene; the extrachromosomal array also contains a toxin under heat shock control to counterselect for mutagenized survivors that have been able to lose the rescuing array. A screen of ∼14,000 mutagenized haploid genomes produced 17 independent surviving strains. Whole genome sequencing was performed to identify genes that incurred independent mutations in more than one surviving strain. The C. elegans gene tasp-1 was mutated in four independent strains. tasp-1 encodes the C. elegans homolog of Taspase, a threonine-aspartic acid protease that has been found, in both mammals and insects, to cleave several proteins involved in transcription, in particular MLL1/trithorax and TFIIA. A second gene, pqn-82, was mutated in two independent strains and encodes a glutamine-asparagine rich protein. tasp-1 and pqn-82 were verified as loss-of-function modifiers of the end-1p::elt-2 transgene by RNAi and by CRISPR/Cas9-induced mutations. In both cases, gene loss leads to modest increases in the level of ELT-2 protein in the early endoderm although ELT-2 levels do not strictly correlate with rescue. We suggest that tasp-1 and pqn-82 represent a class of genes acting in the early embryo to modulate levels of critical transcription factors or to modulate the responsiveness of critical target genes. The screen’s design, rescuing lethality with an extrachromosomal transgene followed by counterselection, has a background survival rate of <10⁻⁴ without mutagenesis and should be readily adapted to the general problem of identifying suppressors of C. elegans lethal mutations.

TFIIA transcriptional activity is controlled by a 'cleave-and-run' Exportin-1/Taspase 1-switch

Transcription factor TFIIA is controlled by complex regulatory networks including proteolysis by the protease Taspase 1, though the full impact of cleavage remains elusive. Here, we demonstrate that in contrast to the general assumption, de novo produced TFIIA is rapidly confined to the cytoplasm via an evolutionary conserved nuclear export signal (NES, amino acids 21VINDVRDIFL30), interacting with the nuclear export receptor Exportin-1/chromosomal region maintenance 1 (Crm1). Chemical export inhibition or genetic inactivation of the NES not only promotes TFIIA's nuclear localization but also affects its transcriptional activity. Notably, Taspase 1 processing promotes TFIIA's nuclear accumulation by NES masking, and modulates its transcriptional activity. Moreover, TFIIA complex formation with the TATA box binding protein (TBP) is cooperatively enhanced by inhibition of proteolysis and nuclear export, leading to an increase of the cell cycle inhibitor p16INK, which is counteracted by prevention of TBP binding. We here identified a novel mechanism how proteolysis and nuclear transport cooperatively fine-tune transcriptional programs.

Disease-relevant signalling-pathways in head and neck cancer: Taspase1's proteolytic activity fine-tunes TFIIA function

Head and neck cancer (HNC) is the seventh most common malignancy in the world and its prevailing form, the head and neck squamous cell carcinoma (HNSCC), is characterized as aggressive and invasive cancer type. The transcription factor II A (TFIIA), initially described as general regulator of RNA polymerase II-dependent transcription, is part of complex transcriptional networks also controlling mammalian head morphogenesis. Posttranslational cleavage of the TFIIA precursor by the oncologically relevant protease Taspase1 is crucial in this process. In contrast, the relevance of Taspase1-mediated TFIIA cleavage during oncogenesis of HNSCC is not characterized yet. Here, we performed genome-wide expression profiling of HNSCC which revealed significant downregulation of the TFIIA downstream target CDKN2A. To identify potential regulatory mechanisms of TFIIA on cellular level, we characterized nuclear-cytoplasmic transport and Taspase1-mediated cleavage of TFIIA variants. Unexpectedly, we identified an evolutionary conserved nuclear export signal (NES) counteracting nuclear localization and thus, transcriptional activity of TFIIA. Notably, proteolytic processing of TFIIA by Taspase1 was found to mask the NES, thereby promoting nuclear localization and transcriptional activation of TFIIA target genes, such as CDKN2A. Collectively, we here describe a hitherto unknown mechanism how cellular localization and Taspase1 cleavage fine-tunes transcriptional activity of TFIIA in HNSCC.

A transcription factor IIA-binding site differentially regulates RNA polymerase II-mediated transcription in a promoter context-dependent manner

RNA polymerase II (pol II) is required for the transcription of all protein-coding genes and as such represents a major enzyme whose activity is tightly regulated. Transcriptional initiation therefore requires numerous general transcriptional factors and cofactors that associate with pol II at the core promoter to form a pre-initiation complex. Transcription factor IIA (TFIIA) is a general cofactor that binds TFIID and stabilizes the TFIID-DNA complex during transcription initiation. Previous studies showed that TFIIA can make contact with the DNA sequence upstream or downstream of the TATA box, and that the region bound by TFIIA could overlap with the elements recognized by another factor, TFIIB, at adenovirus major late core promoter. Whether core promoters contain a DNA motif recognized by TFIIA remains unknown. Here we have identified a core promoter element upstream of the TATA box that is recognized by TFIIA. A search of the human promoter database revealed that many natural promoters contain a TFIIA recognition element (IIARE). We show that the IIARE enhances TFIIA-promoter binding and enhances the activity of TATA-containing promoters, but represses or activates promoters that lack a TATA box. Chromatin immunoprecipitation assays revealed that the IIARE activates transcription by increasing the recruitment of pol II, TFIIA, TAF4, and P300 at TATA-dependent promoters. These findings extend our understanding of the role of TFIIA in transcription, and provide new insights into the regulatory mechanism of core promoter elements in gene transcription by pol II.

Cleaving for growth: threonine aspartase 1--a protease relevant for development and disease

From the beginning of life, proteases are key to organismal development comprising morphogenesis, cellular differentiation, and cell growth. Regulated proteolytic activity is essential for the orchestration of multiple developmental pathways, and defects in protease activity can account for multiple disease patterns. The highly conserved protease threonine aspartase 1 is a member of such developmental proteases and critically involved in the regulation of complex processes, including segmental identity, head morphogenesis, spermatogenesis, and proliferation. Additionally, threonine aspartase 1 is overexpressed in numerous liquid as well as in solid malignancies. Although threonine aspartase 1 is able to cleave the master regulator mixed lineage leukemia protein as well as other regulatory proteins in humans, our knowledge of its detailed pathobiological function and the underlying molecular mechanisms contributing to development and disease is still incomplete. Moreover, neither effective genetic nor chemical inhibitors for this enzyme are available so far precluding the detailed dissection of the pathobiological functions of threonine aspartase 1. Here, we review the current knowledge of the structure-function relationship of threonine aspartase 1 and its mechanistic impact on substrate-mediated coordination of the cell cycle and development. We discuss threonine aspartase 1-mediated effects on cellular transformation and conclude by presenting a short overview of recent interference strategies.

TBP-like protein (TLP) interferes with Taspase1-mediated processing of TFIIA and represses TATA box gene expression

TBP-TFIIA interaction is involved in the potentiation of TATA box-driven promoters. TFIIA activates transcription through stabilization of TATA box-bound TBP. The precursor of TFIIA is subjected to Taspase1-directed processing to generate α and β subunits. Although this processing has been assumed to be required for the promoter activation function of TFIIA, little is known about how the processing is regulated. In this study, we found that TBP-like protein (TLP), which has the highest affinity to TFIIA among known proteins, affects Taspase1-driven processing of TFIIA. TLP interfered with TFIIA processing in vivo and in vitro, and direct binding of TLP to TFIIA was essential for inhibition of the processing. We also showed that TATA box promoters are specifically potentiated by processed TFIIA. Processed TFIIA, but not unprocessed TFIIA, associated with the TATA box. In a TLP-knocked-down condition, not only the amounts of TATA box-bound TFIIA but also those of chromatin-bound TBP were significantly increased, resulting in the stimulation of TATA box-mediated gene expression. Consequently, we suggest that TLP works as a negative regulator of the TFIIA processing and represses TFIIA-governed and TATA-dependent gene expression through preventing TFIIA maturation.