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

Abstract

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.

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

“…As regulators of many biological processes, proteases are essential for cell viability, and their deregulation is often associated with various pathologies including cancer. , In particular, the unique threonine protease Taspase 1 (threonine aspartase 1) is not only involved in regular cellular development but also responsible for the progression of leukemias and solid tumors. − In the group of threonine proteases, only Taspase 1 is able to cleave other substrates in trans by recognizing a conserved Q 3 [FILV] 2 D 1 ↓G 1 X 2’ D 3’ D 4’ motif. − Thus, Taspase 1 is an endopeptidase that utilizes the N-terminal threonine (Thr 234 ) of its mature β-subunit as the active site. Besides the mixed-lineage leukemia protein (MLL), the general transcription factor IIA (TFIIA) ,− and the upstream stimulatory factor 2 (USF2) could all be identified as Taspase 1 target proteins . Importantly, Taspase 1 is preferentially expressed during embryonic development, and thus, pharmacological intervention should not affect healthy adult cells. ,,− In contrast, tumor cells have been demonstrated to upregulate the expression of Taspase 1 to promote their proliferation and counteract apoptotic cell death. ,,, This classifies Taspase 1 as a ″non-oncogene addiction″ protease. , However, the full repertoire of physiological and pathological targets and pathways affected by Taspase 1 is still not fully understood.…”

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

“…S21†), a plethora of NLSs have been identified in many cancer-/disease-relevant proteins, such as p53, NPM, TFIIA, or the superfamily of nuclear receptors, with the vast majority classified as monopartite signals. 19,30,66–68…”

“…S21 †), a plethora of NLSs have been identied in many cancer-/ disease-relevant proteins, such as p53, NPM, TFIIA, or the superfamily of nuclear receptors, with the vast majority classi-ed as monopartite signals. 19,30,[66][67][68] However, recent studies revealed that the traditional denition of bipartite NLSs might be too restrictive and linker length can vary within a broader range. 69 As such, extension of the surface-exposed, importin-interacting amino acid residues of NLSs initially classied as monopartite might render them amenable to analogous interference strategies.…”

“…1). Besides the protooncogene Mixed Lineage Leukemia (MLL), 25 other essential proteins such as the precursor of the general transcription factor IIA (TFIIA) 18,[28][29][30] or the Upstream Stimulatory Factor 2 (USF2) 18 could be identied as bona de Taspase 1 targets in the protease's degradome. 18 Since Taspase 1 is normally expressed mainly during embryonic development, interference with its activity would not affect healthy adult tissue.…”

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

“…Some of Taspase1's verified target proteins such as USF2 [1] and TFIIA [6,58] have been annotated as estrogen-regulated genes, as well as the known Taspase1 interaction partner Nucleophosmin1 (NPM1). MLL proteins, the most prominent Taspase1 substrates, interact with hormone receptors (NR) and are involved in steroid-hormone induced transcriptional activation [22,59].…”