Dimerization choice and alternative functions of ZBTB transcription factors

Zinc Finger DNA-binding domain-containing proteins are the most populous family among eukaryotic transcription factors. Among these, members of the BTB domain-containing ZBTB sub-family are mostly known for their transcriptional repressive functions. In this Viewpoint article, we explore molecular mechanisms that potentially diversify the function of ZBTB proteins based on their homo and heterodimerization, alternative splicing and post-translational modifications. We describe how the BTB domain is as much a scaffold for the assembly of co-repressors, as a domain that regulates protein stability. We highlight another mechanism that regulates ZBTB protein stability: phosphorylation in the zinc finger domain. We explore the non-transcriptional, structural roles of ZBTB proteins and highlight novel findings that describe the ability of ZBTB proteins to associate with poly adenosine ribose in the nucleus during the DNA damage response. Herein, we discuss the contribution of BTB domain scaffolds to the formation of transcriptional repressive complexes, to chromosome compartmentalization and their non-transcriptional, purely structural functions in the nucleus.

Sibling rivalry among the ZBTB transcription factor family: homodimers versus heterodimers

BTB domains potentially can form homo- or heterodimers. The study examines the dimerization choice of several BTB domains and finds only one heterodimer, while all tested pairs can homodimerize.

The BTB domain is an oligomerization domain found in over 300 proteins encoded in the human genome. In the family of BTB domain and zinc finger–containing (ZBTB) transcription factors, 49 members share the same protein architecture. The N-terminal BTB domain is structurally conserved among the family members and serves as the dimerization site, whereas the C-terminal zinc finger motifs mediate DNA binding. The available BTB domain structures from this family reveal a natural inclination for homodimerization. In this study, we investigated the potential for heterodimer formation in the cellular environment. We selected five BTB homodimers and four heterodimer structures. We performed cell-based binding assays with fluorescent protein–BTB domain fusions to assess dimer formation. We tested the binding of several BTB pairs, and we were able to confirm the heterodimeric physical interaction between the BTB domains of PATZ1 and PATZ2, previously reported only in an interactome mapping experiment. We also found this pair to be co-expressed in several immune system cell types. Finally, we used the available structures of BTB domain dimers and newly constructed models in extended molecular dynamics simulations (500 ns) to understand the energetic determinants of homo- and heterodimer formation. We conclude that heterodimer formation, although frequently described as less preferred than homodimers, is a possible mechanism to increase the combinatorial specificity of this transcription factor family.

Nanobodies as molecular imaging probes

Camelidae derived single-domain antibodies (sdAbs), commonly known as nanobodies (Nbs), are the smallest antibody fragments with full antigen-binding capacity. Owing to their desirable properties such as small size, high specificity, strong affinity, excellent stability, and modularity, nanobodies are on their way to overtake conventional antibodies in terms of popularity. To date, a broad range of nanobodies have been generated against different molecular targets with applications spanning basic research, diagnostics, and therapeutics. In the field of molecular imaging, nanobody-based probes have emerged as a powerful tool. Radioactive or fluorescently labeled nanobodies are now used to detect and track many targets in different biological systems using imaging techniques. In this review, we provide an overview of the use of nanobodies as molecular probes. Additionally, we discuss current techniques for the generation, conjugation, and intracellular delivery of nanobodies.

Structural analysis of the PATZ1 BTB domain homodimer

PATZ1 is a ubiquitously expressed transcriptional repressor belonging to the ZBTB family that is functionally expressed in T lymphocytes. PATZ1 targets the CD8 gene in lymphocyte development and interacts with the p53 protein to control genes that are important in proliferation and in the DNA-damage response. PATZ1 exerts its activity through an N-terminal BTB domain that mediates dimerization and co-repressor interactions and a C-terminal zinc-finger motif-containing domain that mediates DNA binding. Here, the crystal structures of the murine and zebrafish PATZ1 BTB domains are reported at 2.3 and 1.8 Å resolution, respectively. The structures revealed that the PATZ1 BTB domain forms a stable homodimer with a lateral surface groove, as in other ZBTB structures. Analysis of the lateral groove revealed a large acidic patch in this region, which contrasts with the previously resolved basic co-repressor binding interface of BCL6. A large 30-amino-acid glycine- and alanine-rich central loop, which is unique to mammalian PATZ1 amongst all ZBTB proteins, could not be resolved, probably owing to its flexibility. Molecular-dynamics simulations suggest a contribution of this loop to modulation of the mammalian BTB dimerization interface.

Primary tumours neoangiogenesis and P53 expression in oral carcinoma patients

Paraffin embebbed tumour tissues from 47 T1-2 N0-1 M0 primary oral squamous carcinoma have been utilized for immunohistochemical analysis of p53 expression (moab DO-7) and microvessel density (MVD) analysis (moab CD34). Fifty percent of cases showed p53 immunostaining with an average of 21% of p53 positive cells. A strong trend for a longer survival in patients with tumor p53- versus p53+ was evidenced (median survival: 12 months versus not reached, respectively; p=0.08 by log-rank test). A mean value of 27 MVD was found. The probability of overall survival did not result significantly different in the subgroups of tumours with high and low MVD (median survival: 6 months versus 6 months, respectively; p=0.24). Cox multivariate analysis confirmed that the only prognostic factor significantly related to the overall survival was clinical nodal status (O.R.=2.7; 95% C.I. 1.09-6.9), while p53 status only approached the statistical significance (O.R.=2.5; 95% C.I. 0.96-6.5; p=0.06).

Early, late symptoms and histological type of nasopharyngeal carcinoma

After a wide literature review, we retrospectively analyzed the accurately recorded early onset and late symptoms at first diagnosis of nasopharyngeal carcinoma (NPC) in a series of 85 patients. Thirty-seven (44%) and 48 (56%) of cases had a squamous (SCC) and undifferentiated (UCNT) histological NPC subtype, respectively. Thirteen (15%), 21 (25%) and 51 (60%) of cases were T2, T3 and T4, respectively. The involvement of locoregional lymph nodes resulted significantly more frequent in UCNT with respect to SCC (35% versus 18% respectively; p<0.05). Overall, the early onset symptoms were represented by locoregional lymph node enlargement in 35% of cases; nasal symptoms in 32%, otological symptoms in 36%, while neurological symptoms were reported in only 2% of cases. On the contrary, symptoms at first diagnosis were more frequently represented by lymph node enlargement (53%) and nasal symptoms (68%) which were the symptoms effectively conducting the patients to the specialist. A protocol for management of ORL symptomatic patients according to the incidence of described early onset and at first diagnosis symptoms is suggested.