Clinical Significance of T2-Weighted Sequence Intensity on Magnetic Resonance Imaging in Clinically Non-Functioning Pituitary Adenomas.

BACKGROUND: Little is known about the relationship between signal intensity patterns on T2-weighted magnetic resonance imaging (MRI) in non-functioning pituitary adenomas (NFPAs). OBJECTIVE: In this study, the clinical, hormonal, histological features, and therapeutic responses were evaluated according to the T2 signal intensity in NFPAs. METHODS: This retrospective and multicenter study included a group of 166 NFPA patients (93 men, 56%, mean age 58.5 ±14.8 yr). RESULTS: Approximately half of the tumors (n=84, 50.6%) were hyperintense, while 34.3% (n=57) and 15.1% (n=25) were iso- and hypointense, respectively. The median maximum tumor diameter of the isointense group [16 (13-25) mm] was significantly lower than that of the hyperintense [23 (16.6-29.7) mm] group (p=0.003). Similarly, the tumor volume of the isointense group [1,523 (618-5,226) mm3] was significantly lower than that of the hyperintense [4,012 (2,506-8,320) mm3] group (p=0.002). Chiasmatic compression occurred less frequently in tumors with isointense signal characteristics (38.6%) compared to tumors with hypointense (68%) and hyperintense (65.5%) signal characteristics (p=0.003). Invasive adenomas (p=0.001) and the degree of cavernous sinus invasion (p<0.001) were more frequent in the hyperintense adenoma group compared to the remaining groups. Plurihormonal tumors and silent lactotroph adenomas were more frequent in the isointense tumor group. CONCLUSION: In conclusion, hyperintensity on T2-weighted MRI in NFPAs is associated with larger and more invasive tumors compared to isointense NFPAs.

Effect of cabergoline on tumor remnant after surgery in nonfunctioning pituitary adenoma.

BACKGROUND: In recent years, dopamine agonists (DAs) have become an attractive therapeutic option to prevent both tumor growth and post-surgical tumor remnant growth in clinically non-functioning pituitary adenoma (NFPA). AIM: To analyze our experience on the effect of cabergoline (CAB) on tumor remnant after initial surgery in NFPA patients. PATIENTS AND METHODS: A retrospective and multicenter study of NFPA patients with tumor remnant after surgery treated with CAB was performed. RESULTS: From a total of 142 NFPA patients (79 men, 55.2%; mean age 57.2 ± 14.2 year) who underwent surgery, we selected 62/142 (43.7%) patients (32 men, 51.6%; mean age 59.3 ± 13.9 year) with tumor persistence (TP) after surgery. In 22/62 (35.5%) TP patients CAB was used (CAB group), while the rest of the patients (40/62, 64.5%) underwent active surveillance [observation (OBS) group)]. The maximum diameter of the tumor remnant did not change significantly in either the CAB group [11.5 (6.0-16.9) mm vs. 12.0 (7.0-15.0) mm, p = 0.85) or the OBS group [8.5 (6.0-13.7) mm vs. 9.0 (6.2-14.0) mm, p = 0.064) at the end of the follow-up [13 (10.5-17) vs. 77.5 (50.2-107.2) months, CAB vs. OBS group; p < 0.001]. At the end of the treatment period with CAB most of the patients (n = 20/22, 90.9%) showed no progression of the tumor remnant [stable disease, SD (n = 17/22, 77.2%) and partial response, PR (n = 3/22, 13.6%)], while 2/22 patients (9.1%) exhibited progression. Similar response rates were observed in the OBS group [SD (n = 32/40, 80%), PR (n = 2/40, 5%), and progression (n = 6/40, 15%)]. Although no statistically significant differences (p = 0.42) were found in these responses, the percentage of progression was 1.65 times higher in the OBS group compared to the CAB group. On the contrary, the percentage of PR was 2.72 times higher in the CAB group compared to the OBS group, despite a significantly shorter follow-up period in the CAB group. CONCLUSION: Although the present study showed no significant differences in the type of tumor response between the CAB and OBS groups of patients, the percentage of PR was higher and that of progression lower in the CAB group compared to the OBS group. This finding does not rule out a potential therapeutic benefit of CAB in the management of tumor remnant in patients with NFPA undergoing surgery.

Structural insights into the ability of nucleoplasmin to assemble and chaperone histone octamers for DNA deposition.

Nucleoplasmin (NP) is a pentameric histone chaperone that regulates the condensation state of chromatin in different cellular processes. We focus here on the interaction of NP with the histone octamer, showing that NP could bind sequentially the histone components to assemble an octamer-like particle, and crosslinked octamers with high affinity. The three-dimensional reconstruction of the NP/octamer complex generated by single-particle cryoelectron microscopy, revealed that several intrinsically disordered tail domains of two NP pentamers, facing each other through their distal face, encage the histone octamer in a nucleosome-like conformation and prevent its dissociation. Formation of this complex depended on post-translational modification and exposure of the acidic tract at the tail domain of NP. Finally, NP was capable of transferring the histone octamers to DNA in vitro, assembling nucleosomes. This activity may have biological relevance for processes in which the histone octamer must be rapidly removed from or deposited onto the DNA.

A Quantitative Characterization of Nucleoplasmin/Histone Complexes Reveals Chaperone Versatility.

Nucleoplasmin (NP) is an abundant histone chaperone in vertebrate oocytes and embryos involved in storing and releasing maternal histones to establish and maintain the zygotic epigenome. NP has been considered a H2A-H2B histone chaperone, and recently it has been shown that it can also interact with H3-H4. However, its interaction with different types of histones has not been quantitatively studied so far. We show here that NP binds H2A-H2B, H3-H4 and linker histones with Kd values in the subnanomolar range, forming different complexes. Post-translational modifications of NP regulate exposure of the polyGlu tract at the disordered distal face of the protein and induce an increase in chaperone affinity for all histones. The relative affinity of NP for H2A-H2B and linker histones and the fact that they interact with the distal face of the chaperone could explain their competition for chaperone binding, a relevant process in NP-mediated sperm chromatin remodelling during fertilization. Our data show that NP binds H3-H4 tetramers in a nucleosomal conformation and dimers, transferring them to DNA to form disomes and tetrasomes. This finding might be relevant to elucidate the role of NP in chromatin disassembly and assembly during replication and transcription.

Histones and DNA compete for binding polyphosphoinositides in bilayers.

Recent discoveries on the presence and location of phosphoinositides in the eukaryotic cell nucleoplasm and nuclear membrane prompted us to study the putative interaction of chromatin components with these lipids in model membranes (liposomes). Turbidimetric studies revealed that a variety of histones and histone combinations (H1, H2AH2B, H3H4, octamers) caused a dose-dependent aggregation of phosphatidylcholine vesicles (large unilamellar vesicle or small unilamellar vesicle) containing negatively charged phospholipids. 5 mol % phosphatidylinositol-4-phosphate (PIP) was enough to cause extensive aggregation under our conditions, whereas with phosphatidylinositol (PI) at least 20 mol % was necessary to obtain a similar effect. Histone binding to giant unilamellar vesicle and vesicle aggregation was visualized by confocal microscopy. Histone did not cause vesicle aggregation in the presence of DNA, and the latter was able to disassemble the histone-vesicle aggregates. At DNA/H1 weight ratios 0.1-0.5 DNA- and PIP-bound H1 appear to coexist. Isothermal calorimetry studies revealed that the PIP-H1 association constant was one order of magnitude higher than that of PI-H1, and the corresponding lipid/histone stoichiometries were ~0.5 and ~1, respectively. The results suggest that, in the nucleoplasm, a complex interplay of histones, DNA, and phosphoinositides may be taking place, particularly at the nucleoplasmic reticula that reach deep within the nucleoplasm, or during somatic and nonsomatic nuclear envelope assembly. The data described here provide a minimal model for analyzing and understanding the mechanism of these interactions.

The intrinsically disordered distal face of nucleoplasmin recognizes distinct oligomerization states of histones.

The role of Nucleoplasmin (NP) as a H2A-H2B histone chaperone has been extensively characterized. To understand its putative interaction with other histone ligands, we have characterized its ability to bind H3-H4 and histone octamers. We find that the chaperone forms distinct complexes with histones, which differ in the number of molecules that build the assembly and in their spatial distribution. When complexed with H3-H4 tetramers or histone octamers, two NP pentamers form an ellipsoidal particle with the histones located at the center of the assembly, in stark contrast with the NP/H2A-H2B complex that contains up to five histone dimers bound to one chaperone pentamer. This particular assembly relies on the ability of H3-H4 to form tetramers either in solution or as part of the octamer, and it is not observed when a variant of H3 (H3C110E), unable to form stable tetramers, is used instead of the wild-type protein. Our data also suggest that the distal face of the chaperone is involved in the interaction with distinct types of histones, as supported by electron microscopy analysis of the different NP/histone complexes. The use of the same structural region to accommodate all type of histones could favor histone exchange and nucleosome dynamics.