TTT (Tel2-Tti1-Tti2) Complex, the Co-Chaperone of PIKKs and a Potential Target for Cancer Chemotherapy.

The heterotrimeric Tel2-Tti1-Tti2 or TTT complex is essential for cell viability and highly observed in eukaryotes. As the co-chaperone of ATR, ATM, DNA-PKcs, mTOR, SMG1, and TRRAP, the phosphatidylinositol 3-kinase-related kinases (PIKKs) and a group of large proteins of 300-500 kDa, the TTT plays crucial roles in genome stability, cell proliferation, telomere maintenance, and aging. Most of the protein kinases in the kinome are targeted by co-chaperone Cdc37 for proper folding and stability. Like Cdc37, accumulating evidence has established the mechanism by which the TTT interacts with chaperone Hsp90 via R2TP (Rvb1-Rvb2-Tah1-Pih1) complex or other proteins for co-translational maturation of the PIKKs. Recent structural studies have revealed the α-solenoid structure of the TTT and its interactions with the R2TP complex, which shed new light on the co-chaperone mechanism and provide new research opportunities. A series of mutations of the TTT have been identified that cause disease syndrome with neurodevelopmental defects, and misregulation of the TTT has been shown to contribute to myeloma, colorectal, and non-small-cell lung cancers. Surprisingly, Tel2 in the TTT complex has recently been found to be a target of ivermectin, an antiparasitic drug that has been used by millions of patients. This discovery provides mechanistic insight into the anti-cancer effect of ivermectin and thus promotes the repurposing of this Nobel-prize-winning medicine for cancer chemotherapy. Here, we briefly review the discovery of the TTT complex, discuss the recent studies, and describe the perspectives for future investigation.

Branching the Tel2 pathway for exact fit on phosphatidylinositol 3-kinase-related kinases.

Phosphatidylinositol 3-kinase-related kinases (PIKKs), are structurally related to phosphatidylinositol 3-kinase (lipid kinase), but possess protein kinase activities. PIKKs include ATM, ATR, DNA-PK, mTOR and SMG1, key regulators of cell proliferation and genome maintenance. TRRAP, which is devoid of protein kinase activity, is the sixth member of the PIKK family. PIKK family members are gigantic proteins in the range of 300-500 kDa. It has become apparent in the last decade that the stability or maturation of the PIKK family members depends on a molecular chaperone called the Tel2-Tti1-Tti2 (TTT) complex. Several lines of evidence have established a model in which TTT connects to the Hsp90 chaperone through the Rvb1-Rvb2-Tah1-Pih1 (R2TP) complex in mammalian and yeast cells. However, recent studies of yeast cells indicate that TTT is able to form different complexes. These observations raise a possibility that several different mechanisms regulate TTT-mediated protein stability of PIKKs.

The epigenetic regulator ULTRAPETALA1 suppresses de novo root regeneration from Arabidopsis leaf explants.

Plants have the potency to regenerate adventitious roots from aerial organs after detachment. In Arabidopsis thaliana, de novo root regeneration (DNRR) from leaf explants is triggered by wounding signaling that rapidly induces the expression of the ETHYLENE RESPONSE FACTOR (ERF) transcription factors ERF109 and ABR1 (ERF111). In turn, the ERFs promote the expression of ASA1, an essential enzyme of auxin biosynthesis, which contributes to rooting by providing high levels of auxin near the wounding side of the leaf. Here, we show that the loss of the epigenetic regulator ULTRAPETALA1 (ULT1), which interacts with Polycomb and Trithorax Group proteins, accelerates and reinforces adventitious root formation. Expression of ERF109 and ASA1 was increased in ult1 mutants, whereas ABR1 was not significantly changed. Cultivation of explants on media with exogenous auxin equates adventitious root formation in wild-type with ult1 mutants, suggesting that ULT1 negatively regulates DNRR by suppressing auxin biosynthesis. Based on these findings, we propose that ULT1 is involved in a novel mechanism that prevents overproliferation of adventitious roots during DNRR.

Comparative Efficacy of Intrathecal Bupivacaine Alone and Combination of Bupivacaine with Clonidine in Spinal Anaesthesia.

INTRODUCTION: Clonidine is an α2 agonist agent that has been used as an adjuvant to local anaesthetics in regional anaesthesia. AIM: This study compared two combinations of bupivacaine and clonidine with bupivacaine alone for surgeries below the level of umbilicus in spinal anaesthesia. MATERIALS AND METHODS: We conducted a randomized double blind study on 90 patients of ASA I and ASA II aged 20-60 years, 30 in each group, undergoing surgery below the level of umbilicus in spinal anaesthesia. For intrathecal block, Group 1 received bupivacaine hydrochloride 12.5mg (2.5ml) in 8% dextrose (0.5% sensorcaine heavy) + 1ml (150µg) of preservative free clonidine. Group 2 received bupivacaine hydrochloride 12.5mg (2.5ml) in dextrose (0.5% sensorcaine heavy) + 0.5ml (75µg) of preservative free clonidine + 0.5ml of normal saline to make the volumes of all the groups same. Group 3 received bupivacaine hydrochloride 2.5ml in 8% dextrose (0.5% sensorcaine heavy) + 1ml of normal saline to make the volumes of all the groups same. Heart rate, NIBP, oxygen saturation and respiratory rate were monitored. The onset and duration of sensory block, the highest dermatomal level of sensory block, motor block, time to complete motor block recovery and duration of spinal anaesthesia were recorded. STATISTICAL ANALYSIS: The data of the study was recorded in the record chart and results were evaluated using statistical tests (ANOVA test, post-hoc turkey hsd test, paired t-test and chi-square test). RESULTS: Demographic data, the incidence and duration of bradycardia were comparable amongst the groups. The duration of sensory and motor block were greatest in group 1, followed by group 2 and group 3 (p <0.01). Decrease in the systolic blood pressure of group 2 and group 3 was noted as compared to group 1. No significant sedation or respiratory depression was observed in any group. CONCLUSION: Addition of clonidine to bupivacaine intrathecally is although a reliable method to prolong spinal anaesthesia but close monitoring for hypotension is desirable.