R2TP/PAQosome as a promising chemotherapeutic target in cancer

Drugs targeting the particle for arrangement of quaternary structure (PAQosome) and protein complex assembly

INTRODUCTION

The PAQosome is a 12-subunit complex that acts as a co-factor of the molecular chaperones HSP90 and HSP70. This co-chaperone has been shown to participate in assembly and maturation of several protein complexes, including nuclear RNA polymerases, RNA processing factors, the ribosome, PIKKs, and others. Subunits of the PAQosome, adaptors, and clients have been reported to be involved in various diseases, making them interesting targets for drug discovery.

AREA COVERED

In this review, the authors cover the detailed mechanisms of PAQosome and chaperone function. Specifically, the authors summarize the status of the PAQosome and some related chaperones and co-chaperones as candidate targets for drug discovery. Indeed, a number of compounds are currently being tested for the development of treatments against diseases, such as cancers and neurodegenerative conditions.

EXPERT OPINION

Searching for new drugs targeting the PAQosome requires a better understanding of PAQosome subunit interactions and the discovery of new interaction partners. Thus, PAQosome subunit crystallization is an important experiment to initiate virtual screening against new target and the development of in silico tools such as AlphaFold-multimer could accelerate the search for new interaction partner and determine more rapidly the interaction pocket needed for virtual drug screening.

Maturation and Assembly of mTOR Complexes by the HSP90-R2TP-TTT Chaperone System: Molecular Insights and Mechanisms

The mechanistic target of rapamycin (mTOR) is a master regulator of cell growth and metabolism, integrating environmental signals to regulate anabolic and catabolic processes, regulating lipid synthesis, growth factor-induced cell proliferation, cell survival, and migration. These activities are performed as part of two distinct complexes, mTORC1 and mTORC2, each with specific roles. mTORC1 and mTORC2 are elaborated dimeric structures formed by the interaction of mTOR with specific partners. mTOR functions only as part of these large complexes, but their assembly and activation require a dedicated and sophisticated chaperone system. mTOR folding and assembly are temporarily separated with the TELO2-TTI1-TTI2 (TTT) complex assisting the cotranslational folding of mTOR into a native conformation. Matured mTOR is then transferred to the R2TP complex for assembly of active mTORC1 and mTORC2 complexes. R2TP works in concert with the HSP90 chaperone to promote the incorporation of additional subunits to mTOR and dimerization. This review summarizes our current knowledge on how the HSP90-R2TP-TTT chaperone system facilitates the maturation and assembly of active mTORC1 and mTORC2 complexes, discussing interactions, structures, and mechanisms.

Discriminating Potential Genetic Markers for Complete Response and Non-Complete Response Patients to Neoadjuvant Chemotherapy with Locally Advanced Rectal Cancer

Background: Neoadjuvant chemoradiotherapy (nCRT) prior to surgery is considered standard therapy for locally advanced rectal cancer. Unfortunately, most patients with rectal cancer are resistant to radiotherapy. This might be a genetic cause. The role of certain rectal cancer-causing genes has not been completely elucidated. This study aims to investigate the genes responsible for locally advanced rectal cancer patients not reacting to radiotherapy. Methods: Whole exome sequencing of the DNA samples was performed on the samples. Bioinformatic analysis on the subjects was established. Individual genetic information was screened to identify differently expressed genes that more frequently appeared in non-complete response (NCR) compared to complete response (CR) patients after nCRT. All variations were verified by Sanger sequencing. Results: Genotyping information and pathway analyses of the samples indicated genes such as FLCN, CALML5, and ANTXR1 to be commonly mutated in CR group, whereas genes such as GALNTL14, CNKSR1, ACD, and CUL3 were more commonly mutated in the NCR group. Chi-square test revealed some significant variants (<0.05) such as rs3744124 (FLCN), rs28365986 (ANTXR1), rs10904516 (CALML5), rs3738952 (CUL3), rs13394 and rs2293013 (PIH1D1), rs2274531 (GPA33), rs4963048 (BRSK2), rs17883366 (IL3RA), rs2297575 (PSMD5), rs2288101 (GALNT14), and rs11954652 (DCTN4). Conclusion: Identifying an array of genes that separate NCRs from CRs would lead to finding genetic biomarkers for early detection of rectal cancer patients that are resistant to nCRT. A further investigation to validate the significance of genetic biomarkers to segregate NCRs from CRs should be performed with a larger CRC dataset. Protein expression levels, as well as transcriptomic analysis, would also help us understand the mechanism of how these genes could play a role in preventing radiation therapy to patients. This would be essential to prevent redundant radiation therapy.

Rba50 and Gpn2 recruit the second largest subunits for the assembly of RNA polymerase II and III

Although remarkable progress has been made toward understanding the structures of eukaryotic RNA polymerases, the pathways and factors that facilitate their assembly remain unresolved. Essential proteins Rba50 and Gpn2 are required for Rpb3 subcomplex assembly, but whether they participate in subsequent assembly steps is unknown. Herein, we performed comprehensive genetic screens to explore Rba50 function. We identified two unique extragenic rba50-3-suppressing mutations that map to genes encoding the Rba50-interacting protein Gpn2, and Rpb2, the second largest subunit of RNAPII. Both gpn2-R347S and rpb2-V1171G variants bypass Rpb1 cytoplasmic arrest and temperature-sensitive growth defects of the rba50-3 mutant. GPN2 and RPB2 were also identified as novel multicopy suppressors of the rba50-3 mutant. Rapid depletion of Rba50 affected Rpb3-Rpb2 association during RNAPII assembly. Importantly, we demonstrated that Gpn2 facilitates the association of Rba50 and Rpb2. Our results imply that Rba50-Gpn2 interaction is essential for Rpb2 recruitment during RNAPII assembly following Rpb3 subcomplex assembly. Furthermore, the Rba50-Gpn2 complex appears to play a similar role in the assembly of RNAPIII. We therefore propose a model in which Rba50 interacts with Gpn2 and thereby promotes loading of the second largest subunit of RNAP II and III onto the previously assembled subcomplex.

OUP accepted manuscript

MicroRNAs silence mRNAs by guiding the RISC complex. RISC assembly occurs following cleavage of pre-miRNAs by Dicer, assisted by TRBP or PACT, and the transfer of miRNAs to AGO proteins. The R2TP complex is an HSP90 co-chaperone involved in the assembly of ribonucleoprotein particles. Here, we show that the R2TP component RPAP3 binds TRBP but not PACT. The RPAP3-TPR1 domain interacts with the TRBP-dsRBD3, and the 1.5 Å resolution crystal structure of this complex identifies key residues involved in the interaction. Remarkably, binding of TRBP to RPAP3 or Dicer is mutually exclusive. Additionally, we found that AGO(1/2), TRBP and Dicer are all sensitive to HSP90 inhibition, and that TRBP sensitivity is increased in the absence of RPAP3. Finally, RPAP3 seems to impede miRNA activity, raising the possibility that the R2TP chaperone might sequester TRBP to regulate the miRNA pathway.