Valluri, S. | Search bioRxiv

bioRxiv2025

Loss-of-Function RUP-Variants Influence Ubiquitin-Proteasome System and Enhance Carotenoid and Folate Levels in Tomato

REPRESSOR OF UV-B PHOTOMORPHOGENESIS (RUP) negatively regulates UV- B signalling, yet its broader physiological roles in crop plants remain largely unexplored. We compared two tomato accessions bearing truncated RUP proteins--rup-1 and rup-2 (rup- variants)--with the cultivar Arka Vikas (AV), which harbours the native RUP protein. Seedlings of rup-variants exhibited enhanced tolerance to supplemental UV-B light. Red ripe (RR) fruits of rup-variants showed significantly elevated carotenoid and folate levels compared to AV. Introgression of rup-variants into AV confirmed that the increased carotenoid accumulation is genetically linked to RUP truncation. Metabolomic profiling of rup-variants revealed a substantial shift in primary metabolic homeostasis, particularly at the breaker stage, marked by a pronounced reduction in sugars and amino acids. Proteomic analyses of rup- variants across ripening stages identified that a significant proportion of differentially expressed proteins belonged to chaperones and ubiquitin-proteasome system (UPS). Upregulation of four key enzymes in the carotenoid biosynthesis pathway likely contributed to increased lycopene content in rup-variants. Elevated folate levels in rup-variants were associated with the upregulation of folate biosynthesis and C1 metabolism enzymes. Despite widespread metabolic reprogramming in rup-variants, hormonal regulatory pathways remained largely unaltered. Our results suggest that RUP modulates metabolic pathways during fruit ripening, and its loss triggers metabolic reprogramming associated with elevated folate/carotenoid levels.

plant biology↗

bioRxiv2023

Arrested Agonist Paradigm For Selective Radiosensitization of Prostate Cancer

As a prototypical nuclear hormone receptor, the androgen receptor (AR) signals via a sequential cascade triggered by binding to androgenic ligands such as testosterone and dihydrotestosterone (DHT). This cascade includes dimerization of the ligand-receptor complex, nuclear translocation, chromatin binding to response elements, recruitment of TOP2B and co-activator complexes, and induction of an effector transcriptional program. In prostate cancers, this AR signaling cascade is an essential driver of growth and survival, yet its activity confers potential vulnerabilities through transient TOP2B-mediated DNA double strand breaks. We investigated the ability of non-steroidal AR ligands to activate initial steps of the AR signaling cascade up to the point of AR- and TOP2B-mediated double strand breaks, with subsequent arrest of the signaling cascade to prevent induction of pro-growth/survival transcriptional programs in prostate cancer cells. We identified hydroxyflutamide (FLU) as such an androgen receptor arrested agonist; in androgen-deprived conditions, FLU induced AR nuclear translocation, chromatin binding, and TOP2B-mediated double strand breaks, but failed to induce AR target gene expression and prostate cancer cell growth. The FLU-mediated arrest in the signaling cascade could be attributed to the inability of FLU to allow association of AR with SMARCD2, a critical component of the BAF chromatin remodeling complex required for androgen induced AR co-activation. Interestingly, the FLU-induced, AR- and TOP2B-mediated double strand breaks could be used to selectively sensitize AR-positive prostate cancer cells to ionizing radiation in vitro and in vivo. These findings support a novel arrested agonist paradigm for selective radiosensitization of prostate cancer cells without inducing AR-mediated pro-growth and survival transcriptional programs.

cancer biology↗