A genome-wide screen links peroxisome regulation with Wnt signaling through RNF146 and TNKS/2.

Peroxisomes are membrane-bound organelles harboring metabolic enzymes. In humans, peroxisomes are required for normal development, yet the genes regulating peroxisome function remain unclear. We performed a genome-wide CRISPRi screen to identify novel factors involved in peroxisomal homeostasis. We found that inhibition of RNF146, an E3 ligase activated by poly(ADP-ribose), reduced the import of proteins into peroxisomes. RNF146-mediated loss of peroxisome import depended on the stabilization and activity of the poly(ADP-ribose) polymerases TNKS and TNKS2, which bind the peroxisomal membrane protein PEX14. We propose that RNF146 and TNKS/2 regulate peroxisome import efficiency by PARsylation of proteins at the peroxisome membrane. Interestingly, we found that the loss of peroxisomes increased TNKS/2 and RNF146-dependent degradation of non-peroxisomal substrates, including the ß-catenin destruction complex component AXIN1, which was sufficient to alter the amplitude of ß-catenin transcription. Together, these observations not only suggest previously undescribed roles for RNF146 in peroxisomal regulation but also a novel role in bridging peroxisome function with Wnt/ß-catenin signaling during development.

Baseline unfolded protein response signaling adjusts the timing of the mammalian cell cycle.

The endoplasmic reticulum (ER) is a single-copy organelle that cannot be generated de novo, suggesting coordination between the mechanisms overseeing ER integrity and those controlling the cell cycle to maintain organelle inheritance. The Unfolded Protein Response (UPR) is a conserved signaling network that regulates ER homeostasis. Here, we show that pharmacological and genetic inhibition of the UPR sensors IRE1, ATF6, and PERK in unstressed cells delays the cell cycle, with PERK inhibition showing the most penetrant effect, which was associated with a slowdown of the G1-to-S/G2 transition. Treatment with the small molecule ISRIB to bypass the effects of PERK-dependent phosphorylation of the translation initiation factor eIF2α had no such effect, suggesting that cell cycle timing depends on PERK's kinase activity but is independent of eIF2α phosphorylation. Using complementary light and electron microscopy and flow cytometry-based analyses, we also demonstrate that the ER enlarges before mitosis. Together, our results suggest coordination between UPR signaling and the cell cycle to maintain ER physiology during cell division.

Engineering water exchange is a safe and effective method for magnetic resonance imaging in diverse cell types.

Aquaporin-1 (Aqp1), a water channel, has garnered significant interest for cell-based medicine and in vivo synthetic biology due to its ability to be genetically encoded to produce magnetic resonance signals by increasing the rate of water diffusion in cells. However, concerns regarding the effects of Aqp1 overexpression and increased membrane diffusivity on cell physiology have limited its widespread use as a deep-tissue reporter. In this study, we present evidence that Aqp1 generates strong diffusion-based magnetic resonance signals without adversely affecting cell viability or morphology in diverse cell lines derived from mice and humans. Our findings indicate that Aqp1 overexpression does not induce ER stress, which is frequently associated with heterologous expression of membrane proteins. Furthermore, we observed that Aqp1 expression had no detrimental effects on native biological activities, such as phagocytosis, immune response, insulin secretion, and tumor cell migration in the analyzed cell lines. These findings should serve to alleviate any lingering safety concerns regarding the utilization of Aqp1 as a genetic reporter and should foster its broader application as a noninvasive reporter for in vivo studies.

Engineering water exchange is a safe and effective method for magnetic resonance imaging in diverse cell types.

Aquaporin-1 (Aqp1), a water channel, has garnered significant interest for cell-based medicine and in vivo synthetic biology due to its ability to be genetically encoded to produce magnetic resonance signals by increasing the rate of water diffusion in cells. However, concerns regarding the effects of Aqp1 overexpression and increased membrane diffusivity on cell physiology have limited its widespread use as a deep-tissue reporter. In this study, we present evidence that Aqp1 generates strong diffusion-based magnetic resonance signals without adversely affecting cell viability or morphology in diverse cell lines derived from mice and humans. Our findings indicate that Aqp1 overexpression does not induce ER stress, which is frequently associated with heterologous expression of membrane proteins. Furthermore, we observed that Aqp1 expression had no detrimental effects on native biological activities, such as phagocytosis, immune response, insulin secretion, and tumor cell migration in the analyzed cell lines. These findings should serve to alleviate any lingering safety concerns regarding the utilization of Aqp1 as a genetic reporter and should foster its broader application as a noninvasive reporter for in vivo studies.