Wnt canonical pathway activates macropinocytosis and lysosomal degradation of extracellular proteins.

Canonical Wnt signaling is emerging as a major regulator of endocytosis. Wnt treatment markedly increased the endocytosis and degradation in lysosomes of BSA. In this study, we report that in addition to receptor-mediated endocytosis, Wnt also triggers the intake of large amounts of extracellular fluid by macropinocytosis, a nonreceptor-mediated actin-driven process. Macropinocytosis induction is rapid and independent of protein synthesis. In the presence of Wnt, large amounts of nutrient-rich packages such as proteins and glycoproteins were channeled into lysosomes after fusing with smaller receptor-mediated vesicles containing glycogen synthase kinase 3 (GSK3) and protein arginine ethyltransferase 1 (PRMT1), an enzyme required for canonical Wnt signaling. Addition of Wnt3a, as well as overexpression of Disheveled (Dvl), Frizzled (Fz8), or dominant-negative Axin induced endocytosis. Depletion of the tumor suppressors adenomatous polyposis coli (APC) or Axin dramatically increased macropinocytosis, defined by incorporation of the high molecular weight marker tetramethylrhodamine (TMR)-dextran and its blockage by the Na+/H+ exchanger ethylisopropyl amiloride (EIPA). Macropinocytosis was blocked by dominant-negative vacuolar protein sorting 4 (Vps4), indicating that the Wnt pathway is dependent on multivesicular body formation, a process called microautophagy. SW480 colorectal cancer cells displayed constitutive macropinocytosis and increased extracellular protein degradation in lysosomes, which were suppressed by restoring full-length APC. Accumulation of the transcriptional activator ß-catenin in the nucleus of SW480 cells was inhibited by methyltransferase inhibition, EIPA, or the diuretic amiloride. The results indicate that Wnt signaling switches metabolism toward nutrient acquisition by engulfment of extracellular fluids and suggest possible treatments for Wnt-driven cancer progression.

Canonical Wnt is inhibited by targeting one-carbon metabolism through methotrexate or methionine deprivation.

The nutrient-sensing metabolite S-adenosylmethionine (SAM) controls one-carbon metabolism by donating methyl groups to biochemical building blocks, DNA, RNA, and protein. Our recent work uncovered a requirement for cytoplasmic arginine methylation during Wnt signaling through the activity of protein arginine methyltransferase 1 (PRMT1), which transfers one-carbon groups from SAM to many protein substrates. Here, we report that treatments that decrease levels of the universal methyl donor SAM were potent inhibitors of Wnt signaling and of Wnt-induced digestion of extracellular proteins in endolysosomes. Thus, arginine methylation provides the canonical Wnt pathway with metabolic sensing properties through SAM. The rapid accumulation of Wnt-induced endolysosomes within 30 minutes was inhibited by the depletion of methionine, an essential amino acid that serves as the direct substrate for SAM production. We also found that methionine is required for GSK3 sequestration into multivesicular bodies through microautophagy, an essential step in Wnt signaling activity. Methionine starvation greatly reduced Wnt-induced endolysosomal degradation of extracellular serum proteins. Similar results were observed by addition of nicotinamide (vitamin B3), which serves as a methyl group sink. Methotrexate, a pillar in the treatment of cancer since 1948, decreases SAM levels. We show here that methotrexate blocked Wnt-induced endocytic lysosomal activity and reduced canonical Wnt signaling. Importantly, the addition of SAM during methionine depletion or methotrexate treatment was sufficient to rescue endolysosomal function and Wnt signaling. Inhibiting the Wnt signaling pathway by decreasing one-carbon metabolism provides a platform for designing interventions in Wnt-driven disease.

Recent progress in modeling and treating diabetes using stem cell-derived islets.

Stem cell-derived islets (SC-islets) offer the potential to be an unlimited source of cells for disease modeling and the treatment of diabetes. SC-islets can be genetically modified, treated with chemical compounds, or differentiated from patient derived stem cells to model diabetes. These models provide insights into disease pathogenesis and vulnerabilities that may be targeted to provide treatment. SC-islets themselves are also being investigated as a cell therapy for diabetes. However, the transplantation process is imperfect; side effects from immunosuppressant use have reduced SC-islet therapeutic potential. Alternative methods to this include encapsulation, use of immunomodulating molecules, and genetic modification of SC-islets. This review covers recent advances using SC-islets to understand different diabetes pathologies and as a cell therapy.

Antibiofilm Activity of PEGylated Branched Polyethylenimine.

Biofilm formation is an adaptive resistance mechanism that pathogens employ to survive in the presence of antimicrobials. Pseudomonas aeruginosa is an infectious Gram-negative bacterium whose biofilm allows it to withstand antimicrobial attack and threaten human health. Chronic wound healing is often impeded by P. aeruginosa infections and the associated biofilms. Previous findings demonstrate that 600 Da branched polyethylenimine (BPEI) can restore ß-lactam potency against P. aeruginosa and disrupt its biofilms. Toxicity concerns of 600 Da BPEI are mitigated by covalent linkage with low-molecular-weight polyethylene glycol (PEG), and, in this study, PEGylated BPEI (PEG350-BPEI) was found exhibit superior antibiofilm activity against P. aeruginosa. The antibiofilm activity of both 600 Da BPEI and its PEG derivative was characterized with fluorescence studies and microscopy imaging. We also describe a variation of the colony biofilm model that was employed to evaluate the biofilm disruption activity of BPEI and PEG-BPEI.

The time is now: Student-driven implementation of social justice and anti-racism focused curricula in medical scientist training program education.

There exists a dearth of supplementary programs to educate physician-scientist trainees on anti-racism and topics surrounding social justice in medicine and science. Education on these topics is critical to prevent the perpetuation of systemic racism within the institutions of academia and medicine. Students in the Washington University School of Medicine Medical Scientist Training Program and the Tri-Institutional MD-PhD Program developed journal clubs with curricula focused on social justice and anti-racism for the summer of 2020. In this article, we describe the impact of the Washington University journal club on the education of first year MD-PhD students and summarize the progress to date. The role of the journal club in the midst of the "double pandemic" of COVID-19 and generational systemic racism is discussed, highlighting the need for such supplemental curricula in MD-PhD programs nation-wide.

GSK3 Inhibits Macropinocytosis and Lysosomal Activity through the Wnt Destruction Complex Machinery.

Canonical Wnt signaling is emerging as a major regulator of endocytosis. Here, we report that Wnt-induced macropinocytosis is regulated through glycogen synthase kinase 3 (GSK3) and the ß-catenin destruction complex. We find that mutation of Axin1, a tumor suppressor and component of the destruction complex, results in the activation of macropinocytosis. Surprisingly, inhibition of GSK3 by lithium chloride (LiCl), CHIR99021, or dominant-negative GSK3 triggers macropinocytosis. GSK3 inhibition causes a rapid increase in acidic endolysosomes that is independent of new protein synthesis. GSK3 inhibition or Axin1 mutation increases lysosomal activity, which can be followed with tracers of active cathepsin D, ß-glucosidase, and ovalbumin degradation. Microinjection of LiCl into the blastula cavity of Xenopus embryos causes a striking increase in dextran macropinocytosis. The effects of GSK3 inhibition on protein degradation in endolysosomes are blocked by the macropinocytosis inhibitors EIPA or IPA-3, suggesting that increases in membrane trafficking drive lysosomal activity.