TGFβ and BMP receptor kinases activate Smad transcription factors by C-terminal phosphorylation. We have identified a subsequent agonist-induced phosphorylation that plays a central dual role in Smad transcriptional activation and turnover. As receptor-activated Smads form transcriptional complexes, they are phosphorylated at an interdomain linker region by CDK8 and CDK9, which are components of transcriptional mediator and elongation complexes. These phosphorylations promote Smad transcriptional action, which in the case of Smad1, is mediated by the recruitment of YAP to the phosphorylated linker sites. An effector of the highly conserved Hippo organ size control pathway, YAP supports Smad1-dependent transcription and is required for BMP suppression of neural differentiation of mouse embryonic stem cells. The phosphorylated linker is ultimately recognized by specific ubiquitin ligases, leading to proteasome-mediated turnover of activated Smad proteins. Thus, nuclear CDK8/9 drive a cycle of Smad utilization and disposal that is an integral part of canonical BMP and TGFβ pathways.

Tunneling nanotubes are long, non-adherent F-actin-based cytoplasmic extensions which connect proximal or distant cells and facilitate intercellular transfer. The identification of nanotubes has been limited to cell lines, and their role in cancer remains unclear. We detected tunneling nanotubes in mesothelioma cell lines and primary human mesothelioma cells. Using a low serum, hyperglycemic, acidic growth medium, we stimulated nanotube formation and bidirectional transfer of vesicles, proteins, and mitochondria between cells. Notably, nanotubes developed between malignant cells or between normal mesothelial cells, but not between malignant and normal cells. Immunofluorescent staining revealed their actin-based assembly and structure. Metformin and an mTor inhibitor, Everolimus, effectively suppressed nanotube formation. Confocal microscopy with 3-dimensional reconstructions of sectioned surgical specimens demonstrated for the first time the presence of nanotubes in human mesothelioma and lung adenocarcinoma tumor specimens. We provide the first evidence of tunneling nanotubes in human primary tumors and cancer cells and propose that these structures play an important role in cancer cell pathogenesis and invasion.

He was a co-founder of Seragon, purchased by Genentech/Roche in 2014. J.M. is a science advisor and owns company stock in Scholar Rock. H.C. is an inventor on several patents related to organoid technology. S.W.L. is a co-founder and scientific advisory board member for ORIC Pharm, Blueprint, and Mirimus. He also serves on the scientific advisory board for Constellation, Petra, and PMV and has recently served as a consultant for Forma, Boehringer Ingelheim, and Aileron. J.G.-A. has received support from Medtronic (honorarium for consultancy with Medtronic), Johnson & Johnson (honorarium for delivering a talk), and Intuitive Surgical (honorarium for participating in a webinar by Intuitive Surgical). P.B.R. has received honorarium from Corning to discuss 3D cell culture techniques, has served as a consultant for AstraZeneca, and is a consultant for EMD Serono for work on radiation sensitizers.

Specific chromatin marks keep master regulators of differentiation silent, yet poised for activation by extracellular signals. We report that nodal TGF-β signals use the poised histone mark H3K9me3 to trigger differentiation of mammalian embryonic stem cells. Nodal receptors induce the formation of companion Smad4-Smad2/3 and TRIM33-Smad2/3 complexes. TRIM33-Smad2/3 binds the histone marks H3K9me3 and K18ac on the promoters of mesendoderm regulators Gsc and Mixl1. Binding is through the PHD-Bromo cassette of TRIM33. In the crystal structure of this cassette bound to histone H3 peptides, PHD recognizes K9me3 and Bromo an adjacent K18ac. Binding of TRIM33-Smad2/3 to H3K9me3 displaces the chromatin compacting factor HP1γ and makes nodal response elements accessible to Smad4-Smad2/3 for Pol II recruitment. In turn, Smad4 increases K18 acetylation to augment TRIM33-Smad2/3 binding. Thus, nodal cues use the H3K9me3 mark as a platform to switch master regulators of stem cell differentiation from the poised to the active state.

Optimal functioning of neuronal networks is critical to the complex cognitive processes of memory and executive function that deteriorate in Alzheimer’s disease (AD). Here we use cellular and animal models as well as human biospecimens to show that AD-related stressors mediate global disturbances in dynamic intra- and inter-neuronal networks through pathologic rewiring of the chaperome system into epichaperomes. These structures provide the backbone upon which proteome-wide connectivity, and in turn, protein networks become disturbed and ultimately dysfunctional. We introduce the term protein connectivity-based dysfunction (PCBD) to define this mechanism. Among most sensitive to PCBD are pathways with key roles in synaptic plasticity. We show at cellular and target organ levels that network connectivity and functional imbalances revert to normal levels upon epichaperome inhibition. In conclusion, we provide proof-of-principle to propose AD is a PCBDopathy, a disease of proteome-wide connectivity defects mediated by maladaptive epichaperomes.