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Summary: RIT1 is a rare and understudied oncogene in lung cancer. Despite structural similarity to other RAS GTPase proteins such as KRAS, oncogenic RIT1 activity does not appear to be tightly regulated by nucleotide exchange or hydrolysis. Instead, there is a growing understanding that the protein abundance of RIT1 is important for its regulation and function. We previously identified the deubiquitinase USP9X as a RIT1 dependency in RIT1-mutant cells. Here, we demonstrate that both wild-type and mutant forms of RIT1 are substrates of USP9X. Depletion of USP9X leads to decreased RIT1 protein stability and abundance and resensitizes cells to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors in vitro and in vivo. Our work expands upon the current understanding of RIT1 protein regulation and presents USP9X as a key regulator of RIT1-driven oncogenic phenotypes.

RAS GTPases are highly conserved proteins involved in the regulation of mitogenic signaling. We have previously described a novel Cullin 3 RING E3 ubiquitin ligase complex formed by the substrate adaptor protein LZTR1 that binds, ubiquitinates, and promotes proteasomal degradation of the RAS GTPase RIT1. In addition, others have described that this complex is also responsible for the ubiquitination of classical RAS GTPases. Here, we have analyzed the phenotypes of Lztr1 loss-of-function mutants in both fruit flies and mice and have demonstrated a biochemical preference for their RIT1 orthologs. Moreover, we show that Lztr1 is haplosufficient in mice and that embryonic lethality of the homozygous null allele can be rescued by deletion of Rit1. Overall, our results indicate that, in model organisms, RIT1 orthologs are the preferred substrates of LZTR1.

Somatic KRAS mutations are highly prevalent in many cancers. In addition, a distinct spectrum of germline KRAS mutations causes developmental disorders called RASopathies. The mutant proteins encoded by these germline KRAS mutations are less biochemically and functionally activated than those in cancer. We generated mice harboring conditional KrasLSL-P34Rand KrasLSL-T58I knock-in alleles and characterized the consequences of each mutation in vivo. Embryonic expression of KrasT58I resulted in craniofacial abnormalities reminiscent of those seen in RASopathy disorders, and these mice exhibited hyperplastic growth of multiple organs, modest alterations in cardiac valvulogenesis, myocardial hypertrophy, and myeloproliferation. By contrast, embryonic KrasP34R expression resulted in early perinatal lethality from respiratory failure due to defective lung sacculation, which was associated with aberrant ERK activity in lung epithelial cells. Somatic Mx1-Cre–mediated activation in the hematopoietic compartment showed that KrasP34R and KrasT58I expression had distinct signaling effects, despite causing a similar spectrum of hematologic diseases. These potentially novel strains are robust models for investigating the consequences of expressing endogenous levels of hyperactive K-Ras in different developing and adult tissues, for comparing how oncogenic and germline K-Ras proteins perturb signaling networks and cell fate decisions, and for performing preclinical therapeutic trials.

Angiogenesis requires dynamic endothelial rearrangements and relative position changes within the vascular tubes. Here the authors show that a PI3K/NUAK1/MYPT1/MLCP pathway regulates actomyosin contractility in endothelial cells and cellular rearrangement during vascular patterning.

Estrogen Receptor (ER) and the phosphoinositide 3-kinase (PI3K) pathways participate in regulatory crosstalk in breast cancer. We identified that chromatin regulation is at the intersection of oncogenic PI3K and ER. The PI3K effectors AKT, also known as protein kinase B (PKB), and SGK (serum/glucocorticoid-regulated kinase) play a redundant role by phosphorylating the chromatin regulator KMT2D and modulating ER activity and therapy resistance.

Summary: The PI3K pathway integrates extracellular stimuli to phosphorylate effectors such as AKT and serum-and-glucocorticoid-regulated kinase (SGK1). We have previously reported that the PI3K pathway regulates estrogen receptor (ER)-dependent transcription in breast cancer through the phosphorylation of the lysine methyltransferase KMT2D by AKT. Here, we show that PI3Kα inhibition, via a negative-feedback loop, activates SGK1 to promote chromatin-based regulation of ER-dependent transcription. PI3K/AKT inhibitors activate ER, which promotes SGK1 transcription through direct binding to its promoter. Elevated SGK1, in turn, phosphorylates KMT2D, suppressing its function, leading to a loss of methylation of lysine 4 on histone H3 (H3K4) and a repressive chromatin state at ER loci to attenuate ER activity. Thus, SGK1 regulates the chromatin landscape and ER-dependent transcription via the direct phosphorylation of KMT2D. These findings reveal an ER-SGK1-KMT2D signaling circuit aimed to attenuate ER response through a role for SGK1 to program chromatin and ER transcriptional output. : Toska, Castel, et al. show that the PI3K pathway propagates its effects to control chromatin and estrogen receptor (ER) function through SGK1, a PI3K effector. PI3K inhibitors, via a negative-feedback loop, activate SGK1, which phosphorylates the histone lysine methyltransferase KMT2D to attenuate its activity and regulate ER response. Keywords: SGK1, KMT2D, PI3K pathway, estrogen receptor, breast cancer, chromatin regulation, AKT, PI3K inhibitors

Epithelial morphogenesis and stability are essential for normal development and organ homeostasis. The mouse neural plate is a cuboidal epithelium that remodels into a columnar pseudostratified epithelium over the course of 24 hr. Here we show that the transition to a columnar epithelium fails in mutant embryos that lack the tumor suppressor PTEN, although proliferation, patterning and apical-basal polarity markers are normal in the mutants. The Pten phenotype is mimicked by constitutive activation of PI3 kinase and is rescued by the removal of PDK1 (PDPK1), but does not depend on the downstream kinases AKT and mTORC1. High resolution imaging shows that PTEN is required for stabilization of planar cell packing in the neural plate and for the formation of stable apical-basal microtubule arrays. The data suggest that appropriate levels of membrane-associated PDPK1 are required for stabilization of apical junctions, which promotes cell elongation, during epithelial morphogenesis.

A finales de la Edad Media asistimos a un cambio de percepción respecto a ciertas prácticas de salud llevadas a cabo mayoritariamente por mujeres. Estas prácticas, condenadas durante siglos por las élites laicas y eclesiásticas, adquieren progresivamente un carácter herético y diabólico, dando origen a la imagen de la bruja durante los primeros años del siglo XV. Las etapas de este cambio son perceptibles a través de la documentación catalana, la cual nos permite plantear una evolución que conecta las actuaciones contra la magia popular en el siglo XIV, las primeras acusaciones de brujería a inicios del XV y las grandes persecuciones en época moderna.