Biology subjects

Bankaitis, V. A.

Publications and source records attributed to Bankaitis, V. A..

6 recordsLinked to original sources

bioRxiv2024

A pontine-specific axonal niche supports de novo gliomagenesis

Diffuse intrinsic pontine gliomas (DIPGs), a major type of pediatric high-grade gliomas located in the pons, are the leading cause of death in children with brain cancer. A subset (20-25%) of DIPGs harbor a lysine 27-to-methionine (K27M) mutation in HIST1H3B, which encodes histone H3.1, and an activating ACVR1 mutation. The occurrence of this pair of mutations in DIPGs, but not in pediatric gliomas in other anatomical locations, suggests the existence of a pontine-specific niche that favors DIPG gliomagenesis. Unfortunately, the identity of the underlying pontine niche remains elusive as available mouse models fail to recapitulate the anatomic specificity that characterizes DIPGs. Herein we show that the trigeminal root entry zone (TREZ), a pontine structure where several major axon tracts intersect, is enriched with proliferating oligodendrocyte-lineage cells during brainstem development. Introducing both H3.1K27M and activating Acvr1 and Pik3ca mutations (which co-occur frequently with H3.1K27M in human DIPGs) into the mouse brain leads to rapid gliomagenesis. This pathology recapitulates the pons specificity of DIPGs as glioma cells proliferate on axon tracts at the TREZ. We further show that a hyaluronan receptor important for cell stemness (HMMR) plays a key role in glioma cell proliferation at the TREZ. We propose that H3.1K27M and its co-occurring mutations drive pontine specific gliomagenesis by inducing a proliferative response of oligodendrocyte-lineage cells with enhanced stemness on large TREZ axon tracts. One-Sentence SummaryThe trigeminal root entry zone underlies pontine-specific gliomagenesis driven by H3.1K27M and its co-occurring mutations.

cancer biology↗

bioRxiv2023

A novel bivalent interaction mode underlies a non-catalytic mechanism for Pin1-mediated Protein Kinase C regulation

Regulated hydrolysis of the phosphoinositide phosphatidylinositol(4,5)-bis-phosphate to diacylglycerol and inositol-1,4,5-P3 defines a major eukaryotic pathway for translation of extracellular cues to intracellular signaling circuits. Members of the lipid-activated protein kinase C isoenzyme family (PKCs) play central roles in this signaling circuit. One of the regulatory mechanisms employed to downregulate stimulated PKC activity is via a proteasome-dependent degradation pathway that is potentiated by peptidyl-prolyl isomerase Pin1. Here, we show that contrary to prevailing models, Pin1 does not regulate conventional PKC isoforms and {beta}II via a canonical cis-trans isomerization of the peptidyl-prolyl bond. Rather, Pin1 acts as a PKC binding partner that controls PKC activity via sequestration of the C-terminal tail of the kinase. The high-resolution structure of Pin1 complexed to the C-terminal tail of PKC{beta}II reveals that a novel bivalent interaction mode underlies the non-catalytic mode of Pin1 action. Specifically, Pin1 adopts a compact conformation in which it engages two conserved phosphorylated PKC motifs, the turn motif and hydrophobic motif, the latter being a non-canonical Pin1-interacting element. The structural information, combined with the results of extensive binding studies and in vivo experiments suggest that non-catalytic mechanisms represent unappreciated modes of Pin1-mediated regulation of AGC kinases and other key enzymes/substrates. Impact statementIntegrated biophysical, structural, and in vivo approaches demonstrate a non-canonical and non-isomerizable binding motif-dependent mode of protein kinase C regulation by the peptidyl-prolyl isomerase Pin1 in mammalian cells.

biophysics↗

bioRxiv2023

Phosphatidylinositol-4-phosphate signaling regulates dense granule biogenesis and exocytosis in Toxoplasma gondii

Phosphoinositide metabolism defines the foundation of a major signaling pathway that is conserved throughout the eukaryotic kingdom. The 4-OH phosphorylated phosphoinositides such as phosphatidylinositol-4-phosphate (PtdIns4P) and phosphatidylinositol-4,5-bisphosphate are particularly important molecules as these execute intrinsically essential activities required for the viability of all eukaryotic cells studied thus far. Using intracellular tachyzoites of the apicomplexan parasite Toxoplasma gondii as model for assessing primordial roles for PtdIns4P signaling, we demonstrate the presence of PtdIns4P pools in Golgi/trans-Golgi (TGN) system and in post-TGN compartments of the parasite. Moreover, we show that deficits in PtdIns4P signaling result in structural perturbation of compartments that house dense granule cargo with accompanying deficits in dense granule exocytosis. Taken together, the data report a direct role for PtdIns4P in dense granule biogenesis and exocytosis. The data further indicate that the biogenic pathway for secretion-competent dense granule formation in T. gondii is more complex than simple budding of fully matured dense granules from the TGN.

cell biology↗

bioRxiv2021

Translational control of lipogenesis links protein synthesis and phosphoinositide signaling with nuclear division

Continuously dividing cells coordinate their growth and division. How fast cells grow in mass determines how fast they will multiply. Yet, there are few, if any, examples of a metabolic pathway that actively drives a cell cycle event instead of just being required for it. Here, we show that translational upregulation of lipogenic enzymes in yeast increased the abundance of lipids and accelerated nuclear elongation and division. De-repressing translation of acetyl CoA carboxylase and fatty acid synthase also suppressed cell cycle-related phenotypes, including delayed nuclear division, associated with Sec14p phosphatidylinositol transfer protein deficiencies, and the irregular nuclear morphologies of mutants defective in phosphatidylinositol 4-OH kinase activities. Our results show that increased lipogenesis drives a critical cell cycle landmark and report a phosphoinositide signaling axis in control of nuclear division. The broad conservation of these lipid metabolic and signaling pathways raises the possibility these activities similarly govern nuclear division in mammals.

cell biology↗

bioRxiv2020

Neural stem cell interkinetic nuclear migration is controlled by phosphatidylinositol transfer protein/non-canonical planar cell polarity signaling

The mammalian neocortex undergoes explosive expansion during embryonic development. From an evolutionary perspective, higher complexity of the neocortex is accompanied by a prominent expansion in its lateral dimension so that the neocortical surface area is increased. Expansion in the radial dimension throughout evolution is limited so that neocortical thickness is strongly restricted1-3. The underlying mechanisms for restricting neocortical thickness remain unclear. Expansion of the developing mouse neocortex is driven by neurogenesis which is itself primarily fueled by neural stem cells (NSCs). NSCs form a pseudostratified epithelium and exhibit a hallmark cell cycle-dependent nuclear movement termed interkinetic nuclear migration (IKNM) 2-4. While IKNM plays a critical role in cell fate determination, it remains a poorly understood process. Herein, we demonstrate IKNM relies on a phosphatidylinositol transfer protein (PITP)-noncanonical planar cell polarity (ncPCP) signaling axis that restricts radial expansion of the developing neocortex. Ablation of PITP/PITP{beta} in NSCs compromised IKNM -- resulting in a thickened neocortex and perturbed curvature of its ventricular surface. Those phenotypic derangements in IKNM and neocortical morphogenesis were recapitulated in mouse embryos individually ablated for two ncPCP receptor gene activities and in a mosaic neocortex expressing a dominant-negative variant of a third ncPCP receptor. Finally, PITP signaling links to ncPCP pathway activity by promoting membrane trafficking of a subset of ncPCP receptors from the trans-Golgi network to the NSC cell surface. We conclude IKNM is a driving force for a special form of convergent extension regulated by coupling PITP-mediated phosphoinositide signaling with activity of the evolutionarily conserved ncPCP pathway.

developmental biology↗

bioRxiv2018

Sorting Nexin 27 (SNX27): A Novel Regulator of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Trafficking

The underlying defect in cystic fibrosis is mutation of the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-activated chloride channel expressed at the apical surface of lung epithelia. In addition to its export and maintenance at the cell surface, CFTR regulation involves repeated cycles of transport through the endosomal trafficking system, including endocytosis and recycling. Many of the known disease mutations cause CFTR intracellular trafficking defects that result in failure of ion channel delivery to the apical plasma membrane. Corrective maneuvers directed at improving transport to the plasma membrane are thwarted by rapid internalization and degradation of the mutant CFTR proteins. The molecular mechanisms involved in these processes are not completely understood but may involve protein-protein interactions with the C-terminal type I PDZ-binding motif of CFTR. Using a proteomic approach, we identify sorting nexin 27 (SNX27) as a novel CFTR binding partner in human airway epithelial Calu-3 cells. SNX27 and CFTR interact directly, with the SNX27 PDZ domain being both necessary and sufficient for this interaction. SNX27 co-localizes with internalized CFTR at sub-apical endosomal sites in polarized Calu-3 cells, and either knockdown of the endogenous SNX27, or over-expression of a dominant-negative SNX27 mutant, resulted in significant decreases in cell surface CFTR levels. CFTR internalization was not affected by SNX27 knockdown, but defects were observed in the recycling arm of CFTR trafficking through the endosomal system. Furthermore, knockdown of SNX27 in Calu-3 cells resulted in significant decreases in CFTR protein levels, consistent with degradation of the internalized pool. These data identify SNX27 as a physiologically significant regulator of CFTR trafficking and homeostasis in epithelial cells.

cell biology↗