Sterol and oxysterol synthases near the ciliary base activate the Hedgehog pathway

Vertebrate Hedgehog signals are transduced through the primary cilium, a specialized lipid microdomain that is required for Smoothened activation. Cilia-associated sterol and oxysterol lipids bind to Smoothened to activate the Hedgehog pathway, but how ciliary lipids are regulated is incompletely understood. Here we identified DHCR7, an enzyme that produces cholesterol, activates the Hedgehog pathway, and localizes near the ciliary base. We found that Hedgehog stimulation negatively regulates DHCR7 activity and removes DHCR7 from the ciliary microenvironment, suggesting that DHCR7 primes cilia for Hedgehog pathway activation. In contrast, we found that Hedgehog stimulation positively regulates the oxysterol synthase CYP7A1, which accumulates near the ciliary base and produces oxysterols that promote Hedgehog signaling in response to pathway activation. Our results reveal that enzymes involved in lipid biosynthesis in the ciliary microenvironment promote Hedgehog signaling, shedding light on how ciliary lipids are established and regulated to transduce Hedgehog signals.

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Hedgehog-induced ciliary trafficking of kinesin-4 motor KIF7 requires intraflagellar transport but not KIF7’s microtubule binding

Molecular Biology of the Cell ◽

10.1091/mbc.e21-04-0215 ◽

2021 ◽

Author(s):

Yang Yue ◽

Martin F. Engelke ◽

T. Lynne Blasius ◽

Kristen J. Verhey

Keyword(s):

Transcription Factors ◽

Signaling Pathway ◽

Primary Cilium ◽

Hedgehog Signaling ◽

Intraflagellar Transport ◽

Hedgehog Signaling Pathway ◽

Microtubule Binding ◽

Pathway Activation ◽

Gli Transcription Factors ◽

Ciliary Localization

The kinesin-4 motor KIF7 is a conserved regulator of the Hedgehog signaling pathway. In vertebrates, Hedgehog signaling requires the primary cilium, and KIF7 and Gli transcription factors accumulate at the cilium tip in response to Hedgehog activation. Unlike conventional kinesins, KIF7 is an immotile kinesin and its mechanism of ciliary accumulation is unknown. We generated KIF7 variants with altered microtubule binding or motility. We demonstrate that microtubule binding of KIF7 is not required for the increase in KIF7 or Gli localization at the cilium tip in response to Hedgehog signaling. In addition, we show that the immotile behavior of KIF7 is required to prevent ciliary localization of Gli transcription factors in the absence of Hedgehog signaling. Using an engineered kinesin-2 motor that enables acute inhibition of intraflagellar transport (IFT), we demonstrate that kinesin-2 KIF3A/KIF3B/KAP mediates the translocation of KIF7 to the cilium tip in response to Hedgehog pathway activation. Together, these results suggest that KIF7’s role at the tip of the cilium is unrelated to its ability to bind to microtubules.

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KIF14 controls ciliogenesis via regulation of Aurora A and is important for Hedgehog signaling

The Journal of Cell Biology ◽

10.1083/jcb.201904107 ◽

2020 ◽

Vol 219 (6) ◽

Cited By ~ 6

Author(s):

Petra Pejskova ◽

Madeline Louise Reilly ◽

Lucia Bino ◽

Ondrej Bernatik ◽

Linda Dolanska ◽

...

Keyword(s):

Cell Cycle ◽

Primary Cilium ◽

Hedgehog Signaling ◽

Cell Cycle Progression ◽

Primary Cilia ◽

Aurora A ◽

Pathway Activation ◽

Cilia Formation ◽

Tightly Coupled ◽

Hh Signaling

Primary cilia play critical roles in development and disease. Their assembly and disassembly are tightly coupled to cell cycle progression. Here, we present data identifying KIF14 as a regulator of cilia formation and Hedgehog (HH) signaling. We show that RNAi depletion of KIF14 specifically leads to defects in ciliogenesis and basal body (BB) biogenesis, as its absence hampers the efficiency of primary cilium formation and the dynamics of primary cilium elongation, and disrupts the localization of the distal appendage proteins SCLT1 and FBF1 and components of the IFT-B complex. We identify deregulated Aurora A activity as a mechanism contributing to the primary cilium and BB formation defects seen after KIF14 depletion. In addition, we show that primary cilia in KIF14-depleted cells are defective in response to HH pathway activation, independently of the effects of Aurora A. In sum, our data point to KIF14 as a critical node connecting cell cycle machinery, effective ciliogenesis, and HH signaling.

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Plexins Promote Hedgehog Signaling Through Their Cytoplasmic GAP Activity

10.1101/2021.12.15.472757 ◽

2021 ◽

Author(s):

Justine M Pinskey ◽

Tyler M Hoard ◽

Xiao-Feng Zhao ◽

Nicole E Franks ◽

Zoe C Frank ◽

...

Keyword(s):

Hedgehog Signaling ◽

Primary Cilia ◽

Hedgehog Pathway ◽

Loss Of Function ◽

3T3 Fibroblasts ◽

Pathway Activation ◽

Gli Transcription Factors ◽

Full Complement ◽

Positive Regulators ◽

Nih 3T3

Hedgehog signaling controls tissue patterning during embryonic and postnatal development and continues to play important roles throughout life. Characterizing the full complement of Hedgehog pathway components is essential to understanding its wide-ranging functions. Previous work has identified Neuropilins, established Semaphorin receptors, as positive regulators of Hedgehog signaling. Neuropilins require Plexin co-receptors to mediate Semaphorin signaling, but a role for Plexins in Hedgehog signaling has not yet been explored. Here, we provide evidence that multiple Plexins promote Hedgehog signaling in NIH/3T3 fibroblasts and that Plexin loss-of-function in these cells results in significantly reduced Hedgehog pathway activity. Catalytic activity of the Plexin GTPase activating protein (GAP) domain is required for Hedgehog signal promotion, and constitutive activation of the GAP domain further amplifies Hedgehog signaling. Additionally, we demonstrate that Plexins promote Hedgehog signaling at the level of GLI transcription factors and that this promotion requires intact primary cilia. Finally, we find that Plexin loss-of-function significantly reduces the response to Hedgehoga pathway activation in the mouse dentate gyrus. Together, these data identify Plexins as novel components of the Hedgehog pathway and provide insight into their mechanism of action.

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Pitchfork and Gprasp2 Target Smoothened to the Primary Cilium for Hedgehog Pathway Activation

PLoS ONE ◽

10.1371/journal.pone.0149477 ◽

2016 ◽

Vol 11 (2) ◽

pp. e0149477 ◽

Cited By ~ 16

Author(s):

Bomi Jung ◽

Daniela Padula ◽

Ingo Burtscher ◽

Cedric Landerer ◽

Dominik Lutter ◽

...

Keyword(s):

Primary Cilium ◽

Hedgehog Pathway ◽

Pathway Activation

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Distinctive functioning of STARD1 in the fetal Leydig cells compared to adult Leydig and adrenal cells. Impact of Hedgehog signaling via the primary cilium.

Molecular and Cellular Endocrinology ◽

10.1016/j.mce.2021.111265 ◽

2021 ◽

pp. 111265

Author(s):

Anbarasi Kothandapani ◽

Michele Campaigne Larsen ◽

Jinwoo Lee ◽

Joan S. Jorgensen ◽

Colin R. Jefcoate

Keyword(s):

Primary Cilium ◽

Leydig Cells ◽

Hedgehog Signaling ◽

Adrenal Cells ◽

Fetal Leydig Cells

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Novel small molecules targeting ciliary transport of Smoothened and oncogenic Hedgehog pathway activation

Scientific Reports ◽

10.1038/srep22540 ◽

2016 ◽

Vol 6 (1) ◽

Cited By ~ 10

Author(s):

Bomi Jung ◽

Ana C. Messias ◽

Kenji Schorpp ◽

Arie Geerlof ◽

Günter Schneider ◽

...

Keyword(s):

Small Molecules ◽

Hedgehog Pathway ◽

Pathway Activation

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Trafficking to the primary cilium membrane

Molecular Biology of the Cell ◽

10.1091/mbc.e16-07-0505 ◽

2017 ◽

Vol 28 (2) ◽

pp. 233-239 ◽

Cited By ~ 24

Author(s):

Saikat Mukhopadhyay ◽

Hemant B. Badgandi ◽

Sun-hee Hwang ◽

Bandarigoda Somatilaka ◽

Issei S. Shimada ◽

...

Keyword(s):

Membrane Proteins ◽

Signaling Pathways ◽

Primary Cilium ◽

Hedgehog Signaling ◽

Diffusion Barriers ◽

Disease Pathogenesis ◽

Ciliary Membrane ◽

Multiple Organs ◽

Sensory Reception

The primary cilium has been found to be associated with a number of cellular signaling pathways, such as vertebrate hedgehog signaling, and implicated in the pathogenesis of diseases affecting multiple organs, including the neural tube, kidney, and brain. The primary cilium is the site where a subset of the cell's membrane proteins is enriched. However, pathways that target and concentrate membrane proteins in cilia are not well understood. Processes determining the level of proteins in the ciliary membrane include entry into the compartment, removal, and retention by diffusion barriers such as the transition zone. Proteins that are concentrated in the ciliary membrane are also localized to other cellular sites. Thus it is critical to determine the particular role for ciliary compartmentalization in sensory reception and signaling pathways. Here we provide a brief overview of our current understanding of compartmentalization of proteins in the ciliary membrane and the dynamics of trafficking into and out of the cilium. We also discuss major unanswered questions regarding the role that defects in ciliary compartmentalization might play in disease pathogenesis. Understanding the trafficking mechanisms that underlie the role of ciliary compartmentalization in signaling might provide unique approaches for intervention in progressive ciliopathies.

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Activation of Cilia-Independent Hedgehog/GLI1 Signaling as a Novel Concept for Neuroblastoma Therapy

Cancers ◽

10.3390/cancers13081908 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1908

Author(s):

Anke Koeniger ◽

Anna Brichkina ◽

Iris Nee ◽

Lukas Dempwolff ◽

Anna Hupfer ◽

...

Keyword(s):

Hedgehog Signaling ◽

Primary Cilia ◽

Survival Rates ◽

Genetic Alterations ◽

Novel Therapy ◽

Therapeutic Concept ◽

Pathway Activation ◽

Starting Point ◽

Novel Concept ◽

Neural Crest Differentiation

Although being rare in absolute numbers, neuroblastoma (NB) represents the most frequent solid tumor in infants and young children. Therapy options and prognosis are comparably good for NB patients except for the high risk stage 4 class. Particularly in adolescent patients with certain genetic alterations, 5-year survival rates can drop below 30%, necessitating the development of novel therapy approaches. The developmentally important Hedgehog (Hh) pathway is involved in neural crest differentiation, the cell type being causal in the etiology of NB. However, and in contrast to its function in some other cancer types, Hedgehog signaling and its transcription factor GLI1 exert tumor-suppressive functions in NB, rendering GLI1 an interesting new candidate for anti-NB therapy. Unfortunately, the therapeutic concept of pharmacological Hh/GLI1 pathway activation is difficult to implement as NB cells have lost primary cilia, essential organelles for Hh perception and activation. In order to bypass this bottleneck, we have identified a GLI1-activating small molecule which stimulates endogenous GLI1 production without the need for upstream Hh pathway elements such as Smoothened or primary cilia. This isoxazole compound potently abrogates NB cell proliferation and might serve as a starting point for the development of a novel class of NB-suppressive molecules.

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