This is a mechanism module, not a specific disease. Disorder entries reference individual nodes via conforms_to (e.g., "hedgehog_pathway_activation#Constitutive Smoothened Activity"). Key conformance / treatment target: "Constitutive Smoothened Activity" - the node bound by the approved SMO antagonists. The "Constitutive GLI Transcriptional Output" node is the SMO-independent convergence point: SUFU loss and GLI2 amplification activate the pathway downstream of SMO, which is why SUFU-driven disease and acquired SMO-inhibitor resistance bypass the drug target. Worked conformers: Basal_Cell_Carcinoma (PTCH1 loss / SMO gain-of-function), Gorlin_Syndrome and its PTCH1-related / SUFU-related NBCCS entries, and Medulloblastoma_SHH_Activated. GENE-LEVEL DIRECTION: annotate tumor-suppressor lesions (PTCH1/PTCH2/SUFU) as LOSS_OF_FUNCTION and SMO lesions as GAIN_OF_FUNCTION on the conforming disorder node's genetic_context.functional_impact_category; the PATHWAY-LEVEL direction is activation in every case.
Loss of Hedgehog Pathway Negative Regulation
trigger
In the resting state, the transmembrane receptor PTCH1 (and its paralog PTCH2) tonically suppresses Smoothened (SMO), and SUFU sequesters GLI transcription factors in the cytoplasm. Constitutive Hedgehog activation begins when this restraint is removed by one of two mechanistically opposite but convergent lesions: loss-of-function of a negative regulator (biallelic/Knudson two-hit inactivation of the tumor suppressors PTCH1, PTCH2, or SUFU) OR gain-of-function of the positive transducer SMO (activating mutation). Conforming disorder nodes substitute the tumor-type-specific driver and record the gene-level direction (functional_impact_category = LOSS_OF_FUNCTION for PTCH1/PTCH2/SUFU, GAIN_OF_FUNCTION for SMO); either way the net pathway-level consequence is activation.
Downstream
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Constitutive Smoothened Activity
Loss of PTCH-mediated inhibition (or an activating SMO mutation) releases Smoothened into a constitutively active state at the primary cilium. The SUFU-loss branch bypasses this node and activates GLI directly downstream.
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Constitutive GLI Transcriptional Output
SUFU loss acts downstream of SMO, directly derepressing GLI and activating the pathway independently of Smoothened.
Show evidence (1 reference)
"Approximately, 85% of sporadic BCCs carry mutations in Hedgehog pathway genes, especially in PTCH, SUFU and SMO genes, which lead to the aberrant activation of GLI transcriptional factors, typically silent in cells of adult individuals."
Establishes that PTCH, SUFU, and SMO lesions are the recurrent upstream events that release Hedgehog pathway restraint and drive aberrant GLI activation across Hedgehog-driven tumors. Evidence source is OTHER because this is a review article.
Constitutive Smoothened Activity
central effector
Freed from PTCH restraint (or rendered constitutively active by mutation), SMO accumulates in the primary ciliary membrane and transduces Hedgehog signal ligand-independently. This SMO-active state is the direct molecular target of the approved Hedgehog-pathway inhibitors vismodegib and sonidegib, which bind SMO and restore its inhibited conformation. Lesions acting downstream of SMO (SUFU loss, GLI2 amplification) leave this node bypassed and predict limited SMO-inhibitor efficacy.
Downstream
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Constitutive GLI Transcriptional Output
Constitutively active SMO drives nuclear accumulation of GLI1/GLI2 and loss of the GLI3 repressor, activating Hedgehog target transcription.
Show evidence (1 reference)
"Dysregulated hedgehog signaling is the pivotal molecular abnormality underlying basal-cell carcinomas. Vismodegib is a new orally administered hedgehog-pathway inhibitor that produces objective responses in locally advanced and metastatic basal-cell carcinomas."
Identifies dysregulated Hedgehog signaling (acting at SMO) as the pivotal molecular abnormality and establishes SMO as the druggable point of intervention targeted by vismodegib.
Constitutive GLI Transcriptional Output
effector
Both PTCH loss (via SMO derepression) and SUFU loss (via direct release of GLI sequestration), as well as GLI2 amplification, converge on constitutive nuclear GLI1/GLI2 activity. GLI transcriptionally activates pro-proliferative and pro-survival targets (CCND1, MYCN, BCL2) and drives a positive-feedback loop by inducing PTCH1 and GLI1. Because this node sits below the SMO drug target, it is the SMO-independent convergence point that underlies both SUFU-driven disease and acquired resistance to SMO inhibitors, motivating direct GLI-directed strategies.
Downstream
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Hedgehog-Driven Proliferation and Tumorigenesis
GLI target-gene transcription drives cell-cycle entry and sustained proliferation of the Hedgehog-responsive cell of origin.
Show evidence (2 references)
"SHH tumors contain mutations and alterations in GLI1, GLI2, SUFU, and PTCH1 genes, which constitutively activate the SHH pathway."
Confirms that GLI1/GLI2/SUFU/PTCH1 lesions converge on constitutive GLI transcriptional activation as the shared molecular endpoint of Hedgehog pathway activation.
"Resistance to SMO inhibitors is caused by acquired SMO mutations, SUFU deletions, GLI2 amplification, other by-passing mechanisms of GLI activation and WNT/β-catenin signaling activation."
Documents the downstream-of-SMO bypass mechanisms (SUFU deletion, GLI2 amplification) that sustain constitutive GLI output despite SMO blockade, supporting this node as the SMO-independent convergence point. Evidence source is OTHER because this is a review article.
Hedgehog-Driven Proliferation and Tumorigenesis
consequence
Constitutive GLI activity reactivates a developmental Hedgehog proliferative program in the tissue's Hedgehog-responsive progenitor (e.g., epidermal basal cells in basal cell carcinoma, cerebellar granule neuron precursors in SHH-activated medulloblastoma), producing unchecked proliferation and tumor formation. Conforming disorder nodes substitute the tumor-type-specific cell of origin.
Show evidence (1 reference)
"Treatment of GCPs with Shh prevents differentiation and induces a potent, long-lasting proliferative response."
Foundational evidence that Hedgehog signaling drives a potent proliferative response in a Hedgehog-responsive progenitor, the developmental program hijacked by constitutive pathway activation in Hedgehog-driven tumors. Evidence source is MODEL_ORGANISM (mouse cerebellar granule cell precursors).