Increased USP8 deubiquitinase activity
trigger
Activating USP8 mutations disrupt normal 14-3-3-dependent control and increase USP8 proteolytic cleavage and catalytic deubiquitinase activity.
Downstream
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Sustained EGFR signaling in corticotrophs
Increased USP8 activity deubiquitinates EGFR, impairing receptor downregulation.
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"The mutations clustered in the 14-3-3 protein binding motif and enhanced the proteolytic cleavage and catalytic activity of USP8."
This directly supports increased USP8 catalytic activity as the proximal molecular effect of the hotspot mutations.
Sustained EGFR signaling in corticotrophs
central effector
Increased USP8-dependent EGFR deubiquitination impairs EGFR downregulation, sustaining EGFR signaling in corticotroph pituitary adenoma cells.
Downstream
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Increased POMC transcriptional activation
Sustained EGFR signaling increases transcriptional activation of POMC.
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"Cleavage of USP8 led to increased deubiqutination of the EGF receptor, impairing its downregulation and sustaining EGF signaling."
This directly supports sustained EGFR signaling downstream of USP8 activation.
Increased POMC transcriptional activation
effector
USP8-mutant corticotroph adenoma cells show increased promoter activity of POMC, the precursor gene for ACTH.
Downstream
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Increased corticotropin secretion
Increased POMC transcriptional activation supports excess ACTH production and secretion.
Show evidence (1 reference)
"USP8 mutants enhanced promoter activity of the gene encoding proopiomelanocortin."
This directly links USP8 mutations to increased POMC promoter activity.
Increased corticotropin secretion
consequence
Corticotroph tumor cells secrete excess ACTH downstream of the USP8-EGFR-POMC axis, producing pituitary ACTH hypersecretion and Cushing disease physiology.
Show evidence (1 reference)
"Cushing's disease is caused by corticotroph adenomas of the pituitary."
This anchors the module outcome to corticotroph adenomas that cause Cushing disease.