Thyrotropin subunit beta (TSHB) is the hormone-specific cystine-knot beta chain of thyroid-stimulating hormone (thyrotropin, TSH), synthesized and secreted by thyrotroph cells of the anterior pituitary gland. In the endoplasmic reticulum, TSHB non-covalently heterodimerizes with the common glycoprotein hormone alpha subunit (CGA) via a disulfide-stabilized seatbelt loop to assemble biologically active TSH. Following secretion into the circulation, heterodimeric TSH binds the extracellular leucine-rich-repeat domain of the thyroid-stimulating hormone receptor (TSHR) on the basolateral plasma membrane of thyroid follicular cells, activating Gs- and Gq/11-coupled signaling cascades that drive thyroid follicular growth and thyroid hormone (T3/T4) synthesis and secretion.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005179 hormone activity | IBA GO_REF:0000033 | ACCEPT | Summary: Core molecular function of TSHB as the receptor-specificity-determining beta subunit of heterodimeric thyroid-stimulating hormone (TSH). Reason: PAINT node PTN000162063 (Bilateria root of PANTHER:PTHR11515) appropriately propagates GO:0005179 (hormone activity) across glycoprotein hormone beta subunits. Paired with CGA, TSHB forms secreted heterodimeric TSH, which acts as an endocrine hormone agonist of TSHR on thyrocytes. Supporting Evidence: PMID:36001021 TSH is a member of the glycoprotein hormone family, which includes luteinising hormone, follicle-stimulating hormone, and human chorionic gonadotropin. All are heterodimers of a common Ξ± subunit and subtype-specific Ξ² subunit, which determines the biologic specificity. |
| GO:0005179 hormone activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the glycoprotein hormone beta chain domain (IPR001545 / IPR018245) accurately captures the core hormone activity of TSHB. Reason: Consistent with experimental and phylogenetic evidence that TSHB is the beta subunit of the pituitary glycoprotein hormone thyrotropin (TSH). Supporting Evidence: PMID:36001021 TSH is a member of the glycoprotein hormone family, which includes luteinising hormone, follicle-stimulating hormone, and human chorionic gonadotropin. All are heterodimers of a common Ξ± subunit and subtype-specific Ξ² subunit, which determines the biologic specificity. |
| GO:0005179 hormone activity | TAS PMID:2792087 Thyroid-stimulating hormone (TSH) deficiency caused by a sin... | ACCEPT | Summary: Core molecular function supported by genetic and biochemical characterization of human TSHB as the beta subunit of thyroid-stimulating hormone. Reason: PMID:2792087 demonstrates that intact human TSHB is required to assemble with the alpha subunit into functional thyroid-stimulating hormone in pituitary thyrotrophs. Supporting Evidence: PMID:2792087 Thyroid-stimulating hormone (TSH) deficiency caused by a single base substitution in the CAGYC region of the beta-subunit. |
| GO:0005576 extracellular region | IBA GO_REF:0000033 | ACCEPT | Summary: TSHB is secreted as part of the TSH heterodimer into the extracellular space and systemic circulation. Reason: PAINT node PTN000162063 accurately propagates extracellular region localization across glycoprotein hormone beta chains. Supporting Evidence: PMID:36001021 TSH is a member of the glycoprotein hormone family, which includes luteinising hormone, follicle-stimulating hormone, and human chorionic gonadotropin. All are heterodimers of a common Ξ± subunit and subtype-specific Ξ² subunit, which determines the biologic specificity. |
| GO:0005576 extracellular region | IEA GO_REF:0000120 | ACCEPT | Summary: Automated subcellular localization and InterPro mapping correctly place secreted TSHB in the extracellular region. Reason: TSHB contains a 20-residue N-terminal signal peptide and is secreted from anterior pituitary thyrotrophs as a dimer with CGA. Supporting Evidence: Reactome:R-HSA-378952 Thyroid-stimulating hormone (TSH, thyrotropin) is a glycopeptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland. Like other glycoprotein hormones, TSH consists of a common alpha subunit and a beta subunit unique to TSH which determines its specificty. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-378952 | ACCEPT | Summary: Reactome assertion of extracellular heterodimeric thyrotropin (CGA:TSHB) localization is accurate. Reason: Heterodimeric TSH is secreted into the extracellular space to act on thyroid follicular cells. Supporting Evidence: Reactome:R-HSA-378952 Thyroid-stimulating hormone (TSH, thyrotropin) is a glycopeptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland. Like other glycoprotein hormones, TSH consists of a common alpha subunit and a beta subunit unique to TSH which determines its specificty. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-379044 | ACCEPT | Summary: Reactome GPCR signaling reaction correctly places the extracellular TSH ligand in the extracellular region. Reason: TSHB engages the extracellular domain of TSHR from the extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-391375 | ACCEPT | Summary: Reactome reaction for TSHR binding TSH correctly places TSHB in the extracellular region. Reason: Heterodimeric TSH binds the extracellular leucine-rich-repeat domain of TSHR at the surface of thyroid follicular cells. Supporting Evidence: Reactome:R-HSA-391375 Thyroid-stimulating hormone (TSH, thyrotropin) binds thyrotropin receptor (TSHR) on the basolateral membrane of thyroid cells (Nagayama Y et al., 1989). |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-744886 | ACCEPT | Summary: Reactome GPCR complex dissociation step correctly places the TSHB subunit in the extracellular region. Reason: TSHB remains bound to the extracellular face of TSHR during intracellular Gs dissociation. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-744887 | ACCEPT | Summary: Reactome GPCR-Gs binding step correctly places TSHB in the extracellular region. Reason: TSHB is an extracellular hormone subunit. |
| GO:0007154 cell communication | IEA GO_REF:0000117 | MODIFY | Summary: True but overly general biological process term; refine to thyroid-stimulating hormone signaling pathway (GO:0038194). Reason: GO:0007154 (cell communication) is a high-level ancestor of GO:0038194 (thyroid-stimulating hormone signaling pathway). TSHB specifically mediates pituitary-to-thyroid endocrine signaling by activating TSHR to initiate the thyroid-stimulating hormone signaling pathway. Proposed replacements: thyroid-stimulating hormone signaling pathway Supporting Evidence: PMID:36001021 TSH is a member of the glycoprotein hormone family, which includes luteinising hormone, follicle-stimulating hormone, and human chorionic gonadotropin. All are heterodimers of a common Ξ± subunit and subtype-specific Ξ² subunit, which determines the biologic specificity. |
| GO:0007186 G protein-coupled receptor signaling pathway | IBA GO_REF:0000033 | MODIFY | Summary: Valid family-level GPCR signaling annotation from PTN000162063, but too general for TSHB; refine to the specific child term thyroid-stimulating hormone signaling pathway (GO:0038194). Reason: PAINT node PTN000162063 places GO:0007186 (G protein-coupled receptor signaling pathway) at the Bilateria root of PANTHER:PTHR11515 because different beta-subunit subfamilies activate distinct LGR-family GPCRs (TSHR, FSHR, LHCGR). For human TSHB (PANTHER:PTHR11515:SF5), the precise descendant biological process is GO:0038194 (thyroid-stimulating hormone signaling pathway). Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000162063 Β· GLYCOPROTEIN HORMONES BETA CHAIN Bilateria clade SUPPORTS TRANSFER PAINT node PTN000162063 places generic GO:0007186 at the bilaterian glycoprotein hormone beta root rather than placing GO:0038194 on the TSHB subfamily clade (PANTHER:PTHR11515:SF5). Proposed replacements: thyroid-stimulating hormone signaling pathway Supporting Evidence: PMID:36001021 TSH is a member of the glycoprotein hormone family, which includes luteinising hormone, follicle-stimulating hormone, and human chorionic gonadotropin. All are heterodimers of a common Ξ± subunit and subtype-specific Ξ² subunit, which determines the biologic specificity. |
| GO:0007186 G protein-coupled receptor signaling pathway | TAS PMID:2792087 Thyroid-stimulating hormone (TSH) deficiency caused by a sin... | MODIFY | Summary: Correctly identifies TSHB participation in GPCR signaling, but should be refined to the specific child pathway GO:0038194 (thyroid-stimulating hormone signaling pathway). Reason: TSHB specifically pairs with CGA to activate the G protein-coupled thyrotropin receptor (TSHR), initiating the thyroid-stimulating hormone signaling pathway (GO:0038194, an is_a descendant of GO:0007186). Proposed replacements: thyroid-stimulating hormone signaling pathway Supporting Evidence: PMID:36001021 TSH is a member of the glycoprotein hormone family, which includes luteinising hormone, follicle-stimulating hormone, and human chorionic gonadotropin. All are heterodimers of a common Ξ± subunit and subtype-specific Ξ² subunit, which determines the biologic specificity. |
| GO:0007267 cell-cell signaling | TAS PMID:2792087 Thyroid-stimulating hormone (TSH) deficiency caused by a sin... | MODIFY | Summary: Overly general signaling process term; refine to thyroid-stimulating hormone signaling pathway (GO:0038194). Reason: Intercellular endocrine signaling by TSHB is more precisely captured by GO:0038194 (thyroid-stimulating hormone signaling pathway). Proposed replacements: thyroid-stimulating hormone signaling pathway Supporting Evidence: PMID:36001021 TSH is a member of the glycoprotein hormone family, which includes luteinising hormone, follicle-stimulating hormone, and human chorionic gonadotropin. All are heterodimers of a common Ξ± subunit and subtype-specific Ξ² subunit, which determines the biologic specificity. |
| GO:0009653 anatomical structure morphogenesis | TAS PMID:2792087 Thyroid-stimulating hormone (TSH) deficiency caused by a sin... | MARK AS OVER ANNOTATED | Summary: Over-annotation derived from the congenital hypothyroidism (growth/developmental retardation) phenotype of TSHB deficiency in PMID:2792087. Reason: PMID:2792087 reports a homozygous G29R substitution in the CAGYC motif of TSHB causing inherited isolated TSH deficiency and severe growth/mental retardation secondary to lack of thyroid hormone. Developmental morphogenesis defects in hypothyroidism are a downstream systemic consequence of thyroid hormone (T3/T4) deficiency rather than a direct morphogenetic role of TSHB. Supporting Evidence: PMID:2792087 Thyroid-stimulating hormone (TSH) deficiency caused by a single base substitution in the CAGYC region of the beta-subunit. |
| GO:0023052 signaling | IEA GO_REF:0000117 | MODIFY | Summary: Root-level signaling term; refine to thyroid-stimulating hormone signaling pathway (GO:0038194). Reason: GO:0023052 (signaling) is an uninformative high-level ancestor of GO:0038194 (thyroid-stimulating hormone signaling pathway). Proposed replacements: thyroid-stimulating hormone signaling pathway Supporting Evidence: PMID:36001021 TSH is a member of the glycoprotein hormone family, which includes luteinising hormone, follicle-stimulating hormone, and human chorionic gonadotropin. All are heterodimers of a common Ξ± subunit and subtype-specific Ξ² subunit, which determines the biologic specificity. |
| GO:0038194 thyroid-stimulating hormone signaling pathway | IC PMID:36001021 Novel TSHB variant (c.217A>C) causing severe central hypothy... | NEW | Summary: TSHB is the hormone-specific beta subunit of thyroid-stimulating hormone (TSH) that binds and activates TSHR on thyrocytes to initiate the thyroid-stimulating hormone signaling pathway. Reason: In GOA, GO:0038194 (thyroid-stimulating hormone signaling pathway) was annotated only to the receptor TSHR and downstream scaffold PDE4DIP, omitting the TSH hormone subunits TSHB and CGA (Category A gap in the Ligands in Signaling Pathways audit). Genetic and biochemical evidence (PMID:36001021; Reactome:R-HSA-391375) establishes that heterodimeric TSH (TSHB:CGA) directly binds TSHR on thyrocytes to trigger Gs- and Gq-mediated signaling. Supporting Evidence: PMID:36001021 TSH is a member of the glycoprotein hormone family, which includes luteinising hormone, follicle-stimulating hormone, and human chorionic gonadotropin. All are heterodimers of a common Ξ± subunit and subtype-specific Ξ² subunit, which determines the biologic specificity. Reactome:R-HSA-391375 Thyroid-stimulating hormone (TSH, thyrotropin) binds thyrotropin receptor (TSHR) on the basolateral membrane of thyroid cells (Nagayama Y et al., 1989). |
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Download this section (compressed HTML)Q: How does tissue-specific sulfation versus sialylation of the N-linked oligosaccharide on Asn-43 of human TSHB alter its circulatory half-life and intrinsic efficacy at TSHR in euthyroid versus hypothyroid states?
Experiment: Compare Gs (cAMP) and Gq/11 (IP1/Ca2+) concentration-response curves of recombinant human TSH glycoforms with defined terminal GalNAc-4-sulfate versus alpha-2,6-sialic acid on TSHB Asn-43 using BRET biosensors in primary human thyrocytes.
Hypothesis: Variations in TSHB N-glycan terminal sulfation/sialylation bias TSHR signaling between Gs-cAMP and Gq-PLC pathways in addition to regulating hepatic clearance.
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