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A GUIDED LEARNING PATH · 12 MIN

How can one insulin signal lead to different cell responses?

Follow the receptor into two interacting signaling branches. Then compare muscle, fat, and liver to see why the same hormone does not produce one identical response everywhere.

  1. A hormone meets its receptor

    After a meal, pancreatic beta cells release insulin into the blood. Insulin binds the insulin on a target cell. The is a tyrosine kinase: binding changes its activity and triggers events on the and nearby signaling proteins. The is the sensor; it is not a .

    SourcesInsulin receptor signalling cascade (R-HSA-74751)Reactome · reviewed human pathwayBiochemical and cellular properties of insulin receptor signallingBoucher, Kleinridders & Kahn · Nature Reviews Molecular Cell Biology · 2018

  2. Adaptor proteins pass the message inward

    Activated insulin receptors phosphorylate insulin substrate (IRS) proteins. IRS proteins act mainly as signaling platforms: their phosphorylated sites recruit other proteins, including class IA PI3K. This is a branching handoff, not a single marching down a chain. Other -associated adaptors, including SHC, can route signal toward RAS and MAP kinases.

    SourcesInsulin receptor signalling cascade (R-HSA-74751)Reactome · reviewed human pathwayBiochemical and cellular properties of insulin receptor signallingBoucher, Kleinridders & Kahn · Nature Reviews Molecular Cell Biology · 2018

  3. PI3K builds a membrane signal for AKT

    When recruited and activated, PI3K can convert the membrane lipid PIP2 into PIP3. PIP3 helps recruit AKT and PDPK1 to the membrane. PDPK1 phosphorylates AKT at one site, while mTORC2 can phosphorylate a second site. Other phosphatases and proteins tune this process, so PIP3 is not a magic on-switch and AKT activity is regulated at several levels.

    SourcesBiochemical and cellular properties of insulin receptor signallingBoucher, Kleinridders & Kahn · Nature Reviews Molecular Cell Biology · 2018Insulin action at a molecular level – 100 years of progressKahn et al. · Molecular Metabolism · 2021
    FOLLOW THE BRANCHES

    One receptor, several possible outputs

    The drawing is a selected human teaching model. It names key handoffs, then separates two branches that share receptor inputs and can influence one another.

    Insulinbinds at the cell surfaceInsulin ReceptorReceptor phosphorylation creates docking sites for signaling adaptors.
    BRANCH B · MAP KINASE SIGNALING

    SHC–GRB2–SOS–RAS–RAF–MEK–ERK

    1. SHC / GRB2 / SOS
    2. SOS promotes GTP loading onRAS-GTP (KRAS example)
    3. can recruitBRAF / RAF
    4. phosphorylatesMEK1
    5. acts onERK2
    6. regulatesCellular targets

    ERK can influence cytoplasmic and nuclear targets. Gene-expression and growth outcomes depend on cell state, signal duration, and other receptors and pathways.

    SAME HORMONE, DIFFERENT CELL CONTEXT

    Where is the signal arriving?

    SKELETAL MUSCLE

    Glucose uptake and local glycogen

    Insulin can increase GLUT4 at the cell surface and support glucose uptake. Muscle can use glucose for energy or store some as glycogen for its own work.

    GLUT4 trafficking · glucose uptake · local glycogen
    SourcesReactome · reviewed human pathwayNCBI Bookshelf · StatPearls · updated 2026

    This map shows selected, well-studied human signaling relationships. It is not a quantitative model, a complete pathway inventory, or a prediction for a particular person or cell sample.

  4. In muscle and fat, insulin can move GLUT4

    In skeletal muscle and adipose cells, AKT-linked signaling can regulate TBC1D4 (also called AS160) and the trafficking of -containing vesicles. AKT2 has a prominent role in insulin-stimulated transport, alongside context-dependent contributions from other AKT isoforms. More at the plasma membrane can increase the cell's capacity to take up . Muscle contraction also uses partly distinct signals, so the cell integrates more than one input.

    SourcesTranslocation of SLC2A4 (GLUT4) to the plasma membrane (R-HSA-1445148)Reactome · reviewed human pathwayRoles of TBC1D1 and TBC1D4 in insulin- and exercise-stimulated glucose transportCartee · Diabetologia · 2015Biochemical and cellular properties of insulin receptor signallingBoucher, Kleinridders & Kahn · Nature Reviews Molecular Cell Biology · 2018Biochemistry, Insulin Metabolic EffectsNCBI Bookshelf · StatPearls · updated 2026

  5. The liver uses a different glucose-entry setup

    Do not copy the muscle diagram onto a liver cell. Hepatocytes use GLUT2 for bidirectional transport; this is not recruited to the surface by insulin in the manner. Insulin still changes liver metabolism: AKT regulation of FOXO1 can alter -production gene expression, and AKT inhibition of GSK3B can remove one brake on glycogen synthase. These are parts of broader networks with both fast and slower controls.

    SourcesBiochemistry, Insulin Metabolic EffectsNCBI Bookshelf · StatPearls · updated 2026Regulation of hepatic glucose metabolism in health and diseaseRines et al. · Nature Reviews Endocrinology · 2016Insulin action at a molecular level – 100 years of progressKahn et al. · Molecular Metabolism · 2021

  6. Growth signaling also listens to nutrients

    AKT can inhibit the TSC1–TSC2 complex, changing control of RHEB and mTORC1. mTORC1 can regulate translation through targets such as S6K1 and 4E-BP1, but it also integrates amino-acid, energy, oxygen, and other growth-factor inputs. Calling it simply the final step of insulin signaling hides those other controls and the distinct roles of mTORC1 and mTORC2.

    SourcesInsulin action at a molecular level – 100 years of progressKahn et al. · Molecular Metabolism · 2021Biochemical and cellular properties of insulin receptor signallingBoucher, Kleinridders & Kahn · Nature Reviews Molecular Cell Biology · 2018

  7. A second branch and feedback reshape the response

    Insulin -associated adaptors can also engage the RAS–RAF–MEK–ERK mitogen-activated protein kinase (MAPK) branch, which changes of cytoplasmic and nuclear targets. Its effects on gene expression or growth depend on cell state, signal timing, and other inputs. Feedback matters too: for example, mTORC1–S6K signaling can phosphorylate IRS proteins and dampen upstream signaling. These routes interact, and their strength is not fixed across tissues.

    SourcesInsulin receptor signalling cascade (R-HSA-74751)Reactome · reviewed human pathwayMechanisms of Insulin Action and Insulin ResistancePetersen & Shulman · Physiological Reviews · 2018Insulin action at a molecular level – 100 years of progressKahn et al. · Molecular Metabolism · 2021
PAUSE AND CHECK

Can you follow the branch and its context?

CHECK YOUR UNDERSTANDING

Which comparison best describes insulin and GLUT4 across tissues?

Choose one answer
CHECK YOUR UNDERSTANDING

What is one role of PI3K-generated PIP3 in insulin signaling?

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CHECK YOUR UNDERSTANDING

Why is mTORC1 not just the final step of an insulin-only pathway?

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CHECK YOUR UNDERSTANDING

Which statement best describes insulin-linked PI3K–AKT and RAS–MAPK signaling?

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INSPECT THE SOURCES

References behind this path

Reactome provides reviewed human pathway records. The reviews summarize signaling mechanisms and tissue-specific physiology; they are secondary sources, so each statement here is scoped to the described mechanism rather than presented as a universal rule.