Nonreceptor Tyrosine Kinases

Slide 1 · Nonreceptor Tyrosine Kinases

Oncogenic activation, BCR::ABL, JAK2, and clinicopathologic consequences

Molecular basis of neoplasia

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Distinguish nonreceptor kinases from receptor tyrosine kinases and explain their normal signaling role.

Trace how BCR::ABL fusion and JAK2 point mutations produce persistent mitogenic signaling.

Relate kinase lesions to CML, Philadelphia-positive ALL, and JAK2-associated myeloproliferative neoplasms.

Explain molecular diagnosis, targeted inhibition, and the persistence of residual disease.

Slide 3 · A cellular growth signal must be transmitted

Growth factor or cytokine

Receptor activation

Intracellular kinase relay

Altered gene expression

Normal signaling is temporally controlled by upstream ligand availability.

Cancer-associated kinase lesions uncouple signaling from that restraint.

The location of the kinase does not determine whether it can drive growth.

Slide 4 · Receptor and nonreceptor tyrosine kinases

Receptor tyrosine kinase

Nonreceptor tyrosine kinase

Contains a membrane-spanning receptor component.

Extracellular ligand binding normally initiates activation.

Mutations may constitutively activate receptor signaling.

Typically operates in cytoplasm or nucleus.

Associates with upstream receptors or signaling complexes.

Fusions or point mutations can create persistent activity.

Both kinase classes can activate overlapping progrowth signaling routes.

Slide 5 · Normal intracellular signaling is conditional

Extracellular cue

Receptor-linked signal

Kinase activation

STAT / other effectors

Gene response

Protein phosphorylation relays growth information across compartments.

Removal of the initiating signal helps terminate the response.

Slide 6 · On–off control versus kinase autonomy

Physiologic control

Oncogenic kinase activity

Kinase activity is limited by receptor and regulatory inputs.

Progrowth gene programs respond to cellular context.

Signal amplitude and duration are restricted.

A genetic alteration permits activation without normal input.

Downstream pathways remain persistently engaged.

Proliferation and survival become abnormally favored.

Slide 7 · Two mechanisms of autonomous kinase activation

Nonreceptor tyrosine kinase oncogene

Chromosomal rearrangement

Fusion partner drives self-association; Prototype BCR::ABL.

Activating point mutation

Negative autoregulatory restraint is lost; Prototype JAK2.

Distinct DNA lesions converge on excessive kinase signaling.

Slide 8 · Why a kinase fusion is more than a translocation

The driver lesion is the new fusion gene—not merely the visual chromosome rearrangement.

The chimeric protein retains an enzymatically active tyrosine kinase component.

A nonkinase fusion partner can promote constitutive self-association.

Sustained kinase activity activates growth and survival signaling without normal regulation.

Slide 9 · Where nonreceptor kinases act

They usually do not contain the extracellular ligand-binding structure of receptor tyrosine kinases.

Nonreceptor kinases may localize to cytoplasm or nucleus.

They integrate signals from surface receptors and intracellular protein complexes.

Their oncogenic effects can converge on transcriptional programs promoting proliferation.

Slide 10 · Persistent phosphorylation reaches the nucleus

Constitutively active kinase

Substrate phosphorylation

Downstream signal relay

Transcriptional response

JAK signaling engages STAT transcription factors.

BCR-ABL activates multiple progrowth and prosurvival cascades, rather than just one pathway.

Slide 11 · A fusion oncogene begins with DNA breakage

01

DNA breaks

Chromosomal breaks affect the partner loci.

02

Abnormal joining

DNA ends rejoin into derivative chromosomes.

03

Fusion gene

Coding regions become linked in a new arrangement.

04

Chimeric protein

The novel product acquires oncogenic activity.

The biologic driver is the fused protein encoded after rearrangement.

Slide 12 · Two consequences of oncogenic translocation

Fusion protein: BCR::ABL

Deregulated expression: MYC example

Parts of two coding sequences combine.

A novel chimeric kinase is synthesized.

Constitutive enzymatic activity is the driver.

Regulatory DNA changes raise MYC expression.

The principal consequence is oncogene overexpression.

The coding product need not be a chimeric kinase.

A chromosomal translocation does not always create the same type of oncogene.

Slide 13 · BCR and ABL arise on different chromosomes

Chromosome 9

Chromosome 22

ABL

BCR

BCR resides on chromosome 22; ABL resides on chromosome 9.

Slide 14 · The t(9;22) translocation generates BCR::ABL

Chromosome 9: ABL

Chromosome 22: BCR

Reciprocal exchange at t(9;22)(q34;q11)

Derivative chromosome 22: BCR::ABL

The oncogenic BCR::ABL fusion resides on derivative chromosome 22.

Slide 15 · The Philadelphia chromosome: Interpret carefully

The Philadelphia chromosome is the derivative chromosome 22 resulting from t(9;22).

BCR::ABL encodes the critical chimeric tyrosine kinase; The karyotypic finding is a way to recognize the lesion.

A cryptic or complex rearrangement may create BCR::ABL without a conventional visible Philadelphia chromosome.

Therefore molecular evidence of the fusion can be more informative than conventional karyotype alone.

Slide 16 · BCR::ABL joins self-association and catalytic activity

Fusion polypeptide

BCR-derived region

Self-association

ABL-derived region

Tyrosine kinase activity

Dimerization / oligomerization → constitutive kinase signaling

Slide 17 · BCR-driven self-association releases ABL activity

Isolated fusion molecules

Self-associated fusion molecules

BCR

ABL

BCR

ABL

BCR

ABL

BCR

ABL

Active signaling

BCR-mediated association drives activation of the ABL kinase domain.

Slide 18 · The contribution of the BCR moiety

BCR provides a self-association function within the chimeric protein.

Association of BCR-ABL molecules promotes constitutive activity of the ABL kinase component.

The oncogenic effect is not simply an increased amount of otherwise normally regulated ABL.

Similar partner-driven association mechanisms recur among other oncogenic kinase fusions.

Slide 19 · The contribution of the ABL moiety

ABL supplies the tyrosine kinase enzymatic activity of the fusion oncoprotein.

Constitutive activation removes the need for normal upstream triggering.

The fusion can engage pathways otherwise stimulated by growth factor receptors.

Inhibiting this kinase activity attacks the causal driver of CML proliferation.

Slide 20 · From fusion protein to growth advantage

BCR::ABL expression

Constitutive ABL activity

Pro-growth signaling

Proliferation and survival

The fusion can initiate the disease, but later acquired lesions may alter the course.

Persistent signaling supports excessive growth without requiring the normal stimulus.

Slide 21 · BCR-ABL signals through multiple pathways

BCR-ABL tyrosine kinase

RAS-associated signaling

Downstream progrowth programs support proliferative responses.

JAK / STAT signaling

Transcriptional responses promote growth and survival.

BCR-ABL is an upstream oncogenic node, not a single terminal pathway.

Slide 22 · Growth factor dependence in normal and CML cells

Normal myeloid progenitor

BCR-ABL-positive progenitor

Receives regulated hematopoietic growth signals.

Growth and survival depend on these extracellular cues.

Lineage maturation proceeds within controlled hematopoiesis.

Exhibits kinase signaling without normal ligand dependence.

Proliferation and survival are constitutively favored.

Maturation can continue, generating abundant mature cells.

Slide 23 · CML: Initiation precedes clonal evolution

01

Initiating lesion

BCR::ABL forms in a hematopoietic stem cell.

02

Clonal expansion

The kinase drives progenitor proliferation.

03

Additional lesions

Selected mutations can complement the original driver.

04

Progression

Some clones acquire aggressive properties / blast crisis.

A founding oncogene is not necessarily the only mutation in advanced cancer.

Slide 24 · CML originates in a multipotent stem cell

BCR::ABL-positive multipotent HSC

Myeloid progenitors

Lymphoid potential

Chronic-phase mature myeloid expansion

Lymphoid blast crisis can occur

Slide 25 · Why mature granulocytes predominate in CML

BCR-ABL mitogenic signal

Granulocytic precursor expansion

Differentiation largely preserved

Maturing cells accumulate

Increased proliferation need not imply a complete differentiation block.

Slide 26 · Characteristic CML blood and marrow phenotype

Marked marrow hypercellularity with expansion of maturing granulocytic precursors.

Peripheral blood shows leukocytosis spanning neutrophils and immature granulocytic stages.

Basophils and eosinophils may be increased; Platelets are often elevated.

Splenomegaly reflects prominent extramedullary hematopoiesis.

Slide 27 · CML marrow: Which lineages expand?

Predominant expansion

Other changes

Granulocytic precursors at several maturation stages.

Basophil and eosinophil components are often increased.

Megakaryocytes may be numerous, including small forms.

Erythroid precursors are normal or mildly reduced.

Reticulin deposition can be increased.

Sea-blue histiocytes may be observed in marrow.

Slide 28 · CML peripheral blood: A maturation spectrum

01

Myelocytes

Immature circulating granulocytic precursors.

02

Metamyelocytes

Further maturation is visible.

03

Band forms

Still maturing neutrophils.

04

Segmented forms

Mature neutrophils coexist with precursors.

The hallmark is a broad granulocytic maturation spectrum, not uniform blasts.

Slide 29 · CML megakaryocytes, platelets and fibrosis

Megakaryocytes are typically increased; Small atypical forms may be present.

Thrombocytosis can accompany the prominent granulocytic expansion.

Reticulin increase is characteristic, yet overt fibrotic replacement is uncommon at presentation.

These findings help build a pattern but do not replace fusion-gene testing.

Slide 30 · Why the CML spleen enlarges

Marrow myeloid expansion

Extramedullary hematopoiesis

Splenic red-pulp expansion

Splenomegaly

A markedly enlarged spleen may cause abdominal fullness.

Splenic infarction can produce acute left upper-quadrant pain.

Slide 31 · Symptoms of CML follow the disease biology

High cellular turnover

Extramedullary hematopoiesis

Fatigue, weakness and constitutional symptoms.

Anemia can accompany neoplastic hematopoiesis.

Hypermetabolism contributes to weight loss.

Splenomegaly produces abdominal fullness.

A splenic infarct may produce pain.

Spleen size reflects disease burden, not molecular identity.

Slide 32 · CML identification: Morphology and molecular tests

Domain

Information supplied

Principal limitation

Blood / marrow

Suggest a myeloproliferative pattern

Cannot establish BCR::ABL identity

Karyotype

May show the Philadelphia chromosome

Cryptic rearrangements can be missed

FISH / PCR

Can detect BCR::ABL rearrangement / fusion

Assay targets and specimen adequacy matter

Slide 33 · Conventional cytogenetics in CML

A classic karyotype reveals t(9;22)(q34;q11), producing the Philadelphia chromosome.

Cytogenetic analysis depicts the chromosome-level rearrangement.

Complex or cryptic rearrangements can make the characteristic chromosome change difficult to identify.

Detection of the BCR::ABL fusion establishes the defining molecular lesion.

Slide 34 · FISH and PCR answer related but distinct questions

Fluorescence in situ hybridization

PCR-based testing

Detects characteristic proximity / rearrangement of gene loci.

Useful when karyotype fails to show an obvious translocation.

Provides cell-level localization of probe signals.

Detects fusion-derived sequences or transcripts.

Can support sensitive molecular monitoring.

A defined molecular target enables longitudinal disease assessment.

Slide 35 · A cryptic fusion may escape a visible karyotype

Clinical CML pattern

Karyotype nonclassic / cryptic

FISH or PCR for BCR::ABL

Molecular identity established

A negative visible Philadelphia chromosome does not exclude a cryptic BCR::ABL fusion.

Slide 36 · BCR::ABL in CML and Philadelphia-positive B-ALL

Chronic myeloid leukemia

B-cell acute lymphoblastic leukemia

BCR::ABL is a defining initiating lesion.

Typically produces broad myeloid precursor expansion.

The prevalent fusion protein is about 210 kDa.

A subset of B-ALL carries BCR::ABL.

Immature lymphoid blasts dominate the clinical phenotype.

The prevalent fusion protein is about 190 kDa.

Slide 37 · CML and B-ALL can share a kinase driver

Question

CML

Philadelphia-positive B-ALL

Cell phenotype

Expanded maturing myeloid cells

Immature lymphoblasts

Usual BCR-ABL product

Approximately 210 kDa

Approximately 190 kDa

Clinical model

Myeloproliferation

Acute lymphoblastic leukemia

Slide 38 · Oncogene addiction explains targeted vulnerability

Founding BCR::ABL lesion

Dependence on kinase signaling

Specific ABL inhibition

Major decrease in clone growth

The same driver can initiate disease and become a therapeutic vulnerability.

Oncogene addiction describes dependence, not universal eradication.

Slide 39 · BCR-ABL inhibition blocks the oncogenic relay

BCR-ABL kinase

Downstream signaling

ABL kinase inhibitor

Block of phosphorylation / signaling

Slide 40 · Treatment response is not equivalent to cure

Proliferating CML compartment

Persistent stemlike compartment

Strongly depends on active BCR-ABL signaling.

Usually suppressed effectively by targeted inhibitors.

Hematologic and molecular responses can be profound.

Rare fusion-positive cells may remain.

Can survive with less dependence on BCR-ABL signals.

May seed recurrence after therapy is stopped.

Slide 41 · Residual CML illustrates cellular heterogeneity

01

Large bulk clone

Kinase inhibition sharply reduces proliferating cells.

02

Residual cells

Rare BCR::ABL-positive stemlike cells remain.

03

Dormant reservoir

Some residual cells do not require the driver for survival.

04

Disease recurrence

Regrowth can follow incomplete suppression.

A sensitive target in most cancer cells may be insufficient to remove every malignant cell.

Slide 42 · Stopping a kinase inhibitor: Interpret context

Frequent relapse risk

Selected deep molecular remissions

Residual fusion-positive stemlike cells may remain.

Stopping a drug can permit recurrent disease.

A clinical remission does not prove clone extinction.

The broader Robbins CML section notes that some patients maintain remission off therapy.

This requires careful molecular selection and monitoring.

Do not generalize treatment discontinuation to all patients.

Slide 43 · Resistance can restore oncogenic signaling

Initial kinase inhibition

Selection of resistant cells

Kinase / alternative pathway lesion

Re-emergent proliferation

Later-generation inhibitors can address some resistant kinase variants.

Resistance is biologically distinct from persistence of quiescent stemlike cells.

Slide 44 · CML evolution may culminate in blast crisis

01

Chronic phase

Myeloid expansion with preserved maturation.

02

Additional lesions

Secondary clonal genetic changes accrue.

03

Accelerated disease

Increasing cytopenias or clonal evolution may emerge.

04

Blast crisis

An acute leukemia-like phenotype appears.

The initiating kinase does not fully explain late differentiation arrest.

Slide 45 · CML progression and targeted response

Original initiating oncogene

Secondary molecular evolution

BCR::ABL provides sustained mitogenic drive.

Chronic-phase cells retain differentiation.

Inhibitors interrupt a major growth dependency.

Other mutations add malignant capabilities.

Blast transformation can involve differentiation regulators.

Late lesions complicate disease control.

Slide 46 · JAK2 transmits cytokine receptor signals

Cytokine / growth factor

Receptor lacking own kinase

Associated JAK2 activation

STAT-directed gene expression

Erythropoietin receptor is a relevant hematopoietic example.

This pathway helps regulate hematopoietic cell proliferation.

Slide 47 · The JAK/STAT pathway couples signals to transcription

Activated receptor–JAK2

Tyrosine phosphorylation

STAT pathway activation

Transcriptional response

The response is mitogenic in the relevant hematopoietic setting.

Mutation of the associated kinase may short-circuit receptor dependence.

Slide 48 · JAK2 normally requires autoregulatory restraint

Intact regulatory control

Autoregulatory failure

Receptor-linked signaling engages JAK2 when appropriate.

Autoregulatory regions limit kinase activity.

Target gene activation follows controlled input.

An activating mutation disrupts inhibitory control.

Kinase activity can become excessive.

The clone becomes less dependent on ligand supply.

Slide 49 · A JAK2 point mutation can unlock kinase activity

Normal JAK2

Mutant JAK2

Autoinhibitory regulation

Kinase restrained

Loss of negative restraint

Kinase activated

A point mutation can activate a kinase without creating any fusion protein.

Slide 50 · JAK2 V617F is a canonical activating lesion

Substitution of valine by phenylalanine at residue 617 of JAK2.

This lesion disrupts normal restraint on JAK2 activity.

The associated clone shows markedly reduced dependence on hematopoietic growth factors.

The mutation is strongly associated with polycythemia vera but is not limited to that disorder.

Slide 51 · Erythropoietin-independent growth in PV

Activating JAK2 mutation

Persistent EPO-receptor–associated signal

Erythroid progenitor expansion

Increased red cell mass

The altered kinase is downstream of the erythropoietin receptor.

Low circulating erythropoietin can coexist with high erythrocyte output.

Slide 52 · Polycythemia vera involves panmyelosis

JAK2-activated marrow progenitor

Erythroid

Increased red cell mass

Myeloid

Granulocyte expansion

Megakaryocytic

Platelet expansion

PV increases multiple myeloid lineages; Erythrocytosis drives many symptoms.

Slide 53 · Why serum erythropoietin is often low in PV

JAK2-driven erythropoiesis

Increased red cell mass

Feedback suppresses EPO

Low serum EPO

This contrasts with erythropoietin-driven secondary polycythemia.

The abnormality is within hematopoietic signaling rather than a response to hypoxia.

Slide 54 · PV: Marrow expansion and clinical consequence

Marrow and blood pattern

Clinical effects

Increased erythroid, granulocytic and megakaryocytic production.

Marrow hypercellularity with residual fat can be present.

Platelets may be abnormal in number and function.

Increased hematocrit can raise blood viscosity.

Pruritus, plethoric appearance and organomegaly occur.

Thrombotic and hemorrhagic events are major hazards.

Slide 55 · PV hyperviscosity links signaling to thrombosis

Constitutive JAK2 activity

Increased red cell mass

Hyperviscosity / flow disturbance

Thrombotic risk

Vascular complications may precede an obvious hematologic diagnosis.

Bleeding may coexist because platelet function can be abnormal.

Slide 56 · Primary JAK2-driven versus secondary erythrocytosis

Feature

Polycythemia vera

Secondary erythrocytosis

Dominant driver

Clonal JAK2 activation

Elevated erythropoietin drive

Serum EPO tendency

Often suppressed

Often elevated

Marrow response

Panmyelosis

Predominantly reactive erythropoiesis

Slide 57 · JAK2 alterations span myeloproliferative neoplasms

Entity

Molecular associations

Interpretive point

Polycythemia vera

Usually activating JAK2 alterations

Strong molecular association

Essential thrombocythemia

JAK2, CALR or MPL alterations

Not all cases have JAK2 mutations

Primary myelofibrosis

JAK2, CALR or MPL alterations

Driver class alone does not define morphology

Slide 58 · A JAK2 mutation is not a complete diagnostic label

JAK2 mutations occur in more than one myeloproliferative neoplasm.

Disease assignment also requires the blood count pattern, marrow findings and clinical context.

ET and primary myelofibrosis may instead involve CALR or MPL driver alterations.

Molecular identification must be integrated with phenotype rather than interpreted in isolation.

Slide 59 · BCR::ABL and JAK2: The critical contrasts

Feature

BCR::ABL

Mutant JAK2

Molecular alteration

Fusion from chromosome rearrangement

Activating point mutation

Proximal mechanism

BCR-driven self-association

Loss of negative autoregulation

Illustrative disease

CML; Subset of B-ALL

PV; Some ET and PMF

Therapeutic concept

ABL kinase blockade

JAK pathway inhibition

Slide 60 · Two driver architectures converge on autonomy

Constitutive fusion kinase

Mutated native kinase

New DNA junction generates BCR::ABL.

Fusion partner promotes self-association.

The kinase becomes constitutively active.

CML exemplifies oncogene addiction.

JAK2 coding sequence acquires a point mutation.

Normal negative regulation is impaired.

Cytokine responsiveness becomes abnormal.

PV exemplifies growth factor independence.

Slide 61 · Case application: Marked myeloid proliferation

A patient has persistent marked leukocytosis, circulating granulocytes at multiple stages of maturation, basophilia, and splenomegaly. The marrow is highly cellular.

Which molecular lesion most directly defines the suspected neoplasm?

A. Activating JAK2 alteration

B. BCR::ABL fusion gene

C. IG::MYC translocation

Slide 62 · Case interpretation: A BCR::ABL-driven clone

Maturing myeloid expansion

CML pattern suspected

Test for BCR::ABL fusion

Molecular confirmation

CML is a disease of hematopoietic stem cells with substantial differentiation.

The fusion establishes the molecular identity; Morphology supplies context.

Slide 63 · Case application: Erythrocytosis with low EPO

A patient has increased red cell mass, thrombocytosis, low serum erythropoietin, and marrow panmyelosis. Molecular analysis identifies JAK2 V617F.

What mechanism best accounts for the erythroid expansion?

A. Constitutive signaling despite reduced EPO input

B. Increased ligand-driven erythropoietin receptor activity only

C. BCR-mediated ABL oligomerization

Slide 64 · Case interpretation: Autonomous JAK2 activity

JAK2 V617F mutation

Reduced growth factor requirement

Panmyelosis / erythrocytosis

Feedback suppression of EPO

PV must be separated from secondary EPO-driven erythrocytosis.

Low EPO supports the pathophysiologic model but phenotype and molecular results remain important.

Slide 65 · Three general lessons from nonreceptor kinases

01

Mechanism

Gene fusions or point mutations can create kinase autonomy.

02

Phenotype

Cell context shapes which hematologic neoplasm develops.

03

Therapy

Targeting the initiating kinase exploits a molecular dependence.

04

Limit

Residual cells and acquired lesions can undermine durable eradication.

Molecular cause, lineage phenotype, and treatment response must be interpreted together.

Slide 66 · Primary reading and contextual source sections

Robbins, Cotran & Kumar: Pathologic Basis of Disease. 11th ed. (2026). Chapter 7, Neoplasia: “Nonreceptor Tyrosine Kinases,” pp. 255–256.

Chapter 7: chromosomal translocations and fusion oncogenes (BCR::ABL mechanism).

Chapter 13: chronic myeloid leukemia, polycythemia vera, and associated kinase abnormalities.

Chapter 13: Philadelphia-positive B-cell acute lymphoblastic leukemia (contextual comparison).