The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The requested target is correctly identified. MAP2K3 is the approved human gene symbol for mitogen-activated protein kinase kinase 3, commonly called MKK3 or MEK3; the target corresponds to human UniProt P46734 and Ensembl ENSG00000034152. Its aliases and classification as a STE-family dual-specificity protein kinase agree with the supplied record. No evidence was used from the unrelated plant gene sometimes also called MAP2K3.
MAP2K3 is an intracellular, ATP-dependent signaling enzyme whose principal established function is to phosphorylate the threonine and tyrosine residues in the TGY activation loop of p38-family MAP kinases. The clearest substrate-level evidence concerns p38α/MAPK14, phosphorylated at Thr180 and Tyr182, with additional evidence for p38β. MKK3 therefore occupies the middle tier of a canonical MAP3K → MKK3 → p38 stress-signaling module. It acts in both cytoplasm and nucleus and converts oxidative, osmotic, inflammatory, genotoxic, hypoxic and ischemic inputs into context-dependent stress-adaptation, inflammatory, differentiation, apoptotic and proliferation responses. MKK6 overlaps substantially with MKK3, so neither kinase should be treated as universally indispensable or absolutely isoform-specific. (roux2004erkandp38 pages 2-3, maikrachline2021alternativesplicingof pages 5-6, moralesmartinez2024p38moleculartargeting pages 2-4)
| Aspect | Best-supported annotation | Evidence type / strength | Key source / date |
|---|---|---|---|
| Identity | Human MAP2K3 encodes mitogen-activated protein kinase kinase 3 (MKK3/MEK3); identifiers include UniProt P46734 and Ensembl ENSG00000034152. | High: concordant supplied UniProt identity and human target-database annotation. | UniProt P46734; Open Targets, accessed 2026-09-24 (OpenTargets Search: -MAP2K3) |
| Kinase class and domain | Dual-specificity MAPK kinase in the STE kinase group, containing a conserved protein-kinase catalytic domain and ATP-binding machinery. “Dual specificity” denotes phosphorylation of both threonine and tyrosine in a MAPK activation loop. | High for class/domain: curated sequence annotation; moderate-to-high for mechanism: established MAPK-cascade biochemistry. | UniProt P46734; Roux & Blenis, 2004-06 (roux2004erkandp38 pages 2-3) |
| Catalytic reaction | Transfers phosphate from ATP to threonine and tyrosine in a cognate p38 MAPK activation loop: ATP + p38 → ADP + dual-phosphorylated p38. | High: biochemical consensus and phospho-specific experiments; cited evidence does not supply detailed kinetic constants. | Roux & Blenis, 2004-06; Maik-Rachline et al., 2021-12 (roux2004erkandp38 pages 2-3, maikrachline2021alternativesplicingof pages 5-6) |
| MKK3 activation residue | Thr222 (T222) phosphorylation is used experimentally as a marker of activated human MEK3/MKK3. Leukemia-associated mutant constructs showed reduced pT222 and reduced downstream p38 phosphorylation. This assay supports an activation-associated site but does not define every regulatory event. | Moderate-to-high: phospho-specific immunoblotting of expressed proteins in HEK293 cells rather than purified-enzyme kinetics. | Ayala-Marin et al., 2021-11 (ayalamarin2021quadrupleandtruncated pages 8-10, ayalamarin2021quadrupleandtruncated pages 10-12) |
| Principal substrates | Best-supported substrates are p38-family MAPKs. MKK3 and MKK6 phosphorylate the conserved TGY motif; p38α/MAPK14 is activated at Thr180 and Tyr182. MKK3 can also activate p38β, but context-dependent preferences do not justify strict isoform exclusivity. | High for p38-family specificity and p38α T180/Y182; moderate for individual isoform preferences. | Maik-Rachline et al., 2021-12; Morales-Martínez & Vega, 2024-01 (maikrachline2021alternativesplicingof pages 5-6, moralesmartinez2024p38moleculartargeting pages 2-4) |
| Upstream activation | MKK3 lies below MAP3Ks including MEKK1–4, MLK2/3, DLK, ASK1, Tpl2/Cot and TAK1. Inputs include oxidative stress, UV radiation, hypoxia, ischemia and inflammatory cytokines such as IL-1 and TNF-α. Exact wiring varies by stimulus and cell type. | High at pathway level; variable for particular MAP3K–MKK3 links in individual tissues. | Roux & Blenis, 2004-06 (roux2004erkandp38 pages 2-3) |
| Subcellular localization | MKK3 has been observed in both cytoplasm and nucleus; cytoplasmic predominance occurs in some tumor-cell contexts. Localization is dynamic and context dependent, not confined to one compartment. | Moderate-to-high: cellular localization studies plus context-specific tumor immunohistochemistry. | Ben-Levy et al., 1998-09; Pu et al., 2024-06 (pu2024exploringmap2k3as pages 3-4) |
| Core biological role | Serves as the middle tier of a stress-responsive MAP3K → MKK3 → p38 cascade, converting stress and cytokine inputs into p38 activation. Downstream outcomes include stress adaptation, inflammatory signaling, differentiation, apoptosis and proliferation control, depending on cell context and signal dynamics. | High for pathway position; moderate for individual phenotypic outcomes because they are context dependent. | Roux & Blenis, 2004-06; Maik-Rachline et al., 2021-12 (roux2004erkandp38 pages 2-3, maikrachline2021alternativesplicingof pages 5-6) |
| 2024 glioma finding | Retrospective multi-cohort analyses associated higher MAP2K3 expression with higher glioma grade and shorter overall and progression-free survival; reported 1-, 3- and 5-year prognostic AUCs were 0.89, 0.92 and 0.92. High expression also correlated with immune infiltration and checkpoint expression. These findings do not prove causality or prospective treatment prediction. | Exploratory/moderate: transcriptomic, immunohistochemical and computational analyses with limited functional assays; no prospective clinical validation. | Pu et al., 2024-06 (pu2024exploringmap2k3as pages 14-15, pu2024exploringmap2k3as pages 3-4, pu2024exploringmap2k3as pages 6-10) |
| Development status and limitations | MAP2K3 is a plausible research target and candidate biomarker, but evidence remains predominantly preclinical. No MAP2K3-selective approved therapy or validated companion diagnostic is established in the reviewed evidence. MKK6 redundancy, context-dependent tumor effects and uncertain p38-isoform preferences complicate translation. | Low clinical maturity: mechanistic and association evidence without demonstrated direct clinical utility; database disease associations are not proof of causality. | Open Targets, accessed 2026-09-24; Morales-Martínez & Vega, 2024-01; Pu et al., 2024-06 (OpenTargets Search: -MAP2K3, moralesmartinez2024p38moleculartargeting pages 2-4, pu2024exploringmap2k3as pages 14-15) |
Table: Evidence-tiered functional annotation of human MAP2K3/MKK3 (UniProt P46734), covering molecular identity, catalytic function, pathway position, localization and recent translational findings. The table distinguishes established biochemistry from context-dependent or clinically unvalidated observations.
The supplied identity is internally and externally consistent:
Open Targets independently maps the human approved symbol MAP2K3 to “mitogen-activated protein kinase kinase 3” and ENSG00000034152, supporting the supplied human identity. Its disease-association scores are modest and evidence-set dependent; they confirm target identity but should not be interpreted as proof that MAP2K3 causes those diseases. (OpenTargets Search: -MAP2K3)
MAP2K3 belongs to the MAP kinase kinase branch of the STE protein-kinase group. The supplied InterPro/Pfam annotations—protein-kinase domain, kinase-like fold, ATP-binding site and serine/threonine-kinase active-site signature—are exactly what is expected for an MAP2K. “Dual specificity” refers to its ability to phosphorylate both a threonine and a tyrosine in the activation loop of its MAPK substrate; it does not mean that MKK3 broadly phosphorylates arbitrary serine/threonine and tyrosine substrates.
MKK3 and MKK6 are closely related—approximately 80% similar at the primary-sequence level in one review—and both recognize p38 TGY motifs, although stimulus responses and p38-isoform preferences differ. Two substantially expressed MKK3 splice isoforms have been described, with the principal isoform generally more abundant than MKK3b and relative expression varying by cell type. (maikrachline2021alternativesplicingof pages 5-6)
The functional reaction can be represented as:
ATP + p38-MAPK → ADP + dual-phosphorylated, activated p38-MAPK
More specifically, MKK3 transfers ATP-derived phosphate to the threonine and tyrosine of the p38-family TGY activation motif. In p38α/MAPK14 these sites are Thr180 and Tyr182. Phosphorylation remodels the p38 activation loop and increases its catalytic activity toward downstream protein substrates. (maikrachline2021alternativesplicingof pages 5-6, moralesmartinez2024p38moleculartargeting pages 2-4)
This is a phosphorylation reaction, not a transport or structural function. MKK3 is therefore best annotated as a stress-responsive p38 MAPK activator.
The strongest conclusion is that MKK3 is selective at the MAPK-family level for p38 MAPKs, rather than ERK1/2 or JNK. Established reviews place MKK3 and MKK6 as the principal p38-directed MAP2Ks and report high specificity for p38 over those other MAPK branches. (roux2004erkandp38 pages 2-3)
Within the p38 family, the evidence supports:
Consequently, annotations such as “MKK3 activates only p38α” or “MKK3 activates every p38 isoform equivalently” would both be too strong. Docking interactions, scaffold proteins, relative MKK3/MKK6 abundance, compartment and stimulus help determine effective specificity. MKK3 and MKK6 can preferentially—but not exclusively—activate different p38 isoforms. (maikrachline2021alternativesplicingof pages 5-6)
MKK3 itself is activated by upstream MAP3Ks through activation-loop phosphorylation. In human-cell experiments, phosphorylation at Thr222 was used as an activation-associated readout. Leukemia-derived MEK3 mutants displayed reduced pThr222 together with reduced phosphorylation of p38 Thr180/Tyr182, supporting a functional connection between MKK3 activation state and downstream p38 activation. These assays establish Thr222 as an experimentally informative regulatory site, although they do not imply that it is the only regulatory event affecting MKK3. (ayalamarin2021quadrupleandtruncated pages 8-10, ayalamarin2021quadrupleandtruncated pages 10-12)
The catalytic domain provides the conventional bilobal protein-kinase architecture and ATP-binding machinery. Specificity additionally depends on non-catalytic docking contacts. Recent proteome-scale work on p38α docking showed that p38-selective interactions favor Lys-rich basic motifs that complement acidic residues in the p38 docking groove; MAP2K3 and MAP2K6 contain N-terminal basic docking regions consistent with this recognition principle. This 2023 result refines understanding of how MAPK cascades preserve signaling fidelity despite structurally similar kinase active sites. However, it explains p38 docking generally rather than supplying a complete atomic structure of full-length MKK3 bound to p38.
MAP2K3 occupies the central kinase tier:
stress/cytokine receptor or sensor → MAP3K → MKK3 → p38 MAPK → downstream kinases, transcription factors and other substrates
Reported upstream MAP3Ks include MEKK1–4, MLK2/3, DLK, ASK1, Tpl2/Cot and TAK1. Which MAP3K engages MKK3 depends on cell type, scaffold organization and initiating signal. Established inputs include oxidative stress, UV irradiation, hypoxia, ischemia, physical or chemical stress, and inflammatory cytokines such as IL-1 and TNF-α. (roux2004erkandp38 pages 2-3)
The pathway should not be viewed as a simple isolated linear chain. MKK6 provides overlapping p38 activation; MKK4 can contribute in some contexts; scaffolds spatially organize complexes; phosphatases terminate signaling; and cross-talk occurs with ERK, JNK, PI3K–AKT, NF-κB and other networks.
Through p38, MAP2K3 contributes to:
These are pathway outcomes rather than independent catalytic activities of MKK3. Their direction is context dependent: p38 signaling can suppress proliferation in one cellular state yet support survival, invasion or therapy resistance in another. Expert reviews emphasize this signal-, duration-, isoform- and cell-type dependence rather than assigning p38 signaling a universally pro- or anti-apoptotic role. (roux2004erkandp38 pages 2-3, maikrachline2021alternativesplicingof pages 5-6)
MAP2K3 is a soluble intracellular kinase and has been detected in both cytoplasm and nucleus. This permits it to connect cytoplasmic stress-sensing complexes with p38 pools in either compartment. Localization is dynamic rather than fixed; protein interactions and stimulation can alter compartmental distribution.
Context-specific observations include predominantly cytoplasmic MAP2K3 staining in glioma-related cells and tissues, while earlier cell-biological work and mutant-expression experiments found MKK3/MEK3 in both nuclear and cytoplasmic compartments. The correct annotation is therefore “cytoplasm and nucleus, context dependent,” not an exclusively nuclear or exclusively cytosolic location. In the 2024 glioma analysis, Human Protein Atlas staining placed MAP2K3 in the cytoplasm of the examined SH-SY5Y cell model. (pu2024exploringmap2k3as pages 3-4)
MKK3’s location must also be distinguished from that of its substrate. Activated p38 can redistribute between compartments and can be exported through complexes with downstream proteins such as MK2; p38 localization should not automatically be assigned to MKK3.
A 2021 study investigated four substitutions—P11T, R26T, R65L and R67W—and a truncating Q73* variant identified in an acute-lymphoblastic-leukemia sequence set. R65L and R67W were near the ATP-binding region, whereas P11T and R26T were in the amino-terminal region. Expressed in HEK293 cells, the quadruple mutant was unstable and underwent enhanced degradation; the Q73-truncated protein underwent ubiquitin-independent proteasomal degradation. Both mutant forms showed reduced MKK3 activation and reduced downstream p38 phosphorylation. (ayalamarin2021quadrupleandtruncated pages 1-2)
Phospho-specific assays measured MKK3 pThr222 and p38 pThr180/pTyr182. Mutants showed weaker enzymatic signaling and less suppression of HEK293-cell viability than wild-type MKK3, consistent with loss of a growth-restraining MKK3–p38 output in that experimental system. This is mechanistic evidence from engineered cell expression, not proof that these rare variants are recurrent clinical drivers or actionable biomarkers in leukemia. (ayalamarin2021quadrupleandtruncated pages 8-10, ayalamarin2021quadrupleandtruncated pages 10-12)
An experimentally reported extension beyond canonical p38 signaling is a direct MKK3–MYC protein interaction. The cited study mapped a short MKK3 MYC-binding motif distinct from known p38/upstream-kinase interaction sites and reported stabilization and increased transcriptional activity of MYC. This proposes that MAP2K3 may act as a protein-interaction regulator in addition to phosphorylating p38. Because the non-canonical model has a smaller validation base than the MKK3–p38 reaction, it should be regarded as a supported but less-established function rather than the primary annotation.
A 2023 PNAS study screened thousands of human-proteome-derived sequences against p38α and ERK2. It found distinct motifs for selective versus promiscuous docking; p38α selectivity correlated with increased net positive charge and Lys enrichment, mediated by acidic residues unique to the p38α docking groove. The N-terminal basic regions of MAP2K3 and MAP2K6 fit this emerging specificity model. This work strengthens the mechanistic view that MAP2K-to-MAPK fidelity is determined by docking interfaces in addition to active-site chemistry.
A June 2024 Frontiers in Neurology study integrated TCGA, CGGA, GEO, Human Protein Atlas and single-cell data with limited functional assays. MAP2K3 transcript and protein abundance increased with glioma grade, and higher expression was associated with shorter overall and progression-free survival. Multivariable analyses treated MAP2K3 as an independent prognostic predictor. A reported prognostic model yielded time-dependent AUCs of 0.89, 0.92 and 0.92 at 1, 3 and 5 years, respectively. (pu2024exploringmap2k3as pages 14-15, pu2024exploringmap2k3as pages 3-4)
High-MAP2K3 tumors had higher immune and stromal scores, lower estimated tumor purity and increased expression of seven reported checkpoint-associated molecules, including PD-L1/CD274, PDCD1, PDCD1LG2 and CTLA4. They also showed increased immunosuppressive populations such as T regulatory cells, MDSCs, Th2 cells and M2 macrophages, alongside some effector populations. (pu2024exploringmap2k3as pages 6-10)
Interpretation requires caution. Most evidence was retrospective and computational, and associations between MAP2K3 expression, immune infiltration and outcome do not establish that MKK3 drives glioma progression. Although high expression was associated with possible benefit in several anti-PD-1 cohorts, results were not uniformly significant and were not derived from prospective glioma trials. Functional invasion assays used three replicates and reported p < 0.001, but that limited experiment does not validate clinical utility. (pu2024exploringmap2k3as pages 14-15)
A 2024 review of p38 targeting in multiple myeloma described p38 signaling as relevant to inflammatory cytokines, tumor survival and treatment resistance and identified MKK3 as one upstream activator of p38α/β. The translational activity is primarily directed at p38 or downstream pathway outputs rather than clinically validated MKK3-selective inhibition. The review is useful for pathway context but does not provide direct MAP2K3-specific clinical evidence. (moralesmartinez2024p38moleculartargeting pages 2-4)
MAP2K3 is currently useful as:
No MAP2K3-selective drug, approved therapy or validated companion diagnostic was identified in the reviewed evidence. Therapeutic work has more commonly targeted p38α itself, upstream MAP3Ks or downstream effectors. This has practical limitations: ATP sites are conserved across kinases, MKK3 and MKK6 are partially redundant, and systemic p38-pathway inhibition can disrupt both pathological and homeostatic stress responses.
Open Targets lists MAP2K3 associations with broad phenotypes including skeletal, neurodegenerative, immune and infectious conditions, but the displayed scores are moderate—approximately 0.31–0.46—and several associations share the same small evidence sets. These database statistics are hypothesis-generating, not evidence of approved use or causal disease involvement. (OpenTargets Search: -MAP2K3)
More selective future strategies may target a disease-specific docking interface or scaffolded complex rather than the conserved ATP pocket. The reported MKK3–MYC interface is one experimental example of this concept, but it remains preclinical.
High-confidence annotation: MAP2K3/P46734 is human MKK3, a STE-family dual-specificity MAP2K whose primary biochemical role is ATP-dependent activation of p38 MAPKs through dual phosphorylation of their TGY activation loop. It functions intracellularly in cytoplasmic and nuclear stress-signaling complexes. (roux2004erkandp38 pages 2-3, maikrachline2021alternativesplicingof pages 5-6, moralesmartinez2024p38moleculartargeting pages 2-4)
Moderate-confidence refinements: MKK3 and MKK6 have overlapping but non-identical stimulus and p38-isoform preferences; MKK3 localization and biological output vary by cell state; Thr222 is a useful activation-associated phosphosite. (maikrachline2021alternativesplicingof pages 5-6, ayalamarin2021quadrupleandtruncated pages 8-10)
Emerging or context-specific conclusions: MAP2K3 expression may have prognostic and immunological relevance in glioma, and MKK3 may regulate MYC through direct binding. These observations warrant mechanistic replication and prospective clinical validation before being used diagnostically or therapeutically. (pu2024exploringmap2k3as pages 14-15, pu2024exploringmap2k3as pages 3-4, pu2024exploringmap2k3as pages 6-10)
The most defensible functional annotation is: human MAP2K3 encodes MKK3, an intracellular dual-specificity MAP kinase kinase that receives stress- and cytokine-dependent signals from MAP3Ks and activates p38-family MAPKs by phosphorylating the threonine and tyrosine of their TGY activation motif. Its clearest reaction is activation of p38α at Thr180/Tyr182. It acts in cytoplasm and nucleus, with localization, isoform preference and biological consequences determined by stimulus, scaffold, cell type and competition or redundancy with MKK6. Recent research has refined MAPK docking specificity and identified potentially useful cancer associations, especially in glioma, but MAP2K3 remains a preclinical research target rather than a clinically established drug target or biomarker.
References
(roux2004erkandp38 pages 2-3): Philippe P. Roux and John Blenis. Erk and p38 mapk-activated protein kinases: a family of protein kinases with diverse biological functions. Microbiology and Molecular Biology Reviews, 68:320-344, Jun 2004. URL: https://doi.org/10.1128/mmbr.68.2.320-344.2004, doi:10.1128/mmbr.68.2.320-344.2004. This article has 3501 citations and is from a domain leading peer-reviewed journal.
(maikrachline2021alternativesplicingof pages 5-6): Galia Maik-Rachline, Inbal Wortzel, and Rony Seger. Alternative splicing of mapks in the regulation of signaling specificity. Cells, 10:3466, Dec 2021. URL: https://doi.org/10.3390/cells10123466, doi:10.3390/cells10123466. This article has 40 citations.
(moralesmartinez2024p38moleculartargeting pages 2-4): Mario Morales-Martínez and Mario I. Vega. P38 molecular targeting for next-generation multiple myeloma therapy. Cancers, 16:256, Jan 2024. URL: https://doi.org/10.3390/cancers16020256, doi:10.3390/cancers16020256. This article has 8 citations.
(OpenTargets Search: -MAP2K3): Open Targets Query (-MAP2K3, 5 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
(ayalamarin2021quadrupleandtruncated pages 8-10): Yoshira M. Ayala-Marin, Alice H. Grant, Georgialina Rodriguez, and Robert A. Kirken. Quadruple and truncated mek3 mutants identified from acute lymphoblastic leukemia promote degradation and enhance proliferation. International Journal of Molecular Sciences, 22:12210, Nov 2021. URL: https://doi.org/10.3390/ijms222212210, doi:10.3390/ijms222212210. This article has 2 citations.
(ayalamarin2021quadrupleandtruncated pages 10-12): Yoshira M. Ayala-Marin, Alice H. Grant, Georgialina Rodriguez, and Robert A. Kirken. Quadruple and truncated mek3 mutants identified from acute lymphoblastic leukemia promote degradation and enhance proliferation. International Journal of Molecular Sciences, 22:12210, Nov 2021. URL: https://doi.org/10.3390/ijms222212210, doi:10.3390/ijms222212210. This article has 2 citations.
(pu2024exploringmap2k3as pages 3-4): Bei Pu, Shi Feng, Lijuan Gu, Daniel Smerin, Zhihong Jian, Xiaoxing Xiong, and Liang Wei. Exploring map2k3 as a prognostic biomarker and potential immunotherapy target in glioma treatment. Frontiers in Neurology, Jun 2024. URL: https://doi.org/10.3389/fneur.2024.1387743, doi:10.3389/fneur.2024.1387743. This article has 4 citations and is from a peer-reviewed journal.
(pu2024exploringmap2k3as pages 14-15): Bei Pu, Shi Feng, Lijuan Gu, Daniel Smerin, Zhihong Jian, Xiaoxing Xiong, and Liang Wei. Exploring map2k3 as a prognostic biomarker and potential immunotherapy target in glioma treatment. Frontiers in Neurology, Jun 2024. URL: https://doi.org/10.3389/fneur.2024.1387743, doi:10.3389/fneur.2024.1387743. This article has 4 citations and is from a peer-reviewed journal.
(pu2024exploringmap2k3as pages 6-10): Bei Pu, Shi Feng, Lijuan Gu, Daniel Smerin, Zhihong Jian, Xiaoxing Xiong, and Liang Wei. Exploring map2k3 as a prognostic biomarker and potential immunotherapy target in glioma treatment. Frontiers in Neurology, Jun 2024. URL: https://doi.org/10.3389/fneur.2024.1387743, doi:10.3389/fneur.2024.1387743. This article has 4 citations and is from a peer-reviewed journal.
(ayalamarin2021quadrupleandtruncated pages 1-2): Yoshira M. Ayala-Marin, Alice H. Grant, Georgialina Rodriguez, and Robert A. Kirken. Quadruple and truncated mek3 mutants identified from acute lymphoblastic leukemia promote degradation and enhance proliferation. International Journal of Molecular Sciences, 22:12210, Nov 2021. URL: https://doi.org/10.3390/ijms222212210, doi:10.3390/ijms222212210. This article has 2 citations.