Affinage

MYL12B

Myosin regulatory light chain 12B · UniProt O14950

Round 2 corrected
Length
172 aa
Mass
19.8 kDa
Annotated
2026-04-29
58 papers in source corpus 10 papers cited in narrative 10 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

MYL12B is a non-muscle myosin II regulatory light chain that associates with heavy chains MYH9 and MYH10 and essential light chain MYL6 to maintain myosin II holoenzyme stability, with loss of MYL12B causing degradation of its binding partners and profound defects in cell morphology and spreading (PMID:21126233, PMID:26663899). Phosphorylation of MYL12B at Ser19 by kinases including RSK-2, MLCK, and smMLCK activates the actin-stimulated MgATPase of myosin II, driving actomyosin contractility that underlies Golgi-to-ER retrograde transport, cochlear hair cell apical constriction, and junctional tension-dependent protein sorting (PMID:10965042, PMID:12589046, PMID:33877471, PMID:28493278). MYL12B also serves as a regulatory light chain for Myosin 5c, where it reconstitutes with MYL6 to support tropomyosin-modulated actin-based motility (PMID:38606007). Downregulation of MYL12B by miR-23a-3p in atherosclerotic plaque-derived extracellular vesicles promotes MRTFA cytoplasmic retention and vascular smooth muscle cell phenotypic switching (PMID:41784666).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2000 High

    Identification of RSK-2 as a Ser19-specific kinase for MYL12B established that the MAPK cascade can directly activate myosin II ATPase activity through regulatory light chain phosphorylation, linking growth factor signaling to actomyosin contractility.

    Evidence In vitro kinase assays with site-directed mutants and actin-activated MgATPase reconstitution

    PMID:10965042

    Open questions at the time
    • In vivo relevance of RSK-2-mediated MYL12B phosphorylation not demonstrated
    • Relative contribution of RSK-2 versus MLCK in different cell types unknown
  2. 2003 High

    Expression of a phosphorylation-deficient MYL12B mutant revealed that myosin II activation through RLC phosphorylation is specifically required for Golgi-to-ER retrograde transport but dispensable for anterograde traffic, establishing a selective role for actomyosin contractility in retrograde membrane flow.

    Evidence Dominant-negative MRLC2(AA) mutant, BFA-induced retrograde transport assay, Shiga toxin transport assay with pharmacological validation

    PMID:12589046

    Open questions at the time
    • Molecular cargo specificity of MYL12B-dependent retrograde transport not defined
    • Whether MYL12B acts on vesicle fission, movement, or fusion not resolved
  3. 2011 High

    Proteomic and knockdown studies demonstrated that MYL12B is an obligate stabilizing subunit of non-muscle myosin II, as depletion of regulatory light chains caused coordinated loss of MYH9, MYH10, and MYL6 protein and severe morphological defects.

    Evidence Co-IP/mass spectrometry and siRNA knockdown with Western blot and phenotypic analysis in NIH 3T3 fibroblasts

    PMID:21126233

    Open questions at the time
    • Mechanism of heavy chain destabilization upon RLC loss (proteasomal vs. other) not characterized
    • Whether MYL12B and MYL12A are functionally redundant in all contexts remains unclear
  4. 2015 Medium

    Isoform-specific rescue experiments showed that MYL12B, but not MYL12A (MRLC1), can restore cell spreading after pan-MRLC depletion, revealing functional non-redundancy among paralogous regulatory light chains potentially attributable to N-terminal conformational differences.

    Evidence RNAi knockdown with isoform overexpression rescue, phosphorylation analysis, FRAP, and structural modeling in HeLa cells

    PMID:26663899

    Open questions at the time
    • Structural basis for isoform-specific function not experimentally validated
    • Whether differential function extends to tissues beyond HeLa cells not tested
  5. 2017 Medium

    Localization of phospho-MYL12B to bicellular junctions and its displacement by MYPT1 at high cell density established that MYL12B-generated actomyosin tension acts as a mechanical cue sorting junction proteins such as LSR between bicellular and tricellular contacts.

    Evidence Immunofluorescence of phospho-MRLC2 and MYPT1 at varying cell densities, myosin inhibitor treatment in Sawano endometrial cells

    PMID:28493278

    Open questions at the time
    • Whether MYL12B-dependent tension sorting generalizes to other junction proteins unknown
    • Quantitative force measurements not performed
  6. 2021 Medium

    In cochlear outer hair cells, smMLCK was identified as the kinase phosphorylating apically localized MYL12B, and inhibition of this axis caused apical surface expansion, linking MYL12B phosphorylation to developmental apical constriction in the auditory epithelium.

    Evidence In vitro phosphorylation with purified smMLCK and MYL12B, ML-7 inhibition with apical area measurement in cochlear explants

    PMID:33877471

    Open questions at the time
    • Genetic loss-of-function for MYL12B in cochlear development not performed
    • Whether MYL12A contributes redundantly in this tissue not addressed
  7. 2024 Medium

    Reconstitution of Myosin 5c with MYL12B and MYL6 demonstrated that MYL12B is not exclusive to myosin II but also functions as a regulatory light chain for an unconventional myosin, with activity modulated by specific tropomyosin isoforms.

    Evidence Recombinant co-expression of human Myo5c-HMM with MYL12B and MYL6, ATPase and in vitro motility assays with tropomyosin isoforms

    PMID:38606007

    Open questions at the time
    • In vivo significance of MYL12B as Myo5c light chain not validated
    • Whether phosphorylation of MYL12B regulates Myo5c activity not tested
  8. 2026 Medium

    Identification of MYL12B as a direct target of miR-23a-3p in atherosclerotic plaque-derived EVs revealed that MYL12B downregulation causes MRTFA cytoplasmic retention and VSMC phenotypic switching, positioning MYL12B upstream of the SRF/MRTFA transcriptional axis in vascular remodeling.

    Evidence miRNA target validation, engineered EVs, MRTFA localization assays, in vitro and in vivo VSMC phenotypic switching models

    PMID:41784666

    Open questions at the time
    • Mechanism linking MYL12B loss to MRTFA nuclear exclusion (G-actin dynamics vs. direct interaction) not defined
    • Single study; independent replication needed

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the structural basis for MYL12B versus MYL12A functional divergence, the full repertoire of myosin motors using MYL12B as an RLC, and whether MYL12B phosphorylation status directly controls MRTFA-dependent gene programs in vivo.
  • No high-resolution structure of MYL12B bound to any myosin heavy chain IQ domain
  • No genetic knockout model characterizing in vivo essentiality of MYL12B specifically
  • Relative roles of MYL12B in myosin II versus Myo5c pathways in physiological contexts uncharacterized

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0008092 cytoskeletal protein binding 4 GO:0098772 molecular function regulator activity 3
Localization
GO:0005856 cytoskeleton 3 GO:0005829 cytosol 2 GO:0005886 plasma membrane 1
Pathway
R-HSA-397014 Muscle contraction 3 R-HSA-162582 Signal Transduction 2 R-HSA-5653656 Vesicle-mediated transport 1
Partners
MYH10MYH9MYL6MYO5CRPS6KA3
Complex memberships
Myosin 5cNon-muscle myosin IIA (NM IIA)Non-muscle myosin IIB (NM IIB)

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2011 MYL12B (and paralogs MYL12A, MYL9) are associated with non-muscle myosin heavy chains MYH9 (NMHC IIA) and MYH10 (NMHC IIB), as well as essential light chain MYL6, in NIH 3T3 fibroblasts. Knockdown of MYL12A/MYL12B causes striking changes in cell morphology and dynamics and significantly reduces protein levels of MYH9, MYH10, and MYL6, demonstrating that non-muscle RLCs are required to maintain the stability of myosin II and cellular integrity. Proteomic association analysis (co-IP/MS), siRNA knockdown with phenotypic and Western blot readouts in NIH 3T3 fibroblasts The Biochemical journal High 21126233
2000 The myosin regulatory light chain (MRLC2/MYL12B) is phosphorylated by RSK-2 (MAPK-activated protein kinase-1b) specifically at Ser19 (and not Thr18/Ser19 double mutant), the same site targeted by MLCK. Phosphorylation of myosin II by RSK-2 activates the actin-activated MgATPase activity of myosin II. RSK-2 activity toward MRLC is suppressed by MAPK phosphorylation of RSK-2, suggesting RSK-2 mediates myosin II regulation downstream of the MAPK cascade. In vitro kinase assay with GST-fusion MRLC2 mutants (S19A, T18AS19A), phosphopeptide mapping, phosphoamino acid analysis, actin-activated MgATPase assay Journal of biochemistry High 10965042
2003 Non-muscle myosin II, regulated through MRLC2 (MRLC2(AA) phosphorylation-deficient mutant), mediates retrograde protein transport from the Golgi complex to the endoplasmic reticulum along actin filaments. Cells expressing the non-phosphorylatable MRLC2(AA) mutant show significant reduction in BFA-induced Golgi-to-ER enzyme fusion and impaired Shiga toxin fragment B retrograde transport, without affecting anterograde (ER-to-Golgi) transport. Dominant-negative phosphorylation-deficient MRLC2(AA) mutant expression, pharmacological inhibitors (BDM, ML7), brefeldin A-induced transport assay, Shiga toxin transport assay Molecular biology of the cell High 12589046
2015 Three MRLC isoforms including MRLC2 (MYL12B) are all phosphorylated at Thr18/Ser19 in HeLa cells, colocalize with each other and with myosin II heavy chain, and have similar turnover rates. Depletion of all MRLCs perturbs cell spreading; overproduction of MRLC2 or MRLC3 (but not MRLC1) rescues this defect, indicating MRLC2 plays a dominant role in cell spreading. Structural modeling suggests the N-terminus of MRLC2 differs conformationally from MRLC1. RNAi knockdown, rescue by isoform overexpression, phosphorylation analysis, colocalization and FRAP imaging, 3D protein structure simulation in HeLa cells Cytoskeleton (Hoboken, N.J.) Medium 26663899
2021 In cochlear hair cells, MYL12B is expressed at the apical portion and is phosphorylated by smooth muscle MLCK (smMLCK) in vitro. Inhibition of smMLCK with ML-7 reduces MYL12 phosphorylation and leads to expansion of the outer hair cell apical area, indicating that MYL12B phosphorylation by smMLCK drives apical constriction-like cellular shape changes important for development of auditory epithelia. Droplet digital PCR for isoform expression, immunofluorescence, in vitro phosphorylation assay with purified MYL12B and smMLCK, ML-7 pharmacological inhibition with cellular area measurement Journal of the Association for Research in Otolaryngology : JARO Medium 33877471
2017 Phosphorylated MRLC2 (MYL12B) localizes to bicellular junctions at low cell density, where it generates circumferential tensile forces that determine LSR (lipolysis-stimulated lipoprotein receptor) localization. At high cell density, MYPT1 localizes to bicellular junctions while activated MRLC2 is displaced, reducing tension and causing LSR redistribution to tricellular junctions. Myosin inhibition reduces bicellular LSR localization, confirming MRLC2-mediated tension sorts junction protein localization. Immunofluorescence of phospho-MRLC2 and MYPT1 at different cell densities, myosin inhibitor treatment, junctional localization analysis in endometrial cancer Sawano cells Annals of the New York Academy of Sciences Medium 28493278
2021 The lncRNA MAFG-AS1 physically interacts with three subunits of non-muscle myosin IIA including MYL12B, MYH9, and MYL6. Knockdown of MAFG-AS1 inhibits ATPase activity of MYH9, disrupts interactions among NM IIA subunits, and impairs cell cycle progression in HCC cells. RNA pulldown/co-IP to identify MAFG-AS1-MYL12B interaction, ATPase activity assay after knockdown, cell cycle analysis FASEB journal Medium 33813778
2015 Phosphorylated MYL12B (but not total MYL12B) is specifically upregulated in kidney tissue and plasma of sepsis-induced acute kidney injury (SAKI) mice compared to controls, as identified by 2D-DIGE and validated by Western blot, suggesting phosphorylation of MYL12B is a disease-associated modification in SAKI. 2D-DIGE proteomics of kidney tissue, MALDI-TOF/TOF MS identification, Western blot validation of phosphorylated vs. total MYL12B in plasma and kidney tissue International journal of clinical and experimental pathology Low 26823757
2024 MYL12B functions as a regulatory light chain for Myosin 5c (Myo5c), where it is co-produced with CaM and essential light chain Myl6 in the IQ motif-containing neck domain. Myo5c-HMM reconstituted with Myl6 and Myl12b shows actin-activated ATPase activity modulated by tropomyosin isoforms (Tpm1.6, Tpm1.8, Tpm3.1), with Tpm3.1 most strongly enhancing motility. Recombinant co-expression and purification of human Myo5c-HMM with Myl6 and Myl12b, actin-activated ATPase assays, in vitro motility assays with tropomyosin isoforms Frontiers in physiology Medium 38606007
2026 In atherosclerotic plaque-derived extracellular vesicles (AS-EVs), miR-23a-3p targets Myl12b, and this miR-23a-3p/Myl12b axis regulates MRTFA nuclear translocation, inhibits contractile marker expression, and promotes vascular smooth muscle cell (VSMC) phenotypic switching and carotid artery remodelling. miRNA analysis of EVs, engineered EVs loaded with miR-23a-3p, immunofluorescence and Western blot for MRTFA localization and contractile markers, in vitro and in vivo VSMC phenotypic switching assays Cellular and molecular life sciences : CMLS Medium 41784666

Source papers

Stage 0 corpus · 58 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
2009 Defining the human deubiquitinating enzyme interaction landscape. Cell 1282 19615732
2020 A reference map of the human binary protein interactome. Nature 849 32296183
2012 Genetically distinct subsets within ANCA-associated vasculitis. The New England journal of medicine 726 22808956
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
2022 OpenCell: Endogenous tagging for the cartography of human cellular organization. Science (New York, N.Y.) 432 35271311
2007 Functional specialization of beta-arrestin interactions revealed by proteomic analysis. Proceedings of the National Academy of Sciences of the United States of America 360 17620599
2003 Smooth muscle contraction and relaxation. Advances in physiology education 322 14627618
2010 Dynamics of cullin-RING ubiquitin ligase network revealed by systematic quantitative proteomics. Cell 318 21145461
2004 Transcriptome characterization elucidates signaling networks that control human ES cell growth and differentiation. Nature biotechnology 266 15146197
2022 EWSR1-induced circNEIL3 promotes glioma progression and exosome-mediated macrophage immunosuppressive polarization via stabilizing IGF2BP3. Molecular cancer 257 35031058
2017 Optimized fragmentation schemes and data analysis strategies for proteome-wide cross-link identification. Nature communications 221 28524877
2010 MHC class II-associated proteins in B-cell exosomes and potential functional implications for exosome biogenesis. Immunology and cell biology 221 20458337
2016 A High-Density Map for Navigating the Human Polycomb Complexome. Cell reports 216 27705803
2013 Cortical dynein and asymmetric membrane elongation coordinately position the spindle in anaphase. Cell 212 23870127
2016 An organelle-specific protein landscape identifies novel diseases and molecular mechanisms. Nature communications 211 27173435
2004 Bidirectional signals transduced by DAPK-ERK interaction promote the apoptotic effect of DAPK. The EMBO journal 195 15616583
2020 UFMylation maintains tumour suppressor p53 stability by antagonizing its ubiquitination. Nature cell biology 168 32807901
2009 Prefrontal cortex shotgun proteome analysis reveals altered calcium homeostasis and immune system imbalance in schizophrenia. European archives of psychiatry and clinical neuroscience 159 19165527
2022 A comprehensive SARS-CoV-2-human protein-protein interactome reveals COVID-19 pathobiology and potential host therapeutic targets. Nature biotechnology 140 36217030
2019 Mapping the proximity interaction network of the Rho-family GTPases reveals signalling pathways and regulatory mechanisms. Nature cell biology 137 31871319
2017 RNA-binding activity of TRIM25 is mediated by its PRY/SPRY domain and is required for ubiquitination. BMC biology 135 29117863
2015 Proteomic analyses reveal distinct chromatin-associated and soluble transcription factor complexes. Molecular systems biology 120 25609649
2023 The midnolin-proteasome pathway catches proteins for ubiquitination-independent degradation. Science (New York, N.Y.) 117 37616343
2021 Protein interaction landscapes revealed by advanced in vivo cross-linking-mass spectrometry. Proceedings of the National Academy of Sciences of the United States of America 113 34349018
2011 An important role for CDK2 in G1 to S checkpoint activation and DNA damage response in human embryonic stem cells. Stem cells (Dayton, Ohio) 113 21319273
2011 Myosin regulatory light chains are required to maintain the stability of myosin II and cellular integrity. The Biochemical journal 104 21126233
2010 A QUICK screen for Lrrk2 interaction partners--leucine-rich repeat kinase 2 is involved in actin cytoskeleton dynamics. Molecular & cellular proteomics : MCP 103 20876399
2022 EZH2 depletion potentiates MYC degradation inhibiting neuroblastoma and small cell carcinoma tumor formation. Nature communications 99 35013218
2020 Histone methyltransferase DOT1L coordinates AR and MYC stability in prostate cancer. Nature communications 90 32814769
2003 Myosin motors and not actin comets are mediators of the actin-based Golgi-to-endoplasmic reticulum protein transport. Molecular biology of the cell 73 12589046
2017 Hyperglycaemic memory affects the neurovascular unit of the retina in a diabetic mouse model. Diabetologia 30 28321468
2000 Activation of actin-activated MgATPase activity of myosin II by phosphorylation with MAPK-activated protein kinase-1b (RSK-2). Journal of biochemistry 25 10965042
2021 HBx-upregulated MAFG-AS1 promotes cell proliferation and migration of hepatoma cells by enhancing MAFG expression and stabilizing nonmuscle myosin IIA. FASEB journal : official publication of the Federation of American Societies for Experimental Biology 24 33813778
2007 Proteomics analysis of the proliferative effect of low-dose ouabain on human endothelial cells. Biological & pharmaceutical bulletin 21 17268060
2005 Genomic structure and organization of the high grade Myopia-2 locus (MYP2) critical region: mutation screening of 9 positional candidate genes. Molecular vision 21 15723005
2011 2D-PAGE of ovarian cancer: analysis of soluble and insoluble fractions using medium-range immobilized pH gradients. Biochemical and biophysical research communications 19 21329656
2015 Proteomic and peptidomic insights on myofibrillar protein hydrolysis in a sausage model during fermentation with autochthonous starter cultures. Food research international (Ottawa, Ont.) 16 28433309
2021 Transcriptional profiling of intervertebral disc in a post-traumatic early degeneration organ culture model. JOR spine 12 34611583
2015 Identification of phosphorylated MYL12B as a potential plasma biomarker for septic acute kidney injury using a quantitative proteomic approach. International journal of clinical and experimental pathology 11 26823757
2010 Analysis of factors decreasing testis weight in MRL mice. Mammalian genome : official journal of the International Mammalian Genome Society 11 20157820
2024 Comparison of differentially expressed genes in longissimus dorsi muscle of Diannan small ears, Wujin and landrace pigs using RNA-seq. Frontiers in veterinary science 8 38249550
2021 Phosphorylation of MYL12 by Myosin Light Chain Kinase Regulates Cellular Shape Changes in Cochlear Hair Cells. Journal of the Association for Research in Otolaryngology : JARO 6 33877471
2012 Surface CD3 expression proceeds through both myosin regulatory light chain 9 (MYL9)-dependent and MYL9-independent pathways in Jurkat cells. Journal of smooth muscle research = Nihon Heikatsukin Gakkai kikanshi 6 23538510
2017 The bicellular tensile force sorts the localization of LSRs in bicellular and tricellular junctions. Annals of the New York Academy of Sciences 5 28493278
2015 Characterization of myosin II regulatory light chain isoforms in HeLa cells. Cytoskeleton (Hoboken, N.J.) 5 26663899
2006 Molecular cloning and functional analysis of MRLC2 differential expressed in MeishanxYorkshire F1 crossbreeds and their parents, Meishan pigs. Acta biochimica et biophysica Sinica 5 17091196
2024 Motor properties of Myosin 5c are modulated by tropomyosin isoforms and inhibited by pentabromopseudilin. Frontiers in physiology 3 38606007
2024 Inter3D: Capture of TAD Reorganization Endows Variant Patterns of Gene Transcription. Genomics, proteomics & bioinformatics 3 39394698
2025 An integrative analysis combining bioinformatics, network pharmacology and experimental methods identified key genes of EGCG targets in Nasopharyngeal Carcinoma. Discover oncology 2 40355769
2024 SNP-Based and Kmer-Based eQTL Analysis Using Transcriptome Data. Animals : an open access journal from MDPI 2 39457872
2021 Proteomic and electron microscopy study of myogenic differentiation of alveolar mucosa multipotent mesenchymal stromal cells in three-dimensional culture. Proteomics 2 34674377
2013 Molecular cloning and functional analysis of MRLC2 in Tianfu, Boer, and Chengdu Ma goats. Genetics and molecular research : GMR 2 23546987
2025 Identification of Key Genes and Potential Therapeutic Targets in Sepsis-Associated Acute Kidney Injury Using Transformer and Machine Learning Approaches. Bioengineering (Basel, Switzerland) 1 40428155
2026 Atherosclerotic plaque-derived extracellular vesicles mediate smooth muscle cell phenotypic switching and promote vascular remodeling : EVs promote VSMC phenotypic switching. Cellular and molecular life sciences : CMLS 0 41784666
2025 Myosin Light Chain 12b and MASP1 as Novel Biomarker Candidates in Active Juvenile Idiopathic Arthritis─A Combined Proteomics/Bioinformatics Approach. Journal of proteome research 0 39932158
2025 High Dietary Inclusion of Faba Bean Improved the Meat Quality of Pacific White Shrimp, Litopenaeus vannamei, Rather Than the Growth Performance. Aquaculture nutrition 0 41424699