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Event: 962

Key Event Title

The KE title should describe a discrete biological change that can be measured. It should generally define the biological object or process being measured and whether it is increased, decreased, or otherwise definably altered relative to a control state. For example “enzyme activity, decreased”, “hormone concentration, increased”, or “growth rate, decreased”, where the specific enzyme or hormone being measured is defined. More help

Increase, Mucin production

Short name
The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. The short name should be less than 80 characters in length. More help
Increase, Mucin production

Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. Note, KEs should be defined within a particular level of biological organization. Only KERs should be used to transition from one level of organization to another. Selection of the level of biological organization defines which structured terms will be available to select when defining the Event Components (below). More help
Level of Biological Organization

Cell term

Further information on Event Components and Biological Context may be viewed on the attached pdf.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable. More help
Cell term
goblet cell

Organ term

Further information on Event Components and Biological Context may be viewed on the attached pdf.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable. More help
Organ term

Key Event Components

Further information on Event Components and Biological Context may be viewed on the attached pdf.Because one of the aims of the AOP-KB is to facilitate de facto construction of AOP networks through the use of shared KE and KER elements, authors are also asked to define their KEs using a set of structured ontology terms (Event Components). In the absence of structured terms, the same KE can readily be defined using a number of synonymous titles (read by a computer as character strings). In order to make these synonymous KEs more machine-readable, KEs should also be defined by one or more “event components” consisting of a biological process, object, and action with each term originating from one of 22 biological ontologies (Ives, et al., 2017; See List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling). The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signalling by that receptor).Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description. To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons. If a desired term does not exist, a new term request may be made via Term Requests. Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add. More help
Process Object Action
gene expression mucin-5AC increased
translation mucin-5AC increased

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE. Clicking on the name of the AOP will bring you to the individual page for that AOP. More help
AOP Name Role of event in AOP Point of Contact Author Status OECD Status
Decreased lung function KeyEvent Karsta Luettich (send email) Under development: Not open for comment. Do not cite Under Development


This is a structured field used to identify specific agents (generally chemicals) that can trigger the KE. Stressors identified in this field will be linked to the KE in a machine-readable manner, such that, for example, a stressor search would identify this as an event the stressor can trigger. NOTE: intermediate or downstream KEs in one AOP may function as MIEs in other AOPs, meaning that stressor information may be added to the KE description, even if it is a downstream KE in the pathway currently under development.Information concerning the stressors that may trigger an MIE can be defined using a combination of structured and unstructured (free-text) fields. For example, structured fields may be used to indicate specific chemicals for which there is evidence of an interaction relevant to this MIE. By linking the KE description to a structured chemical name, it will be increasingly possible to link the MIE to other sources of chemical data and information, enhancing searchability and inter-operability among different data-sources and knowledgebases. The free-text section “Evidence for perturbation of this MIE by stressor” can be used both to identify the supporting evidence for specific stressors triggering the MIE as well as to define broad chemical categories or other properties that classify the stressors able to trigger the MIE for which specific structured terms may not exist. More help

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected from an ontology. In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help
Term Scientific Term Evidence Link
human Homo sapiens High NCBI
mouse Mus musculus High NCBI
rat Rattus norvegicus High NCBI

Life Stages

The structured ontology terms for life-stage are more comprehensive than those for taxa, but may still require further description/development and explanation in the free text section. More help
Life stage Evidence
Adult High

Sex Applicability

The authors must select from one of the following: Male, female, mixed, asexual, third gender, hermaphrodite, or unspecific. More help
Term Evidence
Mixed High

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. For example, the biological state being measured could be the activity of an enzyme, the expression of a gene or abundance of an mRNA transcript, the concentration of a hormone or protein, neuronal activity, heart rate, etc. The biological compartment may be a particular cell type, tissue, organ, fluid (e.g., plasma, cerebrospinal fluid), etc. The role in the biology could describe the reaction that an enzyme catalyses and the role of that reaction within a given metabolic pathway; the protein that a gene or mRNA transcript codes for and the function of that protein; the function of a hormone in a given target tissue, physiological function of an organ, etc. Careful attention should be taken to avoid reference to other KEs, KERs or AOPs. Only describe this KE as a single isolated measurable event/state. This will ensure that the KE is modular and can be used by other AOPs, thereby facilitating construction of AOP networks. More help

Mucin production in healthy airway provides an important role in trapping and removing bacterial and viral pathogens and particulates. The major gel-forming mucins of the airways, MUC5AC and MUC5AB, are primarily involved in this function (Lillehoj et al., 2013).  Various stimuli increase mucin production by goblet cells including cigarette smoke, phorbol 12-myristate 13-acetate (PMA), 2,3,7,8-tetrachlorodibenzodioxin (TCDD), ozone, acrolein, and sulfur dioxide (Lamb and Reid, 1968; Shao et al., 2004; Takeyama et al., 2001; Yu et al., 2011; Casalino-Matsuda et al., 2009; Hewson et al., 2004; Lee et al., 2011; Wagner et al., 2003) as well as bacteria and viruses (Dohrman et al., 1998; Hao et al., 2014; Zhu et al., 2009). Many of these stimuli specifically induce MUC5AC mRNA and protein production through activation of the EGFR pathway (Nadel, 2013). However, other signaling pathways, not necessarily requiring EGFR activation, via STAT6, FOXA2, SPDEF or NFkB have also been implicated in MUC5AC overexpression (reviewed by Turner and Jones, 2009).

How It Is Measured or Detected

One of the primary considerations in evaluating AOPs is the relevance and reliability of the methods with which the KEs can be measured. The aim of this section of the KE description is not to provide detailed protocols, but rather to capture, in a sentence or two, per method, the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements. Methods that can be used to detect or measure the biological state represented in the KE should be briefly described and/or cited. These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA).Key considerations regarding scientific confidence in the measurement approach include whether the assay is fit for purpose, whether it provides a direct or indirect measure of the biological state in question, whether it is repeatable and reproducible, and the extent to which it is accepted in the scientific and/or regulatory community. Information can be obtained from the OECD Test Guidelines website and the EURL ECVAM Database Service on Alternative Methods to Animal Experimentation (DB-ALM). ?

To our knowledge, no validated method for the determination of mucin overproduction exists. In the literature, increased mucin production is frequently equated with increased MUC5AC mRNA and protein expression and much less frequently with changes in MUC5AB mRNA and protein levels.

Alterations in MUC5AC mRNA expression in cell and tissue lysates are commonly assessed by RT-PCR or RT-qPCR, whereas Northern blotting is less frequently used. Changes in MUC5AC protein levels can be detected by ELISA or Western blot in cell and tissue lysates and secretions or by immunocyto/histochemistry/immunofluorescence in cytological preparations or histological tissue sections with an appropriate antibody. It is worth noting here that some antibodies are not suitable for ELISA or Western blot, because extensive glycosylation of mucins may mask epitopes or block access of the antibody to the epitope (Rose and Voynow, 2006). Alternatively, labeled and label-free mass spectrometry-based approaches could be utilized for targeted identification of mucins and their quantification in cell and tissue samples. For in vivo studies and clinical samples, an experienced pathologist may judge the presence and severity of mucin production on histological tissue sections stained with hematoxylin/eosin and Alcian blue and/or periodic acid Schiff stains. A grading or scoring system may enable semi-quantitative assessment, but remains subjective at best since corresponding standards are currently lacking.

Domain of Applicability

This free text section should be used to elaborate on the scientific basis for the indicated domains of applicability and the WoE calls (if provided). While structured terms may be selected to define the taxonomic, life stage and sex applicability (see structured applicability terms, above) of the KE, the structured terms may not adequately reflect or capture the overall biological applicability domain (particularly with regard to taxa). Likewise, the structured terms do not provide an explanation or rationale for the selection. The free-text section on evidence for taxonomic, life stage, and sex applicability can be used to elaborate on why the specific structured terms were selected, and provide supporting references and background information.  More help

The MUC5AC gene is conserved in Rhesus monkey, dog, cow, mouse, rat, zebrafish, and frog, and the MUC5B gene is conserved in dog, mouse, rat, and chicken. Evidence in support of this KE primarily derives from in vitro studies with human cell systems, while corroborating in vivo evidence comes from studies in small rodents (mouse or rat).

Evidence for Perturbation by Stressor


Exposure of Sprague-Dawley rats to 3 ppm acrolein for 6 h a day, for 12 days significantly increased lung Muc5ac gene and protein expression (Chen et al., 2013). 

Bronchoalveolar lavage fluid mucin content as well as Muc5ac gene and protein expression were significantly increased in the lungs of Sprague-Dawley rats that were exposed to 3 ppm of acrolein for 6 h a day, 7 days a week, for up to 2 weeks (Liu et al., 2009).

Exposure of Sprague Dawley rats to 3 ppm acrolein for 6 h a day, 5 days a week, for up to 12 days significantly increased Muc5ac gene expression in trachea and lung (Borchers et al., 1998).

Exposure of Sprague Dawley rats to 3 ppm acrolein for 3 h a day, 7 days a week, for up to 4 days significantly increased Muc5ac gene and protein expression in the lungs (Wang et al., 2009).

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Treatment of primary normal human bronchial epithelial cells and immortalized human bronchial epithelial HBE1 cells with 10 nM TCDD for up to 48 h increased MUC5AC gene expression in a time-dependent manner. TCDD treatment (10 nM) of primary normal human bronchial epithelial cells also significantly increased MUC5AC protein levels (Lee et al., 2011).

Wood smoke

In the tracehas of rats that were nose-only exposed to smoke from burning Douglas fir wood (25 g) for up to 20 min, Muc5ac gene expression was increased at 24 h post-exposure (Bhattacharyya etal., 2004).

Cigarette smoke

Treatment of immortalized human bronchial epithelial 16HBE cells with cigarette smoke extract increased MUC5AC gene and protein expression in a concentration-dependent manner (Yu et al., 2011; Yu et al., 2015). Treatment of NCI-H292 lung cancer cells with cigarette smoke extract increased MUC5AC gene and protein expression in a concentration- and time-dependent manner (Takeyama et al., 2001; Shao et al., 2004; Baginski et al., 2006; Lee et al., 2006; Montalbano et al., 2014). Cigarette smoke extract treatment of A549 lung cancer cells (2 h) and primary human bronchial epithelial cells differentiated at the air-liquid interface (6 h and 16 h) increased MUC5AC gene and protein expression (Di et al., 2012).

Whole-body exposure (TE-10 Teague Enterprises, Davis, CA) of rats to smoke from 1R1 research cigarettes (University of Kentucky; increasing dose between 123 to 323 mg/m3 total smoking particulate matter) for 2 h per day, 5 days per week, for 8 weeks significantly elevated Muc5ac levels in the bronchoalveolar fluid (Kato et al., 2020).

Muc5ac gene expression increased in the lungs of male Sprague-Dawley rats that were whole-body exposed to the smoke of 5 cigarettes a day, for 5 consecutive days (Takeyama et al., 2001).


List of the literature that was cited for this KE description. Ideally, the list of references, should conform, to the extent possible, with the OECD Style Guide ( (OECD, 2015). More help

Baginski, T.K., Dabbagh, K., Satjawatcharaphong, C., and Swinney, D.C. (2006). Cigarette smoke synergistically enhances respiratory mucin induction by proinflammatory stimuli. Am. J. Respir. Cell Mol. Biol. 35, 165-174.

Bhattacharyya, S.N., Dubick, M.A., Yantis, L.D., Enriquez, J.I., Buchanan, K.C., Batra, S.K., et al. (2004). In vivo effect of wood smoke on the expression of two mucin genes in rat airways. Inflammation 28, 67-76.

Borchers, M.T., Wert, S.E., and Leikauf, G.D. (1998). Acrolein-induced MUC5ac expression in rat airways. Am. J. Physiol. Lung Cell. Mol. Physiol. 274, L573-L581.

Casalino-Matsuda, S., Monzon, M., Day, A., and Forteza, R. (2009). Hyaluronan fragments/CD44 mediate oxidative stress-induced MUC5B up-regulation in airway epithelium. Am. J. Respir. Cell Mol. Biol. 40, 277–285.

Chen, P., Deng, Z., Wang, T., Chen, L., Li, J., Feng, Y., et al. (2013). The potential interaction of MARCKS-related peptide and diltiazem on acrolin-induced airway mucus hypersecretion in rats. Int. Immunopharmacol. 17, 625-632.

Di, Y.P., Zhao, J., and Harper, R. (2012). Cigarette smoke induces MUC5AC protein expression through the activation of Sp1. J. Biol. Chem. 287, 27948-27958. 

Dohrman, A., Miyata, S., Gallup, M., Li, J.D., Chapelin, C., Coste, A., Escudier, E., Nadel, J., and Basbaum, C. (1998). Mucin gene (MUC 2 and MUC 5AC) upregulation by Gram-positive and Gram-negative bacteria. Biochim. Biophys. Acta 1406, 251–259.

Hao, Y., Kuang, Z., Jing, J., Miao, J., Mei, L.Y., Lee, R.J., Kim, S., Choe, S., Krause, D.C., and Lau, G.W. (2014). Mycoplasma pneumoniae Modulates STAT3-STAT6/EGFR-FOXA2 Signaling To Induce Overexpression of Airway Mucins. Infect. Immun. 82, 5246–5255.

Hewson, C., Edbrooke, M., and Johnston, S. (2004). PMA induces the MUC5AC respiratory mucin in human bronchial epithelial cells, via PKC, EGF/TGF-alpha, Ras/Raf, MEK, ERK and Sp1-dependent mechanisms. J. Mol. Biol. 344, 683–695.

Kato, K., Chang, E.H., Chen, Y., Lu, W., Kim, M.M., Niihori, M., et al. (2020). MUC1 contributes to goblet cell metaplasia and MUC5AC expression in response to cigarette smoke in vivo. Am. J. Physiol. Lung Cell. Mol. Physiol. 319, L82-L90. 

Lamb, D., and Reid, L. (1968). Mitotic rates, goblet cell increase and histochemical changes in mucus in rat bronchial epithelium during exposure to sulphur dioxide. J. Pathol. Bacteriol. 96, 97–111.

Lee, S.Y., Kang, E.J., Hur, G.Y., Jung, K.H., Jung, H.C., Lee, S.Y., et al. (2006). The inhibitory effects of rebamipide on cigarette smoke-induced airway mucin production. Respir. Med. 100, 503-511. 

Lee, Y.C., Oslund, K.L., Thai, P., Velichko, S., Fujisawa, T., Duong, T., Denison, M.S., and Wu, R. (2011). 2,3,7,8-Tetrachlorodibenzo-p-dioxin–Induced MUC5AC Expression. Am. J. Respir. Cell Mol. Biol. 45, 270–276.

Lillehoj, E. P., Kato, K., Lu, W., & Kim, K. C. (2013). Cellular and Molecular Biology of Airway Mucins. Int. Rev. Cell Mol. Biol. 303, 139–202.

Liu, D.-S., Liu, W.-J., Chen, L., Ou, X.-M., Wang, T., Feng, Y.-L., et al. (2009). Rosiglitazone, a peroxisome proliferator-activated receptor-γ agonist, attenuates acrolein-induced airway mucus hypersecretion in rats. Toxicology 260, 112-119.

Montalbano, A.M., Albano, G.D., Anzalone, G., Bonanno, A., Riccobono, L., Di Sano, C., et al. (2014). Cigarette smoke alters non-neuronal cholinergic system components inducing MUC5AC production in the H292 cell line. Eur. J. Pharmacol. 736, 35-43.

Nadel, J.A. (2013). Mucous hypersecretion and relationship to cough. Pulm. Pharmacol. Therap. 26, 510-513.

Rose, M.C., and Voynow, J.A. (2006). Respiratory tract mucin genes and mucin glycoproteins in health and disease. Physiol. Rev. 86, 245-278.

Shao, M., Nakanaga, T., and Nadel, J. (2004). Cigarette smoke induces MUC5AC mucin overproduction via tumor necrosis factor-alpha-converting enzyme in human airway epithelial (NCI-H292) cells. Am. J. Physiol. Lung Cell. Mol. Physiol. 287, L420–L427.

Takeyama, K., Jung, B., Shim, J., Burgerl, P., Dao-Pick, T., Ueki, I., Protin, U., Kroschel, P., and Nadel, J. (2001). Activation of epidermal growth factor receptors is responsible for mucin synthesis induced by cigarette smoke. Am. J. Physiol. Lung Cell. Mol. Physiol. 280, L165–L172.

Turner, J., and Jones, C.E. (2009). Regulation of mucin expression in respiratory diseases (Portland Press Limited).

Wagner, J. G., Van Dyken, S. J., Wierenga, J. R., Hotchkiss, J. A., & Harkema, J. R. (2003). Ozone exposure enhances endotoxin-induced mucous cell metaplasia in rat pulmonary airways. Toxicol. Sci. 74, 437-446.

Wang, T., Liu, Y., Chen, L., Wang, X., Hu, X.-R., Feng, Y.-L., et al. (2009). Effect of sildenafil on acrolein-induced airway inflammation and mucus production in rats. Eur. Resp. J. 33, 1122-1132.

Yu, H., Li, Q., Zhou, X., Kolosov, V., and Perelman, J. (2011). Role of hyaluronan and CD44 in reactive oxygen species-induced mucus hypersecretion. Mol. Cell. Biochem. 352, 65–75.

Yu, H., Li, Q., Kolosov, V.P., Perelman, J.M., and Zhou, X. (2012). Regulation of cigarette smoke‐mediated mucin expression by hypoxia‐inducible factor‐1α via epidermal growth factor receptor‐mediated signaling pathways. J. Appl. Toxicol. 32, 282-292.

Zhu, L., Lee, P., Lee, W., Zhao, Y., Yu, D., & Chen, Y. (2009). Rhinovirus-Induced Major Airway Mucin Production Involves a Novel TLR3-EGFR–Dependent Pathway. Am. J. Resp. Cell Mol. Biol. 40, 610–619.