Mucin Type Location Physiological & pathological roles Corticosteroid effect
MUC1 MT Lung and airways (lining epithelial cells of the lung and alveolar type II cells). Normal nasal mucosa. Nasal polyps.

Other: Nearly all epithelium. Hematopoietic cells. Activated T cells (lymphocytes, dendritic cells). Sperm Corneal endothelial cells. Breast. Pancreas.
Responsible for viscoelastic nature of mucus. Role as protective barrier against invading pathogens and chemicals: Aids in mucociliary clearance of foreign bodies. Provides defense to the upper and lower respiratory tracts.

Anti-inflammatory role during airway infection, controlling the resolution of inflammation through the inhibition of TLR signaling.

Associated with epithelial cell differentiation (in stomach, pancreas, lung, trachea, kidney, salivary and mammary glands and the female reproductive tract).

Tumor-associated molecule (frequent over expression and aberrant glycosilation in many cancers including, breast, pancreas, colon, lung and endometrial cancer). Promotes cancer metastasis and tumorigenesis.

Functions of the different MUC1 segments:
- Ectodomain (anti-adhesive, pro-adhesive, hydration and lubrication of cell surfaces, ERBB signaling).
- Cytoplasmic tail (signal transduction, and transcriptional regulation; participation in cell growth and proliferation mechanisms, cell protection from apoptosis).
YES

In vitro studies: Dexamethasone increases MUC1 expression in cancer cell lines [60,61]. Dexamethasone upregulates MUC1 expression in human corneal epithelial cells [62].

In vivo studies: Corticosteroid therapy increases MUC1 expression in nasal polyps [64].
MUC2 S Lung and airways. Normal nasal mucosa. Nasal polyps.

Other: Intestines (Jejunum, ileum, colon)
Major mucin secreted in the large intestine. Important role in: host innate defense, regulation of secretion, absorption processes, maintaining colonization resistance that contribute in maintaining the integrity of the protective mucus barrier in the large intestine [78].

The expression of MUC2 correlates with the activity of diseases, such as ulcerative colitis and Crohn’s  diseases[78].
YES

In vitrostudies: Budesonide inhibits the induction of MUC2 by inflammatory mediators in airway epithelial cells [58,59].
MUC3 MT Gastrointestinal epithelium (colon, small intestine, gall bladder) Major mucin secreted in the large intestine. Important role in: host innate defense, regulation of secretion, absorption processes, maintaining colonization resistance that contribute in maintaining the integrity of the protective mucus barrier in the large intestine [78].

The expression of MUC3 correlates with the activity of diseases, such as ulcerative colitis and Crohn’s diseases [78].
YES

In vitro studies: Steroids upregulate MUC3 expression in cultured breast cancer cells [79].
MUC4 MT Lung and airway surface epithelial cells. Normal nasal mucosa. Nasal polyps.

Other: Epithelium (eye, oral cavity, lacrimal glands, salivary gland, cervix, prostate gland, stomach, colon and mammary gland).
Responsible for viscoelastic nature of mucus. Role as protective barrier against invading pathogens and chemicals: Aids in mucociliary clearance of foreign bodies. Provides defense to the upper and lower respiratory tracts.

Implicated in tumor progression by inducing increased cell growth, proliferation and survival. Aberrant expression in ovarian tumors and premalignant and malignant pancreatic lesions. Frequently overexpressed lung, breast and colon cancers.

Functions of the different MUC4 segments: - Ectodomain (anti-adhesive, hydration and lubrication of cell surfaces, ERBB signaling).
YES

In vitro studies: Dexamethasone inhibits MUC4 expression in nasal polyps [22]. Dexamethasone downregulates MUC4 expression in human corneal epithelial cells [62]. Inhibitory effect of corticosteroids in MUC4 increased mRNA expression in nasal polyps [63].

In vivo studies: Corticosteroid therapy increases MUC4 expression in nasal polyps [64].
MUC5AC S Lung and airway epithelium (goblet cells) Normal nasal mucosa. Nasal polyps.

Other:
Eyes.
Stomach.
Major gel-forming mucin in the respiratory tract. Responsible for viscoelastic nature of mucus. Protection and stabilization of the ciliated surface.

Role as protective barrier against invading pathogens and chemicals: Aids in mucociliary clearance of foreign bodies. Provides defense to the upper and lower respiratory tracts. Contribute to the defensive barrier function and the rheology of the airways mucus.

Marker for goblet cell metaplasia.

Associated with respiratory diseases, mainly with asthma.  
YES

In vitro studies:  Dexamethasone decreases MUC5AC expression in both human epithelial cell lines [55,56,57] and in primary bronchial epithelial cells [57] and in rat primary airway epithelial cells [56].
Budesonide inhibits the induction of MUC5AC by inflammatory mediators in airway epithelial cells [58,59].

In vivo studies: Corticosteroids decrease secreted mucin MUC5AC expression in nasal polyps [64]
MUC5B S Lung and airway epithelium (submucosal glands) Normal nasal mucosa. Nasal polyps.

Other: Salivary glands. Submandibular glands.
Major gel-forming mucin in the respiratory tract. Responsible for viscoelastic nature of mucus. Protection and stabilization of the ciliated surface.

Role as protective barrier against invading pathogens and chemicals: Aids in mucociliary clearance of foreign bodies. Provide defense to the upper and lower respiratory tracts. Contributes to the defensive barrier function and the rheology of the airways mucus. Associated with respiratory diseases, mainly with COPD.

Interaction between MUC5B and different salivary proteins (important in the maintenance of oral physiology by: enhanced physical protection, enhanced enamel integrity, enhanced non-immune host defense).
YES

In vivo studies: Corticosteroids decrease secreted mucin MUC5B expression in nasal polyps [64].
MUC6 S Stomach, ileum, gall bladder. Breast. MUC6 is expressed in normal, benign and in malignant breast cancer [79]. YES

In vitro studies: Steroids upregulate MUC6 expression in cultured breast cancer cells [79].
MUC7 S Lung and airways. Normal nasal mucosa. Nasal polyps.

Other: Salivary glands. Sublingual and submandibular glands. Lacrimal gland acini.
Secreted but not gel-forming mucin.

Interaction between mucins and different salivary proteins are important in the maintenance of oral physiology (enhanced physical protection, enhanced enamel integrity, enhanced non-immune host defense).  
Unknown.
MUC8 S Lung and airways. Normal nasal mucosa. Nasal polyps. MUC8 overexpression in nasal polyps. Upregulation of MUC8 mRNA expression by inflammatory mediators [80].

MUC8 as a ciliated cell marker in human nasal epithelium [81].
YES

In vitro studies: Dexamethasone suppressed lipopolysaccharide-induced MUC8 mRNA levels in cultured human  nasal epithelial cells [82].
MUC9 S and MT Ovaries. Fallopian tubes MUC9 is expressed in malignant epithelial ovarian tumors [83].

MUC9 or oviductal glycoprotein (OVGP1) is present in serum of women with ovarian cancer and has been described as possible serum marker for the detection of ovarian cancer [83].
Unknown.
MUC10   Submandibular mucin. Salivary mucin. Unknown
MUC11 MT Lung Other: Colon Reproductive tract.   Unknown
MUC12 MT Stomach, colon, pancreas, prostate, uterus.   Unknown
MUC13 MT Lung  and airways.

Other: Colon, trachea, kidney, small intestine, conjunctival epithelium.
Aberrantly expressed in gastric, colorectal, ovarian [84] , pancreatic, lung ovarian carcinomas.

MUC13 overexpression increases cell growth, colony formation, cell migration, and invasion [85].
Unknown
MUC15 MT Lung and airways.

Other [86]: Colon, small intestine, prostate, placenta, salivary gland, thyroid gland, moderately in the kidney, conjunctival epithelium.
Aberrant expression of MUC15 correlates with development of colorectal adenocarcinoma [87].

MUC15 potential marker of malignancy and prognosis in papillary thyroid carcinoma [88].
Unknown
MUC16 MT Lung and airways surface epithelial cells. Nasal polyps.

Other: Epithelium of the ocular surface, reproductive organs and the mesothelium lining body cavities (pleural, peritoneal, and pelvic cavities). Conjunctival epithelium
Role as protective barrier against invading pathogens and chemicals.

Overexpressed in ovarian and endometrial cancer. Well-known serum marker for ovarian cancer (CA 125).
YES

In vitro studies: Dexamethasone upregulates MUC16 expression in vitro in human corneal epithelial cells [62].

Dexamethasone increases MUC16 expression at both the mRNA and protein levels in nasal polyp epithelial cells [22].
MUC17 MT Gastrointestinal tract (duodenum, colon, stomach) Conjunctival epithelium MUC17 has a role in protecting the intestinal mucosa against luminal pathogens [89].

MUC17 is expressed in select pancreatic and colon cancer cell lines and in intestinal absorptive cells [90]. Aberrant overexpression of MUC17 is correlated with pancreatic ductal adenocarcinomas [91].
Unknown.
MUC18 MT Lung and airways. Other: Breast. MUC18 has been shown to promote metastasis in several tumors, such as breast cancer [92] and melanoma [93] by increasing their motility, invasiveness and tumorigenesis.

MUC18 amplifies lung inflammation during bacterial infection [94,95].
Unknown.
MUC19 S Lung and airways (Trachea) Other: Salivary gland. Major  salivary glandular mucin. Unknown.
MUC20 MT Lung and airways. Other: Placenta, colon, prostate, liver. Upregulated in renal injuries [96]. Unknown.
MUC21 MT Lung and airways. MUC21 modulates cell adhesion [97]. Marker for lung  adenocarcinomas. Unknown.
MUC22 MT Lung and airways.   Unknown.
*MT: Membrane-tethered mucin; S: secreted mucin.
*General data in the table reviewed previously in several mucin reviews [14,15,18,21,73,98,99].
Table 1: Mucins, their characteristics and modulation by corticosteroids.