SERPINB5 serpin peptidase inhibitor, clade B (ovalbumin), member 5

2004-06-01   Jim Heighway , Shirley Smith , Naomi Bowers , Daniel Betticher 

Institute of Medical Oncology, University of Bern, 3010 Bern, Switzerland (DCB)





The SERPINB5 gene comprises seven exons and six introns which commonly encode a 2.6kb mRNA. Two alternatively processed splice variants have been reported but their significance is unknown. The ATG start is located in exon 2 with the stop codon in exon 7.


Transcriptional control is complex. SERPINB5 may be induced by p53. In addition to a p53 consensus binding site, the promoter also contains functional Ets and AP-1 sites. In oestrogen receptor-positive breast cancer cells, expression may also be induced either directly or indirectly by the oestrogen antagonist, Tamoxifen. The cell-type specific expression of SERPINB5 is heavily influenced by the level of cytosine methylation in a region of sequence immediately upstream of exon 1. In normal cells that do not express SERPINB5, this region is: heavily methylated, associated with hypoacetylated histones and the local chromatin structure is inaccessible. The converse appears to be true for normal cells that express the gene. The analysis of the SERPINB5 promoter in a range of primary cell cultures provided the first formal demonstration that cytosine methylation is important in the regulation of normal cell-type specific gene expression.


No known pseudogene.



SERPINB5 encodes a 375 amino acid 42kDa protein, maspin, which shows sequence homology to serpins of the ovalbumin-type subfamily. In common with other family members, the protein is predicted to fold in such a way as to expose a short reactive site loop (amino acids 331-345) on the surface. However, it is not currently clear whether maspin actually acts as a true serine protease inhibitor and there are some suggestions that the RSL may represent primarily a serine protease substrate. Maspin is therefore generally classified as a non-inhibitory serpin. A number of isoforms of maspin have been detected in primary tissue samples and cultures. These may reflect processed or modified forms of the protein or else may represent degradation products.


Maspin is expressed strongly in specific populations of cells within a range of normal tissues: for example, in the myoepithelial cells of the breast or the basal epithelial cells of the bronchial airways. Other cell types within such tissues may generally show a complete lack of expression. Particular cell-type specific expression levels are likely to be controlled in the normal situation by strikingly different levels of cytosine promoter methylation. Many studies have reported differences in the expression and methylation status of SERPINB5 between tumours and matched normal tissue. However, given the complex pattern of cell-type specific expression/regulation of this gene and our general lack of knowledge of the identity and expression characteristics of the tumour progenitor cells, the pathological significance of these data are currently difficult to interpret.


Sub-cellular localisation is variable depending on cell type. Consistent with predicted function, maspin may be found in certain cell types in cytoplasmic and peri-cellular locations. However, more recent studies have shown that maspin may be localised predominantly to the nucleus of certain normal or malignant cells. The role of the protein in the nucleus is not yet defined.


The exact cellular role of maspin is not currently clear. Whilst the protein can specifically influence certain aspects of cell behaviour, often tumour and normal tissue derived expression data are at least superficially contradictory. This likely reflects our incomplete understanding of the function of the protein in different situations: that is, in the context of different cell types, differentiation states and gene expression backgrounds.

SERPINB5 was originally described as a breast tumour suppressor, a gene which was active in normal breast epithelial cells and which was down-regulated progressively towards malignancy with increasing degrees of tissue disorder being associated with less frequent instances of expression. Consistent with such a tumour suppressor function, work in vitro and in vivo suggested that maspin suppressed angiogenesis, reduced tumour invasiveness, growth, and metastasis and sensitised cells to apoptosis. It was suggested that maspin exerted these effects, at least in part, through modulation of plasminogen activation. In a breast cancer cell line, the maspin RSL was deemed to be critical for the inhibition of tumour cell invasion and the promotion of cell adhesion to extracellular matrix molecules.

However, recent studies have subsequently painted a more complex and perhaps contradictory picture. Maspin appears to have a critical role in early embryonic development. Homozygous loss of expression in mice knockouts is lethal at the peri-implantation stage. The absence of the protein (-/-) disrupts the formation of the endodermal cell layer whilst maspin heterozygote knockout (+/-) endodermal cells grow more slowly than wild-type (+/+) cells. This is particularly interesting in the context of high-level maspin expression in tumours arising from organs of endodermal origin, such as the GI tract, lungs and thyroid. Furthermore, in LA7 cells, a well characterised rat adenocarcinoma in vitro model of mammary gland differentiation, maspin was shown to negatively regulate dome formation, possibly through the perturbation of cell adhesion. This observation suggests that at least in some situations, maspin expression can block differentiation processes.


Maspin is an ovalbumin (ov-) serpin, located in one of the two ov-serpin clusters (18q21.33, 6p25) in the human genome. Phylogenetic analysis has suggested that maspin is most closely related to the members of the 6q group and SERPINB8 on 18q.



No somatic coding sequence mutations have been described for SERPINB5. Minimally, three validated non-synonymous and one synonymous cSNP are located within the gene at amino acids: 176 (C/T, Phe/Ser), 187 (C/G, Leu/Val), 298 (C/T, Ser/Ser) and 319 (A/G, Ile/Val).

The gene is not thought to be a frequent tumour amplification or translocation target.


However, there are number of reports highlighting differences in promoter methylation status in primary human tumours compared to matched normal tissues. Whilst these studies are difficult to interpret given that cytosine methylation is used appropriately to control the cell-type expression of SERPINB5 in normal tissue (and therefore probably in the tumour cell progenitor), the striking observation of allele-specific differences in promoter methylation in pre-neoplastic gastric lesions suggests that pathological epigenetic alteration may be a significant factor in deregulating (or failing to appropriately inactivate) the gene in certain cancers.

Implicated in

Maspin was classified as a breast cancer suppressor on the basis of functional and observational (immunohistochemical - IHC) studies. However, as more model systems, tumour types and corresponding normal tissues were analysed, the situation became more complex. Several microarray analyses of different human cancers indicated that maspin was frequently strongly expressed in tumour over normal tissue. Furthermore, strong and frequent expression was seen in some instances in pre-neoplastic lesions. Clearly, some tumours in a range of tissues express maspin and some do not, the subcellular localisation of the protein is variable, as is the methylation status of the promoter. Expression may correlate to some degree with the clinical behaviour or characteristics of particular tumours but in many cases the data from different studies of the same diseases and tissues appear to be contradictory. One point that must be borne in mind is that a gene can be associated with good prognostic factors and improved survival and yet it can still be driving the malignant phenotype in the tumours in which it is expressed. In summary, many questions concerning the pathological role of maspin in human cancer remain unanswered.
Entity name
Breast cancer
The terminal duct-lobular system of the breast comprises two specialised epithelial cell types, inner luminal secretory cells and outer contractile myoepithelial cells. It is thought that most breast tumours arise from cell types located within this structure. SERPINB5 is strongly expressed in the outer oestrogen receptor (ER) negative myoepithelial cells, where it is frequently located in both the nucleus and the cytoplasm. The luminal cells appear not to express maspin. The largest study (1068) of maspin expression in breast tumours scored a nuclear signal in 96% of carcinomas and a cytoplasmic signal in 35%. The nuclear staining was correlated with ER and progesterone receptor (PR) positivity whilst the cytoplasmic staining was associated with ER and PR negativity. It has been suggested that breast cancer initiates and is maintained from an aberrant adult stem cell. Maspin expression levels in tumours may therefore reflect a tendency for the tumour initiating stem cell component to differentiate towards cells which lack or retain maspin expression. These lesions may behave differently clinically in a way which is or is not directly related to maspin expression. This would not exclude the possibility that maspin is associated with some aspect of the multipotent stem cell phenotype nor that it might be involved in the actual differentiation process of particular cell types.
Entity name
Lung cancer
Lung cancers generally arise from a component of the bronchial epithelium (BE). This pseudostratified lining of the airways comprises multipotent basal cells and specialised differentiated apical cells. The basal cells represent a reserve component of the epithelium which can differentiate into each of the mature cell types. Alveolar, stromal and normal differentiated epithelial cells are all typically negative for maspin expression. However, strong nuclear staining is seen in all airway basal cells (Figure: A, B). Maspin appears to be strongly expressed, generally in the cytoplasm and nucleus, in >95% of squamous cell carcinomas (Figure C) and 30-50% of adenocarcinomas. The expression of maspin is linked to the degree of promoter methylation and allele-specific transcript analysis suggests that in approximately 50% of lesions, expression in the tumour is predominantly driven from one chromosomal allele. Maspin is strongly and presumably inappropriately expressed in a significant fraction of pre-neoplastic bronchial lesions and a small fraction of histologically non-neoplastic epithelia (Figure D). The observation that maspin is strongly expressed apparently appropriately in the normal stem cell-like basal component of the BE and that this expression appears to be down-regulated in the differentiated BE cells might suggest that the protein has a role in some aspect of maintenance of the basal cell (perhaps lung stem cell) phenotype and that a failure to inactivate maspin appropriately during differentiation may contribute to bronchial neoplasia.
Atlas Image
The images show an immunohistochemical analysis of maspin expression in histologically normal lung (A, B, D) and NSCLC (C) tissues. The tumour cells (C) show intense nuclear and cytoplasmic staining. Panels A and B show typical staining patterns for normal bronchial tissue. Stromal cells are negative, basal epithelial cells in the airway epithelia in the normal sections show strong predominantly nuclear staining whilst apical epithelial cells are negative. A small number of hyperplastic epithelia show strong nuclear/cytoplasmic expression of maspin (D).
Entity name
Gastric cancer
IHC reports are to some extent contradictory and this may reflect differing aetiologies. However, several studies suggest that maspin is strongly expressed in gastric carcinoma over normal mucosa. It has been reported that 80% of primary tumours and all gastric normal mucosa (GNM) with intestinal metaplasia (IM) show dense and diffuse cytoplasmic immunoreactivity while in contrast, GNM without IM show only weak or no staining. They further demonstrated that the GNM with IM show maspin promoter hypermethylation of one parental allele which would be consistent with expression occurring from a single allele in a clonal expansion, either as a result of an aberrant demethylation event or else as a consequence of a failure to methylate appropriately one parental allele at some time during the differentiation process from a maspin expressing precursor. An alternative explanation, that SERPINB5 is developmentally imprinted in a GM with IM precursor, seems less likely but is nevertheless possible. Both alleles were hypermethylated in GNM without IM and both were generally hypomethylated in tumours.
Entity name
Pancreatic cancer
Maspin is strongly expressed in most if not all pancreatic adenocarcinomas whereas normal pancreatic tissue appears to be negative or only weakly positive.
Entity name
Prostate cancer
Whilst maspin expression in prostatic cancer was reportedly correlated with a less aggressive pathological and histological tumour grade, the protein was found to be expressed frequently in high grade prostate intraepithelial neoplasia, an observation which would be consistent with a role for maspin in pre-malignancy of the prostate.
Entity name
Maspin appears to be expressed in a small fraction of primary melanomas but not normal melanocytes. This expression is correlated with the methylation status of the promoter.
Entity name
Maspin expression has been reported in a large fraction of: papillary thyroid carcinomas, undifferentiated carcinomas and poorly differentiated carcinomas but only rarely in well differentiated tumours and not at all in normal thyroid, follicular adenomas or follicular carcinomas. The expression of maspin in thyroid carcinomas was therefore closely associated with a lack of differentiation of the tumour cells.
Entity name
Ovarian cancer
Whilst normal ovarian surface epithelia have low levels of expression, maspin appears to be strongly expressed in a large fraction of primary tumours (37%). Tumours with high levels of maspin were more likely to be invasive and show cytoplasmic staining. Maspin over-expression was further associated with higher tumour grade, the presence of ascites and shorter survival. However, somewhat paradoxically, introduction of wild-type maspin into two ovarian cancer cell lines reduced their invasiveness.
Entity name
Bladder cancer
Maspin does not appear to be expressed in normal transitional cells of the bladder. However, a sizable fraction of tumours show strong nuclear and cytoplasmic expression; which is significantly correlated with muscle-invasive over non-invasive bladder cancer.


Pubmed IDLast YearTitleAuthors
145781902003Cell-type-specific repression of the maspin gene is disrupted frequently by demethylation at the promoter region in gastric intestinal metaplasia and cancer cells.Akiyama Y et al
120217832002Role for DNA methylation in the control of cell type specific maspin expression.Futscher BW et al
149852572004Maspin plays an essential role in early embryonic development.Gao F et al
124000182002Expression profiling of primary non-small cell lung cancer for target identification.Heighway J et al
151455212004Tamoxifen induces the expression of maspin through estrogen receptor-alpha.Liu Z et al
113093272001Expression of the tumor suppressor gene Maspin in human pancreatic cancers.Maass N et al
126351332003Maspin expression in invasive breast cancer: association with other prognostic factors.Mohsin SK et al
127993812003Sufficiency of the reactive site loop of maspin for induction of cell-matrix adhesion and inhibition of cell invasion. Conversion of ovalbumin to a maspin-like molecule.Ngamkitidechakul C et al
147432022004Disruption of cell-type-specific methylation at the Maspin gene promoter is frequently involved in undifferentiated thyroid cancers.Ogasawara S et al
124301372002Maspin is up-regulated in premalignant prostate epithelia.Pierson CR et al
120157532002Maspin is expressed in the nuclei of breast myoepithelial cells.Reis-Filho JS et al
106444481999Human ovalbumin serpin evolution: phylogenic analysis, gene organization, and identification of new PI8-related genes suggest that two interchromosomal and several intrachromosomal duplications generated the gene clusters at 18q21-q23 and 6p25.Scott FL et al
146474622003Maspin - the most commonly-expressed gene of the 18q21.3 serpin cluster in lung cancer - is strongly expressed in preneoplastic bronchial lesions.Smith SL et al
122315372002The paradoxical expression of maspin in ovarian carcinoma.Sood AK et al
147322292004Expression and regulation of tumor suppressor gene maspin in human bladder cancer.Sugimoto S et al
150865682004Aberrant expression of the maspin gene associated with epigenetic modification in melanoma cells.Wada K et al
150480802004Maspin expression in normal lung and non-small-cell lung cancers: cellular property-associated expression under the control of promoter DNA methylation.Yatabe Y et al
90409391997Transactivation through Ets and Ap1 transcription sites determines the expression of the tumor-suppressing gene maspin.Zhang M et al
106923902000p53 regulates the expression of the tumor suppressor gene maspin.Zou Z et al
113317462001Proteomic dissection of dome formation in a mammary cell line: role of tropomyosin-5b and maspin.Zucchi I et al

Other Information

Locus ID:

NCBI: 5268
MIM: 154790
HGNC: 8949
Ensembl: ENSG00000206075


dbSNP: 5268
ClinVar: 5268
TCGA: ENSG00000206075


Gene IDTranscript IDUniprot

Expression (GTEx)



PathwaySourceExternal ID
p53 signaling pathwayKEGGko04115
p53 signaling pathwayKEGGhsa04115
MicroRNAs in cancerKEGGhsa05206
MicroRNAs in cancerKEGGko05206

Protein levels (Protein atlas)

Not detected


Pubmed IDYearTitleCitations
162039892005Detection of the placental epigenetic signature of the maspin gene in maternal plasma.66
122315372002The paradoxical expression of maspin in ovarian carcinoma.50
160490062005Mammary serine protease inhibitor (Maspin) binds directly to interferon regulatory factor 6: identification of a novel serpin partnership.44
220116692012Genome-wide analysis of DNA methylation and the gene expression change in lung cancer.43
120376652002Maspin sensitizes breast carcinoma cells to induced apoptosis.41
147162962004Identification of maspin and S100P as novel hypomethylation targets in pancreatic cancer using global gene expression profiling.41
199660162010Interleukin-6 trans-signalling differentially regulates proliferation, migration, adhesion and maspin expression in human prostate cancer cells.39
127892712003Mutant p53 and aberrant cytosine methylation cooperate to silence gene expression.36
117513842001Pleiotrophic inhibition of pericellular urokinase-type plasminogen activator system by endogenous tumor suppressive maspin.33
171893992006Maspin: the new frontier.32


Jim Heighway ; Shirley Smith ; Naomi Bowers ; Daniel Betticher

SERPINB5 serpin peptidase inhibitor, clade B (ovalbumin), member 5

Atlas Genet Cytogenet Oncol Haematol. 2004-06-01

Online version: