CSTB (cystatin B (stefin B))

2008-07-01   Zala Jevnikar , Janko Kos 

Faculty of Pharmacy, University of Ljubljana, Ljubljana, Slovenia

Identity

HGNC
LOCATION
21q22.3
LOCUSID
ALIAS
CPI-B,CST6,EPM1,EPM1A,PME,STFB,ULD
FUSION GENES

DNA/RNA

Description

The stefin B gene is located on human chromosome 21q22.3 and it contains 3 exons and 2 introns. The transcript length of stefin B mRNA is 294 bps. A novel variant, with retention of the entire intron 2 is transcribed from two exons with an ORF of 249 bp. It encodes a putative 9.0-kDa protein of 83 amino acids, including 57 identical to stefin B followed by 26 amino acids encoded by the intron 2 sequences.

Proteins

Atlas Image
Richardson diagram of stefin B structure: alpha-helixes are shown in red and beta-sheets in green (MEROPS: the peptidase database - I25.003: cystatin B).

Description

The cystatin superfamily comprises at least four families of closely related proteins, such as stefins (family I), cystatins (family II), kininogens (family III), and various structurally related but noninhibitory proteins of family IV. A significant structural difference between stefins and cystatins is the signal peptide, which is responsible for extracellular targeting of cystatins, whereas stefins lack this peptide and have been reported as intracellular inhibitors. Human stefin B is a single chain protein consisting of 98 amino acid residues, with a molecular mass of 11,175 kDa. Stefin B is a neutral protein with pI values between 5.9 - 6.5 and is able to form a dimmer stabilized by noncovalent forces. Like other members of the cystatin superfamily, stefin B is reversible and competitive inhibitor of cysteine proteases, particularly cathepsin L and cathepsin S with Ki values in the picomolar range whereas cathepsin B inhibition is weaker (Ki 10-7M).

Expression

Stefin B is widely distributed among different cell types and tissues. Although it lacks an export signal sequence and is generally thought to function intracellularly, it has also been found in extracellular fluid.

Function

Stefin B is thought to play a role in protecting cytosolic and cytoskeleton proteins against the cysteine proteases accidentally released from lysosomes. Besides protease inactivation stefin B could bind other proteins in a multiprotein complex which might contribute to the disease in patients with progressive myoclonus epilepsy. Decreased levels of stefin B mRNA were detected in patients with progressive myoclonus epilepsy and associated with excessive activity of cathepsin B. Moreover, stefin B may be important in the control of osteoclasts bone resorption. It inhibits bone resorption by down-regulating intracellular cathepsin K activity. On the other hand stefin B protected osteoclasts from experimentally induced apoptosis, promoting cell survival in the nervous system.

Homology

Human stefin B exhibit a high degree of homology to other cysteine protease inhibitors of the cystatin superfamily which includes human stefin A and the homologues in other species. It is 79% identical with cystatin beta from rat liver, but contains only a single cysteine.

Mutations

Note

Eight mutations in the stefin B gene have been reported to associate with an autosomal recessive neurodegenerative disorder, progressive myoclonus epilepsy of Unverricht-Lundborg type (EPM1). Most of the disease alleles harbour an unstable expansion of at least 30 copies of a normally polymorphic 12-nucleotide, dodecamer repeat located in the promoter region of the stefin B gene. Three reported EPM1 mutations affect splice sites, two result in amino-acid changes and two predict truncated proteins either through creating a stop codon or producing a frameshift.

Implicated in

Entity name
Invasive cancers
Disease
Higher levels of stefin B in tumours have been determined in lung, breast, head and neck and prostate cancer as well as in murine lymphosarcomas, hepatomas and Lewis lung carcinomas. These higher levels, up to a certain level, may counter-balance the excessive activity of cysteine cathepsins, associated with matrix remodelling resulting in the progression of the disease. On the other hand, high cytosolic levels of stefins may be relevant for regulation of apoptosis, when initiated via lysosomal cell death pathway inhibiting cathepsin B, which was proposed as a dominant execution protease in the lysosomal apoptotic pathways, induced in a variety of tumour cells by tumour necrosis factor alpha ( TNF-alpha ). In some studies lower levels of stefins in tumours have been reported. Lower mRNA levels of stefin B have been reported in breast and esophagus tumours as compared to adjacent control tissues.
Although stefins are cytosolic proteins, they have also been detected in body fluids of cancer patients. Stefin B has been detected in ascitic fluid from patients with ovarian carcinoma and in bronhoalveolar fluid of lung cancer patients.
Diagnosis: The poor survival rate of hepatocellular carcinoma is in part due to the inability to diagnose patients at an early stage. Stefin B is specifically overexpressed in most hepatocellular carcinoma and is also elevated in the serum of a large proportion of hepatocellular carcinoma patients. Stefin B may be a useful marker for diagnosing patients with hepatocellular carcinoma with a high sensitivity.
Prognosis
Higher levels of stefin B in tumour tissues have been shown to correlate with a favourable prognosis of cancer patients. A significant prognostic value of stefin B was determined in patients with lung and head and neck cancer. On the other hand, animal model with excluded expression of stefin B did not support its suppressive function in cancer. A significantly lower metastatic spread was detected in stefin B knock-out mice than in wild-type animals. Similarly, higher levels of stefin B in body fluids have been associated with a poor prognosis of cancer patients. Alterations in secretion may result in higher extracellular and lower intracellular levels of stefins and, therefore, a reverse correlation with patient survival is to be expected.
Oncogenesis
Increased levels of cysteine protease activity, not being balanced by a corresponding increase of cysteine protease inhibitors are associated with progression of malignant disease and poor patients prognosis. Enhanced expression of stefin B would be expected to diminish the tumour-associated proteolytic activity and indeed, there is evidence of a suppressive role of stefin B in various cancer types.
Entity name
Progressive myoclonus epilepsy
Disease
The progressive myoclonus epilepsy of the Unverricht-Lundborg type (EPM1) is an autosomal recessive disease characterized by progressive myoclonic jerks and decline in cognition. Genetic linkage studies, suggest the involvement of the stefin B gene. A decreased amount of stefin B mRNA is a common finding in EPM1 patients and it may be due to: 1) a mutation in the promoter region causing a decrease in the rate of transcription of the gene or 2) mutations of the coding region/splice sites that may inhibit translation or diminish the half-life of the transcript and/or of the protein. The availability of a stefin B knock-out mouse as a model for the disease has allowed identification of the presence of severe apoptotic damage to the cerebellar granule cells. This observation combined with the anti-protease function of stefin B protein has suggested that it may have an anti-apoptotic function in the cerebellum. It was shown that a number of proteins (manly proteins that are involved in the regulation of cytoskeletal functions) that are not proteases can interact specifically with stefin B, forming a multiprotein complex. The first hypothesis is that stefin B may be active as antiprotease, protecting the complex against the attack of proteases. An alternative hypothesis is that stefin B may bind to the interacting proteins modifying the structure, thus allowing the correct formation of the complex. A further hypothesis is the sequestration of stefin B by the multiprotein complex, thus impeding its interaction with cathepsins.

Bibliography

Pubmed IDLast YearTitleAuthors
90079721997Friends and relations of the cystatin superfamily--new members and their evolution.Brown WM et al
179201382008Cystatin B and its EPM1 mutants are polymeric and aggregate prone in vivo.Cipollini E et al
170038392007Cystatin B: mutation detection, alternative splicing and expression in progressive myclonus epilepsy of Unverricht-Lundborg type (EPM1) patients.Joensuu T et al
158934212006Towards novel anti-cancer strategies based on cystatin function.Keppler D et al
106905312000Cysteine proteinase inhibitors stefin A, stefin B, and cystatin C in sera from patients with colorectal cancer: relation to prognosis.Kos J et al
97693671998Cysteine proteinases and their endogenous inhibitors: target proteins for prognosis, diagnosis and therapy in cancer (review).Kos J et al
182815402008Identification of cystatin B as a potential serum marker in hepatocellular carcinoma.Lee MJ et al
89384341996Isolation and characterization of the mouse cystatin B gene.Pennacchio LA et al
39020201985Amino acid sequence of the intracellular cysteine proteinase inhibitor cystatin B from human liver.Ritonja A et al
151449472004Cysteine cathepsins (proteases)--on the main stage of cancer?Turk V et al

Other Information

Locus ID:

NCBI: 1476
MIM: 601145
HGNC: 2482
Ensembl: ENSG00000160213

Variants:

dbSNP: 1476
ClinVar: 1476
TCGA: ENSG00000160213
COSMIC: CSTB

RNA/Proteins

Gene IDTranscript IDUniprot
ENSG00000160213ENST00000291568P04080
ENSG00000160213ENST00000291568Q76LA1
ENSG00000160213ENST00000639959A0A1W2PQG6
ENSG00000160213ENST00000640406A0A1W2PS52

Expression (GTEx)

0
1000
2000
3000
4000
5000
6000

Pathways

PathwaySourceExternal ID
Immune SystemREACTOMER-HSA-168256
Innate Immune SystemREACTOMER-HSA-168249
Neutrophil degranulationREACTOMER-HSA-6798695

Protein levels (Protein atlas)

Not detected
Low
Medium
High

References

Pubmed IDYearTitleCitations
199131212009Gene-centric association signals for lipids and apolipoproteins identified via the HumanCVD BeadChip.85
200750682010Stefin B interacts with histones and cathepsin L in the nucleus.27
189516262008Proteomic analyses associate cystatin B with restricted HIV-1 replication in placental macrophages.25
124524812002Reduced cystatin B activity correlates with enhanced cathepsin activity in progressive myoclonus epilepsy.20
222871592012The regulation of cysteine cathepsins and cystatins in human gliomas.18
169694752006Cystatins in non-small cell lung cancer: tissue levels, localization and relation to prognosis.14
199551832010Interaction between oligomers of stefin B and amyloid-beta in vitro and in cells.14
170038392007Cystatin B: mutation detection, alternative splicing and expression in progressive myclonus epilepsy of Unverricht-Lundborg type (EPM1) patients.13
159550632005Interaction of human stefin B in the prefibrillar oligomeric form with membranes. Correlation with cellular toxicity.12
182815402008Identification of cystatin B as a potential serum marker in hepatocellular carcinoma.12

Citation

Zala Jevnikar ; Janko Kos

CSTB (cystatin B (stefin B))

Atlas Genet Cytogenet Oncol Haematol. 2008-07-01

Online version: http://atlasgeneticsoncology.org/gene/40181/cstb