| Research Article |
Open Access |
|
| A Signaling Network of Thyroid-Stimulating Hormone |
| Renu Goel1,2, Rajesh Raju1,2, Jagadeesha Maharudraiah1,3,4, Ghantasala S. Sameer Kumar1,2, Krishna Ghosh5, Amit Kumar6, T. Pragna
Lakshmi6, Jyoti Sharma1,7, Rakesh Sharma8, Lavanya Balakrishnan1,2, Archana Pan6, Kumaran Kandasamy11, Rita Christopher8, V. Krishna2,
S. Sujatha Mohan1,2,9, H. C. Harsha1, Premendu P. Mathur6, Akhilesh Pandey10 and T. S. Keshava Prasad1,6,7* |
| 1Institute of Bioinformatics, International Tech Park, Bangalore-560 066, India |
| 2Department of Biotechnology, Kuvempu University, Shankaraghatta-577 451, India |
| 3RajaRajeshwari Medical College and Hospital, Bangalore-560 074, India |
| 4Rajiv Gandhi University of Health Sciences, Bangalore-560 041, India |
| 5Department of Biochemistry and Molecular Biology, Pondicherry University, Pondicherry 605 014, India |
| 6Centre of Excellence in Bioinformatics, School of Life Sciences, Pondicherry University, Pondicherry 605 014, India |
| 7Manipal University, Madhav Nagar, Manipal, Karnataka 576 104, India |
| 8Department of Neurochemistry, National Institute of Mental Health and Neuro Sciences, Bangalore, 560 066, India |
| 9Research Unit for Immunoinformatics, RIKEN Research Center for Allergy and Immunology, RIKEN Yokohama Institute, Kanagawa 230-0045, Japan |
| 10McKusick-Nathans Institute of Genetic Medicine, Departments of Biological Chemistry, Oncology and Pathology, Johns Hopkins University School of Medicine,
Baltimore 21205, Maryland, USA |
| 11Research Center for Molecular Medicine of the Austrian Academy of Sciences,Vienna, Austria |
| *Corresponding author: |
Dr. T. S. Keshava Prasad, Ph.D,
Institute of Bioinformatics,
International Tech Park
Whitefield, Bangalore-560066
Tel: 91-80-28416140
Fax: 91-80-28416132
E-mail: keshav@ibioinformatics.org |
|
| |
| Received September 20, 2011; Accepted October 20, 2011; Published October
29, 2011 |
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| Citation: Goel R, Raju R, Maharudraiah J, Sameer Kumar GS, Ghosh K, et
al. (2011) A Signaling Network of Thyroid-Stimulating Hormone. J Proteomics
Bioinform 4: 238-241. doi:10.4172/jpb.1000195 |
| |
| Copyright: © 2011 Goel R, et al. This is an open-access article distributed under
the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited. |
| |
| Abstract |
| |
| Human thyroid stimulating hormone (TSH) is a glycoprotein secreted by the anterior part of the pituitary gland.
TSH plays an important physiological role in the regulating the hypothalamic-pituitary-thyroid axis by modulating the
release of the thyroid hormones from the thyroid gland. It induces iodine uptake by the thyroid, promotes thyroid
epithelial differentiation and growth, and protects thyroid cells from apoptosis. Impairment of TSH signal transduction
pathway leads to thyroid disorders such as goitre, hypothyroidism and hyperthyroidism, which can have complex
clinical manifestations. TSH signaling is largely effected through two separate pathways, the adenylate cyclase
and the phospholipase C pathways. In spite of its biomedical importance, a concise signaling map of TSH pathway
is not available in the public domain. Therefore, we have generated a detailed signaling map of TSH pathway
by systematically cataloging the molecular reactions induced by TSH including protein-protein interactions, posttranslational
modifications, protein translocation events and activation/inhibition reactions. We have cataloged 40
molecular association events, 42 enzyme-substrate reactions and 16 protein translocation events in TSH signaling
pathway resource. Additionally, we have documented 208 genes, which are differentially regulated by TSH. We
have provided the details of TSH pathway through NetPath (http://www.netpath.org), which is a publicly available
resource for human signaling pathways developed by our group. We have also depicted the map of TSH signaling
using NetSlim criteria (http://www.netpath.org/netslim/) and provided pathway maps in Wikipathways (http://www.wikipathways.org/). We anticipate that the availability of TSH pathway as a community resource will enhance further
biomedical investigations into the function and effects of this important hormone. |
| |
| Keywords |
| |
| Homeostasis; Basic Metabolic Rate; HPT Dysregulation;
Camp; PKA; Osteoporosis; Cretinism; Myxedema; Thyrotoxicosis;
Endocrine Signaling |
| |
| Introduction |
| |
| Thyroid-stimulating hormone (TSH) is synthesized and secreted by
the anterior lobe of the pituitary gland. TSH acts on thyroid follicular
epithelium and triiodothyronine (T3) and thyroxine (T4) hormones
regulate the synthesis and release of TSH at the pituitary level and
indirectly affect TSH production by their effect on thyrotropin releasing
hormone (TRH). These hormones act on diverse types of cells in
human body and are involved in the maintenance of basic metabolism.
TSH secretion is regulated by thyrotropin releasing hormone (TRH)
secreted by hypothalamus. TSH belongs to a subset of the cysteineknot
growth factor super family. It is a heterodimer consisting of one
alpha and one beta subunit associated by non-covalent bonds [1]. TSH
is closely related to luteinizing hormone (LH), chorionic gonadotropin
(CG) and follicle stimulating hormone (FSH). These hormones share
the same alpha subunit encoded by CGA gene [2] but have different
beta subunits. The beta subunit of TSH is encoded by the TSHB gene.
Excess amount of alpha subunits can be found in the free form in normal
pituitary and normal placenta [1,3] indicating that the synthesis of the
alpha and beta subunits is regulated independently. The alpha and beta
subunits consist of 116 and 138 amino acid residues, respectively. |
| |
| TSH mediates its effect through its cognate receptor, thyrotropin receptor or TSHR, located primarily on the cell surface of the thyroid
follicular cells. TSHR belongs to the G protein-coupled receptor
superfamily of integral membrane proteins. TSHR contains 2 subunits
including a large ectodomain (alpha or A subunit) and a small
ectodomain (beta or B subunit), which interacts with G proteins to
initiate signaling. Binding of TSH with TSHR on thyroid epithelial cells
stimulates production of iodine transporter, thyroglobulin, and thyroid
peroxidase proteins, which are essential for the synthesis and secretion
of thyroid hormones. A high concentration of TSH results in increased
endocytosis of colloid from lumen to follicular cells and also increases
release of T3 and T4 into the circulation. Low concentration of TSH
lowers thyroid hormone synthesis and secretion [4]. Thyroid disorders
are one of the commonest endocrine disorders affecting public health in form of cretinism, myxedema, thyrotoxicosis, and goitre of various
subtypes [5,6]. Though the pathophysiology of thyroid disorders is
known to certain extent, the underlying molecular interactions are illunderstood.
In this context, a detailed documentation of molecular
reactions induced by TSH, as reported in scientific literature till date,
will be highly useful. Currently, a comprehensive resource of human
TSH pathway is not available as a public resource. Therefore, we
took an initiative to study molecular reactions occurring downstream
to TSH-TSHR interactions and also documented the genes that are
differentially regulated by TSH. We also generated a detailed TSH
pathway model, which comprises of 104 proteins. We have made
the TSH signaling pathway data available as a part of NetPath at
http://www.netpath.org/pathway/NetPath_23, a resource for human
signaling pathways previously developed by our group [7]. A concise
map of TSH signaling pathway developed based on a set of confidence
criteria is also available at http://www.netpath.org/netslim/TSH_pathway.html. We also uploaded TSH pathway in WikiPathways at
http://www.wikipathways.org/index.php/Pathway:WP2032. |
| |
| Manual curation strategies |
| |
| We carried out an extensive search of literature relevant to TSH
signaling pathway. As the first step towards this, we have created
a pathway resource for molecular reactions, which occur upon
stimulation by TSH. We have used PathBuilder [8] to annotate
features of TSH pathway. Inclusion criteria for molecular reactions in
TSH signaling pathway are (i) molecular reactions must be induced
by TSH-TSHR interaction, (ii) the reactions must have been proven in
vivo, with the exception of ligand-receptor interactions, (where even
in vitro experimental evidence is considered), (iii) experiments must
have been conducted in a mammalian system, with a preference to
reactions from the human system. The proteins involved in the various
reactions reported in mammalian system other than human should
have orthologs in human. |
| |
| Molecular associations |
| |
| We have captured the protein-protein interactions (PPIs) under two
categories as direct and complex. Direct interaction refers to a binary
interaction, which represents either a homomeric or a heteromeric PPI.
On the other hand, when proteins have been analyzed as components
of a complex using co-precipitation assays, and where topology of
binary association of each protein components of such a complex
is unknown, such reactions were termed as complex. Additional
information on protein domains and motifs, subcellular localization,
post-translational modifications (PTMs), experimental methodologies
and biological systems used in the investigation were provided. We
have also documented the species of interacting proteins as well as the
species of the cell-line in which the experiment was carried out. |
| |
| Enzyme-substrate reactions |
| |
| PTMs brought about by enzyme-substrate reactions can change
physiochemical properties, structural conformation, subcellular
localization and the activity of the proteins. Therefore, PTMs assume
critical role in signaling events [9-12]. We documented PTMs including
phosphorylation, dephosphorylation, glycosylation and proteolytic
cleavage reactions in the context of TSH pathway. Whenever an
enzyme was proved to modify a substrate, then those reactions were
curated as direct catalytic events. However, as immediate upstream
enzymes were not reported for many of the PTMs, we have referred to
them as induced. For every enzyme-substrate reactions, we have also
documented additional details on protein species, type of modification and the host cell line in which reactions were studied. Site and residue
information of PTMs if available, were mapped to specific sequence as
provided in Ref Seq database [13]. We have also narrated information
on enzymes, substrates and host cell line for every enzyme-substrate
reaction in the ‘Comments’ section. |
| |
| Protein translocation events |
| |
| We have documented translocation of molecules across various
sub-cellular compartments upon stimulation of TSH. We also
documented the dependence of such translocation events on PPIs
or PTMs, wherever such information is available. We have used
standard Gene Ontology (GO) terms for denoting various subcellular
compartments [14]. |
| |
| Activation/Inhibition |
| |
| Apart from PPIs, PTMs and protein translocations, actiavtion/
inhibition reactions of proteins were also reported in TSH signaling
[15-18]. Such reactions could not be listed under molecular association,
enzyme-substrate or translocation reactions. Ideally, these reactions
can be specifically targeted to investigate their role in TSH signaling |
| |
| Gene regulation |
| |
| Genes that are differentially expressed upon TSH stimulation were
documented. This list of genes was obtained from various experimental
platforms including DNA microarrays, Northern blotting, serial
analysis of gene expression and quantitative RT-PCR. |
| |
| Results and Discussion |
| |
| In all, we cataloged 40 molecular association events, 42 enzymesubstrate
reactions and 16 protein translocation events shown in Figure
1(included as supplementary data). PTM site and residue information
were available for 8 proteins. We have also catalogued more than 208
genes, which were reported to be differentially regulated at the mRNA
level by TSH stimulation (Table 1). Curated data have been reviewed
at various levels by curators and reviewers. We have also involved a
Pathway Authority (PPM, who is a co-author) in the review process. |
| |
|
Table 1: Statistics for data annotated for TSH pathway. |
|
| |
| Based on the TSH pathway map assembled here, TSHR is known
to interact with multiple G-alpha subunits such as GNA12, GNA13,
GNAQ, GNAO1, GNAI2, GNAI1, GNAI3, GNAS, GNA11 [19]. TSHR
activation leads to the dissociation of the GTP bound Gα subunit
from the Gβγ subunit heterodimer. These subunits further regulate
the activities of adenylate cyclases, phospholipase C [20] and ion
channels. Activation of the adenylate cyclases leads to the generation
of cAMP [21,22] and subsequent activation of PKA dependent and
independent pathways [23] mainly PKA/CREB and cAMP-RAP1A/
RAP1B system, respectively. TSH also activates the RAS and PI3K
dependent mitogenesis pathways [24,25]. Various studies have also
proved the association of TSHR with JAK1, JAK2, STAT3 [26], HSPA5,
CALR, CANX [27] and ATP1A1 [28]. |
|
| |
| Visualization of TSH signaling pathway |
| |
| We applied NetSlim criteria [29] to TSH signaling pathway data
and selected 60 molecules involved in 44 reactions, which were made
available in NetSlim resource (http://www.netpath.org/netslim/TSH_pathway.html). These selected reactions were depicted as TSH
pathway map using PathVisio [30] as shown in Figure 2 (included as
supplementary data). A NetSlim map with citation is also provided with
each node (molecules) linked to corresponding NetPath molecule page
and the edges hyperlinked to their respective PubMed identifiers. The
arrangement of molecules in the map was derived from i) inhibition/
activation assays, ii) canonical pathways; and iii) review articles. The
NetSlim version of the TSH pathway map can be downloaded from
NetSlim database in different formats such as .gpml, .GenMAPP, .png
and .pdf. The data collected for TSH pathway can be visualized using
visualization software called Cytoscape [31,32]. We have uploaded
NetSlim version of TSH pathway to WikiPathways in order to reach
wider sections of users. Wikipathways is an open, public platform
dedicated to the curation of biological pathways by and for the scientific
community [33]. The pathway data is freely available for download in a
variety of community standard formats. |
| |
| Availability and data formats |
| |
| The TSH pathway is made freely available through NetPath and
NetSlim. We have provided a textual description for each of the
reactions for TSH pathway in NetPath. The scientific community
can involve in the corrections and enrichment of data by providing
critical comments. Graphical representation of TSH pathway as seen
in NetPath and NetSlim databases are provided in Figure 3 (included
as supplementary data). The comprehensive set of curated data in TSH
pathway can be downloaded from NetPath at
http://www.netpath.org/pathway/NetPath_23.NetSlim version of the TSH pathway
information can be downloaded from NetSlim at
http://www.netpath.org/netslim/TSH_pathway.html. In addition, we have also provided
the list of genes, which are differentially regulated by this signaling
pathway in tab-delimited and Microsoft Excel formats. The pathway
data is compatible with various standard data exchange formats
including Proteomics Standard Initiative-Molecular Interaction (PSIMI
version 2.5) [34], Biological Pathways Exchange (BioPAX level 3)
[35] and Systems Biology Markup Language (SBML 4.1.0) [36]. PSIMI
is used to represent interactions and experiments. SBML is used for
simulation models of molecular pathways and mainly discovered for
representation and exchange of pathway data. |
| |
| Conclusions |
| |
| The TSH pathway reactions cataloged in this study are annotated
from published research articles using a set of defined criteria. We
documented various reactions reported to be induced by TSH to
execute physiological function on their target cells. Also, TSH pathway
data obtained in this study would provide an appropriate platform
to design high-throughput experiments to further investigate this
signaling pathway. It will also provide a basic resource to integrate
the ever increasing information on TSH signaling components in
the future. We hope that our effort would also facilitate biomedical
investigations pertaining to complex regulation of HPT axis and
thereby provide insight into molecular networks in the regulation of
HPT axis. The queries, suggestions and critical comments from the
scientific community can enrich TSH pathway information. |
| |
| Conflict of Interests |
| |
| The author(s) declare that they have no competing interests. |
| |
| Acknowledgements |
| |
| We thank the Department of Biotechnology (DBT), Government of India for
research support to the Institute of Bioinformatics, Bangalore. Rajesh Raju and Jyoti
Sharma are recipients of Senior Research Fellowship from the Council of Scientific
and Industrial Research, New Delhi, India. Dr. H.C. Harsha is a Wellcome Trust/
DBT India Alliance Early Career Fellow. Prof. P.P. Mathur acknowledges receipt of
grants from the DBT (BT/BI/03/015/2002), Department of Information Technology,
Government of India (DIT/R&D/BIO/15(9)2007), University Grants Commission
and Pondicherry University for financial support under various projects. Akhilesh
Pandey was supported by NIH Roadmap grant “Technology Center for Networks
and Pathways” (U54 RR 020839). Dr. T. S. Keshava Prasad is supported by
research grant on “Development of Infrastructure and a Computational Framework
for Analysis of Proteomic Data” from DBT, Government of India, New Delhi, India. |
| |
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