Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression
Placental cathepsin M is alternatively spliced and exclusively expressed in the spongiotrophoblast layer
Introduction
Numerous placenta-specific cysteine peptidases were identified in mouse and rat: cathepsin (CTS) J, M, Q, R, -1, -2, -3 and -6 (reviewed in [1]). These novel members of the papain family C1A share 49–55% identity with CTSL on the protein level. Due to the even higher homology among each other (57–78% identity), these putative peptidases were considered a novel subfamily within the family of peptidases of the CTSL-type. This subfamily was termed as CTSJ-like peptidases according to CTSJ, the first placenta-specific cysteine peptidase identified [2]. Reflecting their close relationship, CTSJ-like peptidases are located in a dense cluster on chromosome 13 in close vicinity to CTSL. Presumably CTSJ-like peptidases evolved from a common ancestral gene due to repeated gene duplication events [3]. The absence of CTSJ-like peptidases in the human genome suggests a rather late origin of the placenta-specific peptidases after the divergence of rodent and primate lineages. Each of these peptidases has a specific temporal expression pattern. Furthermore, for CTSJ, CTS1, CTS2 and CTS6 a specific spatial expression has already been demonstrated by in situ hybridization suggesting the importance of these peptidases in the formation and development of the placenta [3], [4], [5].
The placenta is a temporary organ which is essential for growth and development of the mouse embryo. Its formation depends on the invasion of the uterine tissue by fetal trophoblast cells. Trophoblast invasion during implantation and placentation of the mouse embryo requires the coordinated interaction between extracellular matrix degrading peptidases and their inhibitors. After the attachment of the blastocyst to the uterine epithelium on dpc (day post coitum) 4.5 controlled invasion of the uterine wall by trophoblast giant cells is essential for the implantation of the embryo. A number of peptidases and their respective inhibitors, including matrix metallopeptidases [6], [7] and cysteine peptidases [8], have been shown to be expressed by mouse trophoblast and decidual cells during implantation.
While the first half of gestation around the implantation period has been thoroughly studied, there is little known regarding the role of peptidases in the second half of gestation during the development of the placenta. After implantation, the trophoblast cells differentiate and finally form the four layers of the mature placenta: the chorionic plate, the labyrinth layer, the spongiotrophoblast layer and the maternal decidua with trophoblast giant cells [9]. The maturing murine placenta is continuously subjected to tissue remodelling and cell invasive processes which demand the coordinated action of numerous peptidases.
Here, we report on the genomic organization of CTSM, the detailed characterization of its multiple splice variants and putative promoter region as well as its spongiotrophoblast-restricted expression. Additionally, we compared CTSM with its closest relative CTS3.
Section snippets
PAC isolation and sequencing
A PAC library (library no. 711, RPCI-21) was screened by hybridization with the full-length cDNA of mouse CTSM (CTSM2c–7a accession numberAY014777). Nine PAC clones were received from the Resource Center of the DHGP (Berlin) and rescreened by gene specific primers and Southern blot. Only PAC clone RPCIP711L05241Q2 showed a hybridization pattern identical to genomic DNA (data not shown) and was used to subclone overlapping CTSM-specific PstI and HindIII restriction fragments into pBluescript II
Isolation and characterization of the Ctsm gene
Cloning of the full-length cDNA of CTSM by RT-PCR with gene-specific primers from mouse placenta (19.5 dpc) obtained two distinct cDNAs termed as CTSM2c–7a and CTSM2d–7b (Fig. 1C). These cDNAs differ from the cDNA published by Sol-Church and colleagues [12] — here termed as CTSM2d–7a. Furthermore, the analysis of CTSM-specific ESTs revealed two additional CTSM variants, CTSM2b–7a and CTSM2d–Δ7. (Fig. 1C). Since CTSM is located within a dense cluster of highly homologous placenta-specific
Discussion
Murine CTSM displays the typical genomic organization of cathepsin L-like peptidases comprising of 8 exons which span a region of 6 kb [15]. We identified several splice variants of CTSM affecting either exon 2 or exon 7 (CTSM2a,b,c,d–7a,b,c,d,Δ7). Exon 2 splice variants (CTSM2a,b,c,d-) leave the translated region including the catalytic triad unaffected thus encoding potentially functional cysteine peptidases. Alternative splicing affecting the 5′ untranslated region has also been reported for
Acknowledgements
We thank K. Osoegawa, P. Ioannu and P. de Jong (Roswell Park Cancer Institue) for providing the mouse PAC library RPCI21. We thank J. Wilting, S. Conradi, D. Vogt-Weisenhorn, S. Pirrung, C. Kühne and T. Orschmann for technical assistance. We also thank Natalie Surtees for critical comments on the manuscript. This study was supported by the Fonds der Chemischen Industrie.
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Lost or Forgotten: The nuclear cathepsin protein isoforms in cancer
2019, Cancer LettersCitation Excerpt :Here exon 2 spliced variants of the transcript have been detected and differ in the length of the 5’ UTR region of the mature transcript, thus offering a potential mechanism by which rates of translation may be altered (as reported for cathepsins B and L). Additionally, exon 7 spliced variants were also identified, some of which lacked the residues His276 and Asn300 and which would therefore give rise to catalytically-inactive products [52]. Of note, the subcellular localization of this isoform protein was not determined and which may yield some interesting outcomes.
Positive contribution of IRE1α-XBP1 pathway to the expression of placental cathepsins
2013, Biochemical and Biophysical Research CommunicationsCitation Excerpt :Nevertheless, this study provides the important information on the expression program of placental cathepsins, supporting the normal placental development, and healthy fetal growth. As mentioned above, it has been reported that specific kinds of cathepsins (PECs; placentally expressed cathepsins) are highly expressed in placenta [23–26], and mediates various function [27] including the case of Cts7 and Cts8 [28]. Also, it has been reported that placenta is significantly and constantly under ER stressed status [20], and that an increased ER stress is associated with the impaired placental development and fetal growth restriction [37–39].
Placenta-Specific Cathepsins
2013, Handbook of Proteolytic EnzymesFunction of alternative splicing
2013, GeneEmerging Functions of Placental Cathepsins
2008, PlacentaCitation Excerpt :Cathepsins 1 and 2 are expressed early in gestation and are localized to invasive trophoblast giant cells [30]. Tpbpa and cathepsin M are primarily localized to the spongiotrophoblast layer of the placenta while cathepsins P, R and 6 are found in the labyrinth [31–33]. Most of the PECs are expressed at higher levels in term placenta, but significant message for cathepsins P, 1 and 2 can be detected as early as day 7.5 in ectoplacental cone [21,24,30].
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Present address: Molekulare Neurogenetik, Max-Planck-Institut für Psychiatrie, Kraepelinstr. 2-10, D-80804 München, Germany.