Analysis of epidermal-type transglutaminase (TGase 3) expression in mouse tissues and cell lines

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Abstract

In the formation of the cornified cell envelope in the epidermis, epidermal-type transglutaminase (TGase 3) cross-links a variety of structural proteins. However, its expression in other tissue has not been investigated. Furthermore, no cell line expressing TGase 3 has been found. The tissue distribution of TGase 3 in mice was investigated using reverse-transcription polymerase chain reaction (RT-PCR) and Western blotting analyses. TGase 3 mRNA was expressed in the brain, stomach, spleen, small intestine, testis, skeletal muscle and skin. The stomach and testis expressed TGase 3 protein in size similar to that observed in the epidermis. Screening various cell lines, a gastric human cancer cell line, MKN-1 and mouse neuroblast cell line, neuro2a, were found to express TGase 3.

Introduction

Transglutaminases (TGase:EC 2.3.2.13) constitute a family of the Ca2+-dependent enzymes that covalently cross-link proteins by catalyzing the formation of isopeptide bonds between the γ-carboxyamide group of glutamine and the ε-amino group of lysine [1], [2]. To date, six TGases have been characterized in mammals. Keratinocyte-type TGase (TGase 1) and epidermal-type TGase (TGase 3) are expressed mainly in the skin and the hair follicle [3], [4], [5]. TGase 1 was also recently found in adherent junctions in simple epithelial cells [6]. Tissue-type TGase (TGase 2) is distributed in most tissues and plays a role in a variety of processes, ranging from apoptosis to extracellular matrix formation [7], [8], [9], [10], [11]. TGase 4 is a prostate specific secretory enzyme involved in the formation of copulatory plug [12]. Factor XIII (plasma-type TGase) catalyzes the cross-linking of fibrin monomers during blood coagulation [13]. A sixth novel member (TGase X) was discovered in human keratinocytes in experiments using the reverse transcription-PCR method, taking advantage of homologous sequences in the TGase family [14].

TGase 3 is predominantly involved in the formation of the cornified cell envelope, where it cross-links various structural proteins in the lately differentiated keratinocytes and the inner hair sheath cells. The native TGase 3 protein molecule contains 692 amino acids and has a molecular mass of 77 kDa, both in human and mouse [15]. Similar to TGase 1 and Factor XIII, TGase 3 is activated from its protype by limited proteolysis. Upon activation, unknown protease(s) proteolyzes TGase 3, which is synthesized as a 77 kDa zymogen, into a 47 kDa component containing the catalytic domain and a 30 kDa molecule [15], [16]. Only dispase, a bacterial protease, can proteolyze the zymogen form of TGase 3 in vitro. The activation mechanisms by proteolysis in vivo activation of TGase 3 are not understood.

In respect to the gene expression of the human TGase 3, the promoter sequence was reported from human genomic clone [17]. However, the regulatory mechanisms for the transcription remained unclear. An in vitro culture system expressing TGase 3 is indispensable for examining these questions.

Appropriate cell lines expressing TGase 3 protein or mRNA have not yet been discovered and the distribution of TGase 3 in other tissues have not been reported. Previous reports detected TGase 3 mRNA in differentiated primary cultured keratinocytes, but not TGase 3 protein [15]. To make progress in the in vitro analysis of the gene expression and enzymatic regulation of TGase 3, we attempted to clarify the tissue distribution and to establish cultured cell system expressing of TGase 3.

In this study, we first investigated the tissue distribution by RT-PCR and Western blotting analysis. In addition to the epidermis, the stomach, brain and testis were found to express significant amounts of TGase 3. Furthermore, we examined the ability of cell lines derived from the stomach, brain and skin to express TGase 3. As well as mouse primary keratinocyte cultured cells, MKN-1 and neuro 2a cells both expressed TGase 3.

Section snippets

Cell culture

Pam212 cells, neuro 2a cells, HaCaT cells, MDCK cells were cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% fetal bovine serum (FCS), 50 μg/ml streptomycin and 50 U/ml penicillin at 37°C in an atmosphere of 5% CO2. MKN-1 cells (obtained from Japanese Cancer Research Bank) were maintained in RPMI1640 with the same supplements.

Primary culture of mouse skin keratinocytes was performed as described [18]. Briefly, the skin of newborn mice was peeled off and floated on the

Tissue distribution of mouse TGase 3 by RT-PCR analysis

The expression of TGase 3 mRNA was analyzed by RT-PCR. Since the members of the TGase family are quite similar, the primers were designed to enable specific amplification of both human and mouse TGase 3 cDNA. Furthermore, to avoid using genomic DNA as the template, the sequences used for primers spanned deduced exon/intron junctions.

Of the tissues examined, apparent PCR products with the expected size (360 bp) were obtained from brain, stomach and testis, as well as skin (Fig. 1). There was a

Discussion

Although TGase 3 is required for cross-linking structural proteins in the skin and the hair follicle, its expression in other tissues has not been sufficiently investigated. Since RT-PCR methods are specific and sensitive for detection of mRNA, we examined the TGase 3 expression in total RNAs for various mouse tissues. Since there are significant homologies among the cDNA sequences of the members of TGase family, the primers for PCR reaction were designed not to amplify the DNA fragment of

Acknowledgements

We are grateful JCRB and Dr T. Motoyama in Niigata University for providing MKN-1. Thanks also to D.N.E. Fusenig in the German Cancer Research Center for HaCaT and Dr K. Matumoto in Osaka University for Pam212. We also thank P.A. Davies in the University of Texas for providing us with plasmid containing human TGase 2. This work was supported by a Grant-in-Aid for Scientific Research No. 12660074 from the Ministry of Education, Science, Sports and Culture of Japan (to K.H.).

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