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J. Biol. Chem., Vol. 278, Issue 36, 34364-34372, September 5, 2003

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Identification and Characterization of Two Splice Variants of Human Diacylglycerol Kinase ^*

Tomohiro Murakami , Fumio Sakane  , Shin-ichi Imai , Kiyohiro Houkin ¶ and Hideo Kanoh 

From the Departments of Biochemistry and ^¶Neurosurgery, School of Medicine, Sapporo Medical University, South-1, West-17, Chuo-ku, Sapporo 060-8556, Japan

Diacylglycerol kinase (DGK) participates in regulating the intracellular concentrations of two bioactive lipids, diacylglycerol and phosphatidic acid. DGK (1, 128 kDa) is a type II isozyme containing a pleckstrin homology domain at the amino terminus. Here we identified another DGK isoform (2, 135 kDa) that shared the same sequence with DGK1 except for a sterile motif (SAM) domain added at the carboxyl terminus. The DGK1 mRNA was ubiquitously distributed in various tissues, whereas the DGK2 mRNA was detected only in testis, kidney, and colon. The expression of DGK2 was suppressed by glucocorticoid in contrast to the marked induction of DGK1. DGK2 was shown to form through its SAM domain homo-oligomers as well as hetero-oligomers with other SAM-containing DGKs (1 and 2). Interestingly, DGK1 and DGK2 were rapidly translocated from the cytoplasm to endosomes in response to stress stimuli. In this case, DGK1 was rapidly relocated back to the cytoplasm upon removal of stress stimuli, whereas DGK2 exhibited sustained endosomal association. The experiments using DGK mutants suggested that the oligomerization of DGK2 mediated by its SAM domain was largely responsible for its sustained endosomal localization. Similarly, the oligomerization of DGK2 was suggested to result in negative regulation of its catalytic activity. Taken together, alternative splicing of the human DGK gene generates at least two isoforms with distinct biochemical and cell biological properties responding to different cellular metabolic requirements.

Received for publication, February 13, 2003 , and in revised form, June 16, 2003.

The nucleotide sequence(s) reported in this paper has been submitted to the DDBJ/GenBank^TM/EBI Data Bank with accession number(s) AB078967 (human DGK1) and AB078968 (human DGK2).

^* This work was supported in part by Special Coordination Funds (to H. K.) and grants from the Japanese Ministry of Education, Culture, Sports, Science, and Technology (to F. S. and H. K.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Dept. of Biochemistry, Sapporo Medical University School of Medicine, South-1, West-17, Chuo-ku, Sapporo 060-8556, Japan. Tel.: 81-11-611-2111; Fax: 81-11-622-1918; E-mail: sakane{at}sapmed.ac.jp.

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