K15 protein of Kaposi's sarcoma-associated herpesvirus is latently expressed and binds to HAX-1, a protein with antiapoptotic function.
The Kaposi's sarcoma-associated herpesvirus (KSHV) (or human herpesvirus 8) open reading frame (ORF) K15 encodes a putative integral transmembrane protein in the same genomic location as latent membrane protein 2A of Epstein-Barr virus. Ectopic expression of K15 in cell lines revealed the presence of several different forms ranging in size from full length, approximately 50 kDa, to 17 kDa. Of these different species the 35- and 23-kDa forms were predominant. Mutational analysis of the initiator AUG indicated that translation initiation from this first AUG is required for K15 expression. Computational analysis indicates that the different forms detected may arise due to proteolytic cleavage at internal signal peptide sites. We show that K15 is latently expressed in KSHV-positive primary effusion lymphoma cell lines and in multicentric Castleman's disease. Using a yeast two-hybrid screen we identified HAX-1 (HS1 associated protein X-1) as a binding partner to the C terminus of K15 and show that K15 interacts with cellular HAX-1 in vitro and in vivo. Furthermore, HAX-1 colocalizes with K15 in the endoplasmic reticulum and mitochondria. The function of HAX-1 is unknown, although the similarity of its sequence to those of Nip3 and Bcl-2 infers a role in the regulation of apoptosis. We show here that HAX-1 can form homodimers in vivo and is a potent inhibitor of apoptosis and therefore represents a new apoptosis regulatory protein. The putative functions of K15 with respect to its interaction with HAX-1 are discussed.
Sharp
Tyson V
TV
The CRC Viral Oncology Group, Wolfson Institute for Biomedical Research, University College London, London, United Kingdom WC1E 6BT.
Wang
Hsei-Wei
HW
Koumi
Andrew
A
Hollyman
Daniel
D
Endo
Yoshio
Y
Ye
Hongtao
H
Du
Ming-Qing
MQ
Boshoff
Chris
C
D048868:Adaptor Proteins, Signal Transducing; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017209:Apoptosis; D001665:Binding Sites; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D006367:HeLa Cells; D019288:Herpesvirus 8, Human / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D014162:Transfection; D020798:Two-Hybrid System Techniques; D014764:Viral Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017735:Virus Latency / Q000235:genetics*; D051028:bcl-2-Associated X Protein
D048868:Adaptor Proteins, Signal Transducing; C104759:HAX1 protein, human; C402642:K15 protein, Human herpesvirus 8; D011506:Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D014764:Viral Proteins; D051028:bcl-2-Associated X Protein