Kaposi's Sarcoma-associated Herpesvirus GPCR

6 Pages·2000·0.112 MB·English

by  Geras-Raaka E., Gershengorn M.C.

Kaposi’s Sarcoma-
associated Herpesvirus
GPCR
Elizabeth Geras-Raaka and Marvin C. Gershengorn
*
Department of Medicine, Division of Molecular Medicine, Weill Medical College and Graduate
School of Medical Sciences of Cornell University, 1300 York Avenue, New York, NY 10021, USA
*corresponding author tel: [phone], fax: [phone], e-mail: [email protected]
DOI: 10.1006/rwcy.2000.22013.
SUMMARY BACKGROUND
Kaposi’s sarcoma-associated herpesvirus (KSHV, Discovery
human herpesvirus 8), which is a virus that appears
to be etiologic for Kaposi’s sarcoma, primary effusion Kaposi’s sarcoma-associated herpesvirus (KSHV,
lymphomas, and multicentric Castleman’s disease human herpesvirus 8) is a recently identified member
in humans, encodes a G protein-coupled receptor of the herpesvirus family (Chang et al., 1994; Russo
(ORF 74, KSHV GPCR) that is homologous to et al., 1996). KSHV has been found in Kaposi’s
human chemokine receptors. KSHV GPCR is more sarcoma (KS) lesions of patients with AIDS and of
promiscuous than most chemokine receptors in that non-AIDS-related patients (Chang et al., 1994;
it binds CC and CXC chemokines. For GPCRs Moore and Chang, 1995), in normal-appearing tissue
encodedwithinviralgenomes,KSHVGPCRisnovel adjacent to KS lesions and in lymph nodes and
in that it exhibits constitutive signaling activity. It peripheral blood B cells in patients with KS (Noel,
signals via the phospholipase C-inositol 1,4,5-tri- 1995). KSHV has also been found in two distinct
sphosphate-1,2-diacylglycerol pathway and activates types of lymphoid proliferative disorders primary
the Jun kinase/SAP kinase and p38 MAP kinase effusion lymphomas (PELs) (Cesarman et al., 1995;
pathways. Expression of KSHV GPCR in rat NRK Arvanitakis et al., 1996) and multicentric Castleman’s
fibroblasts stimulates cell proliferation. KSHV disease (Corbellino et al., 1996). KSHV has been
GPCR can transform mouse NIH 3T3 fibroblasts shown to be a transmissible virus that infects human
in vitro and KSHV GPCR-expressing NIH 3T3 cells B cells (Mesri et al., 1996) and human endothelial
form tumors in mice. Thus, KSHV GPCR displays cells (Flore et al., 1998). Extensive sequence analyses
activities of human oncogenes. Moreover, KSHV of fragments of KSHV have shown homology to
GPCR induces expression of vascular endothelial herpesvirus saimiri and Epstein-Barr viruses (Moore
growth factor (VEGF), a potent and efficacious et al., 1996). Since these two viruses infect and
stimulator of angiogenesis, in NIH 3T3 cells. Thus, transformlymphoblastoidcells(Miller,1974;Rangan
because of its tumorigenic and angiogenic potential, et al., 1977), it seemed possible that KSHV may be a
KSHV GPCR is likely to play a role in the transforming agent also. Recently, Flore et al. (1998)
pathogenesis of diseases associated with KSHV showed that KSHV could transform primary human
infection. endothelial cells.
2120 Elizabeth Geras-Raaka and Marvin C. Gershengorn
Lastly, it has been shown that there is seroconver- domains. On the extracellular surface is the N-
sion of antibodies against KSHV before the develop- terminus and three loops. Extracellular loop 1 (ECL-
ment of KS in most patients with AIDS and that 1)connectstransmembranehelix2(TM-2)andTM-3,
KSHV appears to be a sexually transmitted disease ECL-2 connects TM-4 and TM-5, and ECL-3 con-
(Gao et al., 1996a,b; Kedes et al., 1996). Thus, nects TM-6 and TM-7. The cell surface membrane is
accumulatingevidenceisconsistentwiththeideathat spanned by seven (cid:11) helices. On the intracellular side
KSHV is involved in the pathogenesis of human arethreeloopsandtheC-terminus.Intracellularloop
primaryeffusionlymphomas(Nadoretal.,1996)and 1 (ICL-1) connects TM-1 and TM-2, ICL-2 connects
Kaposi’s sarcoma (Offermann, 1996). TM-3andTM-4,andICL-3connectsTM-5andTM-6.
An open reading frame in the genome of KSHV Inthreedimensions,theseven(cid:11)helicesarepredictedto
encodes a protein that was shown to be a cons- formahelicalbundlethatapproximatesacylinder,with
titutively active G protein-coupled receptor (GPCR). TM-7closetoandinteractingwithTM-1andTM-2.
Alternative names Main activities and
pathophysiological roles
KSHVGPCR;HHV8GPCR;IL-8-likeGPCR;viral
GPCR or GCR; KSHV ORF 74.
KSHV GPCR has been shown to be expressed at the
mRNA level in tissues from patients with Kaposi’s
Structure
sarcoma and in B cell lymphomas (Cesarman et al.,
1996). For GPCRs encoded within viral genomes,
The putative two-dimensional structure of KSHV KSHV GPCR is novel in that it exhibits constitutive
GPCR is illustrated in Figure 1. Like all GPCRs, signaling activity (Arvanitakis et al., 1997). Because
KSHV GPCR is an integral membrane protein with constitutive activation of the signaling pathways
extracellular, transmembrane, and intracellular activated by KSHV GPCR induces cell proliferation
Figure1 Putativetwo-dimensionaltopologyofKSHVGPCR.
H2N
M
S M N L T D L A
G E N D F A
Y
TM E C V S V E L S F N G S Y D V V D PC VM SA KQ W S IE RD DS IT L F ED Extracellular
R Y W
TV V I S SR EN A G N M T A RR CY TR GL
W T PY NPI TLG HR C LRHW D D RTLL V NI
TFNLFNNVIGIIHILLKLGYLGSCVV LACMIGSNELFLILSVILSLCDLLLLFI FLRYVYYIISCVVYREDVYSFVLLCLF LLAKKGATSQLWLSGSLAVVDALI LACAVALRTIWLTYFLVVPTRGFVSLLLV HVRFLVFVLGVLAPLLKVFVYVNFIC LLSAAASRPSGSLQYFVTLGYILLVVCL Transmembrane
A L P R R Q
R
S A G L W T R R
R V S T R S K L Q A M
A Y Y Intracellular
G
HOOC T T A L
G S M S Q R L S Q F
F
Kaposi’s Sarcoma-associated Herpesvirus GPCR 2121
and transformation (Post and Brown, 1996), KSHV Description of protein
GPCR expression transforms NIH 3T3 cells (Bais
et al., 1998), and constitutively active GPCRs cause
KSHV GPCR is a protein of 342 amino acids that
tumorsinhumans(Arvanitakisetal.,1998),ithasbeen
appears to have the features of a GPCR including
suggestedthatKSHVGPCRisinvolvedinthepatho-
an extracellular N-terminus, three extracellular
genesis of tumors associated with KSHV infection.
loops, seven hydrophobic, transmembrane-spanning
domains, three intracellular loops, and an intracel-
GENE
lular C-terminus (Figure 1). It is a member of the
rhodopsin/(cid:12)-adrenergicreceptorsubfamilyofGPCRs
Accession numbers butislackingsomeoftheaminoacidresiduesthatare
highlyconservedinsubfamilymembers.Forexample,
U24275; U82242; U71368; AF079845; U75698; it has Ile in place of Asp at position 14 in TM-2, Val
U93872. in place of Asp or Glu at position 24 in TM-3 (of the
Asp/Glu-Arg-Tyr motif) and Val in place of Asn at
Sequence position 17 in TM-7 (of the Asn-Pro-Xaa-Xaa-Tyr
motif); numbering of positions and alignment
according to Baldwin (Baldwin et al., 1997). Most
See Figure 2.
importantly, KSHV GPCR exhibits marked, consti-
tutive signaling activity (i.e. signaling in the absence
PROTEIN
of agonist) when expressed in mammalian cells
(Arvanitakis et al., 1997).
Accession numbers
1718331; 1621029; 3551771; 3386561; Q98146; Relevant homologies and species
2246493; 1930014.
differences
Sequence
The amino acid sequence of KSHV GPCR shows
See Figure 3. homology to the GPCR encoded in the herpesvirus
Figure 2 The nucleotide sequence of the KSHV GPCR gene.
CGTGGTGGCGCCGGACATGAAAGACTGCCTGAGGCTTTGGAAGAGACCGTACATCCT
CTGCCTAAAGAGGGATCCCAGGCAGGAGTATATCAGGGGAACCACGGCGCTGTACAG
TGCCTGCAGTAACGAGGTTACTGCCAGACCCACGTTTATCAACCCCCGCGTATAGCA
GCTGTCCCGGATCCAGCGTCGCCTTAGCAGAGTGTCCAGTAGATTTAGTACGTGGTA
AGGGAAGCAAAACACAAAAAACAGCAGCACCACAGCAACAATCACCCCCCTTACCTT
CCGCCTGGCTTGCAGCTTTGTCCTCCTCACCACACACCAGGTGAGAGCATAAAACAG
AATAAGGAGGGCCAGGGGTAACAGGAAACCTGCAGTAACTGACACGGTTCTGACATG
CAGTCGCCAGTCTGCAGTCATGTTTCCCGCGTTCTCATAACACATGGCCTGCTTGCT
GACCGGGTCGACCACCCTGCTCCTGTGTCGACAGGCATCCCCCGACAGCACCAATGC
AATTAACAGTGCAGCGGATGTCAGTACCCATCCGAGGGACTGCTTCTTGGGCCAGGA
ACGCGTAGAATATGCCACCAGGAGGTACCTCACTAGACTGACGCACACAACACTGAA
GATATCCAAGTAGACATATAAATAGTAAAAAAAAATTTCAAGTCTGCACAAGCCTGT
GGAGATGATATTGGGAAACAAAAACATCAACACTTCTGCCAATAGAGATATGCTAAG
ACACAGCGAGTTTAGGCAGATACCCAGGAGCAGTATATCTATCGCTCCTGCCCGCGA
TCGGTGCTTGCAAAAAATGTAGGTGACCAATCCATTTCCAAGAACATTTATGAGGAA
AATCAGAGAGAGTATTCCAACGTTCCACGTGTAAGGCACCACGGTGGTCATCTCACA
CACGCTCACTTCTAGGCTGAAGTTTCCAGAGTAGTCATATCCGCTCATATTTAGAGT
TTCATTCCAGGATTCATCATCATCTAAGAAGATGGTTAGGAAATCCTCGGCCGCCAT
Figure 3 The amino acid sequence of KSHV GPCR.
1 MAAEDFLTIF LDDDESWNET LNMSGYDYSG NFSLEVSVCE MTTVVPYTWN
51 VGILSLIFLI NVLGNGLVTY IFCKHRSRAG AIDILLLGIC LNSLCLSISL
101 LAEVLMFLFP NIISTGLCRL EIFFYYLYVY LDIFSVVCVS LVRYLLVAYS
151 TRSWPKKQSL GWVLTSAALL IALVLSGDAC RHRSRVVDPV SKQAMCYENA
201 GNMTADWRLH VRTVSVTAGF LLPLALLILF YALTWCVVRR TKLQARRKVR
251 GVIVAVVLLF FVFCFPYHVL NLLDTLLRRR WIRDSCYTRG LINVGLAVTS
301 LLQALYSAVV PLIYSCLGSL FRQRMYGLFQ SLRQSFMSGA TT
2122 Elizabeth Geras-Raaka and Marvin C. Gershengorn
saimiri genome (Nicholas et al., 1992; Ahuja and Regulation of receptor expression
Murphy, 1993) and to several mammalian GPCRs
(Straderetal.,1994;PowerandWells,1996),withthe
RegulationofKSHVGPCRexpressionisnotknown.
highest homology to receptors for IL-8, namely
The levels of KSHV GPCR mRNA can be increased
CXCR1 and CXCR2 (Murphy and Tiffany, 1991;
in lymphomatous B cells in culture by incubation
Holmes et al., 1991).
with phorbol esters (Sarid et al., 1998) or butyrate
The amino acid sequences deduced from several
(E. Cesarman, personal communication).
KSHV DNA isolates from KS tissues and B cell
lymphomas were identical (U24275, U71368,
AF079845; U75698, U93872). One amino acid sequ-
Release of soluble receptors
ence from a B cell lymphoma differed by one residue
(U82242) and another by 13 residues in TM-4
(U82242) caused by the loss of a single nucleotide There is no evidence that this occurs; it is unlikely.
that is recovered by a downstream loss of two
nucleotides.
SIGNAL TRANSDUCTION
Affinity for ligand(s) ThemostimportantaspectofKSHVGPCRsignaling
is that signaling occurs in the absence of any agonist;
that is, KSHV GPCR is constitutively active.
KSHV GPCR appears to bind a number of human
CXC and CC chemokines (Arvanitakis et al., 1997).
However, binding studies have been confounded by
the interactions of many chemokine ligands with Associated or intrinsic kinases
glycosaminoglycans.Therefore,characterizationfrom
measurements of effects of chemokines on signaling KSHV GPCR activates Jun kinase (JNK)/stress-
by KSHV GPCR may be more definitive than those activated protein kinase (SAP kinase) and p38
from binding studies. In general, relative affinities of mitogen-activated protein kinase (p38 MAP kinase)
ligands for GPCRs can be estimated from relative but not extracellular signal-regulated kinase 2 (ERK-
potencies. Although most chemokines tested do not 2)/MAP kinase (Bais et al., 1998). The mechanism(s)
affect KSHV GPCR signaling, a small number were of activation of these protein kinases is not known.
found that further stimulate KSHV GPCR constitu-
tiveactivity(seebelow)andothersthatinhibitKSHV
GPCR signaling. Human growth-related protein (cid:11)
Cytoplasmic signaling cascades
(GRO(cid:11)) (EC (cid:136)15nM) and IL-8 (EC (cid:136)39nM)
50 50
(Gershengorn et al., 1998) further stimulate KSHV
GPCR whereashumanIP-10(EC (cid:136)39nM)(Geras- KSHV GPCR signals via activation of intracellular
50
Raaka et al., 1998b), human SDF-1 (EC (cid:136)43nM) phosphoinositide-specific phospholipase C leading to
50
and viral monocyte inflammatory protein II (vMIP- formation of inositol 1,4,5-trisphosphate (IP ) and
3
II) (EC (cid:136)48nM) inhibit KSHV GPCR signaling 1,2-diacylglycerol second messengers (Arvanitakis
50
(Geras-Raakaetal.,1998a).Thus,IP-10,SDF-1,and et al., 1997). The G protein(s) that couple KSHV
vMIP-IIareinverseagonists(ornegativeantagonists) GPCR to phosphoinositide-specific phospholipase C
of KSHV GPCR signaling. is not known. Protein kinase C is activated but
calcium-dependent protein kinases have not been
studied.
Cell types and tissues expressing
DOWNSTREAM GENE
the receptor
ACTIVATION
KSHV GPCR is encoded by KSHV and has been
Transcription factors activated
found to be expressed at the messenger RNA
(mRNA) level in lesions of patients with Kaposi’s
sarcoma and in lymphomatous B cells (Cesarman KSHVGPCRactivatesaproteinkinaseC-responsive
et al., 1996). promoter introduced by gene transfer (Arvanitakis
Kaposi’s Sarcoma-associated Herpesvirus GPCR 2123
et al., 1997) and therefore probably acts, at least in THERAPEUTIC UTILITY
part, via AP-1 transcription factor.
Effects of inhibitors (antibodies) to
receptors
Genes induced
The effects of inverse agonists have not been studied
The only specific gene that has been shown to be in animal models.
induced by KSHV GPCR is that for VEGF, how-
ever, other genes must be induced because
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