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of E1 protein with LDLr family. 70 The involvement of the LDLr in
HCV infection is still controversial and further studies are needed.
4) SR-BI
Scarselli and colleagues reported that SR-BI is an another candidate
of receptor for HCV by using E2 protein binding assay. 88 SR-BI is a
cell surface membrane protein of CD36 superfamily that binds to
chemically modified lipoproteins and often many other types of lig-
ands. 1 HCV E2 proteins of both 1a and 1b genotypes could bind to
HepG2 cells which lack hCD81 expression, suggesting that recep-
tor(s) other than hCD81 may participate in binding of E2 protein to
HepG2 cells. The E2 proteins could also bind to CHO cells stably
expressing human SR-BI, but not mouse SR-BI, through their hyper
variable region 1 (HVR1). Expression levels of SR-BI in various cell
lines were not correlated with the infectivity of pseudotype MLVs
even in the presence of hCD81 and LDLr. Although CHO cell lines
expressing SR-BI and/or hCD81 were not permissive to pseudotype
MLVs infection, 293T cells over-expressing SR-BI resulted in
enhancement of infection of pseudotype MLVs. 10,52 Furthermore,
knockdown of SR-BI expression by siRNAs and anti-SR-BI antibod-
ies reduced and inhibited the infection of the pseudotype MLVs,
respectively. Recently, it was reported that infection of the pseudotype
MLVs was increased by high density lipoproteins (HDLs) but not by
lipid-free apoA-I and apoA-II and was suppressed by knockdown of
SR-BI or lipid transport inhibitors. 108 Furthermore, HDL-mediated
enhancement of pseudotype MLVs infection was not observed in the
pseudotype deleted in HVR1 of E2 protein. Further studies are
needed to clarify the involvement of human SR-BI in HCV infection.
5) DC-SIGN and L-SIGN
Dendritic cells (DCs) are specialized for the recognition of pathogens
and have a pivotal role in the control of immunity. Recently, several
C-type lectin, DC-SIGN (CD209), and lectin-like receptors, L-SIGN
(CD209L), have been characterized that they are expressed abundantly
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