CD1d, a Sentinel Molecule Bridging Innate and Adaptive Immunity, Is Downregulated by the Human Papillomavirus (HPV) E5 Protein: a Possible Mechanism for Immune Evasion by HPV

Abstract

CD1d and CD1d-restricted natural killer T (NKT) cells serve as a natural bridge between innate and adaptive immune responses to microbes. CD1d downregulation is utilized by a variety of microbes to evade immune detection. We demonstrate here that CD1d is downregulated in human papillomavirus (HPV)-positive cells in vivo and in vitro.CD1d immunoreactivity was strong in HPV-negative normal cervical epithelium but absent in HPV16-positive CIN1 and HPV6-positive condyloma lesions. We used two cell lines for in vitro assay; one was stably CD1d-transfected cells established from an HPV-negative cervical cancer cell line, C33A (C33A/CD1d), and the other was normal human vaginal keratinocyte bearing endogenous CD1d (Vag). Flow cytometry revealed that cell surface CD1d was downregulated in both C33A/CD1d and Vag cells stably transfected with HPV6 E5 and HPV16 E5. Although the steady-state levels of CD1d protein decreased in both E5-expressing cell lines compared to empty retrovirus-infected cells, CD1d mRNA levels were not affected. Confocal microscopy demonstrated that residual CD1d was not trafficked to the E5-expressing cell surface but colocalized with E5 near the endoplasmic reticulum (ER). In the ER, E5 interacted with calnexin, an ER chaperone known to mediate folding of CD1d. CD1d protein levels were rescued by the proteasome inhibitor, MG132, indicating a role for proteasome-mediated degradation in HPV-associated CD1d downregulation. Taken together, our data suggest that E5 targets CD1d to the cytosolic proteolytic pathway by inhibiting calnexin-related CD1d trafficking. Finally, CD1d-mediated production of interleukin-12 from the C33A/CD1d cells was abrogated in both E5-expressing cell lines. Decreased CD1d expression in the presence of HPV E5 may help HPV-infected cells evade protective immunological surveillance.There are approximately 100 identified genotypes (types) of human papillomavirus (HPV). Over 40 of these are classified as genital HPV subtypes that invade the reproductive organs, including the uterine cervix, vaginal wall, vulva, and penis. Genital HPV types are further subclassified into high-risk types that are commonly associated with cervical cancer and low-risk types that cause noninvasive condyloma acuminata. Although exact classification varies among researchers, subtypes 16,18,31,33,35,39, 45, 51, 52, 56, 58, 66, and 68 are typically classified as high risk and subtypes 6,11,40,42,43,44, 54, 61, and 72 as low risk (44). Genital HPV infection involves short-term virus proliferation, followed by the long-term latent presence of a small number of copies of the viral genome within the basal cells of the genital epithelium (44). Infections with high-risk HPV subtypes result in progression to genital tract cancers (most commonly cervical) in only a small percentage of infected women and typically after a long latency period. A high percentage of high-risk HPV DNA-positive infected women resolve their infections during the proliferative phase and thereby clear the virus or progress to latency with...

Immune Regulation and Evasion of Mammalian Host Cell Immunity During Viral Infection

“…and a stably transfected HPV-negative cervical cancer cell line, C33A (C33A/CD1d), HPVs have been found to downregulate CD1d expression by E5 protein mediated disruption of ER traffic. Accordingly, it has been suggested that the decreased CD1d expression in the presence of HPV E5 may facilitate the virus infected cells to evade protective immunological surveillance [97].…”

“…Measles virus [128] Proteases targeting signal transduction Block IFN induction by affecting molecules of the innate immune pathways HAV, HCV [110] Degradation of cellular TRIF Replication and transcription activator (RTA) degrades TRIF KSHV [2] CD1d down regulation Viral protein E5 targets CD1d (a sentinel molecule bridging innate and adaptive immunity) by inhibiting calnexin-related CD1d trafficking HPV [97] Science and Technology, Govt. of India.…”

Host-Pathogen Co-Evolution: Chlamydia trachomatis Modulates Surface Ligand Expression in Genital Epithelial Cells to Evade Immune Recognition

“…The immunoevasive targeting of CD1d is not unique to C. trachomatis. We have also shown that cell surface expression of CD1d is reduced in vitro and in vivo in human papillomavirus (HPV)-positive cells (Miura, Kawana et al 2010). This effect can be isolated to the presence of the E5 proteins of HPV subtype 6 and HPV subtype 16, it occurs at a post-transcriptional level and it is mediated by proteasomal degradation.…”

Human Papillomavirus: Biology and Pathogenesis

“…E7 expression is nevertheless associated with impairment of IFN-gama-induced enhancement of presentation of endogenous antigen to cytotoxic T lymphocytes (Zhou et al, 2011). Further mechanism of HPV-mediated immune escape involve viral proteins: HPV E7 has high and widespread similarity to several humans proteins, causing a limited immunogenicity (Natale et al, 2000); E6 can downregulate IL-18 expression (Cho et al, 2001); E5 mediate acidification of endossomes, affecting antigen processing and presentation in antigen presentation cells (Straight et al, 1995); E5 also downregulate CD1d, a MHC I-like glycoprotein that presents self or microbial lipid antigen to natural killer -the downregulation of this molecule is utilized by a variety of microbes to evade immune detection (Miura et al, 2010). Finally, natural killer (NK) cell activity is also reduced in patients with HR-HPV infection (Stanley, 2009a;O´Brien and Campos, 2002).…”