Cutaneous and mucosal human papillomaviruses differ in net surface charge, potential impact on tropism

Abstract

Papillomaviruses can roughly be divided into two tropism groups, those infecting the skin, including the genus beta PVs, and those infecting the mucosa, predominantly genus alpha PVs. The L1 capsid protein determines the phylogenetic separation between beta types and alpha types and the L1 protein is most probably responsible for the first interaction with the cell surface. Virus entry is a known determinant for tissue tropism and to study if interactions of the viral capsid with the cell surface could affect HPV tropism, the net surface charge of the HPV L1 capsid proteins was analyzed and HPV-16 (alpha) and HPV-5 (beta) with a mucosal and cutaneous tropism respectively were used to study heparin inhibition of uptake. The negatively charged L1 proteins were all found among HPVs with cutaneous tropism from the beta-and gamma-PV genus, while all alpha HPVs were positively charged at pH 7.4. The linear sequence of the HPV-5 L1 capsid protein had a predicted isoelectric point (pI) of 6.59 and a charge of -2.74 at pH 7.4, while HPV-16 had a pI of 7.95 with a charge of +2.98, suggesting no interaction between HPV-5 and the highly negative charged heparin. Furthermore, 3D-modelling indicated that HPV-5 L1 exposed more negatively charged amino acids than HPV-16. Uptake of HPV-5 (beta) and HPV-16 (alpha) was studied in vitro by using a pseudovirus (PsV) assay. Uptake of HPV-5 PsV was not inhibited by heparin in C33A cells and only minor inhibition was detected in HaCaT cells. HPV-16 PsV uptake was significantly more inhibited by heparin in both cells and completely blocked in C33A cells.

Differential binding patterns to host cells associated with particles of several human alphapapillomavirus types

“…These possibilities are supported by recent observations indicating that there are differences in surface charges of the L1 proteins for different HPV types (Mistry et al, 2008).…”

“…The major sites include a conserved region of the C terminus that contains clusters of basic amino acids (Joyce et al, 1999), and a more recent study located at least two different HS-interaction sites on the HPV16 L1 capsid surface, including lysine residues 278, 356 and 361 located within the FG and HI loops (Knappe et al, 2007). These findings, together with structural solutions of the capsomeres of several HPV capsids, could help to explain the differential interactions of HPV capsids with HS and ECM observed in our current study and by other investigators (Johnson et al, 2009;Mistry et al, 2008).…”

“…These earlier studies led investigators to propose general mechanisms for HPV infection that should be applicable to all HPV types. More recent studies have demonstrated that HPV types show differences in capsid structure (Bishop et al, 2007), surface charge (Mistry et al, 2008), binding patterns to HS (Buck et al, 2006;Johnson et al, 2009) and to ECM (this study), and uptake pathways (Bousarghin et al, 2003;Johnson et al, 2009). In addition, in vivo studies using a mouse vaginal PsV infection model showed differences in binding properties between two alphapapillomaviruses and a betapapillomavirus type (Johnson et al, 2009;Roberts et al, 2007).…”

Alcohol Treatment of Oral Streptococcus Spp. Increased the Entry of Human Papillomavirus Type 16 into Non-Malignant and Oral Squamous Cell Carcinoma Cells

“…There are presently documented eight cofactors for HPV 16 entry into epithelial cells that contribute to selective mucotropism. These include: (1) clathrin coated vesicles, (2) endocytosis, (3) transport protein particle subunit 8, (4) a negative charge molecular display on entry membrane, (5) annexin A2 expression, (6) integrinsα 6 β 14 expression, (7) cyclophillin B activity and (8) growth factor receptors activation, such as EGFR, and tetraspanins [18][19][20][43][44][45]. In addition entry event studies for HPV 16 in HOK are sadly lacking.…”

Biology and natural history of human papillomavirus infection

“…Laminin-5 can also contribute to the binding of viral capsids to the extracellular matrix in the epithelial cell lines. 9,46,47 In vivo, the viral particles bind efficiently to regions of the basement membrane (BM) only after these regions have been exposed to mechanical or chemical trauma of the epithelium. The L1 capsid protein binds to heparan sulfate proteoglycans in segments of the BM exposed after epithelial trauma.…”