NK cell recognition of tumor cells is mediated by a delicate balance of signals received by MHC class I-binding inhibitory NK cell receptors and activating NK cell receptors, which mainly bind to virus-, stress- or tumor-induced ligands. In addition, adhesion molecules such as the intercellular adhesion molecule-1 (ICAM-1) and its receptors, the lymphocyte function-associated antigen-1 (LFA-1) and Mac-1, are crucial for immune synapse formation and NK cell-mediated killing. In this study, we show that expression of the adhesion molecule ICAM-1 was rapidly induced by E6 and -E7 oncoproteins of HPV16, -18, -5 and -8, but not of HPV38 and -6 in primary human keratinocytes after retroviral transduction. ICAM-1 was upregulated in E6E7-expressing keratinocytes both at mRNA and protein levels. The observed ICAM-1 upregulation in HPV16-E6E7-expressing keratinocytes was partially dependent on activation of the NF-κB pathway. Importantly, the upregulated ICAM-1 expression in HPV16-E6E7-expressing keratinocytes led to enhanced conjugate formation with NK cells. We previously showed that HPV16-positive cervical carcinomas frequently express low levels of inhibitory NK cell ligands and high levels of activating NK cell ligands. Moreover, levels of the adhesion molecule ICAM-1 are enhanced by HPV16-E6/E7. Therefore, strategies that aim at harnessing NK cells might be beneficial for the treatment of cervical carcinoma.
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