Suppression of ADAM23 is functionally associated with HPV-mediated carcinogenesis

Human Papilloma Virus (HPV) mediated Oropharyngeal Squamous Carcinoma (OPSC) is becoming more relevant and alarming as oral exposure to HPV is increasing. HPV is a DNA virus that infects keratinocytes found in the epithelia of oral cavity. HPV genome translocation to the host nucleus and subsequent expression of oncoproteins E6 and E7 is a hallmark in development of HPV positive OPSCC. E6 allows a cell to bypass p53 regulation, and E7’s interaction with pRb allows progression of cell cycle despite abnormalities, ultimately, permitting proliferation. However, HPV infection alone does not trigger malignant transformation as supported by the fact that only a few individual with persistent HPV infection develop carcinoma. Therefore, we believe that additional genetic alteration or epigenetic regulation must take place to create an environment favorable for malignant transformation and lead to development of cancer. We utilized human oral keratinocyte-16B (HOK-16B), a non-transformed oral keratinocyte harboring HPV-16 genome, and high-throughput RNAi Decode Library to create an event that may alter the phenotype of HOK-16B. We have identified and confirmed A Disintegrin And Metalloproteinase 23 (ADAM23) silencing in HOK-16B results in high cell proliferation rate. It also increases tumorigenic potential in vitro tumor sphere assay and anchorage independent soft agar assay. Furthermore, its increased tumorigenic potential led to formation of cyst in vivo xenograft experiment with immuncompromised mice. Microarray analysis of HOK-16B with ADAM23 silenced showed that a number of genes were upregulated, prominently, CLDN-1, which plays a critical role in cell-cell interaction, and metastasis in aggressive breast cancers. In addition, attenuating E6 or/and E7 expression in ADAM23 knocked-down HOK-16B showed, ADAM23 cooperates with these oncoproteins to enhance tumorigenic potential of HOK-16B. Furthermore, diminished expression of ADAM23 in HPV positive HNSCC supports the silence of ADAM23 and co-expression of E6 and E7 would lead to malignant transformation. These findings imply that ADAM23 could be a useful therapeutic and prognostic marker screening individuals in high-risk of developing HPV positive HNSCC