Role of ADAM23 in Normal Human Keratinocytes

“High risk” human papillomaviruses (HPV) are known to cause or are closely associated with the development of head and neck cancers including oral squamous cell carcinomas (OSCCs). Integration of HPV DNA into host genome and subsequent expression of viral oncogenes, such as E6 and E7, are critical initial events for the HPV-associated cancer development; however, HPV infection alone is not sufficient to convert normal cells to malignant phenotypes, and other additional genetic and/or epigenetic events in the HPV-infected cells are required. Previously, we utilized the high-throughput RNAi Decode Library system on human oral keratinocyte-16B (HOK-16B), an immortalized but non-tumorigenic keratinocyte harboring HPV-16 genome, and identified ADAM23 as a putative tumor suppressor that functionally convert HOK-16B cells to tumorigenic. Here, we aimed to determine effects of ADAM23 in proliferation potential (e.g., population doublings) in the absence of HPV backgrounds in normal human oral and epidermal keratinocytes (NHOKs and NHEKs) and OKF6, hTERT-immortalized human oral keratinocytes. During the serially subcultured NHOKs, ADAM23 expression was significant increased during replicative senescence. Overexpression ADAM23 in NHOKs and NHEKs did not cause any changes in population doubling although they exhibited increased expression of p16. Knockdown of ADAM23 in NHEKs had no significant changes in their population doubling. Similarly, overexpression of ADAM23 OKF6 cells yielded no gross alterations in proliferation potential. When the Wnt signaling pathway is examined by treating LiCl or Wnt3a, overexpression of ADAM23 activated Wnt signaling pathway as demonstrated by increased expression of beta-catenin. Our data suggest that ADAM23 has limited effects on keratinocytes in the absence of HPV