Notch1 can contribute to viral-induced transformation of primary human keratinocytes

The human papillomavirus (HPV) is the most significant causative agent in the development of cervical cancer. Despite its presence in almost all cervical cancers, HPV by itself is unable to transform a normal cell to a cancerous one. Instead, additional cellular mutations are required to supplement the HPV oncoproteins E6 and E7. Activation of the Notch1 signaling pathway has been proposed as one of the cellular changes that cooperate with the E6 and E7 proteins to cause cervical cancers. This proposition is based on: (a) the detection of active Notch1 in high-grade cervical lesions and cancers; (b) the synergism between Notch1 and E6 and E7 to transform immortalized cells; and (c) the obliteration of neoplastic properties of a cervical cancer cell line when Notch1 expression was inhibited. However, this view was put in doubt by a recent report that showed Notch1 expression is markedly reduced in cervical cancer cells, and this was attributed to the ability of Notch1 to repress the expression of the HPV E6 and E7 proteins. Here we report that although exaggerated levels of Notch1 can, indeed, adversely affect HPV E6 and E7 expression, and cellular proliferation in general, moderate levels of Notch1, together with active phosphoinositide 3 kinase, can, instead, exhibit oncogenic properties that transform primary cells containing HPV16 E6 and E7 proteins. In addition, we show that activated Notch1 is readily detected in all cervical cancer cell lines tested. Together, these results show that not only do cervical cancer cells express Notch1, but also that Notch1 signaling, in synergy with other cellular changes, can participate in the transformation of primary cells expressing E6 and E7 proteins.