Cell immortalization is a critical event in the development of cancer and the oncogenic human papillomaviruses encode an E6 oncogene that is primarily responsible for inducing telomerase activity and consequent immortalization.  Recent studies indicate that the HPV E6 protein mediates the increase in telomerase activity via its ability to engage and activate the hTERT promoter and interact directly with at least two promoter-bound proteins, Myc and NFX-1.  E6 also has a post-translational mechanism to increase telomerase activity by binding directly to hTERT proteins.  In the current grant, we show that hTERT immortalization of primary keratinocytes is independent of its telomerase activity or ability to elongate telomeres.  In agreement with recent work with stem cells, our new preliminary findings demonstrate that hTERT can alter the expression of keratinocyte genes as well as increase the expression of HPV genes.  We hypothesize that the transcription activation function of hTERT or its potential role in altering apoptotic responses may play an essential role in bypassing the M1/M2 restriction points in cell proliferation and thereby facilitate cell immortalization.  In this application, we will evaluate these possibilities using a library of mutan hTERT expression vectors.  We will correlate the ability of these mutant proteins to efficiently bypass cellular senescence with their ability to induce reverse transcriptase activity, hTR binding, telomere binding, telomere elongation, promoter transactivation, and modulation of apoptosis.  These studies will provide new insights into a basic event in the etiology of cancer.