TRANSITION OF HUMAN PAPILLOMAVIRUS TYPE-16 AND TYPE-18 TRANSFECTED HUMAN FORESKIN KERATINOCYTES TOWARDS IMMORTALITY - ACTIVATION OF TELOMERASE AND ALLELE LOSSES AT 3P, 10P, 11Q AND OR 18Q/

This study aimed at resolving cellular genetic alterations in the proc ess of in vitro immortalization of human keratinocytes by human papill omavirus (HPV) types 16 and 18. Four cell lines of primary human fores kin keratinocytes transfected with HPV 16 and HPV 18, respectively, we re analysed during the transition from the mortal to immortal state, A ll cell lines showed strong telomerase activity at the immortal state, whereas no or only weak telomerase activity was detected in mortal pr ecursor cells, This was consistent with telomere stabilization or rest oration only observed in immortal cells, HPV physical state and copy n umber appeared constant during immortalization and HPV E6/E7 transcrip ts were present throughout, Immortalization was associated with clonal allele losses at 3p combined with either 11q or 18q or at 10p, depend ent on the cell line, Moreover, a correlation was evident between the onset of telomerase activity and allele loss at 30 or 10p, All immorta lized cells retained the capability to differentiate after growth in t he presence of physiological calcium and serum, Moreover, one of the i mmortal cell lines displayed terminal differentiation after organotypi c culturing on collagen rafts, The data suggest that (a) several pathw ays exist for HPV mediated immortalization that may involve genes resi ding at 3p, 10p, 11q and/or 18q; (b) 3p and 10p may encode genes invol ved in telomerase regulation; and (c) immortalization lit vitro can be correlated with a spectrum of morphological changes varying from mild to severe dysplasia.