PROGRESSIVE GROWTH OF HUMAN PAPILLOMAVIRUS TYPE 16-TRANSFORMED KERATINOCYTES IS ASSOCIATED WITH AN INCREASED RELEASE OF SOLUBLE TUMOR-NECROSIS-FACTOR (TNF) RECEPTOR

Analysis of conditioned media generated by weakly and highly tumorigen ic SKv-1 keratinocyte lines harbouring integrated human papillomavirus type 16 (HPV16) DNA sequences revealed a factor inhibiting TNF-alpha and TNF-beta cytotoxic activity. This inhibitory activity was specific ally blocked by htr-9 monoclonal antibody (MAb) recognising 55/60 kDa type I TNF receptor suggesting that it is related to a soluble farm of this particular receptor (sTNF-RI). The presence of sTNF-RI was confi rmed by Western blot analysis of SKv-1 cell-conditioned medium showing a band of 31.5 kDa as well as by the specific enzyme-linked immunobio logical assay (ELIBA). Release of sTNF-RI was a result of shedding bec ause Northern blot analysis shelved that SKv-1 cells expressed a full- length TNF-RI mRNA, and radioimmunoprecipitation of TNF-RI from [S-32] cysteine-labelled cell extracts demonstrated the presence of normal 55 kDa molecule. Evaluation by ELIBA showed that highly tumorigenic SKv- 12 cells released significantly more sTNF-RI than their weakly tumorig enic SKv-11 parental cells. Furthermore, human recombinant as well as SKv cell-derived sTNF-RI stimulated proliferation of weakly tumorigeni c SKv-11 cells. This suggests that a progressive growth of some neopla stic cells may be, at least partially,a result of an increased spontan eous release of sTNF-RI that enables the cells to escape from local TN F-alpha-mediated growth inhibition.