THE PREDOMINANT MESSENGER-RNA CLASS IN HPV16-INFECTED GENITAL NEOPLASIAS DOES NOT ENCODE THE E6 OR THE E7 PROTEIN

Human papillomavirus (HPV) type 16 is strongly implicated in the devel opment of progressive neoplasias of the uterine cervix. Its oncogenic potential is decisively determined by the activity of the early gene p roducts E6 and E7. To look for changes in the expression of these gene s during tumour progression we cloned subgenomic fragments of HPV16 in to RNA expression vectors, which allowed the generation of S-35-labell ed riboprobes specific for distinct mRNA classes. Four constructs were made to differentiate between transcripts starting upstream of the E6 ORF or the E1 ORF, and one probe was specific for unspliced E6/E7 reg ion transcripts. Five other constructs were used to identify transcrip ts covering the E1, E2, E4, L1 and L2 regions. With the help of these constructs, we analyzed by in situ hybridization 2 low-grade intraepit helial neoplasias of the vulva, 1 high-grade neoplasia of the cervix a s well as 4 vulvar and 3 cervical carcinomas. Transcripts from the E1, E2, E4, L1 and L2 region that were consistently detected in the diffe rentiated layers of benign lesions were variably expressed in precance rs and carcinomas. None of the investigated cases revealed detectable amounts of unspliced E6/E7 transcripts with a coding potential for a f ull-length E6 protein. In benign lesions, the E7 transcripts were conf ined to isolated nuclei of differentiated cells, whereas high-grade le sions and invasive cancers showed elevated levels of equally distribut ed E7-specific signals in the cytoplasm of all tumour cells. The most abundant transcripts observed in intraepithelial neoplasias and in inv asive cancers appear to initiate within ORF E7 and therefore have no c oding potential for full-length E6 and E7 proteins. Our data show that the actual level of E7-specific transcripts in cancers is lower than anticipated from earlier studies using an ORF E6/E7-specific probe tha t hybridizes with the 5'-ends of the abundant mRNA class. (C) 1993 Wil ey-Liss, Inc.