Sequence rearrangements in the upstream regulatory region of human papillomavirus type 6: are these involved in malignant transition?

Human papillomavirus type 6 (HPV-6) was isolated from a tongue papilloma which subsequently progressed to an invasive carcinoma. Three biopsies were taken from the same patient at different intervals during the tumour development. The HPV-6 genome in all three biopsies contained a GT-rich 94 bp insertion at nucleotide 7350 in the upstream regulatory region (URR). In comparison to previously published HPV-6 DNA isolates, this insertion seems to be the most prevalent and constant modification, not present in the prototype HPV-6b, and allows an improved alignment with the sequence of the HPV-11 genome. The possible biological significance of these GT-rich clusterings at the beginning of the URR, present not only in these HPV-6 isolates but observed in all other 'genital' HPVs also, is discussed.