The BPV-4 co-carcinogen quercetin induces cell cycle arrest and up-regulates transcription from the LCR of BPV-4

Abstract

Bracken fern is the environmental co-carcinogen of BPV-4 in the induction of neoplasias of the upper alimentary canal of cattle. The¯avonoid quercetin is one of the most potent and best characterised mutagens present in the fern. We have shown that transfection with BPV-4 DNA and exposure to a single dose of quercetin leads to tumorigenic transformation of primary bovine cells. We now show that quercetin induces cell cycle arrest and up-regulates transcription from the BPV-4 long control region (LCR). This up-regulation is mediated by a 21 nucleotide-long cis-element in the LCR, designated QRE-1, which is located immediately downstream of the TATA box. Cellular proteins bind to QRE-1 and removal or substitution of QRE-1 lead to the abrogation of the response to quercetin. As expression of the viral oncogenes is controlled by the LCR, perturbation in this control and increased oncoprotein expression are likely to contribute to fully malignant cell transformation by overcoming the cell cycle arrest induced by quercetin, thus forcing damaged cells to proliferate.

An Enhanced Epithelial Response of a Papillomavirus Promoter to Transcriptional Activators

“…Previously it has been suggested that there is an initiator in the BPV-4 promoter just downstream from the TATA box (32). The addition of this putative initiator to the BPV-4 promoter sequence used here resulted in a slight elevation in response to E2 but played no role in the epithelial-specific response to E2.…”

Bovine papillomaviruses, papillomas and cancer in cattle

“…In this system, quercetin confers anchorage-independence, immortalisation and tumourigenicity, so that the only BPV-4 oncogene required for full transformation is E7 [26]. A cis-acting element responding to quercetin has been mapped in the BPV-4 LCR [42] whose activation leads to E7 oncoprotein expression. This likely induces the transformed cells to bypass the quercetin-induced G1 cell cycle arrest and to proliferate [13].…”

“…Quercetin is mutagenic in both prokaryotic and eukaryotic cells, and is clastogenic, leading to single-strand DNA breaks [33,106] and chromosomal rearrangements [77]. It promotes the full in vitro transformation of primary bovine cells infected with BPV-4 DNA [26,99] and upregulates viral DNA transcription via a cis-acting element in the viral transcriptional promoter [42]. Moreover, bracken eating cattle with BEH and/or suffering from bladder cancer develop chromosomal abnormalities [67,80,88,101,129] due to a clastogenic activity of compounds from fern.…”

Neoplasias do trato alimentar superior de bovinos associadas ao consumo espontâneo de samambaia (Pteridium aquilinum)

“…O sinergismo entre a infecção por BPV-4 e a exposição à quercetina, um flavonóide carcinogênico presente na samambaia (Pamucku et al 1980, Musonda & Chipman 1999) na transformação celular foi estabelecido em estudos in vitro (Pennie & Campo 1992, Cairney & Campo 1995, Connolly et al 1998, Beniston et al 1999, 2001). Entretanto, a comprovação deste sinergismo in vivo não foi completa, pois bovinos infectados pelo BPV-4 e tratados somente com quercetina não apresentaram malignização dos papilomas (Campo et al 1994).…”