Detection of MMTV-like LTR and LTR-env gene sequences in human breast cancer

We have previously reported, using the polymerase chain reaction (PCR), the presence of a 660 bp sequence homologous to the env gene of MMTV in 38% of the human breast cancers studied, but not in normal breasts nor in other t umors or tissues. We have now investigated the presence of MMTV-like LTR se quences in human breast cancer and normal breast tissue, Primers were selec ted to amplify a 630 bp sequence homologous to MMTV, but not to the endogen ous retrovirus HERV-K10. This sequence was detected in 41.5% of the breast cancers and none of the normal breasts. A larger 1.2 kb LTR fragment was al so amplified with high homology to MMTV. Finally, a 1.6 kb fragment contain ing env and LTR sequences was amplified, cloned and sequenced from breast c ancer DNA. The human LTRs were highly homologous to MMTV contain enhancer a nd promoter elements, the glucocorticoid responsive element (GRE) and the s uperantigen (Sag) sequences. Presence of functional sequences implies invol vement in transcriptional regulation, whereas presence of an env-LTR sequen ce indicates contiguity within the genome of a potential provirus. Their pr esence in breast cancer DNA, but not in normal tissue, suggest an exogenous origin.