Expression of human endogenous retrovirus k envelope transcripts in human breast cancer.
OBJECTIVE
We investigated the expression of human endogenous retroviral (HERV) sequences in breast cancer.


METHODS
Reverse transcription-PCR (RT-PCR) was used to examine expression of the envelope (env) region of ERV3, HERV-E4-1, and HERV-K in breast cancer cell lines, human breast tumor samples, adjacent uninvolved breast tissues, nonmalignant breast tissues, and placenta. Expression of HERV transcripts was confirmed by Northern blot analysis and in situ hybridization (ISH). To evaluate coding potential, amplified HERV sequences were cloned into vectors for expression and sequence analysis.


RESULTS
No expression of ERV3 or HERV-E4-1 RNA was detected in the analyzed breast samples. In contrast, HERV-K transcripts were detected in most breast cancer cell lines and many breast tumor tissues. Expression was detected in a small percentage of matched, uninvolved breast tissues and in placentas but not nonmalignant breast tissues. In HERV-K-positive breast cancer tissues, Northern blot analysis demonstrated full-length proviral and spliced env transcripts. ISH demonstrated expression of HERV-K transcripts in breast tumor cells but not in normal or uninvolved breast epithelial cells. Independently isolated clones of HERV-K env cDNA generated recombinant proteins of the expected size. Sequence analysis of env cDNA clones derived from four breast tumor samples revealed >97% identity with the type I HERV-K102, with no premature termination codons. Independent isolates from the same breast tumor sample showed nucleotide sequence differences, suggesting that multiple loci may be transcribed.


CONCLUSIONS
These data indicate that HERV-K transcripts with coding potential for the envelope region are expressed frequently in human breast cancer.
Wang-Johanning
F
F
The Comprehensive Cancer Center and Division of Hematology Oncology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294-3300, USA.
Frost
A R
AR
Johanning
G L
GL
Khazaeli
M B
MB
LoBuglio
A F
AF
Shaw
D R
DR
Strong
T V
TV
D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism* / Q000821:virology*; D003001:Cloning, Molecular; D003062:Codon; D017931:DNA Primers / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D020077:Endogenous Retroviruses / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D015686:Gene Products, env / Q000096:biosynthesis*; D005822:Genetic Vectors; D006801:Humans; D017403:In Situ Hybridization; D008957:Models, Genetic; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000096:biosynthesis* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic; D014170:Transformation, Genetic; D014407:Tumor Cells, Cultured
D003062:Codon; D017931:DNA Primers; D018076:DNA, Complementary; D015686:Gene Products, env; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins