Introduction:
In recent years, the key environmental and genomic changes that "drive" melanoma
have become more clearly elucidated but much remains to be understood. Data
published in 2003 demonstrated expression of Human Endogenous Retrovirus K
(HERV-K) in melanomas but not in normal tissues, indicating a potential oncogenic
role. Furthermore, HERV-K proviruses encode the putative oncogenic proteins Rec and
Np9. In this work the feasibility of reliable detection of HERV-K expression from
formalin-fixed paraffin-embedded (FFPE) tissue has been determined. Expression has
been correlated with melanoma subtype and histological markers of poor outcome.
Methods:
HERV-K mRNA expression in melanoma cell lines (A375 and WM2664), FFPE
primary melanoma (n=39), normal skin (n=31) and benign naevus (n=16) tissues was
investigated by a novel real-time quantitative RT-PCR (qRT-PCR). Expressed HERVK
env sequences were cloned and sequenced.
Results:
A375 cells expressed all HERV-K genes and produced putative viral particles. Full-length
mRNA was expressed in all primary melanoma and control tissues investigated
with no differences in expression levels between the groups (pol: n=47, p=0.267;
unspliced env: n=40, p=0.823). No correlation was observed with melanoma subtype or
stage (Breslow). A proportion of all tissue types expressed np9 with no differences in
expression levels between them (p=0.964). Spliced env was expressed in 8/39
melanoma, compared with 1/16 benign naevus and 0/31 normal skin samples (p=0.003).
Expression of rec was found in 9/39 melanomas but not in control samples (p=0.009)
nor extra-lesional skin in five rec-positive cases (p=0.06). The rec-positive melanomas
were histologically in vertical growth phase and thicker than rec-negative tumours
(median Breslow 2.1mm versus 1.05mm, p=0.009). Sequencing of expressed env cDNA
clones derived from melanoma and control samples (n=8) revealed expression of
multiple HERV-K loci.
Conclusions:
Gene expression can be studied in FFPE tissue. The expression of potentially
oncogenic rec in approximately 25% primary melanomas merits further evaluation.