Identification and isolation of novel
telomerase suppressor genes involved in sporadic prostate cancer
Prof Robert Newbold
Prostate cancer is the most commonly diagnosed malignant neoplasm
and the second leading cause of deaths in males in the west, and
its incidence is increasing at an alarming rate. It has been predicted
that prostate cancer will be the most common cause of death in males
by 2010. There is no curative therapy once the carcinoma has spread
locally or distantly. There has been an increase in the early detection
of prostate cancer but current methodologies do not distinguish
between cancers that will remain indolent, and require no treatment,
and those that will prove to be highly progressive and life threatening.
Therefore there is an urgent need for molecular markers to detect
the malignant nature and pathological states of the human prostate
and to develop new approaches to treat patients with progressive
Our aim is to identify and characterise new prostate cancer-specific
gene(s) that could provide new potential markers for diagnosis,
prognosis and aid in the development of new targeted treatment.
Telomerase may be used for targeted therapy for prostate cancer
because high telomerase activity has been detected in 90% of prostate
tumors whereas normal and BPH tissues have very low or absent activity.
Telomerase is a specialised RNA dependent ribonucleoprotein polymerase
that maintains and elongates telomeres by telomeric repeat sequence
TTAGGG at the ends of chromosomes. Telomerase activation is required
for cells to overcome replicative senescence and to obtain immortal
capacity, and is therefore a critical step in carcinogenesis.
We are using a technique called microcell-mediated monochromosome
transfer for genetic analysis. The method allows a single normal
human chromosome, tagged with a hygromycin resistance gene, to be
introduced into a well established prostate cell line PC-3 and maintained
therein by selection as an intact functional and structural entity.
By using this technique, individual chromosomes can be screened
for the presence of active genes specifying a particular cellular
phenotype on the basis of genetic complementation.
To date, we have been able to transfer all 22 normal human chromosomes
plus the X chromosome individually into PC-3. We have assayed telomerase
activity in 10 sets of monochromosomal hybrids of PC-3, using the
commercially available telomere repeat amplification protocol (TRAP)
kit. Initial results with PC-3/Chr10 and PC-3/Chr17 hybrids revealed
a high percentage of hybrids exhibiting telomerase repression, suggesting
that telomerase repressor sequences exist on these chromosomes.
A typical example of a TRAP assay of PC-3/Chr 4
clones showing telomerase activity