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Cell lines have been created by immortalising the primary cells with the over expression of hTERT, the active subunit of the telomerase enzyme. Telomerase is a cellular reverse transcriptase that adds new DNA to the telomeres that are at the very ends of chromosomes (Shay, et al., 2008). The telomeres are looped structures that prevent the ends of the chromosome being detected as doubles strand breaks. They are naturally eroded every time a cell divides and therefore each cell has a finite number of divisions it can perform before the telomeres reach a critical length and the cell senescences (Shay, et al., 2008).

Telomerase is switched on in 90% of all malignant tumours, stem cells, and embryonic cells (Shay, et al., 2008). Certain cell lines have been immortalised by over expressing the hTERT subunit without neoplastic effects. Human cell lines that have been immortalised using hTERT include retinal pigment cells (RPE) (Bodnar, et al., 1998) foreskin fibroblasts (Bodnar, et al., 1998), urothelial cells (Chapman, et al., 2006), esophageal keratinocytes (Harada, et al., 2003) oesophageal squamous cells (Morales, et al., 2008), myometrial cells (Condon et al., 2002), and corneal epithelial cells (Robertson, et al., 2005).

Berger et al. (2004) initially transduced primary human prostate epithelial cells with hTERT. The cells had detectable up regulation of hTERT levels but the hTERT expressing cells senesced at the same time as the control cell line which was transduced with a control vector (Berger, et al., 2004).

A human prostate epithelial cell line was immortalised from tissue from primary tumours of familial prostate cancer patients with the gene telomerase (Yasunaga, et al., 2001). As these cell lines are derived from carcinomas they are models for prostate carcinoma. Carcinoma tissue was taken from the patients and established in culture. The 957E/hTERT cells were immortalised at passage 5 and the control cells 957E senesced at passage 4. The cell lines were transduced through infection with a retrovirus expressing hTERT and the successful transduction enabled the prostate carcinoma cells to grow to passage 40. The cell line 957E/hTERT line was fully characterised and found to express p16, prostate stem cell antigen (PSCA), cytokeratin 8, but not androgen receptor (AR). The chromosome complement was near diploid but there were random losses of chromosome 8, 13, X, and Y. Other alterations included an alteration on 4q and a trisomy 20. This cancer cell line, established from a primary tumour, is a useful tool for researching into prostate carcinoma but researchers have been attempting to create “normal” human prostate cell lines from normal prostate tissue.

Human prostate cells from a primary tumour of patients with prostate cancer were immortalised by transduction with a retroviral vector which contained the hTERT gene five months later by the same group (Yasunaga, et al., 2001). The cell line was called RC-58T/hTERT and was not only immortalised but exhibited tumourigenic characteristics after hTERT over expression (Yasunaga,

et al., 2001). The cells propagated colonies when grown in agar, expressed cytokeratin 8, p16 and PSCA, but not PSA or AR. The cells exhibited a number of chromosome alterations including loss of Y, 3p, 10p, 17p, and 18q and the gain of chromosome 16 and 20 (trisomy 20). The cell line RC-58T/hTERT was characterised and a clonal line called RC-58T/hTERT SA#4 was created by picking an anchorage independent clone (Gu, et al., 2004). The clonal line called RC- 58T/hTERT SA#4 produced adenocarcinomas when transplanted into SCID mice (Gu, et al., 2004).

Cell lines ideal for the study of human primary prostate tumours would be those derived from spontaneously immortalised tumour cells (Gu, et al., 2006). However, this occurrence is very rare

and to make an authentic model human prostate cells derived from benign and malignant prostate carcinoma and immortalised with over expression of hTERT provide a suitable model. The cell lines derived from malignant tissue, immortalised with over expression of hTERT, were reported to retain original phenotypes and express some of their prostatic markers but all cell lines (malignant and benign tissue derived) showed chromosomal abnormalities including often loss of the Y chromosome and loss of 8 and 13 chromosomes. They also all were positive for Alpha-methylacyl-CoA racemase (AMACR), also known as p504S, which is a biomarker which distinguish cells from benign cancer and normal tissue (Gu, et al., 2004). Therefore these cell lines derived from benign tissue are useful models of benign cancer as they express numerous chromosomal abnormalities and all express AMACR which shows that they are benign cancer cell lines. One of these hTERT immortalised cell lines (RC-170N/h) from benign tissue was cloned and a clone line (RC-170N/h/clone 7) was derived from single cell cultures and found to retain properties of multipotent stem cells (Li, et al., 2008). They were found to express stem cell markers CD133, CD44, integrin α2, integrin β1, and differentiate into multi-tissues when transplanted into the sub-renal capsule of non-obese diabetic severe combined immunodeficient (NOD-SCID) mice (Li, et al., 2008).

In the same year human prostate epithelial and stromal cells were immortalised with telomerase (Kogan, et al., 2006). Tissue was taken from human patients with progressive prostate tumours (Gleason Score 5 and 7 where the tumour had extended beyond the prostate capsule) and established in primary culture first, then immortalised with hTERT (Kogan, et al., 2006). Only one of the four cell lines immortalised could be propagated in culture for ~200 population doublings. Their results showed that hTERT alone was not sufficient to cause immortalisation as the cultures that did not survive were successfully expressing the hTERT gene and thus suggests the cell line that survived up to 200 population doublings was immortalised due to another factor as well as