Modulation of cell cycle leads to phenotypical changes of prostate cancer cell lines

Prostate cancer is one of the leading types of cancer in men worldwide. Androgen deprivation therapy (AD T) is an important treatment especially for advanced stages of prostate cancer, achieved by androgen receptor blockade and/or medical or surgical castration. Although AD T is initially very effective, treated tumors inevitably progress to androgen-independent prostate cancer, which is currently incurable and fatal. The mechanism through which AD T causes androgen-independence is therefore of high research interest.

One of the possible events contributing to the development of androgen independence of originally androgen-dependent prostate cancer cells is neuroendocrine transdifferentiation (NED ) and emergence of neuroendocrine (NE )-like cancer cells after AD T. The action of androgens is dominantly mediated through AR , which was shown to be a critical regulator of the G1-S transition in prostate cancer cells. Prolonged cultivation of prostate cancer cell lines in the absence of androgens leads to cell cycle arrest associated with changes in expression of a number of cell cycle regulators including family of cyclin D proteins, cyclin dependent kinase 2 (Cdk2) and inhibitor of Cdk p27Kip1.

Here we therefore focused on elucidating the role of cell cycle modulation in promotion of NED of prostate cancer cells using prostate cancer cell lines LNCaP and LAPC-4. First, we tested involvement of family of cyclin D proteins, which are down-regulated in response to androgen ablation. Although decreased level of cyclin D1 and/or cyclin D3 led to modulation of cell cycle, there was no induction of NED when levels of NED markers were observed. Next, we focused on the role of Cdk2, down-regulated by androgen depletion. Inhibition of Cdk2 by inhibitor CVT-313 led to significant deregulation of cell cycle, which was accompanied by increased level of NED marker γ-enolase in LAPC-4 cells. Since CVT-313 can inhibit activity of both Cdk2 and Cdk1 we focused on elucidating whether inhibition of Cdk1, Cdk2 or both succeeded by cell cycle deregulation contributes to promotion of NED . We used RNA interference approach to down-regulate simultaneously levels of Cdk1 and Cdk2. Furthermore we treated cells with another inhibitors of Cdk1 (CGP74514A and RO -3306) and Cdk2 (NU-6140) and examined its effect on cell cycle deregulation and possible promotion of NED .

Our results imply how modulation of cell cycle caused by deregulation of several cell cycle regulators may affect promotion of NED of prostate cancer cells.

This work was supported by grants IGA MZD NT13573- 4/2012, AV ČR M200041203, GA ČR P301/12/P407, HistoPARK (CZ.1.07/2.3.00/20.0185), and by project FNUSA-ICRC (no. CZ.1.05/1.1.00/02.0123) from the European Regional Development Fund. Institutional support was provided by the Academy of Sciences of the Czech Republic