Activation of Survival Signalings under Androgen Ablation Conditions in LNCaP Cells

In order to define the survival signaling pathways that allow LNCaP cells to avoid cell death induced by androgen withdrawal, the levels of Bcl-2 in LNCaP and its derivatives were examined. Shown in Figure 1C, expression of Bcl-2 was increased under acute and chronic androgen ablation conditions. Additionally, PI3-Kinase activity in LNCaP and its derived cells was determined. Shown in Figure 2, PI3-kinase was active in parental LNCaP cells when cultured in regular culture medium. However, higher activity of PI3-Kinase was seen in the LNCaP-tNED cells. Approximately 4.0-fold higher level of PI3-kinase activity was found in the LNCaP-Rf cells as that found in the parental LNCaP cell line. PI3K-dependent activation of Akt has been shown to require phosphorylation at residues T308 and S473. To assess Akt activation, a specific antibody for phosphorylated Akt was used. In Figure 2, Akt phosphorylation at serine 473 was dramatically increased in LNCaP-tNED and LNCaP-Rf cells but no changes were detected in total Akt protein levels. Therefore, consistent with previous reports (18, 20), we found that PI3K and Akt signaling pathway is constitutively activated in LNCaP cells when cultured in medium containing whole serum. Thus, our data demonstrate that PI3-Kinase activity is increased by androgen withdrawal.

Figure 2. Activities of PI3K and Akt in LNCaP and its derivatives. PIP, phophatidylinositol monophophate; O, origin of sample loading.

Figure 3. Immunohistochemistry of PTEN and Bcl-2 proteins in primary prostate tumors.

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