Bicheng Nan

Changes in Androgen Receptor Nongenotropic Signaling Correlate with Transition of LNCaP Cells to Androgen Independence

A cure for prostate cancer (CaP) will be possible only after a complete understanding of the mechanisms causing this disease to progress from androgen dependence to androgen independence. To carry on a careful characterization of the phenotypes of CaP cell lines before and after acquisition of androgen independence, we used two human CaP LNCaP sublines: LNCaPnan, which is androgen dependent (AD), and LNCaP-HP, which is androgen independent (AI). In AD LNCaPnan cells, dihydrotestosterone (DHT) stimulated in an androgen receptor (AR)-dependent way a phosphorylation signaling pathway involving steroid receptor coactivator (Src)–mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase (MEK)-1/2–ERK-1/2–cAMP-response element binding-protein (CREB). Activation of this pathway was associated with increased [3H]thymidine incorporation and resistance to apoptosis. Use of dominant-negative forms of MEK-1/2 and CREB demonstrated in LNCaPnan cells that DHT induced [3H]thymidiine incorporation through a thus far unidentified molecule activated downstream of MEK-1/2, and antiapoptosis through phosphorylation of the transcription factor CREB. In contrast, in AI LNCaP-HP cells, the Src–MEK-1/2–ERK-1/2–CREB pathway was constitutively active. Because it was not further stimulated by addition of DHT, no increase of [3H]thymidine incorporation or apoptosis resistance was demonstrated in LNCaP-HP cells. Additional experiments showed that Src and the scaffold protein MNAR coimmunoprecipitated with AR, indicating a role for Src as an apical molecule in the Src–MEK-1/2–ERK-1/2–CREB pathway. Interestingly, differences between the two cell lines were that in LNCaP-HP cells presence of an AI phenotype and lack of response to DHT were associated with constitutive activation of the protein kinase Src and interaction among Src, AR, and MNAR. In contrast, in LNCaPnan cells, presence of an AD phenotype and ability to respond to DHT were associated with DHT-dependent activation of Src kinase activity and interaction among Src, AR, and MNAR. Intriguingly, in LNCaPnan cells, we found that transcription through the prototypical CREB-responsive promoter c-fos could be induced in a DHT-dependent way, and this action was inhibited by the AR antagonist Casodex and MEK-1 inhibitor PD98059. In contrast, transcription through the PSA P/E promoter, a prototypical AR-dependent promoter directly activated by agonist, was obliterated only by Casodex. Additional experiments with genital skin fibroblasts derived from patients with a variety of AR abnormalities indicated that nongenotropic AR signaling does not depend on an intact DNA-binding domain or on the ability of AR to translocate to the nucleus. The results suggest the following: (1) Constitutive activation of the Src–MEK-1/2–ERK-1/2–CREB pathway is associated with the AI phenotype observed in LNCaP-HP cells. (2) Activation of the Src–MEK-1/2–ERK-1/2–CREB pathway is DHT dependent in AD LNCaPnan cells. (3) DHT activation of this pathway is associated with induction of [3H]thymidine incorporation by a molecule activated downstream of MEK-1/2 and of antiapoptosis through activation of the transcription factor CREB in AD LNCaPnan cells. (4) AR regulates transcription either directly upon ligand binding and nuclear translocation or indirectly through kinase pathways leading to activation of downstream transcription factors. (5) Nuclear translocation and ability of the DNA-binding domain of AR to interact with DNA are not prerequisites for nongenotropic AR activity.

Heregulin-induced apoptosis is mediated by down-regulation of Bcl-2 and activation of caspase-7 and is potentiated by impairment of protein kinase C α activity

Heregulins are a group of growth factors that play diverse and critical roles in the signaling network of the human epidermal growth factor receptor (HER or EGFR) superfamily. Our earlier studies have shown that recombinant heregulinβ1 (HRG) induces apoptosis in SKBr3 breast cancer cells that overexpress HER2. Here we report molecular mechanisms of HRG-induced apoptosis. HRG treatment of SKBr3 cells for 72 h decreased the level of Bcl-2 protein. HRG treatment led to degradation of poly (ADP-ribose) polymerase (PARP) and activated both caspase-9 and caspase-7. No significant activation of caspase-3, -6, or -8 was detected. Expression of exogenous caspase-7 by adenovirus-caspase-7 (Ad-casp-7) in SKBr3 cells resulted in apoptosis, which mimicked the effect of HRG treatment. Expression of exogenous caspase-7 had no impact on Bcl-2 expression, but promoted PARP degradation. Two highly selective inhibitors of protein kinase C (PKC), GF109203X (GF) and Ro318425 (Ro), significantly enhanced HRG-induced apoptosis as determined by flow cytometric analysis and DNA fragmentation assay. Accordingly, the PKC inhibitor GF further decreased the level of Bcl-2 protein and further degraded PARP in HRG-treated cells. Assay of PKC activity indicated that HRG activated PKC in SKBr3 cells, predominantly affecting the PKCα isoform. To confirm which PKC isoform(s) mediated potentiation of HRG-induced apoptosis, the profile of PKC isoforms was measured in SKBr3 cells. Five PKC isoforms, PKCα, PKCι, PKCζ, PKCλ, and PKCδ as well as their receptors (RACK1) were expressed in this cell line. Treatment with PKC inhibitors GF and Ro decreased protein levels of both PKCα and PKCδ at 24 h. PKCα levels were still depressed at 72 h. GF and Ro had little effect on the expression of other PKC isoforms. An inhibitor of classical PKC isoforms (Go6976) enhanced HRG-induced apoptosis, whereas the PKCδ selective inhibitor rottlerin did not. As PKCα was the only classical isoform expressed in SKBr3 cells, the effect of Go6976 on HRG-induced apoptosis largely related to inhibition of PKCα. Constitutive expression of wild-type PKCα attenuated the apoptosis produced by HRG and GF. Consequently, HRG-induced apoptosis in SKBr3 cells appeared to involve down-regulation of Bcl-2 protein, activation of caspase-9 and caspase-7, and degradation of PARP. Inhibition of PKC function enhanced HRG-induced apoptosis, leading to synergistic down-regulation of Bcl-2 expression. Impairment of the PKCα isoform alone was sufficient to potentiate HRG-induced apoptosis.

Monogene and Polygene Therapy for the Treatment of Experimental Prostate Cancers by Use of Apoptotic Genes bax and bad Driven by the Prostate-Specific Promoter ARR2PB

We have shown that adenovirus-mediated manipulation of apoptotic genes such as bax could be a therapeutic option for prostate cancer. Unfortunately, the response of experimental prostate tumors to a single therapeutic gene of the apoptotic pathway is short-lived, and most of these tumors relapse after a short period of time. In this investigation we present data generated with adenovirus AvARR(2)PB-Bad, in which the apoptotic gene bad was placed under the control of the dihydrotestosterone (DHT)-inducible third-generation probasin-derived promoter ARR(2)PB. This therapeutic virus was given alone or in combination with other therapeutic viruses to a variety of in vitro and in vivo experimental models of prostate cancer. On infection with AvARR(2)PB-Bad, DHT-induced Bad overexpression occurred specifically in androgen receptor-positive (AR(+)) cells of prostatic derivation. The apoptotic effect of AvARR(2)PB-Bad (group 1) was compared with that of AvARR(2)PB-Bax (which overexpresses the apoptotic protein Bax) (group 2), with that of the combination AvARR(2)PB-Bad plus AvARR(2)PB-Bax (group 3), and with that of the control virus AvARR(2)PB-CAT (group 4) in the cell line LNCaP. In addition to identifying the modality of apoptosis induction by overexpressed Bad, the results suggested that group 3 contained more apoptotic cells than any other group. In additional studies, AR(+) androgen-dependent LNCaP cells or AR(+) and androgen-independent C4-2 cells were injected subcutaneously into nude mice. Four groups of six LNCaP or C4-2 tumors were treated with the same combinations of viruses discussed above for groups 1, 2, 3, and 4. Treatment resulted in decreased tumor size in groups 1, 2, and 3 compared with group 4. There was a better response in group 3 compared with group 2, and in group 2 compared with group 1. A better response in group 3 was confirmed during a 8-week follow-up period, in which no treatment was administered. Two LNCaP and C4-2 tumors of group 3 disappeared at the end of treatment and did not recur after an 8-week follow-up period. The data suggest that polygene therapy with apoptotic molecules is more effective in experimental models of androgen-dependent or -independent prostate cancer than monogene therapy.

From Castration‐Induced Apoptosis of Prostatic Epithelium to the Use of Apoptotic Genes in the Treatment of Prostate Cancer

Abstract: Current knowledge of the mechanisms regulating androgen‐ablation‐induced apoptosis is reviewed, and our efforts to develop a system in which genes of the apoptotic pathway are used to induce therapeutic apoptosis in experimental models of prostate cancer are described.