Biomedical subjects

Allen C Gao

Publications and source records attributed to Allen C Gao.

24 records · Page 2Linked to original sources

PubMed2003

Stat3 activation regulates the expression of vascular endothelial growth factor and human pancreatic cancer angiogenesis and metastasis.

Expression of vascular endothelial growth factor (VEGF), a key angiogenic protein, has been linked with pancreatic cancer progression. However, the molecular basis for VEGF overexpression remains unclear. Immunohistochemical studies have indicated that VEGF overexpression coincides with elevated Stat3 activation in human pancreatic cancer specimens. In our study, more than 80% of the human pancreatic cancer cell lines used exhibited constitutively activated Stat3, with Stat3 activation correlated with the VEGF expression level. Blockade of activated Stat3 via ectopic expression of dominant-negative Stat3 significantly suppressed VEGF expression, angiogenesis, tumor growth, and metastasis in vivo. Furthermore, constitutively activated Stat3 directly activated the VEGF promoter, whereas dominant-negative Stat3 inhibited the VEGF promoter. A putative Stat3-responsive element on the VEGF promoter was identified using a protein-DNA binding assay and confirmed using a promoter mutagenesis assay. These results indicate that Stat3 directly regulates VEGF expression and hence angiogenesis, growth, and metastasis of human pancreatic cancer, suggesting that Stat3 signaling may be targeted for treatment of pancreatic cancer.

Adenocarcinoma↗

PubMed2003

Regulation of androgen and vitamin d receptors by 1,25-dihydroxyvitamin D3 in human prostate epithelial and stromal cells.

PURPOSE: The mechanisms of the interaction between 1,25-dihydroxyvitamin D(3) (1,25 D) and androgens, and their respective receptors in their action on the prostate are not completely understood. We examined the interplay of 1,25 D and androgens on the epithelial and stromal cells of the prostate. MATERIALS AND METHODS: The human neonatal prostatic epithelial cell line 267B-1 (BRFF, Inc., Ijamsville, Maryland) and primary cultures of human prostate stromal cells were treated with medium containing 5 or 10 microM 1,25 D or ethanol (control) in the presence or absence of 10 nM dihydrotestosterone (DHT) (Sigma Chemical Co., St. Louis, Missouri). Protein levels of androgen receptor (AR) and vitamin D receptor (VDR) were determined by immunoblot analysis of whole cell extracts. Electrophoresis mobility shift assays were used to determine AR and VDR DNA binding activities. RESULTS: The VDR protein level of 267B-1 cells was increased in the presence of 1,25 D (with the maximum effects seen at 24 hours) regardless of the presence or absence of DHT. In addition, exogenous DHT increased the AR and VDR DNA binding activities of 267B-1 and stromal cells in the presence of 1,25 D. CONCLUSIONS: ARs in the normal prostate are regulated by androgens, whereas VDRs in the normal prostate can be regulated by 1,25 D as well as by other androgens such as testosterone. This finding further supports the concept that 1,25 D as a steroid hormone, in addition to other androgens such as DHT, may have a role in the growth and differentiation of normal prostate.

Calcitriol↗

PubMed2003

Interleukin-6 promotes androgen-independent growth in LNCaP human prostate cancer cells.

PURPOSE: Prostate cancer frequently progresses from an initial androgen dependence to androgen independence, rendering the only effective androgen ablation therapy useless. The mechanism underlying the androgen-independent progression is incompletely understood. Interleukin (IL)-6 has been implicated in this androgen-independent progression. In this study, we tested whether IL-6 induces androgen-independent growth both in vitro and in vivo. EXPERIMENTAL DESIGN: IL-6 was expressed in androgen-sensitive LNCaP cells. The effects of IL-6 on androgen receptor activity was determined by Northern blots and gel shift assays. The effects of IL-6 on LNCaP cell growth were determined in vitro by MTT assay and in vivo. RESULTS: IL-6 can enhance the growth of androgen-sensitive LNCaP cells in the androgen-deprived condition in vitro, which is accompanied by elevation of androgen-regulated prostate-specific antigen mRNA expression. IL-6 promotes androgen-sensitive LNCaP cell tumor growth in the castrated male mice. IL-6 enhances androgen receptor DNA binding activity and nuclear translocation. The androgen-independent phenotype induced by IL-6 in LNCaP cells is accompanied by significant activation of signal transducers and activators of transcription 3 and mitogen-activated protein kinase signal pathways. CONCLUSIONS: These studies clearly provide experimental evidence that IL-6 initiates and/or enhances the transition of prostate cancer cells from an androgen-dependent to an androgen-independent phenotype.

Animals↗

PubMed2002

Stat3 enhances the growth of LNCaP human prostate cancer cells in intact and castrated male nude mice.

BACKGROUND: Prostate cancer frequently progresses from an initial androgen dependence to androgen independence, rendering the only effective androgen ablation therapy useless. The mechanism underlying the androgen-independent progression is unknown. Stat3, a member of the family of signal transducers and activators of transcription, is activated in numerous cancers, including prostate. This study is to investigate the role of Stat3 activation in the growth of prostate cancer cells. METHODS: A constitutively active Stat3 was ectopically expressed in androgen-sensitive LNCaP prostate cancer cells and resulting stable clones expressing activated Stat3 were isolated. The effect of Stat3 activation on LNCaP cell growth in response to androgen in vitro and in vivo was examined. RESULTS: We show that the levels of activated Stat3 are associated with the progression of androgen-independent prostate cancer. Activation of Stat3 in androgen-sensitive LNCaP prostate cancer cells results in enhancement of tumor growth in both intact and castrated male nude mice and enhances androgen receptor-mediated prostate specific antigen expression. CONCLUSIONS: These findings demonstrate that intracellular signaling mediated by Stat3 can enhance the growth of androgen-sensitive human LNCaP prostate cancer cells in both intact and castrated male nude mice.

Androgens↗

PubMed2002

Stat3 activation in prostatic carcinomas.

BACKGROUND: Activated Stat3 is found in various types of immortal cell lines and cancers. We and others have previously demonstrated that Stat3 is constitutively activated in rat and human prostate cancer cell lines, and that Stat3 activation is involved in IL-6-mediated signaling transduction in prostate cancer cells. The aim of this study is to examine quantitative Stat3 activity in benign and malignant human prostate tissues and analyze the association between Stat3 activity levels and the clinical and pathologic parameters. METHODS: Stat3 activity levels were analyzed in a total of 104 human primary prostate tissues using electromobility shift assay and immunohistochemical staining for phosphorylated Stat3. The tissue samples used were 42 prostate carcinomas, 42 matched normal prostate tissues from patients with prostatic adenocarcinoma (normal adjacent to tumor), and 20 normal prostate tissues from organ donors. RESULTS: Significantly higher levels of constitutive Stat3 activity were detected in both prostate carcinomas and the matched normal prostate tissues adjacent to tumors compared to the normal prostates from donors without prostate cancer. There was no significant difference of Stat3 activity in foci of tumor and normal prostate tissue adjacent to tumor. No correlation was seen between Stat3 activity and Gleason grade or serum PSA levels in samples from prostate carcinomas. CONCLUSIONS: These results indicate that Stat3 is constitutively activated in prostate cancer. The high level of Stat3 activity in both the prostate carcinomas and the normal prostate tissues adjacent to tumors suggests that Stat3 activation may occur before detectable histological alterations of the prostate.

Cell Transformation, Neoplastic↗

PubMed2002

Selective activation of members of the signal transducers and activators of transcription family in prostate carcinoma.

PURPOSE: Cytokines, hormones and growth factors use signal transducers and activators of transcription (STAT) signaling pathways to control various biological responses, including development, differentiation, cell proliferation and survival. Constitutive activation of STATs has been found in a wide variety of human tumors. In this study we examined the activity of STATs in primary human prostate tissues. MATERIALS AND METHODS: STAT activity was determined in 104 human primary prostate tissues, including 42 tumors, 42 matched normal prostates adjacent to tumors and 20 normal prostates from donors without cancer by electromobility shift assay. RESULTS: Significant levels of activated Stat4 and Stat6 were detected in primary prostate tissues. However, little or no expression of active Stat1, Stat2 or Stat5 was detected in primary prostate tissues. Significantly higher levels of constitutive Stat6 activity were found in prostate carcinomas compared with levels in normal tissue adjacent to tumors and normal prostates from donors without prostate cancer. There was no significant difference in Stat6 activity in normal prostate tissues adjacent to tumors and normal prostates from donors without prostate cancer. The levels of Stat4 activity varied but failed to yield statistically significant differences among tumors, matched normal prostates adjacent to tumors and normal prostates from donors without cancer. CONCLUSIONS: We have previously shown that Stat3 is activated in prostate cancer. The results of the current study demonstrate that in addition to Stat3, Stat6 is selectively activated in prostate cancer.

Adult↗