Transcription Factor Signal Transducer and Activator of Transcription 5 Promotes Growth of Human Prostate Cancer Cells In vivo

Abstract

Purpose: Signal transducer and activator of transcription 5a/b (Stat5a/b) is the key mediator of prolactin effects in prostate cancer cells via activation of Janus-activated kinase 2. Prolactin is a locally produced growth factor in human prostate cancer. Prolactin protein expression and constitutive activation of Stat5a/b are associated with high histologic grade of clinical prostate cancer. Moreover, activation of Stat5a/b in primary prostate cancer predicts early disease recurrence. Here, we inhibited Stat5a/b by several different methodologic approaches. Our goal was to establish a proof of principle that Stat5a/b is critical for prostate cancer cell viability in vitro and for prostate tumor growth in vivo. There are currently no effective pharmacologic therapies for primary or recurrent prostate cancer. Androgen deprivation therapy only provides a temporary inhibition of the cancer growth before the hormone-refractory form of prostate cancer develops. Moreover, no effective pharmacologic treatments exist for elimination of residual cancer cells after prostate cancer surgery. We propose here transcription factor signal transducer and activator of transcription 5a/b (Stat5a/b) as a potential therapeutic target for prostate cancer.Stat5 is one of the seven members of Stat gene family of transcription factors (1). Two highly homologous isoforms of Stat5, 94-kDa Stat5a and 92-kDa Stat5b, are encoded by separate genes (1). Stat5a and Stat5b (hereafter referred to as Stat5a/b) are latent cytoplasmic proteins that act as both cytoplasmic signaling proteins and nuclear transcription factors. Phosphorylation of a specific tyrosine residue in the COOH-terminal domain (1) by a tyrosine kinase, typically of the Janus-activated kinase protein family (2, 3), activates Stat5a/b. After phosphorylation, Stat5a and Stat5b homodimerize or heterodimerize and translocate to the nucleus where they bind to specific Stat5a/b response elements of target gene promoters (1).Stat5 proteins are divided into five structurally and functionally conserved domains. The NH 2 -terminal domain is involved in stabilizing interactions between two Stat5 dimers to form tetramers, which are needed for maximal transcriptional activation of weak promoters (4). Next to the NH 2 -terminal domain is the coiled-coil domain that facilitates protein-protein interactions (5, 6) important for transcriptional regulation. The DNA-binding domain mediates direct binding of Stat5a/b to DNA and recognizes members of the IFN-g -activated site

Jak2-Stat5a/b Signaling Induces Epithelial-to-Mesenchymal Transition and Stem-Like Cell Properties in Prostate Cancer

“…pcDNA-CMV-PrlR and pcDNA-CMV-WTStat5a were cloned into an adenoviral vector using BD Adeno-XTM Expression System 2 (BD Biosciences, Palo Alto, CA), as previously described, 38,41,44,45,61 and according to the manufacturer's protocol. Viral stocks of adPrlR, adWTStat5a, and adLacZ were expanded in large-scale cultures, purified by double cesium chloride gradient centrifugation, and titered side-by-side using standard plaque assay in QBI-293A cells.…”

“…39,41,44,75 Protein concentrations of clarified cell lysates were determined by simplified Bradford method (BioRad, Hercules, CA). Stat5a, Stat5b, and E-cadherin were immunoprecipitated from whole cell lysates with 4 mL/mL anti-Stat5a or anti-Stat5b (Millipore, Billerica, MA) polyclonal antibodies or 4 mL/mL antieE-cadherin (BD Biosciences) monoclonal antibody.…”

Transcription Factor Stat5 Knockdown Enhances Androgen Receptor Degradation and Delays Castration-Resistant Prostate Cancer Progression In vivo

“…The signal transducer and activator of transcription (Stat5) signaling cascade is known to play a pivotal role in the progression of PCa (20)(21)(22)(23). Stat5 expression in human PCa tissue correlates with high histological grades of PCa and predicts early disease recurrence after initial treatment with radical prostatectomy (24,25).…”

“…Stat5a is involved in the maintenance of prostate epithelial structures whereas Stat5b mediates cell growth (21,27). In vitro, Stat5 promotes PCa progression by increasing the expression levels of cyclin D1 and Bcl-xL (23) and transcriptional activity of the androgen receptor (AR; ref. 26).…”

STAT5a-targeting miRNA enhances chemosensitivity to cisplatin and 5-fluorouracil in human colorectal cancer cells

“…Evidence reveals that inhibition of STAT5 affects biological behavior of cancer cells. Studies in vitro and in vivo have shown that STAT5a and STAT5b differentially regulate the motility and migration of human mammary carcinoma cells (20,21), and inhibition of Stat5a/b by antisense oligonucleotides, RNA interference, or adenoviral expression of dominant-negative Stat5a/b can induce cell death of human prostate cancer cells (22).…”