Hongxia Huang

Prostate cancer is the second most prevalent cancer in males in the United States. Standard therapy relies on removing, or blocking the actions of, androgens. In most cases, this therapy results in a regression of the cancer because the prostate and most primary prostate tumors depend on androgens for growth and the avoidance of apoptosis. However, a portion of the cancers eventually relapse, at which point they are termed "androgen refractory" and can no longer be cured by conventional therapy of any type. The precise molecular events that lead from androgen-sensitive prostate cancer to androgen-refractory prostate cancer are, therefore, of great interest. This review seeks to identify specific molecular events that may be linked directly to the progression to androgen-refractory cancer. Some of the mechanisms appear to involve the androgen receptor (AR) directly and include mutations in, or amplification of, the AR gene in a manner that allows the AR to respond to low doses of androgens, other steroids, or antiandrogens. In a less direct manner, coactivators may increase the sensitivity of the AR to androgens and even other nonandrogenic substances through a number of mechanisms. Additional indirect mechanisms that do not result from mutation of the AR may involve activation of the AR by peptide growth factors or cytokines or may involve bypassing the AR entirely via other cellular pathways. Identification of the role of these mechanisms in the progression to androgen-refractory prostate cancer is critical for developing therapies capable of curing this disease.

Mechanisms of androgen dependence of the prostate are critical to understanding prostate cancer progression to androgen independence associated with disease mortality. Transient elevation of transforming growth factor-beta (TGF-beta) occurs after androgen ablation. To determine the role of TGF-beta on prostate response to androgen ablation, conditional TGF-beta type II receptor knockout mouse models of the epithelia (Tgfbr2(NKX3.1KO)) and stromal fibroblasts (Tgfbr2(fspKO)) were used. After castration, the prostates of Tgfbr2(NKX3.1KO) mice had apoptosis levels similar to those expected for control Tgfbr2(floxE2/floxE2) mice. Prostates of Tgfbr2(fspKO) mice, however, had reduced regression and high levels of proliferation associated with canonical Wnt activity throughout the glandular epithelia regardless of androgen status. In contrast, Tgfbr2(floxE2/floxE2) prostates had epithelial canonical Wnt activity only in the surviving proximal ducts after castration. In vitro studies showed that androgen antagonist, bicalutamide, transiently elevated both Tgfbr2(floxE2/floxE2) and Tgfbr2(fspKO) stromal expression of Wnt-2, Wnt-3a, and Wnt-5a. The neutralization of Wnt signaling by the expression of secreted frizzled related protein-2 (SFRP-2) resulted in decreased LNCaP prostate epithelial cell proliferation in stromal conditioned media transfer experiments. In vivo tissue recombination studies using Tgfbr2(fspKO) prostatic stromal cells in combination with wild-type or SV40 large T antigen expressing epithelia resulted in prostates that were refractile to androgen ablation. The expression of SFRP-2 restored the Tgfbr2(fspKO)-associated prostate responsiveness to androgen ablation. These studies reveal a novel TGF-beta, androgen, and Wnt paracrine signaling axis that enables prostatic regression of the distal ducts after androgen ablation while supporting proximal duct survival.

BACKGROUND AND AIMS: Autoimmune pancreatitis (AIP) is a poorly understood human disease affecting the exocrine pancreas. The goal of the present study was to elucidate the pathogenic mechanisms underlying pancreatic autoimmunity in a murine disease model. METHODS: A transgenic mouse with an S100A4/fibroblast-specific protein 1 (FSP1) Cre-mediated conditional knockout of the transforming growth factor beta (TGFbeta) type II receptor, termed Tgfbr2(fspKO), was used to determine the direct role of TGFbeta in S100A4(+) cells. Immunohistochemical studies suggested that Tgfbr2(fspKO) mice develop mouse AIP (mAIP) characterised by interlobular ductal inflammatory infiltrates and pancreatic autoantibody production. Fluorescence-activated cell sorting (FACS)-isolated dendritic cells (DCs) from diseased pancreata were verified to have S100A4-Cre-mediated DNA recombination. RESULTS: The Tgfbr2(fspKO) mice spontaneously developed mAIP by 6 weeks of age. DCs were confirmed to express S100A4, a previously reported protein expressed by fibroblasts. Adoptive transfer of bone marrow-derived DCs from Tgfbr2(fspKO) mice into 2-week-old syngenic wild-type C57BL/6 mice resulted in reproduction of pancreatitis within 6 weeks. Similar adoptive transfer of wild-type DCs had no effect on pancreas pathology of the host mice. The inability to induce pancreatitis by adoptive transfer of Tgfbr2(fspKO) DCs in adult mice suggested a developmental event in mAIP pathogenesis. Tgfbr2(fspKO) DCs undergo elevated maturation in response to antigen and increased activation of naïve CD4-positive T cells. CONCLUSION: The development of mAIP in the Tgfbr2(fspKO) mouse model illustrates the role of TGFbeta in maintaining myeloid DC immune tolerance. The loss of immune tolerance in myeloid S100A4(+) DCs can mediate mAIP and may explain some aspects of AIP disease pathogenesis.