Although the fates of the internalized hormone-receptor complexes formed by the lutropin/choriogonadotropin and the TSH receptors have been examined in some detail, much less is known about the fate of the internalized FSH-FSH receptor (FSHR) complex. Using biochemical and imaging approaches we show here that the majority of the internalized FSH-FSHR complex accumulates in endosomes and subsequently recycles back to the cell surface where the bound, intact hormone dissociates back into the medium. Only small amounts of FSH and the FSHR are routed to a lysosomal degradation pathway, and the extent of FSH-induced down-regulation of the cell surface and total FSHR is minimal. This pathway was detected in heterologous (human kidney 293T) cells transfected with the rat (r) or human (h) FSHR as well as in a mouse Sertoli cell line (MSC-1) or a mouse granulosa cell line (KK-1) transfected with the rFSHR.Additional experiments using a series of C-terminal deletions of the rFSHR and the hFSHR showed that the recycling of the internalized FSH-FSHR complex and the extent of hFSH-induced down-regulation is dictated by a short stretch of amino acids present at the extreme C-terminal end of the receptor.We conclude that most of the internalized FSH-FSHR complex is recycled back to the cell surface, that this recycling pathway is highly dependent on amino acid residues present near the C terminus of the FSHR, and that it is an important determinant of the extent of down-regulation of the FSHR.

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Although the involvement of the nonvisual arrestins in the agonist-induced internalization of the human lutropin receptor (hLHR) has been documented previously with the use of dominant-negative mutants, a physical association of the nonvisual arrestins with the hLHR in intact cells has not been established. In the studies presented herein, we used a cross-linking/coimmunoprecipitation/immunoblotting approach as well as confocal microscopy to document the association of the hLHR with the nonvisual arrestins in co-transfected 293 cells. We also used this approach to examine the relative importance of receptor activation and receptor phosphorylation in the formation of this complex. Using hLHR mutants that impair phosphorylation, activation, or both, we show that the formation of the hLHR-nonvisual arrestin complex depends mostly on the agonistinduced activation of the hLHR rather than on the phosphorylation of the hLHR. These results stand in contrast to those obtained with several other G protein-coupled receptors (i.e. the ␤ 2 -adrenergic receptor, the m2 muscarinic receptor, rhodopsin, and the type 1A angiotensin receptor) where arrestin binding depends mostly on receptor phosphorylation rather than on receptor activation. We have also examined the association of the nonvisual arrestins with naturally occurring gain-offunction mutations of the hLHR found in boys with Leydig cell hyperplasia or Leydig cell adenomas. Our results show that these mutants associate with the nonvisual arrestins in an agonist-independent fashion. Internalization of G protein-coupled receptors (GPCRs)1 is a ubiquitous response that follows agonist activation (reviewed in Refs. 1-4). Although GPCRs can be internalized by several distinct pathways (3), the most common and best understood pathway is facilitated by the G protein-coupled receptor kinase (GRK)-catalyzed phosphorylation of GPCRs and the subsequent formation of a complex between the agonist-activated and phosphorylated GPCRs and a family of proteins known as the nonvisual arrestins or ␤arrestins. The nonvisual arrestins (arrestin-2 also known as ␤-arrestin-1 and arrestin-3, also known as ␤-arrestin-2) bind with high affinity to clathrin and to adaptor protein-2 (5, 6) and thus target the activated and phosphorylated GPCRs to clathrin coated pits. Once localized to clathrin-coated pits, the GPCRs are internalized by a process that requires the participation of dynamin, a GTPase involved in the fission of clathrin-coated pits (7).Studies from this and other laboratories have shown that the binding of agonist to the rat, mouse, porcine, or human lutropin receptor (LHR) triggers the internalization of the agonist-receptor complex via clathrin-coated pits by a pathway that can be inhibited with dominant-negative mutants of the nonvisual arrestins and a dominant-negative mutant of dynamin (8 -12). Although the large number of studies on the ␤ 2 -adrenergic receptor emphasize the importance of GPCR phosphorylation on the process of internalization (1-4), our recent mutagenesis studie...

The insulin-like growth factor binding protein IGFBP-3 is a pro-apoptotic and anti-angiogenic protein in prostate cancer (CaP). Epidemiological studies suggest that low IGFBP-3 is associated with greater risk of aggressive, metastatic prostate cancers, but in vivo functional data are lacking. Here we show that mice that are genetically deficient in IGFBP-3 exhibit weaker growth of primary prostate tumors growth but higher incidence of metastatic disease. Prostates in IGFBP-3 knockout mice (IGFBP-3KO mice) failed to undergo apoptosis after castration. Spontaneous prostate tumors did not develop in IGFBP-3KO mice, but splenic lymphomas occured in 23% of female IGFBP-3KO mice by 80 weeks of age. To assess the effects of IGFBP-3 deficiency on prostate cancer development, we crossed IGFBP-3KO mice with a c-Myc-driven model of CaP that develops slow-growing, non-metastatic tumors. By 24 weeks of age, well-differentiated prostate cancers were observed in all mice regardless of IGFBP-3 status. However, by 80 weeks of age IGFBP-3KO mice tended to exhibit larger prostate tumors than control mice. More strikingly, lung metastases were observed at this time in 55% of the IGFBP-3KO mice but none of the control animals. Cell lines established from Myc:IGFBP-3KO tumors displayed more aggressive phenotypes in proliferation, invasion and colony formation assays, relative to control Myc tumor cell lines. In addition, Myc:IGFBP-3KO cells exhibited evidence of epithelial-mesenchymal transition (EMT). Our findings establish a function for IGFBP-3 in suppressing metastasis in prostate cancer, and they also offer the first reported transgenic model of spontaneous metastatic prostate cancer for studies of this advanced stage of disease.

Preclinical studies suggest lowering dietary fat and decreasing the ratio of omega-6 to omega-3 polyunsaturated fatty acids decreases the risk of prostate cancer development and progression. We conducted a phase II randomized trial to test the effect of decreasing dietary fat combined with decreasing the dietary omega-6:omega-3 ratio on biomarkers related to prostate cancer development and progression. Patients undergoing radical prostatectomy were randomly assigned to receive a low-fat diet with 5 grams of fish oil daily (dietary omega-6:omega-3 ratio of 2:1) or a control western diet (omega-6:omega-3 ratio of 15:1) for 4–6 weeks prior to surgery. The primary endpoint was change in serum IGF-1 between arms. Secondary endpoints were serum IGFBP-1, prostate prostaglandin E-2 levels, omega-6:omega-3 fatty acid ratios, COX-2 and markers of proliferation and apoptosis. Fifty-five patients were randomized and 48 completed the trial. There was no treatment difference in the primary outcome. Positive secondary outcomes in the low-fat fish oil vs. western group were reduced benign and malignant prostate tissue omega-6:omega-3 ratios, reduced proliferation (Ki67 index), and reduced proliferation in an ex-vivo bioassay when patient sera was applied to prostate cancer cells in vitro. In summary, 4–6 weeks of a low-fat diet and fish oil capsules to achieve an omega-6:omega-3 fatty acid ratio of 2:1 had no effect on serum IGF-1 levels, though in secondary analyses the intervention resulted in decreased prostate cancer proliferation and decreased prostate tissue omega-6:omega-3 ratios. These results support further studies evaluating reduction of dietary fat with fish oil supplementation on modulating prostate cancer biology.