High-fat diet promotes prostate cancer growth through histamine signaling.

Western high-fat diets (HFD) are regarded as a major risk factor for prostate cancer (PCa). Using prostate-specific Pten-knockout mice as a PCa model, we previously reported that HFD promoted inflammatory PCa growth. The composition of the gut microbiota changes under the influence of diet exert various effects on the host through immunological mechanisms. Herein, we investigated the etiology of HFD-induced inflammatory cancer growth and the involvement of the gut microbiome. The expression of Hdc, the gene responsible for histamine biosynthesis, and histamine levels were upregulated in large prostate tumors of HFD-fed mice, and the number of mast cells increased around the tumor foci. Administration of fexofenadine, a histamine H1 receptor antagonist, suppressed tumor growth in HFD-fed mice by reducing the number of myeloid-derived suppressor cells and suppressing IL6/STAT3 signaling. HFD intake induced gut dysbiosis, resulting in the elevation of serum lipopolysaccharide (LPS) levels. Intraperitoneal injection of LPS increased Hdc expression in PCa. Inhibition of LPS/Toll-like receptor 4 signaling suppressed HFD-induced tumor growth. The number of mast cells increased around the cancer foci in total prostatectomy specimens of severely obese patients. In conclusion, HFD promotes PCa growth through histamine signaling via mast cells. Dietary high-fat induced gut dysbiosis might be involved in the inflammatory cancer growth.

Molecular Basis of the Ligand Binding Specificity of αvß8 Integrin.

αvß8 is an integrin that recognizes an Arg-Gly-Asp (RGD) motif and interacts with fibronectin, vitronectin, and latent TGF-ß1. We comprehensively determined the binding activity of the αvß8 integrin toward 25 secreted proteins having an RGD motif. The αvß8 integrin strongly bound to latent TGF-ß1 but showed marginal activity for other RGD-containing proteins, including fibronectin and vitronectin. Site-directed mutagenesis of latent TGF-ß1 demonstrated that the high affinity binding of αvß8 integrin to latent TGF-ß1 was defined by Leu-218 immediately following the RGD motif within the latency-associated peptide of TGF-ß1. Consistent with the critical role of Leu-218 in latent TGF-ß1 recognition by αvß8 integrin, a 9-mer synthetic peptide containing an RGDL sequence strongly inhibited interactions of latent TGF-ß1 with αvß8 integrin, whereas a 9-mer peptide with an RGDA sequence was ∼60-fold less inhibitory. Because αvß3 integrin did not exhibit strong binding to latent TGF-ß1 or distinguish between RGDL- and RGDA-containing peptides, we explored the mechanism by which the integrin ß8 subunit defines the high affinity binding of latent TGF-ß1 by αvß8 integrin. Production of a series of swap mutants of integrin ß8 and ß3 subunits indicated that the high affinity binding of αvß8 integrin with latent TGF-ß1 was ensured by interactions between the Leu-218 residue and the ß8 I-like domain, with the former serving as an auxiliary recognition residue defining the restricted ligand specificity of αvß8 integrin toward latent TGF-ß1. In support of this conclusion, high affinity binding toward the αvß8 integrin was conferred on fibronectin by substitution of its RGDS motif with an RGDL sequence.

Molecular basis of the recognition of nephronectin by integrin alpha8beta1.

Integrin alpha8beta1 interacts with a variety of Arg-Gly-Asp (RGD)-containing ligands in the extracellular matrix. Here, we examined the binding activities of alpha8beta1 integrin toward a panel of RGD-containing ligands. Integrin alpha8beta1 bound specifically to nephronectin with an apparent dissociation constant of 0.28 +/- 0.01 nm, but showed only marginal affinities for fibronectin and other RGD-containing ligands. The high-affinity binding to alpha8beta1 integrin was fully reproduced with a recombinant nephronectin fragment derived from the RGD-containing central "linker" segment. A series of deletion mutants of the recombinant fragment identified the LFEIFEIER sequence on the C-terminal side of the RGD motif as an auxiliary site required for high-affinity binding to alpha8beta1 integrin. Alanine scanning mutagenesis within the LFEIFEIER sequence defined the EIE sequence as a critical motif ensuring the high-affinity integrin-ligand interaction. Although a synthetic LFEIFEIER peptide failed to inhibit the binding of alpha8beta1 integrin to nephronectin, a longer peptide containing both the RGD motif and the LFEIFEIER sequence was strongly inhibitory, and was approximately 2,000-fold more potent than a peptide containing only the RGD motif. Furthermore, trans-complementation assays using recombinant fragments containing either the RGD motif or LFEIFEIER sequence revealed a clear synergism in the binding to alpha8beta1 integrin. Taken together, these results indicate that the specific high-affinity binding of nephronectin to alpha8beta1 integrin is achieved by bipartite interaction of the integrin with the RGD motif and LFEIFEIER sequence, with the latter serving as a synergy site that greatly potentiates the RGD-driven integrin-ligand interaction but has only marginal activity to secure the interaction by itself.