Treatment with individual anti-androgens is associated with the development of hot-spot mutations in the androgen receptor (AR), including T877A (hydroxyflutamide [HF]) and W741(C/L) (bicalutamide [CDX]). Here, we found that anti-androgens bound mt-ARs (HF-T877A-AR-LBD and CDX-W741L-AR-LBD) have similar binary structure to the 5α-dihydrotestosterone (DHT) bound wild type (wt) AR (DHT-wt-AR-LBD). Phage display revealed that these ARs bound to similar peptides, including BUD31, containing an Fxx(F/H/L/W/Y)Y motif cluster with Tyr in the +5 position. Structural analyses of the AR-LBD-BUD31 complex at 2.1 Å resolution revealed formation of an extra hydrogen bond between the Tyr+5 residue of the peptide and Gln733 of the AR AF2 domain, suggesting that peptides with Fxx(F/H/L/W/Y)Y motifs can interact with wt or mutated ARs. Functional studies showed that BUD31-related peptides suppressed transactivation of both DHT-wt-AR and HF-T877A-AR by interrupting AR N- and C-terminal interactions, thereby inhibiting wt and mutant AR-mediated prostate cancer cell growth. Collectively, these results suggest the combination of peptide screening and X-ray structure analysis as a new strategy for developing anti-androgens that simultaneously suppress both wt and mutated AR function.

HDGF (hepatoma-derived growth factor) stimulates cell proliferation by functioning on both sides of the plasma membrane as a ligand for membrane receptor binding to trigger cell signalling and as a stimulator for DNA synthesis in the nucleus. Although HDGF was initially identified as a secretory heparin-binding protein, the biological significance of its heparin-binding ability remains to be determined. In the present study we demonstrate that cells devoid of surface HS (heparan sulfate) were unable to internalize HDGF, HATH (N-terminal domain of HDGF consisting of amino acid residues 1-100, including the PWWP motif) and HATH(K96A) (single-site mutant form of HATH devoid of receptor binding activity), suggesting that the binding of HATH to surface HS is important for HDGF internalization. We further demonstrate that both HATH and HATH(K96A) could be internalized through macropinocytosis after binding to the cell surface HS. Interestingly, HS-mediated HATH(K96A) internalization is found to exhibit an inhibitory effect on cell migration and proliferation in contrast with that observed for HATH action on NIH 3T3 cells, suggesting that HDGF exploits the innate properties of both cell surface HS and membrane receptor via the HATH domain to affect related cell signalling processes. The present study indicates that MAPK (mitogen-activated protein kinase) signalling pathways could be affected by the HS-mediated HATH internalization to regulate cell migration in NIH 3T3 fibroblasts, as judged from the differential effect of HATH and HATH(K96A) treatment on the expression level of matrix metalloproteases.

Severe tissue necrosis with a retarded wound healing process is a major symptom of a cobra snakebite. Cardiotoxins (CTXs) are major components of cobra venoms that belong to the Ly-6 protein family and are implicated in tissue damage. The interaction of the major CTX from Taiwan cobra, i.e. CTX A3, with sulfatides in the cell membrane has recently been shown to induce pore formation and cell internalization and to be responsible for cytotoxicity in cardiomyocytes (Wang, C.-H., Liu, J.-H., Lee, S.-C., Hsiao, C.-D., and Wu, W.-g. (2006) J. Biol. Chem. 281, 656 -667). We show here that one of the non-cytotoxic CTXs, i.e. CTX A5 or cardiotoxin-like basic polypeptide, from Taiwan cobra specifically bound to ␣v␤3 integrin and inhibited bone resorption activity. We found that both membrane-bound and recombinant soluble ␣v␤3 integrins bound specifically to CTX A5 in a dose-dependent manner. Surface plasmon resonance analysis showed that human soluble ␣v␤3 bound to CTX A5 with an apparent affinity of ϳ0.3 M. Calf pulmonary artery endothelial cells, which constitutively express ␣v␤3, showed a CTX A5 binding profile similar to that of membrane-bound and soluble ␣v␤3 integrins, suggesting that endothelial cells are a potential target for CTX action. We tested whether CTX A5 inhibits osteoclast differentiation and bone resorption, a process known to be involved in ␣v␤3 binding and inhibited by RGD-containing peptides. We demonstrate that CTX A5 inhibited both activities at a micromolar range by binding to murine ␣v␤3 integrin in osteoclasts and that CTX A5 co-localized with ␤3 integrin. Finally, after comparing the integrin binding affinity among CTX homologs, we propose that the amino acid residues near the two loops of CTX A5 are involved in integrin binding. These results identify CTX A5 as a non-RGD integrin-binding protein with therapeutic potential as an integrin antagonist.Severe tissue necrosis and inflammation with a retarded wound healing process are the major symptoms of a victim surviving from a cobra bite (1-4). Cobra cardiotoxins (CTXs) 3 are the major toxin peptides and constitute ϳ50% of the weight of cobra venom. CTXs are believed to play a critical role in cobra venom toxicity (5). We have shown that CTXs bind to glycosaminoglycans with specificity and are retained on the membrane surface for action (6 -8). Interestingly, one of the CTXs, CTX A3, interacts with sulfatide to form a pore and becomes internalized to further target mitochondria in cardiomyocytes and H9C2 myoblasts (9 -12). The mechanisms for CTX-induced perturbation of the wound healing process and severe tissue damage are unknown. It is not clear whether there are cellular receptors for CTXs, although other cobra venom components such as secretory phospholipase A 2 are known to have diverse targets for their actions by involving glycosaminoglycans, protein receptors, and membrane lipids (13,14). CTXs are all ␤-sheet basic polypeptides of 60 -62 amino acid residues with a three-fingered loop-folding topology and are members of the Ly-6 protei...