We studied the mechanical properties of dragline threads of the edible golden silk spider Nephila edulis that are produced under spinning speeds ranging from 0.1 to 400 mm s 71 and temperatures ranging from 5 to 40 8C. These conditions a¡ected the silk in all of the mechanical traits we tested (strain at breaking, breaking energy, initial Young's modulus and point of yielding). We argue that both trade-o¡s (between mechanical properties) and constraints (in the manufacturing process) have a large role in de¢ning spider silk ¢bres.

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The PLU-1 gene is expressed at the level of message in breast cancers and breast cancer cell lines and shows restricted expression in normal adult tissues with the exception of testis. The predicted protein sequence contains several domains, including the PLU domain, which is shared by other proteins involved in transcription and/or development. We have developed a polyclonal antiserum to a C-terminal fragment of the PLU-1 protein, which shows little homology to other family members. Immunohistochemic analysis with the antiserum ␣-PLU-1C confirmed the nuclear localisation of PLU-1. ␣-PLU-1C also reacted with the mouse homologue of PLU-1 (mPlu-1) but not with the closest family member, RBP2. Using Western blot analysis, PLU-1 was shown to be well expressed in breast cancers and breast cancer cell lines, while it was not detected in a range of normal adult tissues. Our results suggest that the PLU-1 protein may belong to the class of testis/cancer antigens. © 2002 Wiley-Liss, Inc. Key words: breast cancer: PLU-1 protein; testis/cancer antigenThe PLU-1 gene was identified as being downregulated in a human mammary epithelial cell line (MTSV1-7) transfected with HER2/c-erbB2, 1 after treatment with the 4D5/HERCEPTIN antibody, which inhibits c-erbB2 signaling. 2 However, in situ hybridisation and Northern blot analyses showed that PLU-1 mRNA is expressed in most breast cancers and breast cancer cell lines, regardless of the level of c-erbB2. 3 However, Northern blot analysis of total mRNA from normal human adult tissues showed high levels of expression in testis and detectable levels in placenta, but levels were undetectable in the other tissues examined.Following our own report on the identification and characterisation of PLU-1, other investigators reported on the cloning of cDNAs of splice and transcriptional variants of the PLU-1 gene. These were referred to as RBP2-H1 4 and RBBP2H1A, 5 respectively. The nomenclature of the splice and transcriptional variants of PLU-1 reflects the high homology between the predicted protein sequence of PLU-1 and the RBP2 6 in conserved domains, particularly in the novel PLU domain. 3,7 PLU-1 binds to a conserved consensus sequence in 2 transcriptions factors through the novel PLU domain. 8 Additionally, PLU-1 was a potent transcriptional repressor and may be involved in gene regulation in breast cancer. We also defined the sequence of mPlu-1 cDNA, which shows at the amino acid level an overall homology with human PLU-1 of 94% and almost 100% identity within the conserved domains. 9 The very conserved sequence of PLU-1 from human to mouse in combination with an almost identical expression pattern in adult tissues and breast cancers in both species suggests a conserved function in breast cancer.The later studies by Vogt et al. 4 and Kashuba et al. 5 on the RNA variants of PLU-1 examined mRNA expression using polyAϩ RNA and probes that would pick up all 3 transcripts. Expression was reported to be less restricted in normal tissues than we observed using total RNA. However, as we repo...

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Very low density lipoprotein receptor (VLDL-R) was found to be expressed in bovine mammary gland and the human breast carcinoma cell line MCF-7 as an M(r) 105,000 variant, and in Chinese hamster ovary (CHO) cells transfected with human VLDL-R cDNA as an M(r) 130,000 variant. The receptor was purified by ligand affinity chromatography with immobilized M(r) 40,000 receptor-associated protein (RAP). The purified receptor was found to bind urokinase-type plasminogen activator-type-1 plasminogen activator inhibitor complex (u-PA.PAI-1), while there was no or very weak binding of active site blocked u-PA (DFP-u-PA), PAI-1 or u-PA-type-2 plasminogen activator inhibitor complex. The binding of u-PA.PAI-1 was blocked by RAP. The transfected CHO cells had an efficient, RAP-sensitive endocytosis of u-PA.PAI-1, severalfold higher than non-transfected parental CHO cells. u-PA.PAI-1 endocytosis was partially inhibited by DFP-u-PA, which blocks binding of the complex to the u-PA receptor. RAP and DFP-u-PA sensitive u-PA.PAI-1 endocytosis was also observed in MCF-7 cells, which were without detectable levels of other RAP-binding endocytosis receptors. These results show that VLDL-R represents a novel endocytosis mechanism for u-PA receptor-bound u-PA.PAI-1.

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