Identification of a common epitope in the sequences of COL4A1 and COL6A1 recognized by monoclonal antibody #141.

Identification of a type IV collagen α1 polypeptide in non-triple helical form [NTH α1(IV)], possibly involved in angiogenesis, introduces the further possibility of the existence of non-triple helical forms of other collagen chains. We previously reported that an anti-NTH α1(IV) monoclonal antibody #141 recognizes not only NTH α1(IV) but also a novel non-triple helical collagen polypeptide NTH α1(VI) encoded by COL6A1. In this study, we identified the recognition sequence in order to better understand the properties of antibody #141 and provide clues regarding the biological function of the two non-triple helical molecules. Additionally, we determined the common epitope between COL4A1 and COL6A1 as PXXGXPGLRG, with surface plasmon resonance analyses revealing KD values for the COL4A1 epitope as 5.56±1.81×10-9 M and for the COL6A1 epitope as 7.15±0.44×10-10 M. The specific recognition of NTH α1(IV) and NTH α1(VI) by antibody #141 can be explained by the common epitope sequence. Moreover, epitope localization supports previous finding that NTH α1(IV) and NTH α1(VI) differ in conformation from the α1 chains in triple-helical type IV and type VI collagen. These findings suggest that antibody #141 might be useful for diagnosis of type VI collagen myopathies.

Identification of target genes of synovial sarcoma-associated fusion oncoprotein using human pluripotent stem cells.

Synovial sarcoma (SS) is a malignant soft tissue tumor harboring chromosomal translocation t(X; 18)(p11.2; q11.2), which produces SS-specific fusion gene, SYT-SSX. Although precise function of SYT-SSX remains to be investigated, accumulating evidences suggest its role in gene regulation via epigenetic mechanisms, and the product of SYT-SSX target genes may serve as biomarkers of SS. Lack of knowledge about the cell-of-origin of SS, however, has placed obstacle in the way of target identification. Here we report a novel approach to identify SYT-SSX2 target genes using human pluripotent stem cells (hPSCs) containing a doxycycline-inducible SYT-SSX2 gene. SYT-SSX2 was efficiently induced both at mRNA and protein levels within three hours after doxycycline administration, while no morphological change of hPSCs was observed until 24h. Serial microarray analyses identified genes of which the expression level changed more than twofold within 24h. Surprisingly, the majority (297/312, 95.2%) were up-regulated genes and a result inconsistent with the current concept of SYT-SSX as a transcriptional repressor. Comparing these genes with SS-related genes which were selected by a series of in silico analyses, 49 and 2 genes were finally identified as candidates of up- and down-regulated target of SYT-SSX, respectively. Association of these genes with SYT-SSX in SS cells was confirmed by knockdown experiments. Expression profiles of SS-related genes in hPSCs and human mesenchymal stem cells (hMSCs) were strikingly different in response to the induction of SYT-SSX, and more than half of SYT-SSX target genes in hPSCs were not induced in hMSCs. These results suggest the importance of cellular context for correct understanding of SYT-SSX function, and demonstrated how our new system will help to overcome this issue.