Plasticity of protein expression during culture of fetal skin cells.

In order to gain insight into the biology of fetal skin during culture, cellular proteins were studied during four culture passages (P00, P01, P04 as well as P10) using high-resolution two-dimensional (2-D) gel electrophoresis and mass spectrometry (MS). Bioinformatic analyses were focused on a region of each gel corresponding to pI between 4 and 8 and M(r) from 8000 to 35 000. In this area, 373 +/- 42 spots were detected (N = 18). Twenty-six spots presented an integrated intensity that increased in the higher passages, whereas five spots showed a progressively lower intensity in subsequent passaging. MS analysis was performed on spots that were unambiguously identified on preparative 2-D gels. Among the 26 spots showing an increased size between P00 and P10, 9 were identified, and corresponded to 3 proteins: (i) peptidyl-prolyl cis-trans isomerase A (P05092; cyclophilin A or cyclosporin A-binding protein), (ii) triosephosphate isomerase (P00938), and (iii) enoyl-CoA hydratase (P30084). Among these nine identified spots, three were absent at P00, but were present at P10. They corresponded to isoforms of peptidyl-prolyl cis-trans isomerase and triosephosphate isomerase, respectively. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses of the acidic isoforms of triosephosphate isomerase showed modifications of cysteine residues to cysteic acid. All these isoforms were clearly present in the skin cells of a 4-year-old child, as well as in skin cells from a 80-year-old man, at P00. These observations probably reflect either an oxidative stress related to cell culture, or, alternatively, maturation, differentiation and the aging of the cells.

IgM are associated to Sp alpha (CD5 antigen-like).

In 1993, we reported the presence of an IgM-associated peptide (M(r) 44 kDa; pI 5.45) in all immunoglobulin M (IgM) fractions purified from plasma/serum by various methods. This peptide was absent in Ig fractions of non-IgM isotypes. The N-terminal sequence was determined as being APPSGVRLVGGLH. To gain insight into the nature of this peptide, we further analyzed, using modern proteomic tools, the IgM-associated peptide isolated from cryoglobulins. Mass spectrometry revealed three peptides of different masses: 2203.13 (ELGCGAASGTPSGILYEPPAEK), 1564.83 (KPIWLSQMSCSGR), and 1544.77 (EATLQDCPSGPWGK). Theses sequences together with the already known N-terminal sequence allowed us to identity the IgM-associated peptide as Sp alpha (O43866 in TrEMBL database; CD5 antigen-like). Sp alpha is a member of the scavenger receptor cysteine-rich superfamily of proteins. This family includes the T-and B-cell antigens CD5 and CD6, and several of its members influence immune cell fate. Our finding may have important implications in the understanding of the homeostasis of IgM antibodies.