news
Sialylation alterations of acute-phase proteins in mice with tumors
was removed from the samples, and the proteins were analyzed in parallel workflows. For protein identifications, the samples were run on a 1DE gel, and excised bands were digested with trypsin and analyzed by LC/MS and LC/MS/MS. For glycan analyses, peptides were treated with peptide-N-glycosidase F (known as PNGaseF) to release the glycans, which were analyzed by MALDI
samples from mice that had colon cancer transplants. Humans cannot make Neu5Ac, so what is the relevance of this change to human patients? “I think that When acute-phase proteins are found to insofar as the sialylation is changing, be differentially expressed between disthere is probably some relevance, but for ease and control populations in prothe Neu5Gc and Neu5Ac change, there’s teomics experiments, researchers often probably not a lot,” says Khoo. “Aldismiss these results as uninteresting though [this finding] is not relevant to because, by definition, these proteins are humans, it will be for mice since there up- or down-regulated in many condiare specific endogtions that cause enous lectins that inflammation. would preferenBecause these tially recognize changes are not one form and not specific for a conthe other, and dition or disease, thus it is of signifithey have little cance for those use as convenstudying cancer tional biomarkers and tumor profor diagnosis or gression in mice.” prognosis. HowFinally, the reever, as reported Flowing along. A schematic of the workflow that researchers used to identify glycopeptides. searchers wanted in JPR (DOI 10.1021/ to pinpoint the pr800093b), Kayproteins that had Hooi Khoo and MS and MALDI MS/MS. sialylation changes. “The obvious candicolleagues at Academia Sinica (Taiwan) Changes in protein levels were obdates would be those proteins that are have found that the glycosylation patserved on 1DE gels as early as the secabundant, for a start,” explains Khoo. terns of some acute-phase proteins are ond and third weeks, but only the Acute-phase proteins are abundant, so altered in mice with tumors. samples from weeks 0 and 5 were fully the team analyzed a couple of these proThe investigators didn’t start out by characterized in the glycomics and proteins. Levels of serotransferrin did not targeting acute-phase proteins. Instead, teomics workflows. For example, haptochange before and after transplantation, Khoo and colleagues were interested in globin, an acute-phase protein, was but the protein is known to have a disiacancer-induced glycosylation changes present in serum samples from tumorlylated antenna sequence. Therefore, and the development of workflows to bearing mice only at week 5, not at week Khoo and colleagues performed a selecdetect these changes. The first obvious 0. In general, protein abundances in astive glycopeptide analysis on serotransstep was to use a mouse model. Typicitic fluid and serum of mice with colon ferrin and found that the protein in cocally, researchers who study human or breast cancer tumors were similar to lon cancer samples had increased tumors in mice implant this tissue in each other. Therefore, protein levels did sialylation on its antenna sequence commice with severe combined immunonot distinguish the mice with different pared with the form that was present in deficiency (SCID) to avoid rejection. cancers. the control samples. In addition, haptoHowever, important changes could be When the researchers looked at the globin from colon cancer samples promissed if mice without a fully working glycosylation profiles, they found that duced spectra that were consistent with immune system are used. Because huthe N-glycan pattern varied between Neu5Ac substitutions, but because the man tumors can’t be implanted back weeks 0 and 5 as well as between mice protein was absent from the control into humans for experimentation, and with breast cancer and colon cancer tusamples, a meaningful comparison could SCID mice have immune-system defimors. Both types of tumor-bearing mice not be made. ciencies, the scientists took the unhad increased levels of internal sialylaFor now, the group will move on usual step of implanting mouse tumors tion on disialylated antenna sequences, from serum and ascitic fluid to examinto normal mice. which are complex branched structures, ine molecular changes in tissues. “To Mice implanted with murine colon or compared with the control samples. study molecular mechanisms, it’s diffibreast cancer tissue were monitored for “Sialic acid is quite an important issue in cult to trace back the serum because glycosylation changes. Control serum glycobiology,” Khoo points out. He says proteins in serum are secreted from samples were taken from these mice bethat sialylation increases the half-life of everywhere,” explains Khoo. A longerfore they received the transplants, and some therapeutics. In addition, sialic term goal, however, is to develop betsamples of serum and ascitic fluid (fluid acid often is involved in signaling. ter glycoproteomics methods and that can accumulate in the abdomen as Another interesting finding was that platforms. a result of illness) were taken weekly for an increased substitution of Neu5Ac for 5 weeks after transplantation. Albumin —Katie Cottingham Neu5Gc was observed specifically with
3068
Journal of Proteome Research • Vol. 7, No. 8, 2008
10.1021/pr800446h
© 2008 American Chemical Society
