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Sifting through the p53 lung-cancer secretome
sents the same difficulties as human serum. So, Seve and colleagues used the H358 lung-cancer cell line, which can grow in the absence of FBS. “Usually, cells undergo apoptosis when you remove FBS,” he explains. However, in a previous paper, the researchers demonstrated that these cells do not die (J. Biol. Chem. 2001, DOI 10.1074/ jbc.M102683200). “This is a particular
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MALDI, the high intensity of the laser “breaks all the bonds between the PTMs [posttranslational modifications] Just as you might alert your friends and the peptides, so you don’t see about what you are doing through FacePTMs,” he explains. So, 2DE was used book updates, a cell releases proteins instead to look for PTM changes, but and other factors into the extracellular none were detected. Seve cautions that space to communicate to its neighbors. proteins with extreme pIs or hydrophoTo intercept these intercellular messages bicities may not be found with 2DE, so released by lung-cancer cells, researchers PTM changes still might have occurred. at Universite´ Joseph Fourier (INSERM) Most of the differentially and CHU de Grenoble secreted proteins had sig(both in France) analyzed nal peptides; these prothe secretomes of tumor teins probably are secreted cells that express or do not through the classical sigexpress p53. The results, naling pathway. A small reported in JPR (DOI percentage of the proteins 10.1021/pr900383g), ultiwere secreted by either an mately may help researchunknown pathway or the ers identify biomarkers for exosome pathway. the early detection of the Finally, the researchers disease or help them deinjected the tumor cells velop better therapies. into mice to produce xeAccording to the Cennografts. After the tumors ters for Disease Control reached a certain size, and Prevention (http:// p53 expression was inwww.cdc.gov/cancer/lung/ duced in a subset of mice. statistics/), lung cancer is In total tumor extracts, responsible for more U.S. the levels of three prodeaths than any other teins in the in vivo system cancer. Michel Seve, the matched those in the in corresponding author of vitro secretion study. In the JPR paper, says that addition, the level of one patients usually receive protein, GDF-15, was the diagnosis at late Reading between the cells. To find possible lung-cancer biomarkers, higher in plasma of instages, when little can be researchers analyzed proteins secreted from tumor cells and xenografts that duced mice than in done. Often, most or all of expressed or did not express p53. plasma of noninduced a lung is removed. “We mice. This result also corneed biomarkers to find related with the in vitro the lung cancer earlier” so case; you can’t use the method defindings for GDF-15. that the treatment might not require as scribed in the paper directly on other Akhilesh Pandey of Johns Hopkins much lung tissue to be removed, he cell lines,” he clarifies, but tackling this University applauds the team for going explains. issue is on the group’s “to-do” list. the extra mile to show in vitro and in The ideal biomarker would be deAnother interesting feature of H358 vivo results. “I would hope that many tectable in blood. However, the discells is that they have a homozygous deother people would take this kind of covery of biomarkers in plasma has letion of the p53 gene, which is mutated approach,” he notes. Hathout points proven to be difficult because of its in many cancers. The researchers transout that this part of the study is “anlarge dynamic range. That’s why fected the cell line with a plasmid that other step forward”. many researchers are turning to had an inducible p53 gene so that they The JPR work is just the beginning, secretomes for candidate biomarkers, could determine the effect of its protein says Seve. “We needed a first step to says Yetrib Hathout of the Children’s product on the composition of the demonstrate that the secreted proteins National Medical Center. “If you can secretome. from tumor cells could be measured characterize and quantify what tumor With LC/MALDI-MS/MS, the team and detected in plasma.” Next, the recells secrete, you may go back and identified 91 proteins whose secretion searchers will study the secretomes of look at it in serum or even urine,” he was modulated by p53. The offline additional lung-cancer cell lines and states. MALDI method was implemented becompare these with the secretomes of Studying the secretome of cell lines cause more proteins can be identified normal lung cells. They also plan to is challenging because most cells must with it compared with online techanalyze human samples. be cultured in a medium that contains niques, says Seve. However, in offline —Katie Cottingham fetal bovine serum (FBS), which pre-
10.1021/pr9007283
© 2009 American Chemical Society
Journal of Proteome Research • Vol. 8, No. 10, 2009 4395
