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RESEARCH PROFILE
Proteomics confirms it: Eat your fiber!
to a recent report linking overexpression of hnRNP A1 to sporadic colorectal Nutritionists recommend fiber as cancers, led the researchers to focus on part of a healthy diet to help prevent the characterization of hnRNP A1 incolorectal cancer. But how does fiber volvement in butyrate activity. work its magic? According to Sandra The 3 down-regulated full-length Tan at the National University of SingahnRNP A1 forms and the 2 up-regupore (NUS), researchers used to think lated forms ran at apparent molecuthat fiber bound to carcinogens and lar weights of 38 and 26 kDa, respeckept them away from the walls of the tively. To see whether the differences in lower digestive tract. “Interestingly, in pI were due to posttranslational modthe mid-1990s, it was shown that fiber ifications, the researchers performed undergoes fermentation by colonic baca western blot and probed with antiteria to short-chain fatty acbodies to phosphoserine and ids,” says Tan. She adds that phosphotyrosine. The 3 38these short-chain fatty ackDa spots contained phosButyrate ids, in particular butyrate, phorylated hnRNP A1, and are responsible for the prothe protein was posttranslaFermentation tective effects of fiber. tionally modified to a simiWhen colorectal canlar degree in both treated and cer cells are exposed to buuntreated samples. Theretyrate, they stop growing fore, phosphorylations exand undergo apoptosis. Buplained the shifts in pI. tyrate specifically targets But what could explain the Fiber Anti-tumorigenic effects cancer cells; it does not afpresence of smaller hnRNP fect normal cells. As deA1 forms? According to the scribed in this issue of JPR researchers, reports in the litHelpful molecule. Butyrate, which is found in fiber, specifically arrests (pp 1098–1106), Tan, Maxerature suggest that hnRNP the growth of and induces apoptosis in colorectal cancer cells. ey Chung, and colleagues at A1 might be cleaved and loNUS have studied the effect calized to the cytoplasm durof butyrate on a colorectal cancer cell When heparin columns and narrowing apoptosis. To check on the localizaline. Using a proteomics approach, the range IPG strips were used, resolution tion of the 26-kDa forms within cells, was enhanced and additional proresearchers found that several proteins the researchers performed subcelluwere differentially regulated by butyr teins were isolated. A total of 46 spots lar fractionation of the treated and unate treatment. The researchers say that were quantitatively different between treated samples and analyzed the cytothese proteomics studies on the fatty the butyrate-treated and untreated solic fraction for hnRNP A1 by western acid could help them develop new thercolorectal cancer cells. The researchblotting. The 26-kDa forms were presapies for colorectal cancer. ers identified proteins from 24 of these ent in the cytosolic fraction of treated In an initial study, the researchers spots by MS. Only 19 unique proteins cells but not untreated cells. Therefore, left a control group of HCT-116 colorecwere identified; some proteins apthe researchers say that the smaller tal cancer cells untreated but added bupeared in several spots. Of the unique forms are probably truncated versions tyrate to another group of HCT-116 cells proteins, 10 were down-regulated and 9 of the full-length protein. were up-regulated in response to butyr for 24 h. They analyzed whole-cell exSeveral additional projects are in the tracts of both groups of cells on the ate treatment. works in the Chung laboratory to delve same 2DE gel by difference in-gel elecThe researchers were intrigued when deeper into this topic. “We’re thinking they found heterogeneous nuclear ribo trophoresis (known as DIGE). A total that instead of using the heparin preof 20 spots were differentially regulatnucleoprotein (hnRNP) family memfractionation, we could take subproed. Cytokeratin 8 (which was present in bers in six spots. These proteins are inteomics approaches,” says Chung. For 4 spots), ornithine aminotransferase, volved in mRNA biogenesis, according example, he says that lab members are and cytochrome c oxidase peptide VIb to Tan. One protein, hnRNP K, was upstudying mitochondrial proteins for were identified. regulated in 1 spot, but hnRNP A1 was butyrate effects. The researchers are The researchers suspected that they down-regulated in 3 spots and up-regalso validating some of the targets that were missing some butyrate targets ulated in 2 spots in response to butyrate they identified in this study. with this method, however, so they treatment. This discovery, in addition —Katie Cottingham MAXEY CHUNG/Photodisc
added prefractionation steps to the protocol. “We thought that heparin [columns] could be used as a routine method of separation [for this study] because you can preferentially separate basic proteins, including nuclear factors and transcription factors. [These proteins] are of interest in cancer biology,” explains Chung. The researchers also implemented narrow-range immobilized pH gradient (IPG) strips in acidic and basic pH ranges to better separate proteins on the 2DE gels.
© 2006 American Chemical Society
Journal of Proteome Research • Vol. 5, No. 5, 2006 1045
