M E E T I N G Elizabeth Zubritsky reports from the HUPO Third Annual World Congress—Beijing, China.
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Fortunately, there was a relationship in one of the NGF pathways: High levels of TrkA correspond to a better prognosis for a patient. “That sounds contradictory, [doesn’t] it?” HonderA role for NGF in breast cancer marck asks. After all, the TrkA pathway Hubert Hondermarck and colleagues at stimulates cell proliferation, so wouldINSERM in Lille, France, have uncovn’t low levels of TrkA be better for a paered the role of nerve growth factor tient? “In fact, it isn’t.” A hallmark of (NGF) in some breast cancers. Using very aggressive cancers, he explains, is functional proteomics, the researchers so-called autonomous growth stimulamapped two pathways: one that begins tion, in which the cancer cells lose when NGF activates the p75NTR recepgrowth factor receptors and hormone tor, which has a role in the mediation of receptors. Instead of receiving external apoptosis, and the other that begins signals that when NGF actimight reguvates the TrkA late their tyrosine kinase growth, the receptor, which cells proliferis involved in cell ate at their proliferation. own rapid Hondermarck pace. says that NGF’s “This is role was unextypically the pected because case with no association estrogen with breast canreceptors, cer had been which are the reported previmain bioously in the literArresting apoptosis. (a) A control sample vs (b) cells in which the ceramide C2 induces DNA fragmentamarker used ature and NGF is tion and cell death. (c) Apoptosis is prevented when NGF is present in addition to C2. to date in not expressed in clinical pracnormal breast tice,” says epithelial cells. Hondermarck. “[They] are down-regution, they captured molecules that were In fact, the researchers originally chose lated in more aggressive forms of breast bound to p75NTR and identified them NGF as a negative control to study the cancer.” NGF, he adds, follows the same with LC/MS/MS. The researchers found mitogenic effects of other growth facpattern. two tumor necrosis factor receptortors, such as epidermal growth factor The last experiment to confirm associated factors (TRAF2 and TRAF6), and insulin-like growth factor. “To our NGF’s role was the introduction of small both of which are known to be involved surprise, NGF was stimulating breast interfering RNA (siRNA) to reduce the in p75NTR signaling, and a protein cancer cell growth, and therefore, the protein’s expression in breast cancer called tumor necrosis factor receptornegative control became our main cells injected into immunodeficient associated death domain (TRADD). This [focus] of interest,” he explains. mice. When the siRNA was injected into last protein had not been previously reUsing LC/MS/MS, the researchers the bloodstream, the tumors in mice ported to be associated with p75NTR, determined that breast cancer cells exwere smaller, and there was less metasbut the researchers determined that press NGF. They confirmed this result tasis into the liver, Hondermarck says. TRADD is involved in the activation of with Western blot analysis and reverseAlthough pleased that the group NF-B. transcriptase PCR. Although NGF rewas able to trace the two NGF pathways The story of NGF’s role in breast ceptors are produced in both normal from scratch and to correlate TrkA excancer was proceeding well at that breast epithelial cells and breast cancer pression with prognosis, Hondermarck point, but a crucial piece was still misscells, “the expression of NGF itself is is still cautious. “It’s a nice story,” he ing: a relationship between the expreslimited to cancer cells,” Hondermarck says, “but we should not forget the sion of one of these proteins and the notes. complexity of the system.” Breast canprognoses of patients. Proteomics has The differential expression pattern cer is a heterogeneous disease, he exgenerally fallen short in making this was interesting but not enough to prove plains, and the cancer cells are not type of correlation, says Hondermarck. anything. Hondermarck likes to quote stimulated by only one growth factor or He points to the cell-cycle regulator 14the French philosopher René Descartes hormone at a time. A lot more work 3-3 as an example. Although 14-3-3 is here: “To know does not mean to underremains to be done before researchers expressed at lower-than-normal levels stand.” So, the group set out to detercan provide information that truly in breast cancer, this fact has no bearing mine whether there was a plausible biohelps patients. on prognosis. logical role for NGF in breast cancer. COURTESY OF HUBERT HONDERMARCK
Further investigation revealed that the protein works in two ways: It enhances cell survival, and it stimulates cell proliferation. In the first case, binding of NGF to the p75NTR receptor activates the transcription factor NF-B, which prevents apoptosis. In the second case, binding of NGF to the TrkA receptor triggers mitogen-activated protein kinases and associated signaling events, which in turn stimulate cell proliferation. To help complete the picture, the group looked for signaling partners of p75NTR. Using co-immunoprecipita-
Journal of Proteome Research • Vol. 4, No. 1, 2005
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