Proteomics. 2013 Jan;13(1):48-60. doi: 10.1002/pmic.201200188.

A Proteomic Snapshot of Breast Cancer Cell Cycle: The G1/S Transition Point.

Tenga MJ, Lazar IM.

Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 246021, USA.



The biological processes that unfold during the G1-phase of the cell cycle are dependent on extracellular mitogenic factors that signal the cell to enter a state of quiescence, or commit to a cell-cycle round by passing the restriction point (R-point) and enter the S-phase. Unlike normal cells, cancer cells evolved the ability to evade the R-point and continue through the cell cycle even in the presence of extensive DNA damage or absence of mitogenic signals. The purpose of this study was to perform a quantitative proteomic evaluation of the biological processes that are responsible for driving MCF-7 breast cancer cells into division even when molecular checkpoints such as the G1/S R-point are in place. Nuclear and cytoplasmic fractions of the G1 and S cell-cycle phases were analyzed by LC-MS/MS to result in the confident identification of more than 2700 proteins. Statistical evaluation of the normalized data resulted in the selection of proteins that displayed twofold or more change in spectral counts in each cell state. Pathway mapping, functional annotation clustering, and protein interaction network analysis revealed that the top-scoring clusters that could play a role in overriding the G1/S transition point included DNA damage response, chromatin remodeling, transcription/translation regulation, and signaling proteins.

© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

PMID: 23152136



The accumulation of mutations, loss- or over-expression of genes that control cell growth and proliferation, leads, ultimately, to the on-set of cancer.  Proteomic analysis of the G1 and S cell cycle stages of MCF-7 estrogen receptor positive breast cancer cells revealed that the enhanced proliferative capacity of these cells spans the entire array of tumorigenesis hallmarks. An examination of the cell cycle proteomic profiles revealed that proteins that change abundance at the G1/S boundary form functionally related clusters that match pathways of relevance to the disease. Intertwined biological mechanisms that encompass DNA repair and transcriptional activities associated with the repression of CDK inhibitors and acquisition of insensitivity to growth inhibition, results ultimately in evasion of apoptosis, enhanced cell proliferation, limitless replicative potential and metastasis. The molecular regulatory machinery of the cell cycle encompassed a broad range of putative therapeutic targets. Further comparisons with MCF-10 non-tumorigenic cells resulted in the identification of several hundreds of proteins that displayed a change in abundance, of which, only ~20 % have been already targeted with small molecule drugs. It is likely, therefore, that many additional drug-targets may be present in the same interacting protein networks. Earlier studies have also pinpointed the central role that enzyme and receptor proteins had in stimulating the development of new drugs, Ser/Thr/Tyr kinases representing ~22 % of the drug targets [1]. Overall, in the MCF-7 cells, we were able to identify 73 kinases and 31 phosphatases, with functions that clustered in two major categories: signaling/cell cycle and glycolysis/energy metabolism. As anomalies in kinase function due to mutations or up/down regulation were linked to over 400 diseases, the likelihood for further advancement of kinase/phosphatase-based therapies is very high. The ability of proteomic technologies to provide novel insights into the functional roles of proteins and their interactions within a network will prove critical for the development of novel therapeutic strategies that target either proteins with multiple functions or clusters of networked proteins.


[1] Hopkins A.L., Groom C.R., The druggable genome, Nature Reviews, Drug Discovery 1, 727-730 (2002).

Iuliana lazar-figSTRING protein-protein interaction diagram of 73 kinases identified in MCF-7 cells.

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