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I've worked with stem cells for a relatively brief time. Yet, I can't help noticing certain common features between stem cells and cancer cells (I was trained as a cancer biologist). There's even an emerging vocabulary to encapsulate that idea. The terms "cancer stem cell" (CSC) or "tumor-initiating cell" (TIC) has crept into cancer biology lexicon during the past decade. The main thrust of this hypothesis supposes that the bulk tumor contains a subpopulation of cells that spawns a tumor-the seeds, if you will. These cells are also believed to be responsible for treatment-resistance and recurrence. The idea makes intuitive sense. Stem cells and CSCs share much of the same awkward biological features (namely self-renewal, quiescence, and differentiation), and they are both fundamentally different from normal somatic cells in terms of growth kinetics. These differences may be enough to allow CSCs to evade traditional chemo- or radio-therapies, and these residual cells may initial another tumor at a later time. However, it is unclear if CSCs are native stem cells run amok, cancer cells that somehow acquired stem-like characteristics or something else entirely. 
I brought this whole subject up not to simply focus on the links between CSCs and stem cells, but also to illustrate how typical (and easy) it is for ideas to cross-pollinate between niche fields. This is me just thinking out loud, so please bear with me.
A recent paper was published in Nature by Cheung et al. that describes the discovery of a specific microRNA (miRNA) that appears to switch muscle satellite cells (muscle stem cells) between the quiescent and proliferative states, which contributes to muscle repair following injury. Cheung et al. found that miRNA-489 (miR-489) was expressed highly in quiescent muscle stem cells, and when miR-489 production is blocked the stem cells are kicked out of hibernation, and then they begin to proliferate and differentiate into mature muscle cells. In short, miR-489 can maintain the quiescent state in a specific adult stem cell population. It's not clear if this miRNA performs the same function in other kinds of stem cells.
I find this pretty intriguing because another paper from 2010 by Kikkawa et al. reported miR-489 as a tumor suppressor in hypopharyngeal squamous cell carcinoma (HSCC), which is a particularly nasty type of head and neck cancer. In this report, miR-489 was downregulated in cancer cells and inhibited cancer cell growth when it is added back in in vitro assays. I wasn't too excited about the rest of this paper, mainly because they tried too hard to establish a regulatory link between miR-489 and a predicted target gene (PTPN11) to cancer cell growth, and then tried to correlated PTPN11 expression to cancer growth...only they didn't find a significant correlation.
I'm starting to wonder if the Kikkawa group should have probed for quiescence in those HSCC cell lines they studied, since quiescence can also account for the lack of proliferation observed. MiR-489 may help explain the lethality of HSCC because a hibernating cell can escape conventional treatments, which tend to target actively dividing cells. I also think this little ribo-molecule may be used as a type of combinational therapy. Blocking miR-489 may force slow-growing, residual cancer cells to proliferate, which would make them more sensitive to conventional treatment. The main roadblock I can see is we don't have a practical way to specifically block miR-489 in a whole animal, which I'm guessing would require introduction of antisense miR-489 and that would need an efficient delivery system. So, who wants to take a crack at these problems and contribute to the greater good?
P.S. If anyone wants to try this out and later publishes, I'll appreciate a mention in the acknowledgements.
Image credit: © andersdenkend via Flickr (http://www.flickr.com/photos/andersdenkend/2063090148/)
References:
Cheung TH, et al. Maintenance of muscle stem-cell quiescence by microRNA-489. Nature 482(7386):524-8 (2012).
Kikkawa N, et al. MiR-489 is a tumour-suppressive miRNA target PTPN11 in hypopharyngeal squamous cell carcinoma (HSCC). Br J Cancer 103(6):877-84 (2010).
