The list of accomplishments on MYC's resumé continues to grow, as Yuzuru Shiio et al. report in EMBO Journal that increased expression of MYC reduces the level of actin stress fibres and focal adhesions within cells, which could influence their ability to invade and metastasize.

The authors analysed global protein expression using isotope-coded affinity-tag reagent labelling and tandem mass spectrometry in two rat cell lines — Myc(−), in which c-Myc is deleted, and Myc(+), which is the same cell line but with c-Myc reintroduced. Myc is present in Myc(+) cells at ∼fivefold the level of that in wild-type cells. This is within the range of Myc expression that is found in tumour-derived cell lines.

Of the 528 proteins analysed, 177 had at least a twofold expression difference between the two cell lines. Functionally related groups tended to have similar expression patterns; for example, adhesion molecules, actin-binding proteins and Rho pathway proteins, which might influence cell morphology and adhesion, were downregulated in Myc(+) cells, and those involved in protein synthesis and anabolism, which would influence cell growth, were upregulated in Myc(+) cells.

The link between Myc and cell growth has been made before, and is strengthened by Myc's ability to regulate genes that are important in this; however, a link between Myc and cell morphology has not. To investigate this further, the authors performed immunofluorescence on Myc(−) and Myc(+) cells, and found that Myc(+) cells possessed fewer focal adhesions and actin stress fibres. This was shown to be due to a decrease in signalling from the Rho pathway, and introduction of a hyperactive RhoA into Myc(+) cells significantly restored the actin stress fibres.

Expression of Myc in mouse NIH-3T3 cells also results in a reduction of actin stress fibres and focal adhesions, but this does not seem to be caused by decreased expression of RhoA. Instead, levels of Cdc42 — a Rho protein family member — and actin are reduced.

So, this proteomic analysis has revealed yet another potential function for Myc in tumorigenesis. By reducing adhesion and increasing motility, Myc might promote invasion and metastasis.