Myocardin-related transcription factors and SRF are required for cytoskeletal dynamics and experimental metastasis

Abstract

Rho GTPases control cytoskeletal dynamics through cytoplasmic effectors, and regulate transcriptional activation by the Myocardin Related Transcription Factors (MRTFs), coactivators for Serum Response Factor (SRF). We used RNAi to investigate the contribution of the MRTF-SRF pathway to cytoskeletal dynamics in MDA-MB-231 breast carcinoma and B16F2 melanoma cells, where basal MRTF-SRF activity is Rho-dependent. Depletion of MRTFs or SRF reduces cell adhesion, spreading, invasion and motility in culture, without affecting proliferation or inducing apoptosis; MRTF-depleted tumor cell xenografts exhibit reduced cell motility but proliferate normally. MRTF- and SRF-depleted tumor cells fail to colonise the lung from the bloodstream, being unable to persist following their initial arrival at the lung. Only a few genes exhibit MRTF-dependent expression in both cell lines. Two of these, MYH9 (MLC2) and MYL9 (NMHCIIa), are also required for invasion and lung colonisation. Conversely, expression of an activated MRTF increases lung colonisation by poorly metastatic B16F0 cells. Actin-based cell behaviour and experimental metastasis thus requires Rho-dependent nuclear signalling through the MRTF-SRF network.

Leucine-Rich Repeat-Containing G-Protein Coupled Receptor 5/GPR49 Activates G12/13-Rho GTPase Pathway

“…C3 transferase also inhibited the reporter activity significantly, but not completely, probably due to incomplete diffusion of the protein into the cell. In addition, some reports had already shown that even overexpression of C3 transferase in cells does not abrogate all activity of Rho signaling in terms of SRF reporter activity (Medjkane et al, 2009;Merdek et al, 2008). These data collectively demonstrated that Rho GTPase is required for the activation of the SRF-RE reporter by LGR5.…”

Smooth muscle differentiation identifies two classes of poorly differentiated pleomorphic sarcomas with distinct outcome

“…18,25 However, in some cellular models such as breast carcinoma cell lines or mesenchymal stem cells, they have been described as cell migration enhancers that do not interfere with cell proliferation. 26,27 The hypothesis that the impact of smooth muscle differentiation on diverse cellular processes could be distinct according to the phosphorylation status of proteins, the balance involved between various proteins with opposite functions, the proteins interactions implicated and the activated pathway could be made. The cellular context thus appears critical for smooth muscle proteins functions.…”

Targeting Cell Spreading: A Method of Sensitizing Metastatic Tumor Cells to TRAIL-Induced Apoptosis

“…Figure 1A shows that the metastatic 1205Lu cell line was more resistant to TRAIL-mediated apoptosis than its poorly metastatic counterpart, using the colon carcinoma cell line SW480 as a TRAIL sensitive control. The metastatic human breast cancer cell line MDA-MB-231 had intermediate TRAIL sensitivity (29). Apoptosis is indicated by a reduction in viability over 18 hours following TRAIL treatment, with an increase in caspase 3-like activity (Fig.…”

“…SW480, a human colon carcinoma cell line was sourced from the American Type Culture Collection and maintained in Dulbecco's modified Eagle's medium supplemented with 10% FBS. MDA-MB-231 human breast cancer cells were a kind gift from Prof. Richard Treisman (CRUK London Research Institute, London), along with MDA-MB-231 cells carrying tetracycline-inducible shRNA for myocardinrelated transcription factor (MRTF)-A and -B, as described previously (29). Cells were proven to be mycoplasma free by routine testing.…”