Abstract
BACKGROUND: Intratumoral pressure may stimulate cancer proliferation whereas intravascular pressure promotes metastatic adhesion. α-Actinin proteins facilitate focal adhesion formation and link focal adhesion complexes to the cytoskeleton. We hypothesized that α-actinin is the mechanotransducer that mediates the effects of pressure on cancer cell proliferation and adhesion. METHODS: We treated SW620 colon cancer cells with specific short interfering RNA to reduce α-actinin-1 and/or α-actinin-4, the 2 key epithelial isoforms. Proliferation was measured in adherent cells by microculture tetrazolium (MTT) assay after 24 hours at ambient or 40 mm Hg increased pressure. For comparison, we evaluated the effects of 30 minutes of ambient or 15-mm Hg increased pressure on adhesion of suspended SW620 cells. Because the transcription factor nuclear factor-κB (NF-κB) influences proliferation, we used co-immunoprecipitation to evaluate NF-κB-α-actinin association and a lentiviral reporter assay for NF-κB activity. RESULTS: A total of 40 mm Hg increased pressure increased SW620 proliferation 41% ± 6% (n = 10; P < .05) versus ambient pressure controls. Reducing α-actinin-1 and α-actinin-4 together or α-actinin-4 alone blocked this effect, but reducing α-actinin-1 alone did not (n = 6; P < .05). We observed a 72% ± 11% increase in NF-κB activity (n = 6; P < .05), and increased association between NF-κB and α-actinin-4 in adherent cells under pressure. NF-κB and α-actinin-1 did not co-immunoprecipitate. However, reducing α-actinin-4 did not prevent pressure-induced NF-κB activation (n = 8). CONCLUSIONS: α-actinin-4 may mediate pressure stimulation of proliferation within large rapidly growing tumors, perhaps by binding transcription factors such as NF-κB. α-actinins may be important targets to inhibit cancer proliferation and metastasis.