Ras stimulation of E2F activity and a consequent E2F regulation of integrin α6β4 promote the invasion of breast carcinoma cells

Active Ras proteins contribute to breast carcinogenesis and progression. Here, we provide evidence that active H-Ras regulates the expression and activity of the E2F family of transcription factors in SUM-159 breast carcinoma cells. In addition, we show by using a DNA-binding mutant of E2F, as well as expression of specific E2Fs that are transcriptionally active, that the active E2Fs1-3 can mediate the H-Ras-dependent invasion of SUM-159 cells. The inhibitory E2Fs4-5, in contrast, do not influence invasion. One mechanism by which the active E2Fs promote H-Ras-dependent invasion seems to be their ability to increase expression of the beta(4) integrin subunit, a component of the alpha(6)beta(4) integrin that is known to enhance carcinoma invasion. Specifically, expression of E2Fs1-3 increased beta(4) mRNA, protein, and cell surface expression. The active E2Fs were unable to stimulate invasion in cells that expressed a beta(4) short hairpin RNA. This effect of the active E2Fs on beta(4) expression does not seem to result from E2F-mediated beta(4) transcription because the beta(4) promoter lacks known E2F binding motifs. In summary, the data reported here indicate a novel mechanism by which H-Ras can promote the invasion of breast carcinoma cells. This mechanism links active H-Ras, transcriptionally active E2F, and the alpha(6)beta(4) integrin in a common pathway that culminates in enhanced alpha(6)beta(4)-dependent invasion.